On-chip high-Q Micro-Ring Resonators （MRRs） have emerged as essential building blocks for high-performance microwave photonic systems， thanks to their compact footprint， narrow resonance bandwidth， and excellent tunability. They are widely employed in applications such as ultra-narrowband Microwave Photonic Filters （MPFs） for channel selection in radio-over-fiber networks， low-phase-noise Optoelectronic Oscillators （OEOs） for high-frequency microwave signal generation， and broadband optical frequency combs for high-resolution spectroscopy and microwave-to-optical conversion. Recent advances have focused on pushing Q factors into the multi-million range or even higher to further enhance device performance. This paper reviews the fundamental principles， design strategies， and material considerations for on-chip high-Q MRRs， with emphasis on their integration and practical deployment in these representative microwave photonic applications.

The Q factor of a MRR characterizes the energy storage capability and loss level within the optical cavity. A higher Q indicates a longer photon lifetime， lower round-trip loss， and a narrower resonance linewidth. In microwave photonic system， this translates into a narrower filtering bandwidth of MPFs， a lower phase noise of OEOs， and enhances nonlinear optical effects. Accordingly， we present a detailed discussion of the fundamental structure， theoretical framework， and key parameters of high-Q MRRs， establishing a solid foundation for their design and optimization. From a coupling perspective， MRR behavior can be understood via two complementary models： power coupling and energy coupling， which correspond to frequency-domain steady-state analysis and time-domain transient analysis， respectively.

Subsequently， we elaborate on implementation strategies for high‑Q MRRs from three key aspects： material platform selection （including silicon， silicon nitride， lithium niobate， and lithium tantalate）， fabrication process optimization， and waveguide engineering. A cross‑platform comparison is carried out to evaluate material systems in terms of refractive index contrast， optical transparency window， nonlinear optical properties， and fabrication maturity. This analysis reveals the inherent trade‑offs among platforms—for instance， silicon offers high index contrast and mature CMOS compatibility but suffers from two‑photon absorption in the telecom band， whereas silicon nitride exhibits broad transparency and ultralow loss， albeit requiring more advanced processing to reach ultrahigh Q values. On the waveguide engineering front， techniques such as adiabatic width tapering， Matched bend， Euler bend， and Bezier bend are employed to minimize radiative and bending losses， enabling smooth mode transitions and supporting ultrahigh‑Q operation in compact footprints. Recent progress in high‑Q MRR development across these material platforms is also reviewed.

Furthermore， we examine the typical implementations of high‑Q MRRs in microwave photonic systems， with a particular focus on MPFs and OEOs. For MPFs， we begin by highlighting the potential of ultra‑high‑Q MRRs with large Free Spectral Range （FSR） in constructing ultra‑narrowband， widely tunable MPFs. We then review various system architectures developed to achieve ultra‑high out‑of‑band rejection and high reconfigurability. However， for real‑world RF applications， MRR‑based MPFs still require significant improvement in key RF performance metrics such as insertion loss， Noise Figure （NF）， and Spurious-Free Dynamic Range （SFDR）. Regarding OEOs， we discuss developments in on‑chip OEOs based on MRR， as well as emerging PT‑symmetry breaking schemes that eliminate the requirement for additional narrowband optical or electrical filters. In recent years， on‑chip integrated OEOs have made notable progress in frequency tuning range， Side‑Mode Suppression Ratio （SMSR）， and system compactness. However， the limited on‑chip effective delay， combined with additional noise introduced by active components， results in overall phase noise performance that remains considerably higher than that of discrete fiber‑based systems—particularly evident at intermediate and low frequency offsets. We also summarize recent progress in fully integrated on‑chip MPFs and OEOs， which is of great significance for achieving compact， lightweight microwave photonic systems.

Prospectively， high‑Q MRR‑based microwave photonic devices are poised to transition into practical use across a range of fields， including radar signal processing， 5 G/6 G wireless communications， and RF signal generation. By leveraging programmable architectures and adaptive control schemes， these devices can simultaneously achieve miniaturization， low power consumption， and high performance. This progress is expected to drive the broader adoption of microwave photonics in cutting‑edge domains such as telecommunications， national defense， aerospace， and intelligent sensing， while gradually narrowing the performance gap between on chip solutions and discrete high performance systems.

The ability to generate dynamically reconfigurable broadband arbitrary waveforms is of paramount importance for advanced radar imaging， next-generation wireless communications， integrated sensing and communication， and electronic warfare systems. These applications demand waveforms with large time-bandwidth products， complex modulation， and low phase noise to ensure high resolution， superior data throughput， and robust anti-jamming resilience. However， traditional electronic approaches are fundamentally constrained by the electronic bottleneck， which severely restricts instantaneous bandwidth， tuning agility and power efficiency， particularly at high frequencies. In this context， microwave photonics has emerged as a transformative paradigm by leveraging the intrinsic advantages of photonic technologies， including ultra-wide bandwidth， low transmission loss， and immunity to electromagnetic interference. In this field， opto-electronic oscillators are well known for generating microwave signals with ultra-high spectral purity， which is enabled by high-quality-factor resonators formed using long optical fiber delay lines. However， the inherently single-frequency nature of conventional opto-electronic oscillators renders them ill-suited for complex and wideband waveform synthesis.

The incorporation of mode-locking mechanism into opto-electronic oscillator architectures has given rise to mode-locked opto-electronic oscillators， representing a major breakthrough that enables the coherent synthesis of broadband waveforms while maintaining low phase noise. This review systematically presents three representative mode-locked opto-electronic oscillator architectures： the Fourier-domain mode-locked opto-electronic oscillator， the wideband injection-locked opto-electronic oscillator， and the active mode-locked opto-electronic oscillator. The Fourier-domain mode-locked opto-electronic oscillator employs a high-speed tunable filter that is periodically scanned in synchronization with the cavity round-trip time， thereby creating a dynamic spectral storage mechanism that enables the sequential amplification of distinct frequency components. Initially demonstrated for the generation of wideband linear frequency-modulated waveforms， the Fourier-domain mode-locked opto-electronic oscillator has since evolved to produce dual-chirp signals， phase-coded linear frequency-modulated waveforms， and fully programmable arbitrary waveforms through precise control of the filter scanning trajectory. In contrast to the Fourier-domain mode-locked opto-electronic oscillator， the wideband injection-locked opto-electronic oscillator introduces an external broadband seed signal， typically generated by an arbitrary waveform generator， into a free-running opto-electronic oscillator cavity. The high-quality-factor resonator functions as a spectral purifier， substantially reducing phase noise and enhancing the signal-to-noise ratio while faithfully replicating the modulation profile of the injected seed signal. Alternately， the active mode-locked opto-electronic oscillator employs periodic gain modulation at a frequency matched to the cavity free spectral range or its harmonics， thereby actively phase-locking multiple longitudinal modes to form a coherent microwave frequency comb that manifests as a pulse train in the time domain. The active mode-locked opto-electronic oscillator facilitates precise repetition-rate control and has evolved to support tunable dual-band operation， multidimensional pulse coding （time， phase， and amplitude）， and fully programmable architectures for seamless switching between diverse waveform formats.

This review provides a comprehensive analysis of the operating principles and system architectures for each approach， alongside a comparative evaluation of critical metrics such as bandwidth， phase noise， and time-bandwidth product. The wideband arbitrary waveforms generated by mode-locked opto-electronic oscillators hold great potentials for various applications. In high-resolution radar and imaging， these waveforms provide the bandwidth necessary to achieve millimeter-scale spatial resolution while ensuring robust resilience against electronic interference. In integrated sensing and communication systems， the wideband microwave signals leverage a unified hardware platform to support high-throughput communications alongside high-resolution sensing， effectively eliminating the trade-offs between data rate and detection accuracy. Furthermore， in advanced LiDAR systems， such waveforms support high-fidelity 4D imaging， capturing 3D structural details and instantaneous Doppler velocity with millimeter-level accuracy.

Future research is expected to advance along several key frontiers multi-material hybrid integration using materials such as InP， Si₃N₄， and LiNbO₃ to realize compact， stable， chip-scale devices； extension of high-frequency and ultra-wideband operation into the millimeter-wave and terahertz regimes； and the realization of software-defined， intelligent reconfiguration enabled by artificial intelligence for cognitive waveform adaptation. In summary， mode-locked opto-electronic oscillators constitute a versatile and powerful photonic platform that effectively overcomes the electronic bottleneck. They establish a robust foundation for the generation of wideband software-defined microwave waveforms， which are essential for advancing next-generation radar， communication， and sensing systems.

A Microwave Photonic Filter （MPF） is a device that filters microwave signals by first modulating them into the optical domain， then processing them using optoelectronic components. Compared to traditional electronic microwave filters， they exhibit advantages such as superior frequency tuning range， flexible spectrum reconfiguration， and inherent immunity to electromagnetic interference， etc. These benefits make MPFs highly promising for widespread applications in wireless communication， radar， and electronic warfare systems. With the advancement of integrated optoelectronic technologies， MPFs are progressively evolving from discrete fiber-optic devices towards integrated solutions. This transition aims to substantially reduce their size， weight， power consumption， and cost. In this review， firstly the system architectures and working principles of both incoherent and coherent integrated MPFs are presented. Subsequently， recent research advances in these two categories of MPFs are reviewed.

For incoherent integrated MPFs， multi-tap configurations are typically adopted， utilizing Finite Impulse Response （FIR） digital filter architectures rooted in discrete signal processing algorithms. Some key integrated optical components enabling dispersion-delayed sampling in multi-tap MPFs are given， such as integrated high-dispersion chips， multi-wavelength light sources， and spectral shaping chips. By adopting these functional chips into microwave photonic filter links， some MPFs with good frequency tuning capabilities and out-of-band RF suppression have been reported. But the limited number of taps and unattainable complex tap coefficients resulting in insufficient spectral reconstruction capability of the achieved incoherent MPFs. To date， only aforementioned integrated chips have been integrated into microwave photonic filter links， while other critical components still rely on discrete fiber-based devices. Incoherent MPFs with higher integration levels remain unreported in the literature.

For coherent integrated MPF， typically microwave signals are modulated onto a single-wavelength laser source， where various integrated optical filters are adopted to spectrally shape modulated optical signal， followed by down-conversion at a photodetector to convert optical domain filtering response into microwave domain. Various integrated optical components to construct coherent MPFs such as Micro-Ring Resonator （MRR）/Micro-Disk Resonator （MDR）， nonlinear As2S3 waveguide with Stimulated Brillouin Scattering （SBS）， photonic crystal cavity， microsphere， phase shifted waveguide Bragg grating， Surface Acoustic Wave （SAW） based on suspended waveguide have been reviewed. Based on these integrated optical components， various MPF link architectures to realized band-stop and band-pass MPFs have been introduced. Band-stop MPFs can be realized through optical-to-microwave mapping based on Optical Single Sideband （OSSB） modulation. Furthermore， by employing Radio Frequency （RF） cancellation techniques via Unbalanced Optical Double Sideband （UODSB） modulation， this approach can overcome the limitation imposed by optical filter’s extinction ratio on RF suppression performance and enables band-stop MPF with RF rejection ratio larger than 60 dB. On the other hand， Band-pass MPFs can be realized through either by optical carrier separation and re-entry techniques enabling direct one-to-one mapping of optical band-pass responses to the microwave domain， or phase-to-intensity conversion schemes that transform optical band-stop filtering into microwave band-pass responses. In addition， some technologies to enhance MPF's frequency resolution have been introduced， such as improving quality factors of MRR/MDR with mode manipulation， incorporating on-chip narrow-band SBS gain/loss spectra， adopting SiO₂ microsphere， etc. Up to date， frequency resolution down to about ten MHz have been demonstrated for band-pass and band-stop MPFs. Building on recent advances in integrated optical filters for MPF links， this work futher surveys highly integrated microwave photonic filter chips implemented on Thin-Film Lithium Niobate （TFLN）， Silicon-On-Insulator （SOI）， and indium phosphide （InP） platforms， providing a comparative analysis of their respective advantages and limitations.

Finally， quantitative comparative analysis of key performance metrics of the reported incoherent and coherent integrated MPFs have been given. Some key technical challenges in integrated MPFs， including the trade-offs between filter's bandwidth and frequency tuning range， insufficient noise figure/out-of-band RF rejection ratio/frequency stability， immature heterogeneous integration， and broadband photonic packaging solution with low crosstalk and high RF integrity. Moreover， an outlook on the future development trends of integrated MPF is presented.

Phased array antennas， renowned for their capability to flexibly control spatially radiated electromagnetic waves， are widely used in fields such as communications， detection， and electronic warfare. As system demands for higher gain and broader operating bandwidth continue to increase， phased array antennas are evolving toward larger scales and higher operating frequencies.

Photonics technology exhibits notable advantages including strong resistance to electromagnetic interference， low transmission loss， and large operating bandwidth， offering new possibilities for further enhancing the performance of phased array antennas. By integrating optical and electromagnetic waves and leveraging the flexible control of optical parameters such as delay and intensity， it has become an important direction for the development of microwave and millimeter-wave phased array antennas. Within the framework of optoelectronic integration， relevant technical approaches can be categorized into three typical implementations： optical true-time-delay phased arrays， laser-space-fed phased arrays， and optically controlled metasurface antennas. The first two focus on providing high-precision time delay in the optical domain or through optical links， while the latter employs optical means to dynamically control the electromagnetic response of metasurface units.

Specifically， optical true-time-delay phased arrays utilize the large tuning range and low-loss characteristics of optical delay lines to achieve real-time delay control in the optical domain， effectively mitigating beam squint issues during wideband， large-angle scanning， thereby supporting beamforming and steering of wideband signals. Laser-space-fed phased arrays leverage the low-crosstalk nature of laser carriers to transmit optically carried microwave and millimeter-wave signals to radiating elements via free-space optical links， offering the potential to simplify complex electrical interconnections in large-scale arrays and providing a new technical pathway for implementing high-frequency， large-scale phased arrays. Optically controlled metasurface antennas retain the advantages of electronic metasurfaces， such as low cost and easy integration， while introducing light as an additional control dimension to enhance flexible beam manipulation. Moreover， thanks to the good penetration of light in underwater environments， this technology shows potential for future integrated space-air-ground-sea systems. It is worth noting that the rapid development of optoelectronic integration technology is driving continuous improvements in the performance， integration level， and cost-effectiveness of photonic devices. This lays a solid foundation for the miniaturization， integration， and weight reduction of optoelectronically integrated phased array systems， and also points to important technical directions for addressing the limitations in array scale.

This paper focuses on optoelectronically integrated microwave and millimeter-wave phased array antenna technology， with emphasis on the three typical architectures mentioned above： optical true-time-delay phased arrays， laser-space-fed phased arrays， and optically controlled metasurface antennas. It outlines their key technologies and development trajectories， reviews representative research progress， and， on this basis， analyzes and prospects the future application potential of optoelectronic integration technology in the field of optoelectronically converged phased arrays.

Magnetic field sensing is essential in applications such as power equipment monitoring， geomagnetic exploration， biomedical diagnostics， and intelligent sensing infrastructures. Although electrical magnetic sensors， including Hall-effect， magnetoresistive， fluxgate， and superconducting quantum interference device sensors， have achieved technical maturity， their deployment in complex or distributed environments is often constrained by electromagnetic interference， bulky shielding requirements， and limited scalability. By contrast， microwave photonic approaches exploit the immunity， flexibility， and low cost of optical fibers together with the high resolution and wide bandwidth of microwave-domain processing， offering a promising route toward high-performance magnetic field sensing. This paper reviews the fundamental principles and recent progress of microwave photonic magnetic field sensing technologies， with emphasis on their demodulation mechanisms and system architectures.

Two microwave photonic sensing routes have emerged as representative approaches. The first is based on the Optoelectronic Oscillator （OEO）， in which the fiber-optic magnetic field sensing unit is embedded within the OEO feedback loop. In this configuration， magnetic-field-induced optical perturbations are translated into shifts in the oscillation frequency or phase of OEO. Owing to the intrinsically high-Q and low phase noise of OEOs， even minute wavelength shifts from fiber Bragg grating Fabry-Perot cavities bonded to magnetostrictive materials can be amplified into measurable frequency shifts at the MHz to GHz level. Furthermore， Mach-Zehnder interferometer assisted OEO architectures enable alternating magnetic field sensing by converting magnetostrictive phase modulation into frequency or phase variations of the OEO oscillation signal， allowing sensitivities approaching the sub-nT/Hz^1/2 level in the kHz magnetic field band. Responsivity enhancement strategies， such as the Vernier effect in dual loop OEOs and prestressed magnetostrictive packaging， have been demonstrated to improve the scale factor by more than an order of magnitude without modifying the single loop OEO configuration.

The second route is based on Microwave Photonic Filters （MPFs）. In this scheme， an optical carrier is modulated by an electro-optic modulator and subsequently passes through a magnetic field sensing unit. After photodetection， the magnetic field information is retrieved by tracking the shift of the filter passband， typically using a vector network analyzer. MPF-based magnetic field sensing systems naturally support multi-tap and reconfigurable architectures， and can be applied to both static and alternating magnetic field measurements. Advanced implementations incorporating Fabry-Perot interferometers， polarization-maintaining fibers and cascaded fiber rings， MPF-based schemes enable enhanced responsivity， dual-parameter sensing， and quasi-distributed or vector magnetic field measurement capabilities.

To render microwave photonic magnetic field sensing systems practical for engineering applications， advanced post-processing techniques are essential to mitigate nonidealities originating from both magnetic transducers and microwave photonic components. Magnetostrictive and magnetic fluid elements inherently exhibit hysteresis and temperature-dependent behavior， while fiber packaging may introduce mechanical vibrations that manifest as excess phase noise. In addition， instabilities in lasers and photodetectors can induce power and wavelength fluctuations. Model-based hysteresis compensation approaches， including Preisach and Prandtl-Ishlinskii families and their dynamic or separated loop extensions， have been shown to substantially suppress nonlinear errors and restore near-linear relationship between magnetic field and frequency. In parallel， data-driven techniques based on recurrent or feedforward neural networks， support vector machines， and hybrid model-network frameworks enable online learning of the complex coupling among magnetic field， temperature， and packaging-induced stress. These techniques enable effective suppression of nonlinear errors and adaptive decoupling of magnetic field， temperature， and packaging-induced disturbances， thereby enhancing long-term stability and measurement fidelity.

In summary， microwave photonic magnetic field sensing technology combines the low cost and lightweight of fibers with the high accuracy of microwave-domain signal processing. At the hardware level， magnetic field demodulation can be achieved through microwave photonic architectures， including high-Q OEOs and tunable multi-tap MPFs. At the digital level， hysteresis can be effectively compensated using advanced signal processing and algorithms. Most reported systems still rely on discrete optoelectronic components. This reliance increases susceptibility to optical path loss and environmental perturbations， which in turn degrades demodulation accuracy and long-term stability. Future efforts should therefore focus on monolithic or hybrid photonic microwave integration to realize low loss， low cost， and compact on-chip sensing and demodulation architectures. Through coordinated control of the optical and microwave domains， this technology offers a versatile route toward high sensitivity magnetic field measurement. With continued advances in integrated microwave photonic platforms， intelligent signal processing algorithms， and novel magnetic transduction materials， microwave photonic magnetic field sensing is expected to evolve toward higher sensitivity and stronger environmental adaptability. These developments will also promote improved system integration and support future applications in power equipment monitoring， geomagnetic exploration， and biomedical magnetic detection.

The temporal Talbot effect represents the time domain counterpart to the classical spatial self-imaging phenomenon， strictly governed by the fundamental physical principle of space-time duality. This coherent interference effect occurs when a periodic optical pulse train propagates through a dispersive medium， such as a standard single mode optical fiber or a chirped Bragg grating， where the group velocity dispersion acts as a quadratic phase filter on the optical signal. Depending on the precise relationship between the pulse repetition period and the accumulated dispersion， the system exhibits two primary behaviors： integer order self imaging， where the original waveform is perfectly reproduced， or fractional order self imaging， which results in the generation of pulse trains with multiplied repetition rates. Furthermore， the dispersive propagation inherently functions as a real-time Fourier transform， mapping the frequency spectrum of an imposed modulation directly into its temporal intensity profile at the output. This review systematically explores these mechanisms， emphasizing their utility as passive， linear， and energy efficient tools for high speed signal processing in the field of microwave photonics.

A significant portion of this review addresses the manipulation of pulse repetition frequencies. While early approaches relied on fixed dispersion values， recent advancements allow for flexible multiplication factors. We discuss techniques such as phase pre-coding， which modifies the input phase to transition between fractional Talbot orders without energy loss， and binary intensity modulation， which offers a simpler implementation but suffers from optical power loss. A comparative analysis highlights that complex amplitude pre-coding scheme offers a balanced trade-off between energy efficiency and control complexity. By utilizing a Mach-Zehnder modulator to sculpt the spectrum into a flat profile， this method overcomes the bandwidth limitations of arbitrary waveform generators required for phase coding and the high extinction ratio constraints typical of intensity modulation schemes.

In contrast to multiplication， the paper examines passive amplification and weak signal recovery via the inverse temporal Talbot effect. By reversing the dispersion process， distributed energy from a continuous wave or a high-rate pulse train can be coherently focused into high peak power pulses. This concept， realized as a temporal Talbot array illuminator， effectively converts continuous wave light into high-quality pulse trains with tunable parameters. Crucially， this enables noiseless amplification where random， non-coherent noise does not sum up constructively， thereby significantly enhancing the signal-to-noise ratio. Experimental results have demonstrated amplification gains exceeding one hundred and ten times， allowing for the recovery of weak signals that are otherwise submerged below the noise floor of the photodetector.

The review further details the application of the real time Fourier transform in real-time spectrum analysis. Standard real-time spectrum analysis faces an inherent trade-off between measurement bandwidth and frequency resolution. To address this， the authors introduce a resolution enhanced architecture using the inverse temporal Talbot effect to temporally stretch the output observation window， effectively magnifying the resolution. Conversely， a bandwidth-enhanced architecture utilizing fractional-order multiplication is proposed to increase the effective sampling rate and measurement range. These innovations successfully decouple the resolution bandwidth constraint， enabling gap free analysis of wideband dynamic radio frequency signals. Additionally， the paper explores arbitrary waveform generation and pulse position control. By manipulating the spectral content via multi-tone modulation， complex temporal waveforms can be synthesized through frequency to time mapping. Similarly， precise control over pulse timing is achieved by modulating the carrier with a frequency modulated signal. This technique effectively converts instantaneous frequency shifts into temporal delays. This capability is applied to non-uniform sampling systems， such as the photonic Nyquist folding receiver， to significantly extend signal reception bandwidth beyond the traditional aliasing limits.

Finally， the review outlines emerging applications in other domains， such as temporal cloaking which hides events within dispersion induced time gaps， and prime number factorization via Gaussian sum calculation. The paper concludes by identifying critical challenges for future implementation. These include the precise management of high order dispersion to achieve perfect self imaging and the mitigation of Kerr non-linearities at high optical power levels. Furthermore， the review emphasizes the need for on-chip integration， noting the engineering difficulties in realizing sufficient dispersion on photonic integrated circuits while maintaining a compact Size， Weight， Power， and Cost （SWaP-C） footprint. Despite these hurdles， the temporal Talbot effect remains a versatile and promising foundation for next generation all optical signal processing networks.

Integrated Sensing and Communication （ISAC） has become a pivotal technology for 6G networks， addressing the increasing demands for data transmission and environmental awareness in advanced applications such as autonomous vehicles and smart IoT homes. However， conventional Radio Frequency （RF）-based ISAC systems face inherent challenges， including limited bandwidth， susceptibility to electromagnetic interference， and frequency-dependent losses， which constrain their ability to generate and process high-frequency broadband signals. Microwave Photonics （MWP） has emerged as a transformative solution that leverages optical technologies to overcome electronic bottlenecks， offering three key advantages： high-bandwidth signal processing capability， inherent immunity to RF interference， and a compact architecture with low power consumption. In communication systems， traditional multiplexing methods—such as Time Division Multiplexing （TDM）， Frequency Division Multiplexing （FDM）， and hybrid approaches—have been widely employed to enhance channel efficiency. Nevertheless， these methods exhibit limited resilience to interference. Code Division Multiplexing （CDM）， a well-established wireless technology derived from spread spectrum communication， uses unique codes to differentiate user data， enabling simultaneous transmission over the same frequency band for multiple users. CDM provides three significant benefits： robust multiple-access capability， intrinsic resistance to multipath interference， and improved signal security. Although prior research has demonstrated the potential of CDM， the integration of photonic-based Code Division Multiple Access （CDMA） with ISAC systems remains an underexplored area that warrants further investigation.

To address this research gap， we introduce a photonics-based ISAC system that combines spread spectrum coding， CDMA， and chirp waveform modulation. The proposed scheme features two main innovations： First， it achieves orthogonalization of user signals through specialized spread spectrum codes and scrambling sequences， effectively reducing random noise， inter-user interference， and multipath effects. This significantly enhances interference resistance and enables multi-user scalability. Second， the DC-biased spread spectrum encoding applied to Linear Frequency Modulation （LFM） signals generates integrated waveforms with unique chirp-phase characteristics and improved cross-correlation performance. This approach not only supports synchronization of communication sequences but also facilitates radar sensing via simplified photonic de-chirping processing， substantially lowering the Analog-to-Digital Converter （ADC） sampling rate requirements in radar receivers. For 3D positioning， we employ the Time Difference of Arrival （TDOA） method combined with a Chan-Taylor hybrid algorithm， enabling accurate localization with smaller network overhead. This integration of communication， sensing， and measurement systems has been successfully realized. Simulation results demonstrate the system's robustness： even under negative Signal-to-Interference-plus-Noise Ratio （SINR） conditions， spread spectrum phase coding sustains simultaneous multi-user communication and sensing. The system achieves decimeter-level distance resolution and high-precision near-field positioning. Parameter analysis evaluates the impact of DC bias， Voltage Peak-to-Peak （Vpp）， Received Optical Power （ROP）， and gain on communication performance in terms of Bit Error Rate （BER） and Signal-to-Interference Ratio （SIR）.

This research provides valuable insights for designing high-performance， interference-resistant integrated sensing and communication systems applicable to areas such as UAV control and management， smart homes， and intelligent transportation.

With the explosive growth of next-generation information technologies， such as ultra-high-speed 5G/6G wireless communication networks， ultra-wideband radar systems， and quantum information processing， the requirements for the generation， transmission， and manipulation of high-frequency microwave signals have reached unprecedented levels. Facing the escalating challenges of bandwidth， speed， and energy efficiency， Integrated Microwave Photonics （IMWP） has emerged as a transformative solution. By leveraging the ultrawideband characteristics of photons propagating within integrated circuits， IMWP achieves high-precision modulation， distribution， and processing of microwave signals through interference and multiplexing across diverse optical paths， thereby surmounting the performance bottlenecks inherent in traditional electronic systems. Furthermore， on-chip programmable photonic-microwave signal processors provide a robust hardware foundation for next-generation high-performance microwave systems by reconfiguring their internal architectures to achieve multi-functionality and flexible configuration. Although various architectures based on interferometer arrays， such as finite impulse response filters with delay-line arms and cascaded ring resonators， have been demonstrated， a critical bottleneck hindering their engineering transition is the difficulty in balancing architectural reconfigurability with system scalability in complex application scenarios. Conventional designs often suffer from fixed interconnection topologies and a lack of directness in functional implementation， which constrains their practical deployment in diverse and dynamic environments.

Addressing these limitations， this work proposes and experimentally demonstrates an adaptive programmable integrated photonic signal processor based on a hexagonal waveguide mesh topology. The processor utilizes Mach-Zehnder Interferometers （MZIs） as fundamental tuning units， featuring an optimized physical-layer design to ensure high-fidelity functional mapping across the network. The device was fabricated on a 220 nm Silicon-on-Insulator （SOI） platform， with a compact footprint of approximately 3 mm×1 mm， integrating 32 tunable MZIs， 32 thermo-optic phase shifters， and 24 optical I/O ports. Comprehensive characterization of the MZI test structures reveals excellent performance， including extinction ratios exceeding 20 dB and a half-wave heating power of 4.41 mW. A central innovation of this study is the implementation of a self-adaptive control framework driven by the Crested Porcupine Optimizer （CPO） algorithm. The operational logic of the CPO-based configuration is divided into three distinct phases： initialization， closed-loop evaluation， and strategy evolution. By generating a random population within the predefined voltage range and iteratively calculating fitness values based on real-time experimental spectral feedback， the system autonomously converges to the optimal voltage configuration. During the evolution process， the algorithm dynamically toggles between exploration and exploitation modes using four distinct evolutionary strategies， ensuring both global search coverage and local refinement precision. This self-adaptive framework enables the processor to achieve immediate operational readiness with minimal control complexity， establishing a highly stable hardware-software co-design for universal signal processing.

Experimentally， the fabricated processor was configured to demonstrate two representative microwave photonic functionalities： topological filtering and frequency measurement. In the topological filtering experiments， the mesh’s high degree of reconfigurability was leveraged to synthesize diverse spectral responses， including both Finite Impulse Response （FIR） and Infinite Impulse Response （IIR） filters. By precisely controlling the power splitting ratios and phase shifts within the hexagonal units， we successfully realized Asymmetric MZIs （AMZIs） with tunable extinction ratios exceeding 25 dB and Free Spectral Ranges （FSR） ranging from 0.17 nm to 0.64 nm. Furthermore， Optical Ring Resonators （ORRs） with a 6-BUL （Basic Unit Length） cavity and two-stage Coupled Resonator Optical Waveguides （CROWs） were implemented， demonstrating the mesh's capability to synthesize complex recursive structures with flattened transmission spectra. For frequency measurement， a broadband frequency identification system was constructed using an Amplitude Comparison Function （ACF） based on a Carrier-Suppressed Single-Sideband （CS-SSB） modulation scheme. The system utilized the mesh's ability to switch between multi-stage frequency discrimination channels with different FSRs. By synergistically combining the results from a wideband coarse-measurement channel and a narrowband high-precision channel， the system achieved a broad frequency identification range from 0.01 GHz to 30 GHz with a significantly improved Root Mean Square Error （RMSE） of 131 MHz. This collaborative measurement scheme effectively eliminates the periodic ambiguity typical of narrowband discriminators while maintaining high resolution across the entire spectrum.

In summary， this work provides a viable and scalable pathway for realizing high-performance， low-complexity integrated microwave photonic systems. The hexagonal mesh architecture demonstrates exceptional functional adaptability and structural scalability， marking a paradigm shift from Application-specific Integrated Circuits （ASPICs） to software-defined universal photonic processors. Beyond the filtering and frequency measurement demonstrations， the architecture serves as a general-purpose hardware platform capable of supporting diverse tasks， including tunable delay lines for wideband beamforming， arbitrary waveform generation， and reconfigurable optoelectronic oscillators. Theoretical analysis and experimental validation suggest that this self-adaptive framework can be extended to larger-scale networks， providing a clear evolutionary path for multi-functional， adaptive measurement systems in complex electromagnetic environments. The successful implementation of these functionalities on a single programmable chip paves the way for the future deployment of integrated photonics in advanced radar systems， 5G/6G communication infrastructures， and high-dimensional optical signal manipulation.

To meet the demands of future high-performance radar systems with superior resolution， agility and adptability， a reconfigurable radar waveform generation method based on the period-one （P1） oscillation dynamics of optically injected semiconductor laser is comprehensively investigated. The underlying principle involves perturbing the oscillation state of semiconductor laser through the injection of external continuous wave light. This perturbation alters the intracavity photons and carrier densities of laser， thereby exciting various nonlinear dynamics. Among these， P1 oscillation state exhibits asymmetric sideband modulation， which provides a theoretical basis for microwave signal generation.

Firstly， the characteristics of P1 oscillation， including the frequency tunability and fast frequency-switching capability， are numerically analysed by solving the nonlinear rate equations. Simulation results demonstrate that the transition between distinct oscillation frequencies can be achieved with a switching speed on the order of ns level， highlighting the inherent agility of the optical injection system. The evolution routing of the nonlinear dynamics is also explored through the dynamical map as a function of injection strength and detuning frequency， which provides a guide to achieve and maintain the desired P1 oscillation state. Based on this， the experimentally generation of broadband radar signals are demonstrated. To generate broadband radar signal， a dynamical control unit of injection parameters is proposed to manipulate the instantaneous frequency of generated wideband waveform. By programming the control signals， various broadband radar signals are generated successfully， including linear frequency modulated signal， triangular wave signal， stepped-frequency signal， frequency-codded signal， frequency-codded linear and frequency modulated signal. The key waveform parameters of broadband signal such as bandwidth， time period， operating band and duty cycle， can also be flexibly adjusted by tuning the injection parameters， which further validate the feasibility of the proposed system. However， the optical injection system in application falls short in performance due to a challenge induced by the intrinsic noise of semiconductor lasers. to address this， approaches for enhancing the system performance are proposed and demonstrated. For single-frequency signal generation， a dual-loop optoelectrical feedback structure incorporating balanced photodetection is employed to improve the Side-Mode Suppression Ratio （SMSR） and phase noise of generated signals.

Compared with conventional optical injection system， the linewidth of generated signal based above method is significantly narrowed by three-orders of magnitude. The SMSR is enhanced by about 65.5 dB due to the Vernier effect. In addition， the system maintains excellent frequency tunability while achieving a phase noise of below -124.10 dBc/Hz at 10 kHz offset. For broadband radar waveform generation， pre-compensation of the injection intensity and Fourier Domain Mode Locking （FDML） mechanism are incorporated， through which the in-band Signal-to-Noise Ratio （SNR） and frequency accuracy of generated radar waveforms are significantly improved. In the experiment， a broadband signal with a bandwidth of 6.3 GHz is generated， of which in-band SNR is improved by about 47 dB. In addition， limited by the transient properties of semiconductor laser， when the P1 oscillation frequency is fast changed with a large frequency step， strong damping oscillation of the output frequency occurs， resulting in deterioration of the frequency stability and accuracy. The application of the FDML mechanism is shown to effectively suppress the damping oscillation， once again underscoring the advantages of the proposed signal generation method.

To validate the practical utility of the proposed radar waveform generation method， both Single-Input Single-Output （SISO） radar and a Multiple-Input Single-Output （MISO） radar systems are established. Firstly， based on the proposed SISO radar system， high resolution radar ranging is successfully realized， clearly distinguishing two closely spaced targets. The measured result shows excellent agreement with the actual distance. For MISO radar system， in the transmitter， the generated signal is emitted by means of time-division multiplexing across multiple transmitter channels. In the receiver， broadband de-chirp processing is performed via IQ mixing. When detecting a drone in an experimental scenario， the target is precisely located， which verifies that the proposed radar waveform generation system is a promising solution to construct efficient and low-complexity microwave photonic radars.

This research is driven by the critical need to overcome the inherent limitations of conventional Radio Frequency （RF）-based Over-The-Horizon （OTH） communication systems. Traditional systems， which rely on the propagation of microwave signals through the atmosphere or via ionospheric reflection， face significant challenges that constrain their performance in modern， high-demand scenarios. These challenges include severely limited bandwidth capacity， which restricts data throughput； vulnerability to both intentional jamming and unintentional electromagnetic interference， compromising reliability； and a lack of operational flexibility， making real-time reconfiguration and multi-channel parallel processing difficult. Furthermore， achieving wideband， cross-frequency operation often necessitates complex， bulky， and power-intensive electronic components. The primary objective of this work is to conceptualize， design， and validate a next-generation OTH communication system architecture that fundamentally transcends these electronic bottlenecks. By strategically integrating the field of microwave photonics—which utilizes light to generate， process， and distribute microwave signals—this study aims to create a system prototype capable of delivering unprecedented levels of bandwidth， robust anti-interference performance， and dynamic reconfigurability. The ultimate goal is to establish a concrete technological foundation for future OTH platforms that can meet the escalating demands for secure， high-capacity， and resilient long-distance tactical and strategic communication links.

To achieve the stated objectives， a comprehensive system design and simulation-based research methodology was employed， centered on a novel architecture that synergizes three core microwave photonic subsystems. The system's front-end is a microwave photonic phased-array antenna. This antenna comprises 64 independent elements designed to simultaneously capture weak wireless signals from free space. The received RF signals from each element are first amplified by a dedicated Low-Noise Amplifier （LNA） to mitigate front-end noise. Subsequently， each amplified RF signal is used to directly modulate the intensity of a continuous-wave optical carrier generated by a Directly Modulated Laser （DML）， thereby translating the electrical signals into the optical domain. This process creates 64 parallel optical RF channels. A critical innovation lies in the beamforming network. The 64 optical signals are fed into a tunable optical delay and attenuation module. A centralized digital control unit precisely and independently adjusts the time delay and attenuation for each of the 64 optical paths. This optical True-Time-Delay （TTD） approach is frequency-independent， enabling wideband， squint-free beam steering and shaping. The individually processed optical signals are then coherently combined via a Wavelength Division Multiplexing （WDM） stage， effectively synthesizing the desired radiation pattern in the optical domain before detection. The combined optical beam is converted back into a consolidated electrical RF signal using a high-speed Photodetector （PD）. This aggregated RF signal is then routed to the second core subsystem： the microwave photonic frequency conversion unit. The heart of this unit is a coherent dual Optical Frequency Comb （OFC） setup. One OFC serves as a multi-wavelength Local Oscillator （LO）， while the other is used for signal modulation. Electro-Optic Modulators （EOMs） are used for precise signal imprinting and frequency shifting. A key technique implemented is Carrier-Suppressed Single-Sideband （CS-SSB） modulation， achieved by carefully biasing the EOMs， which eliminates LO leakage and provides excellent channel isolation. This setup allows for the simultaneous up-conversion or down-conversion of multiple RF channels across a ultra-wide bandwidth. The final subsystem is an integrated communication terminal， which performs demodulation， decoding， and protocol processing on the recovered baseband signals. The feasibility and performance of this integrated architecture were rigorously validated through detailed theoretical modeling and extensive link-level simulations using the industry-standard Optisystem software， which models the complex interactions between optical and RF components.

The simulation and analysis of the proposed microwave photonic OTH system yielded highly promising results across multiple performance dimensions， confirming the effectiveness of the chosen architectural approach. Core Communication Performance： The system successfully demonstrated stable and high-fidelity signal transmission across the entire 4~16 GHz operational bandwidth. Within this spectrum， a sustained communication data rate of 200 Mbps was achieved， representing a significant improvement over typical narrowband OTH links and validating the system's high-bandwidth capability. Reconfigurable Channelized Processing： A major accomplishment was the implementation of reconfigurable microwave photonic channelized frequency conversion. The system possesses the ability to dynamically process signals across 13 independent wavelength channels. This channelization allows for simultaneous， parallel handling of multiple communication streams or signal sub-bands within the wide RF aperture， greatly enhancing spectral efficiency and multi-user capacity. Phased Array Link Performance： For the 64-element microwave photonic phased array link， detailed simulation confirmed that multi-channel parallel processing was feasible with minimal signal quality degradation. Critically， the complex beamforming and signal combining processes were achieved with a signal-to-noise ratio （SNR） degradation of less than 3 dB， indicating highly efficient optical processing and minimal noise introduction from the photonic beamforming network. Optical Frequency Comb Conversion Performance： The dual-OFC frequency conversion subsystem exhibited exceptional precision and spectral purity. Using an array of 23 finely spaced optical comb lines， the system realized the reconfigurable switching functionality for the 13 channels. Specifically， it accomplished the up-conversion of a 336 MHz Intermediate Frequency （IF） signal to the target 4~16 GHz RF band. The converted spectrum showed excellent characteristics： a well-defined channel spacing of 1 GHz， a spurious suppression ratio better than 20 dB （indicating minimal unwanted harmonic generation）， and a high in-band amplitude flatness with fluctuations not exceeding 4 dB across the entire 12 GHz range. This suite of metrics confirms the system's ability to perform precise， MHz-level frequency control and management with high spectral integrity.

In conclusion， this research has successfully established the technical viability and superior potential of a microwave photonic approach to revolutionizing over-the-horizon communication. The proposed and analyzed system architecture， integrating a photonic phased array， a dual-optical-frequency-comb-based channelizer， and an integrated terminal， directly addresses and overcomes the fundamental bandwidth， interference， and flexibility constraints inherent in traditional electronic OTH systems. The simulation results provide compelling evidence that such a system can deliver wideband （4~16 GHz）， high-data-rate （200 Mbps）， multi-channel （13 channels）， and reconfigurable communication links with high spectral purity and efficient beamforming. Beyond the immediate performance metrics， this work lays a critical and substantial foundation for the future engineering and deployment of advanced OTH communication systems. It demonstrates a clear pathway toward building more secure， resilient， and high-capacity strategic communication infrastructures. Future work will naturally focus on the practical implementation of this architecture， including the development of integrated photonic chips to reduce size， weight， and power consumption （SWaP）， experimental validation in real-world propagation environments， and the exploration of advanced signal processing algorithms to further enhance performance. This study marks a significant step forward in the convergence of photonics and wireless communications for national security and civilian long-range connectivity applications.

The advancement of modern communication， radar， and electronic warfare systems imposes stringent requirements on microwave signal sources， including exceptional spectral purity， low phase noise， broad frequency tunability， and operation at high-frequency bands. Conventional electronic oscillators， such as quartz crystal oscillators， typically require multiple frequency-multiplication stages to generate high-frequency signals. This process inherently degrades phase noise by 20log N （where N is the multiplication factor）， thereby limiting their applicability in high-frequency systems. In contrast， the optoelectronic oscillator employs an optoelectronic feedback loop to generate microwave signals， offering the distinctive advantage of low phase noise that is independent of oscillation frequency. This makes the optoelectronic oscillator a pivotal solution for high-frequency， high-stability microwave generation. Since its inception by YAO X S in 1996， research on high-frequency optoelectronic oscillators has advanced considerably. The K-band （18~27 GHz）， with its broad available bandwidth， compact antenna size， and promising applications in satellite communications， high-resolution radar， and future fifth-generation and sixth-generation mobile systems， is regarded as an ideal frequency range for such investigations.

However， conventional optoelectronic oscillators operating at high frequencies are susceptible to multi-mode oscillation and frequency hopping due to the limited quality factor of available radio frequency filters， resulting in degraded side-mode suppression ratio and frequency instability. Injection locking is a well-established technique to suppress side modes and stabilize the output. Nevertheless， it requires an injection signal with a frequency close to the free-running oscillation frequency of the optoelectronic oscillator. At high frequencies， this typically depends on expensive and complex high-frequency signal sources， which hinders the adoption of injection locking in high-frequency optoelectronic oscillators.

This paper proposes and experimentally demonstrates a novel scheme for a fifth-order subharmonic injection-locked optoelectronic oscillator in the K-band， utilizing a dual-polarization Mach-Zehnder modulator. The system exploits the polarization independence of the two optical paths within the dual-polarization Mach-Zehnder modulator. An external， relatively low-frequency radio frequency signal is injected into the modulator that drives the X-polarization state， generating high-order optical sidebands. Following photodetection， the electrical spectrum contains harmonics of the injected signal. A subsequent bandpass filter then selects the fifth harmonic component. This filtered high-frequency signal， precisely at the target K-band frequency （five times the injection frequency）， is injected into a conventional optoelectronic oscillator loop constructed using the Y-polarization state of the same dual-polarization Mach-Zehnder modulator. This architecture effectively integrates harmonic frequency multiplication with injection locking within a single， compact photonic configuration. Crucially， it eliminates the need for a dedicated high-frequency signal source for injection， as the high-frequency locking signal is internally generated from a low-frequency input.

An experimental system was implemented to validate the proposed concept. A 1 550 nm laser diode served as the optical source. The dual-polarization Mach-Zehnder modulator provided independent modulation paths for the X-and Y-polarization states. A low-frequency radio frequency signal from a signal generator was injected into the X-polarization modulator. A photodetector converted the modulated optical signal into an electrical signal. A broadband bandpass filter （24~26 GHz） selected the fifth harmonic， which was then amplified and fed into the optoelectronic oscillator loop formed by the Y-polarization path； this loop included an additional modulator bias point， a fiber delay line， an amplifier， and a filter. When an injection signal with a power of 17.5 dBm and a tunable frequency range of 4.8~5.2 GHz was applied， the system successfully achieved fifth-order subharmonic injection locking， producing stable single-mode oscillation outputs at 24.0 GHz， 24.5 GHz， 25.0 GHz， 25.5 GHz， and 26.0 GHz， respectively.

The performance of the injection-locked optoelectronic oscillator was thoroughly characterized. Output spectra at all five frequencies exhibited excellent spectral purity， with side-mode suppression ratio values consistently exceeding 70 dB—a significant improvement over free-running optoelectronic oscillators， which are prone to multi-mode oscillation. The output power variation across the 24-26 GHz tuning range was less than 1 dB， indicating good gain flatness. Phase noise measurements revealed outstanding performance： below -70 dBc/Hz at 10 Hz offset and below -129 dBc/Hz at 10 kHz offset for all output frequencies. The near-in phase noise is primarily determined by the quality of the low-frequency injection source， whereas the far-out phase noise retains the inherently low noise floor of the optoelectronic oscillator's long delay line， thereby effectively circumventing the 20log N degradation associated with pure electronic frequency multiplication. Frequency stability， assessed via Allan deviation measurements over averaging times （τ） from 1 μs to 10 s， demonstrated consistent behavior across the five output frequencies. For short averaging times （τ<1 s）， the stability followed that of the injection source due to the locking effect. For longer τ， stability was influenced by environmental perturbations on the fiber delay.

In conclusion， this work successfully demonstrates a tunable， high-performance K-band optoelectronic oscillator based on a dual-polarization Mach-Zehnder modulator-enabled subharmonic injection-locking scheme. The system efficiently generates high-frequency （24~26 GHz）， high-spectral-purity microwave signals using only a low-frequency radio frequency source， thereby overcoming key limitations of traditional approaches. The demonstrated performance in terms of side-mode suppression ratio （>70 dB） and phase noise （<-70 dBc/Hz at 10 Hz offset， <-129 dBc/Hz at 10 kHz offset） meets the requirements for advanced microwave systems. Although the current tuning range is constrained by the components employed （filter bandwidth， modulator response）， the underlying principle is not inherently frequency limited. Utilizing devices with higher bandwidths or adopting cascaded modulation structures could potentially extend operation to even higher frequencies， including millimeter-wave and terahertz bands. This approach offers a promising and practical photonic pathway toward realizing compact， low-noise， and tunable high-frequency oscillators

Ionic liquids， as a new type of molten salts with high thermal stability， low vapor pressure， and strong designability， have important application value in cutting-edge fields such as electrochemistry， catalytic synthesis， and biomedicine. However， the accuracy and efficiency of ionic liquid type identification still need to be continuously explored and optimized. Traditional characterization methods， such as infrared spectroscopy and nuclear magnetic resonance， usually rely on large precision instruments， which have limitations such as complex operating procedures， high equipment costs， and long analysis cycles. At the same time， the inherent strong hygroscopicity of ionic liquids makes the control of sample purity more stringent， and existing moisture detection methods find it difficult to achieve rapid and precise measurement. Against this background， metasurfaces， as two-dimensional artificial materials that can flexibly control the amplitude， phase， and polarization of electromagnetic waves， provide a new technical path for the development of high-performance sensing technologies. This type of structure has both high sensitivity and non-contact detection advantages， and has shown significant potential in dielectric property analysis and substance identification. However， existing metasurface sensors still have certain limitations in practical applications， such as being easily affected by external electromagnetic interference or requiring direct contact with samples. These issues not only reduce measurement accuracy but may also cause sensor contamination， thereby limiting their widespread application in practical scenarios.

Aiming at the technical bottlenecks of ionic liquid type identification and moisture content detection mentioned above， this paper proposes a metasurface microwave sensor based on a dielectric substrate integrated with a double-layer metal resonant structure. The sensor converts the dielectric properties of ionic liquids into significant changes in resonant frequency shift and resonance linearity through its unique electromagnetic field localization and enhancement mechanism， providing a new way to achieve rapid and precise sensing analysis. To deeply study the working mechanism of the sensor， this study adopted a multi-level research method： from the physical mechanism level， the formation and energy distribution of electromagnetic resonance were intuitively presented through surface current distribution analysis； from the model construction level， the physical structure was transformed into circuit parameters through equivalent circuit analysis， and the regulation law of resonant frequency was quantitatively revealed； from the performance prediction level， the electromagnetic response characteristics of the sensor were accurately obtained through full-wave numerical simulation， and the structure was optimized； from the final verification level， experimental tests confirmed that the sensor can not only accurately distinguish six different types of ionic liquids but also achieve high-precision detection of trace moisture content.

Before conducting experimental characterization， this study first compared and analyzed the reflection characteristic changes of the sensor before and after loading ionic liquids in the 7~10 GHz frequency band based on electromagnetic simulation software. The simulation results show that the introduction of ionic liquids not only changed the original resonant mode of the sensor but also induced a stronger electromagnetic response through the dielectric regulation mechanism， thereby verifying that the metasurface sensor has excellent dielectric sensitivity and electromagnetic regulation capabilities. Subsequently， six representative ionic liquids were selected as the measured samples for actual measurement analysis. The experimental measurement results show that when the sample to be tested in the sample holder is changed from ［EMIm］［BF₄］ to ［OMIm］［BF₄］， the resonant peak position of the reflection spectrum shifts from 8.37 GHz to 8.86 GHz， resulting in a significant frequency shift of 490 MHz. Calculations show that the sensor's average sensitivity to dielectric constant changes can reach 185.42 MHz/ε′. In addition， this study systematically evaluated the sensor's ability to detect trace moisture content. Experimental data show that when the water content increases from 0% to 10%， the resonant peak of the reflection spectrum shows a significant frequency shift of 180 MHz （8.22 GHz→8.40 GHz）， proving that the sensor can effectively detect moisture changes in ionic liquids at the ppm level.

In summary， this paper successfully designed and verified a metasurface microwave sensor based on a double-layer metal resonant unit. By using a three-layer structure constructed with an FR4 epoxy resin substrate， combined with an open sample holder and a fully copper-plated bottom plate design， the sensor exhibits excellent detection performance in the 7~10 GHz working frequency band， achieving non-contact and high-precision detection of ionic liquid types and their moisture content. Simulation and experimentalresults show that the sensor has different characteristic frequency responses for six typical ionic liquids （including ［EMIm］［BF₄］， ［BMIm］［SCN］， ［BMIm］［OTf］， ［BMIm］［BF₄］， ［HMIm］［NTf₂］， and ［OMIm］［BF₄］）， with a maximum frequency shift of 490 MHz and a detection sensitivity of 185.42 MHz/ε′. In terms of moisture detection， the sensor shows a good resonant response to 0~10% moisture content changes in ［EMIm］［BF₄］ solutions， with a resonant frequency shift of 180 MHz. The metasurface sensor designed in this study has high sensitivity and good measurement repeatability， providing an effective technical means for ionic liquid purity detection and deterioration monitoring， and has important engineering application prospects in fields such as chemical process control and real-time monitoring in hazardous environments.

Frequency-Modulated Continuous-Wave （FMCW） radar is widely used in military， autonomous driving， and other fields for its high resolution， low power consumption， and strong anti-interference. However， traditional microwave electronic radars fail to meet broadband signal generation/processing needs， leading to the development of microwave photonic radar. By combining photonics and electronics， it overcomes the “electronic bottleneck，” with optical frequency multiplication and dechirping reception architectures gaining attention for large bandwidth and simple structure. Nevertheless， in this architecture， frequency multiplication degrades phase noise （by 20 log₁₀（n） dB for multiplication factor n）， while electro-optic/optoelectronic conversion worsens it. Phase noise impairs radar accuracy， resolution， and anti-interference， limiting broadband advantages. Existing suppression technologies for microwave photonic radar often suffer from complexity， high cost， or new noise introduction， demanding more effective compensation.

This paper proposes a phase noise compensation scheme for microwave photonic FMCW radar using deskew filtering. The system adopts an optical quadrupling structure （boosting distance resolution） plus reference delay and mixing branches. The baseband linear frequency-modulated （LFM） signal splits into two paths： one drives the microwave photonic quadrupling module to generate a transmitted signal （4× baseband frequency/bandwidth， 4× phase noise）， whose echo is processed via a microwave photonic mixer to get an echo dechirped signal with phase jitter； the other undergoes reference delay/mixing to produce a reference dechirped signal. Deskew filtering compensates the echo dechirped signal as follows： apply Hilbert transforms to both signals for complex signals， estimate phase noise via the reference， remove phase noise's delay dependence in the echo using the deskew filter， and eliminate phase noise to mitigate radar performance impacts.

An experimental setup was built to verify the feasibility of the proposed scheme. The initial frequency of the baseband linear frequency-modulated signal was 5 GHz， with a bandwidth of 100 MHz. After passing through the microwave photonic quadrupling module， a quadrupled frequency signal in the range of 20~20.4 GHz was generated， effectively expanding the bandwidth. The reference and echo dechirped signals were collected and processed using the deskew filtering algorithm. To evaluate the effectiveness of phase noise compensation in the dechirped echo signal， we analyze two key aspects： first， comparing the stability of the half-period of the dechirped echo signal before and after compensation， and second， examining its phase noise characteristics. A reference group processed using the equal phase interval sampling method was introduced for comparative analysis. The results show that before compensation， the standard deviation of the half-period was 0.54 ns. After compensation with the equal phase interval sampling method， this value decreased to approximately 0.24 ns. Further compensation using the deskew filtering method reduced the standard deviation to 0.15 ns， representing a 3.6 times improvement in stability compared to the pre-compensation state. This indicates that the phase noise compensation achieved through the deskew filtering method significantly enhances the stability of the half-period of the dechirped echo signal. Regarding phase noise characteristics， the experimental results demonstrate that within the frequency offset range of less than 10 kHz， the deskew filtering method outperforms the equal phase interval sampling method in suppressing phase noise， resulting in a lower phase noise level in the processed signal. Additionally， a time-frequency analysis was conducted on the signals before and after compensation to compare the range profiles. The results reveal that the target energy in the compensated range profile becomes more concentrated， and the deviation range of the distance measurement results is effectively suppressed. Specifically， the distance corresponding to 10 dB bandwidth decreased from 49.57 m （pre-compensation） to 41.28 m （post-compensation）， while the standard deviation of distance measurement results reduced from 0.97 m （pre-compensation） to 0.78 m （post-compensation）. Collectively， these findings demonstrate that the deskew filtering method effectively improves the range resolution and distance measurement stability of the radar system.

This work aims to design， fabricate， and characterize a low-power， reconfigurable 16×16 thermo-optic switch array on a polymer-based photonic platform， addressing the critical challenges of high consumption and thermal crosstalk associated with scaling large-scale photonic integrated circuits. The primary goal is to develop a reliable hardware platform that demonstrates the feasibility of utilizing the unique material properties of polymers， specifically a high thermo-optic coefficient and low thermal conductivity for efficient and dense on-chip dynamic optical path control. The overarching purpose is to provide a foundational device solution to enable future low-power， flexible， and intelligent photonic systems for applications such as data center optical interconnects， photonic neural networks， and secure optical communications. The central research questions involve validating the performance metrics of a scalable polymer waveguide switch architecture and establishing its advantages over traditional inorganic platforms.

The study employed a comprehensive methodology integrating theoretical design， numerical simulation， process fabrication， and systematic experimental characterization. The core architectural innovation was the design of a cascadable unit cell termed the Directional Coupler-Honeycomb （DC-HC） structure， which combines a DC for power switching and a honeycomb HC interferometer for phase modulation. Multi-segment S-bend waveguides interconnect these units to achieve the required 127 μm port pitch for fiber array compatibility. A low-loss waveguide structure was meticulously designed and simulated. The core layer utilized a fluorinated photosensitive polymer， FSU-8， chosen for its low optical absorption at the 1 550 nm communication wavelength. The cladding material was an Organic-Inorganic Grafting Polymethyl Methacrylate （OIG-PMMA）， selected for its enhanced thermal stability， self-planarization capability， and precise refractive index tunability. The optimized cross-section featured a 3 μm × 3 μm core， a 2 μm coupling gap between adjacent DC waveguides， and a 3 μm separation between the aluminum thin-film heater and the waveguide core. Beam Propagation Method （BPM） simulations using R-soft software were extensively conducted to optimize the waveguide geometry， including the DC coupling length， bending losses， and fiber-to-chip coupling loss. Finite Element Method （FEM） thermal simulations in COMSOL Multiphysics were performed to analyze heat distribution and cross-talk， confirming effective thermal confinement within individual switch units. Fabrication leveraged standard， cost-effective， and Complementary Metal-Oxide-Semiconductor （CMOS）-backend-compatible processes. The waveguide layers were defined through spin-coating， Ultraviolet （UV） lithography， and etching. Aluminum electrodes with a serpentine geometry were patterned via wet etching and precisely aligned atop the modulation arm of each DC unit. The fabricated devices were characterized using optical microscopy and SEM to verify dimensional accuracy and morphology. A dual-system testing approach was implemented for performance evaluation. A static switching performance test system was constructed using a 1 550 nm continuous-wave laser source， a polarization controller， single-mode fibers for edge coupling， and an optical power meter. This system measured key static parameters： insertion loss and the required switching power consumption by applying a controlled DC voltage to the heaters. A separate dynamic pulse response system was built， incorporating an Arbitrary Waveform Generator （AWG）， a Photodetector （PD）， and an oscilloscope. This system measured the temporal response， specifically the rise and fall times， of the switches under square-wave modulation at frequencies of 500 Hz and 1 kHz.

The fabricated 16×16 polymer thermo-optic switch array exhibited compact dimensions of approximately 7.0 cm in length and 0.2 cm in width. Comprehensive testing at the 1 550 nm operational wavelength yielded a comprehensive set of performance data. The device achieved a minimum insertion loss of 11.4 dB. A detailed loss budget analysis attributed this to constituent factors： waveguide propagation loss， structural loss from cascaded bends， fiber-to-chip coupling loss， and additional scattering losses arising from fabrication imperfections such as sidewall roughness and imperfect cleavage planes. A core achievement was the demonstration of low-power operation. The minimum power required to toggle a single channel between its cross and bar states was measured to be 33.38 mW. This corresponds to applying a temperature change of approximately 21 K to the modulation arm， as predicted by thermal-optical simulations. The maximum extinction ratio achieved was 12.12 dB. While this value shows room for improvement compared to some inorganic platforms， it is attributed in part to a slight broadening of the fabricated waveguide width， which can support higher-order modes and introduce phase errors， as confirmed by supplementary simulations. Dynamic performance tests confirmed operation in the sub-millisecond regime. Under 500 Hz square-wave modulation， the measured rise time was 226.7 μs， and the fall time was 294.0 μs. When driven at a higher frequency of 1 kHz， the response times were 222.2 μs （rise） and 255.9 μs （fall）， establishing this as the practical operational limit for the current device design. Simulation results for the full array predicted an average optical transmission of 71.87% and an adjacent channel crosstalk better than -31.94 dB for a signal routed from a single input to any output， indicating good routing fidelity. Crucially， thermal simulation results validated a key material advantage： the temperature field from an active heater decayed to ambient levels within 20~30 μm from its center. Given that adjacent switch electrodes are spaced approximately 172 μm apart， this confirms effective suppression of thermal crosstalk， a major bottleneck in densely packed inorganic switch arrays. A comparative analysis with state-of-the-art switches on platforms like silicon-on-insulator （SOI）， Silica， and lithium niobate on insulator （LNOI） contextualizes the results. The polymer-based array demonstrates a compelling trade-off： its switching power is significantly lower than that of typical SOI or silica-based units， its unit-length propagation loss is advantageous， and its response speed is competitive with other polymer and hybrid systems. Most notably， it delivers this performance at a substantially larger port count， highlighting the scalability benefits of the polymer platform for large-scale photonic networks.

This research successfully validates the polymer material platform as a highly viable and competitive candidate for implementing scalable， low-power reconfigurable photonic integrated circuits. The developed DC-HC architecture and the associated fabrication methodology provide a concrete pathway toward constructing large-scale optical switching networks. The work conclusively demonstrates that the inherent material properties of polymers， specifically the high thermo-optic coefficient and low thermal conductivity， can be effectively harnessed to overcome key limitations of traditional platforms， namely high consumption and thermal crosstalk in dense arrays. The fabricated device， with its integrated combination of low switching energy， acceptable optical performance， microsecond-scale reconfigurability， and inherent programmability， establishes a significant hardware prototype. It serves as a critical enabling component for next-generation systems requiring dynamic optical path management. The findings are offering a practical device solution and a clear material and structural strategy for future work aimed at achieving even larger scale， lower loss， and higher-speed intelligent photonic processing systems.

Non-polarizing beam splitter is an optical component widely used for beam splitting. It is primarily designed to divide incident light into two beams with specified reflection and transmission ratios while maintaining the original polarization state of the input light. Thanks to its low polarization discrimination， minimal stress birefringence， and strong polarization-maintaining capability， non-polarizing beam splitters are extensively employed in optical systems such as space remote sensing， projectors， and Michelson interferometers. Although an ideal non-polarizing beam splitter is designed to preserve the polarization state of the incident light， practical non-polarizing beam splitters exhibit certain non-ideal polarization characteristics due to inherent limitations in materials and coating designs. Moreover， these polarization properties are highly sensitive to both the angle and direction of the incident light. In some complex optical systems， a non-polarizing beam splitter may need to simultaneously process light incident from both forward and reverse directions， inevitably operating under reverse incidence. Therefore， a systematic study of the polarization properties of the non-polarizing beam splitter under reverse incidence is of great significance for high-precision optical measurement and polarization-sensitive systems. Currently， most research focuses on the influence of factors such as temperature and angular deviation on the polarization performance of the non-polarizing beam splitter， while studies on polarization characteristics under reverse incidence remain limited. This paper addresses scenarios in complex optical systems where the non-polarizing beam splitter must be used in reverse. We systematically analyze the polarization properties of the non-polarizing beam splitter under different incident directions from three perspectives： fundamental principles， simulation analysis， and experimental validation. The variations in polarization characteristics of both reflected and transmitted channels with respect to incident wavelength are analyzed and compared， and the mechanism underlying the influence of incident direction on the polarization properties of the non-polarizing beam splitter is revealed.

To achieve this objective， a combined theoretical， numerical， and experimental approach was adopted. Numerical simulations were performed using Essential Macleod thin-film design software to construct a realistic model of a non-polarizing beam splitter coating stack. The model enabled quantitative calculation of wavelength-dependent polarization parameters， including diattenuation and phase retardation， for both reflected and transmitted channels under forward and reverse incidence conditions. The simulations covered the visible spectral range and assumed identical angles of incidence for both illumination directions to isolate the effect of direction reversal. To validate the simulation results， high-precision experimental measurements were conducted using Mueller matrix ellipsometer. Commercial non-polarizing beam splitter samples （models CCM1-BS013/M and CCM5-BS016/M） were selected as representative specimens. The complete 4×4 Mueller matrices of the samples were measured over a wavelength range from 380 nm to 800 nm under both forward and reverse illumination. Subsequently， the Lu-Chipman decomposition method was applied to the measured Mueller matrices to extract key polarization parameters， specifically diattenuation and phase retardation， for the reflected and transmitted channels. Multiple measurements were performed to ensure repeatability and to assess sample-to-sample consistency.

The simulation results reveal a pronounced dependence of polarization characteristics on the direction of incident light， particularly for the reflected channel of the non-polarizing beam splitter. Under forward and reverse incidence， substantial discrepancies were observed in both diattenuation and phase retardation of the reflected beam. Specifically， the maximum change in phase retardation between the two incidence conditions reached approximately 53.64°， with an average variation on the order of 29.49°， while the maximum difference in diattenuation was approximately 0.321， with an average difference of about 0.027 3. These findings indicate that reversing the illumination direction significantly alters the polarization behavior of the reflected channel. In contrast， the transmitted channel exhibited negligible variation in both diattenuation and phase retardation across the same conditions. Experimental measurements corroborated these trends with strong qualitative and quantitative agreement. Mueller matrix ellipsometry data showed that， for the reflected channel， the maximum difference in diattenuation between forward and reverse incidence was approximately 0.11， with an average difference of around 0.03， while the maximum difference in phase retardation reached approximately 51.5°， with an average difference of about 28.76°. Importantly， repeated experiments on different non-polarizing beam splitter samples consistently demonstrated the same directional dependence： significant polarization variation in the reflected channel and nearly identical polarization behavior in the transmitted channel under both illumination directions.

The accurate and efficient calculation of the Beam Shape Coefficients （BSCs） is one of the key issues in researching the interaction between a structured or shaped beam and the particles. For this reason， different techniques have been established， such as the quadrature method， the Localized Approximation （LA） or its variants， the Finite Series （FS） method， the Angular Spectrum Decomposition （ASD）， and the others. Among these methods， the Localized approximation has been widely used due to its advantages including mainly the efficiency in numerical calculation， the conciseness of the expressions and the straightforwardness in deducing the BSCs for the beams in both the on-axis and off-axis scenarios. However， this method， just as it is named， is an approximate one. The beam remodeling takes place when the beam field is reconstructed from the BSCs， i.e. the reconstructed beam field deviates from the originally given field. Up to date， the remodeling of the beam field has not been studied systematically.

In this work， the two-step indirect method is employed to study the remodeling effects of the localized approximation method for the Gaussian beams. In the first step， the expression of the BSCs is obtained， by using the localized approximation， for the Gaussian beam which is centered in the coordinate system （called beam system） and is described by using a scalar potential function （therefore the BSCs are called scalar BSCs）. Subsequently， the scalar translational addition theorem is used to transform the BSCs into another coordinate system whose axes are parallel to those of the beam system. The second coordinate system in which the spherical particle is centered is called particle system. In the second step of the indirect method， the electric and magnetic （EM） fields of the Gaussian beam are described by using the scalar potential function together with a polarization parameter. Based on this relation， the BSCs of the EM field （called vector BSCs or EM BSCs） are expressed as a linear combination of the scalar BSCs. In this way， the EM BSCs for the off-axis located Gaussian beam are obtained indirectly from the scalar BSCs of the centered beam. The two-step indirect method simplifies the analytical derivation of the BSCs. The expressions of the EM BSCs which are directly deduced in the localized approximation for the off-axis located Gaussian beam are used in the numerical calculations for making a comparison. It is found that the indirect method is at least eight times faster than the direct method in numerical calculation of the BSCs.

The remodeling of the localized approximation is studied， based on a comparison between the originally given field of the Gaussian beam and the fields which are reconstructed from the directly and/or indirectly calculated EM BSCs. The numerical results reveal that， in the direct LA method， the axisymmetric structure of the Gaussian beam is broken in the reconstructed beam field， exhibiting spurious-peaks in the electric field. When the off-axis distance becomes sufficiently large， a ring structure is produced in the field. The deviation of the reconstructed beam field from the given one increases gradually along the increase of the off-axis distance. However， in the indirect method， the reconstructed field is always axisymmetric and the discrepancy between the reconstructed and given fields is independent of the off-axis distance. In both the direct and indirect methods， the reconstructed beam fields deviate from the given one， showing a close dependence on the beam waist radius. Namely， the reconstructed beam fields agree much better with the given field when the beam waist radius is large， but the quality of the remodeled fields become poorer when the beam waist radius decreases， especially when the beam waist radius is close to or less than the wavelength of the light beam.

It is concluded that， compared with the direct localized approximation method， the two-step indirect method has advantages in analytical derivation of the BSCs， in conciseness of the expressions， in efficiency of numerical calculation， and in quality of reconstructed beam field. Besides， the work presented here suggests a warning against the use of the direct/indirect LA methods for strongly focused Gaussian beams and the use of the direct LA for large off-axis located beams.

Single-frequency continuous-wave lasers are critically important for advanced applications in quantum information science， high-precision metrology， and lidar systems. These applications demand laser sources that combine a narrow linewidth， low amplitude and frequency noise， and high temporal coherence. A significant challenge in the field is scaling the output power of such lasers while simultaneously preserving their superior spectral purity and high stability. Conventional techniques for achieving single-frequency operation often face limitations in power scaling due to thermal effects and nonlinearities.

This research demonstrates a high-power， single-frequency Nd∶YVO₄ laser system utilizing the seed injection-locking technique. A stable， narrow-linewidth fiber laser operating at 1 064 nm serves as the master oscillator. The slave laser is configured as an “8”-shaped ring resonator， which is pumped by an 888 nm diode laser. A composite Nd∶YVO₄ crystal is used as the gain medium to mitigate thermal lensing effects. Active frequency stabilization is implemented using the Pound-Drever-Hall （PDH） method. An error signal， derived from the cavity transmission， feeds back to a piezoelectric transducer to control the slave cavity length， thus locking it to the seed laser frequency.

Under optimal injection-locking conditions and at a pump power of 38.12 W， the laser delivers a maximum output power of 13.5 W in a single longitudinal mode. The linewidth of the amplified output is measured to be 7.0 kHz. This represents only a minor broadening compared to the 5.6 kHz linewidth of the original seed laser. The system exhibits excellent power stability， with a root-mean-square power instability of less than 0.18% over a continuous 60-minute period. Furthermore， the frequency stability is significantly enhanced through injection locking. The long-term wavelength drift is reduced to 132.4 MHz， a substantial improvement over the 300 MHz drift observed for the free-running seed laser. A detailed frequency noise characterization reveals effective suppression of noise at low Fourier frequencies （1~100 Hz） in the locked state compared to the free-running slave laser. A slight increase in noise is observed at higher frequency offsets， which is attributed to residual mechanical vibrations from the locking actuator. These results confirm that the seed injection-locking technique successfully amplifies the optical power while maintaining the spectral characteristics of the seed. Crucially， this high stability is achieved without the need for active frequency stabilization of the seed laser itself. This work contributes by achieving a compelling combination of high power （13.5 W）， narrow linewidth （7.0 kHz）， and high stability at the important 1 064 nm wavelength. A key finding is that this high stability is accomplished without requiring active stabilization of the seed laser itself. The results robustly demonstrate that the seed injection-locking technique is a highly effective method for amplifying optical power while simultaneously preserving and even enhancing the frequency stability and spectral characteristics of the original seed source.

In conclusion， this research successfully realizes a high-power， narrow-linewidth， low-noise single-frequency Nd∶YVO₄ laser. The system exhibits outstanding power and frequency stability， making it suitable for demanding applications. The approach provides a viable and practical pathway for developing high-performance single-frequency lasers. Future work will focus on refining the feedback control system to achieve even lower frequency noise. Additionally， the integration of intracavity nonlinear frequency conversion techniques， such as second harmonic generation， could be implemented to produce high-power， single-frequency radiation at other strategically important wavelengths， further expanding the utility of this laser architecture.

Accurate monitoring of atmospheric CO₂ and CH₄ column concentrations is crucial for understanding greenhouse gas source-sink processes， assessing the effectiveness of emission reduction measures， and formulating climate change mitigation strategies. Fourier Transform Infrared （FTIR） spectroscopy， known for its high spectral resolution and sensitivity， is a key ground-based remote sensing technique. The portable EM27/SUN FTIR spectrometer， developed by KIT and Bruker， features a compact and robust design suitable for long-term field observations. Its core is an interferometer： incoming solar radiation is split， reflected by fixed and moving mirrors， and recombined to generate interference signals. Subsequently， the PREPROCESS program and the PROFFAST retrieval algorithm are applied to retrieve the column concentrations of the target gases.

To further improve the retrieval accuracy and reliability of EM27/SUN， this paper evaluates the reliability of the EM27/SUN by comparing its retrieval results in the Hefei area with those from the TCCON high-resolution FTIR spectrometer. Calibration formulas were developed to optimize the EM27/SUN retrieval performance. After calibration， the daily average deviation of the column-averaged dry-air mole fraction of carbon dioxide （XCO₂） between the EM27/SUN and TCCON was 1.259 0 ppm， while that of methane （XCH₄） was 0.003 7 ppm. Furthermore， the observation precision of XCO₂ and XCH₄ was calculated based on continuous observation data from the Dalian observation site during the midday period （11∶00~13∶00） on October 23rd. The observation precision for XCO₂ was found to be 0.12 ppm， and for XCH₄， it was 0.9 ppb， which meets the precision requirements for ground-based remote sensing of greenhouse gas monitoring.

Using the PROFFAST retrieval algorithm， time series of atmospheric XCO₂ and XCH₄ were obtained for selected dates in February， March， September， October， and November 2023 in the Dalian Changxing Island region. The mean XCO₂ was （422.41±0.34） ppm （parts per million by volume）， while the mean XCH₄ was （1.915 2±0.001 8） ppm. The observational data were divided into two periods： the late winter to early spring transition period （late February to March） and the mid-to-late autumn period （late September to early November）. The mean XCO₂ during the late winter to early spring period （422.99 ppm） was higher than that during the mid-to-late autumn period （421.55 ppm）. In contrast， XCH₄ showed an opposite trend， with a lower mean during the late winter to early spring transition period （1.909 9 ppm） compared to the mid-to-late autumn period （1.923 2 ppm）. Although CO₂ and CH₄ have different source-sink mechanisms， their concentration variations exhibited certain correlations in specific months， implying common influences on their variations. The correlation coefficient was 0.73 in the late winter to early spring period and 0.69 in the mid-to-late autumn period. By analyzing the characteristics of CO₂ and CH₄ concentration variations during the observation period and combining this with a backward trajectory model， possible source-sink processes were investigated.

Furthermore， a comparison was conducted between the EM27/SUN observation data and the corrected data from the Japanese GOSAT satellite. The results showed high consistency， with correlation coefficients of 0.87 for XCO₂ and 0.76 for XCH₄， respectively. Additionally， GOSAT satellite data （monthly averages） from December 2021 to November 2024 were analyzed， revealing distinct seasonal variations for both gases： XCO₂ peaked in spring and winter and reached its lowest in summer （spring>winter>autumn>summer）， whereas XCH₄ was lower in spring and higher in summer and autumn （autumn>summer>winter>spring）. Both gases exhibited a clear increasing trend over the years. This study provides important data support for greenhouse gas source-sink analysis in the Dalian region. The portable FTIR spectrometer EM27/SUN can accurately observe atmospheric CO₂ and CH₄ column concentrations and their variations， making it suitable for validating satellite remote sensing data in remote areas.

With the rapid development of cloud computing and large language models， global mobile data traffic has experienced exponential growth， imposing higher demands on data center interconnection technologies. To achieve high-speed data transmission at 800 Gbit/s， coherent optical communication with high spectral efficiency and support for advanced modulation formats has emerged as a key solution for short-reach optical interconnects. However， traditional coherent receivers are hindered by high Digital Signal Processing （DSP） complexity， which makes it difficult to meet stringent power and cost requirements. To address this， this paper proposes a low-complexity DSP scheme based on baud-rate sampling， which reduces computational complexity while maintaining performance for short-reach coherent optical communications.

The proposed DSP architecture integrates a baud-rate clock recovery module with a two-stage adaptive equalizer， both designed for low complexity. The clock recovery module employs a split-path design comprising four independent units， each utilizing a sign-MM Timing Phase Error Detection （TPED） algorithm. Operating at the symbol rate， this module uses a sign function to extract timing errors from signal polarity changes. This approach enables robust compensation of Sampling Clock Offsets （SCO） and In-phase/Quadrature （I/Q） skew without requiring carrier recovery. Subsequently， a Two-stage Real-valued Multiple Input Multiple Output （RV-MIMO） adaptive equalizer is applied. Its tap configuration is flexible： the first stage uses N_{\mathrm{1}} main taps to mitigate intra-polarization impairments， such as chromatic dispersion and inter-symbol interference， while the second stage includes N_{\mathrm{2}} cross-term taps and a 4×4 RV-MIMO with N_{\mathrm{3}} taps to handle residual inter-polarization crosstalk and polarization demultiplexing. This tunable structure allows the equalizer's complexity to be dynamically adjusted based on channel conditions， thereby optimizing the performance-complexity balance.

Simulation results under a 56 GBaud dual-polarization 16QAM transmission over 2 km standard single-mode fiber demonstrate the effectiveness of the proposed scheme. The sign-MM TPED exhibits robust performance against impairments such as carrier frequency offset and phase noise， with timing jitter remaining below -45 dB under various conditions. The two-stage equalizer reliably achieves Bit Error Rate （BER） performance below the hard-decision forward error correction threshold， even in the presence of IQ skew. Compared to conventional oversampling-based DSP schemes， the proposed approach reduces the number of real multipliers required in the equalizer by approximately 50%. This complexity reduction is achieved with only minor penalties of 0.4 dB in Optical Signal-to-Noise Ratio（OSNR） tolerance and 1.1 dB in Received Optical Power（ROP） sensitivity.

In summary， this work presents a low-complexity DSP solution for short-reach coherent optical interconnects， using baud-rate sampling to significantly reduce computational complexity while maintaining performance. The integrated architecture， which combines I/Q-independent clock recovery with a configurable-tap adaptive equalizer， enhances robustness against I/Q skew and sampling offsets， making it suitable for data center applications. These attributes collectively make the scheme a practical and efficient candidate for high-speed， power-and cost-sensitive applications such as intra-data center interconnects.

3D reconstruction techniques have been extensively applied across a wide range of fields in recent years， including medical imaging， robotic navigation， virtual and augmented reality， 3D animation modeling， and online product inspection. Among these techniques， Fringe Projection Profilometry （FPP） has attracted significant attention owing to its non-contact measurement capability， full-field acquisition， and high spatial resolution. These advantages have led to its widespread adoption in industrial inspection， cultural heritage preservation， biomedical applications， and reverse engineering. Within an FPP system， phase recovery constitutes a fundamental and indispensable step， as both the accuracy and computational efficiency of phase estimation directly determine the quality of the reconstructed 3D surface and the overall system performance. Consequently， the development of fast， accurate， and robust phase recovery methods remains a central research topic in fringe projection profilometry.

Traditional phase retrieval techniques mainly include Fourier Transform Profilometry （FTP） and multi-step Phase-Shifting Profilometry （PSP）. Multi-step phase-shifting methods achieve high phase accuracy by projecting and capturing multiple phase-shifted fringe patterns； however， their reliance on multiple frames significantly restricts their applicability in dynamic scenes or high-speed measurement scenarios. In contrast， Fourier transform-based methods can extract phase information from a single fringe image， offering improved measurement efficiency. Nevertheless， their performance tends to degrade considerably when dealing with complex surface geometries， depth discontinuities， severe noise， or strong surface reflectivity， resulting in reduced accuracy and robustness. In recent years， researchers have increasingly integrated deep learning with phase extraction and phase unwrapping processes， achieving high reconstruction accuracy while significantly reducing the number of required projection patterns. Compared with conventional analytical approaches， deep learning-based methods exhibit superior capability in handling noise， nonlinear distortions， and surface discontinuities. Despite these advantages， existing deep learning-based absolute phase recovery methods still suffer from several limitations. Existing deep learning-based absolute phase recovery methods mainly fall into two categories. The first predicts the numerator and denominator terms of wrapped phase at three different frequencies separately， then computes the absolute phase using multi-frequency or number-theoretic methods. The second employs either a dual-network or dual-decoding architecture to separately predict the numerator and denominator terms of the high-frequency wrapped phase along with the fringe order， thereby obtaining the absolute phase. The former suffers from error accumulation during multi-frequency unwrapping， leading to significant inaccuracies and poor stability. The latter incurs high computational complexity and low inference efficiency due to the multi-network or dual-decoder design.

Aiming to address the issues of error accumulation and high model complexity inherent in existing methods， this paper proposes a novel multi-task phase recovery framework based on GD-UNet （UNet with an Information Gather-and-Distribute Mechanism）. The proposed method enables simultaneous prediction of the wrapped phase and fringe order within a single network， thereby allowing direct recovery of the absolute phase. Built upon the classical UNet architecture， the proposed model incorporates residual modules to enhance feature extraction capability and improve training stability. In addition， by integrating an information gather-and-distribute mechanism， the network supports multi-task learning and directly outputs the numerator and denominator of the wrapped phase as well as the corresponding fringe order. This unified design eliminates the need for multiple networks， effectively reducing computational complexity and inference time. Furthermore， to enhance the robustness of fringe order prediction-particularly in challenging regions such as object boundaries， sharp depth discontinuities， and highly reflective surfaces-a fringe order correction strategy based on Connected Domain Segmentation （CDS） of the wrapped phase is introduced. The proposed CDS-based correction method exploits the spatial continuity of the wrapped phase， under the assumption that all pixels within the same connected domain theoretically share an identical fringe order. Since prediction errors tend to occur more frequently near domain boundaries， the final fringe order for each connected region is determined through majority voting， thereby effectively suppressing local misclassifications. This strategy significantly improves the stability and accuracy of fringe order estimation without introducing additional computational burden. Extensive experiments are conducted to evaluate the performance of the proposed method under various conditions， including different surface materials， complex geometries， and discontinuous scenes. Both quantitative and qualitative comparisons with state-of-the-art methods demonstrate that the proposed GD-UNet-based framework achieves superior phase recovery accuracy while maintaining lower model complexity and faster inference speed.

The experimental results indicate that the proposed approach effectively mitigates error accumulation， enhances robustness against noise and surface reflectivity， and exhibits strong generalization capability across diverse measurement scenarios. In conclusion， this paper aims to achieve stable and high-precision phase recovery from a single fringe image in complex scenes containing large surface discontinuities or isolated objects through a unified network model. A single-frame phase extraction method is presented， in which only one fringe image is required， and a single network simultaneously predicts the numerator and denominator of the wrapped phase as well as the fringe order map. The proposed approach demonstrates clear advantages in both accuracy and efficiency. Comprehensive experimental evaluations confirm that the method achieves excellent measurement accuracy and strong robustness in challenging scenarios， including complex surface reconstruction， high noise interference， and multi-material object measurement.

The structure and coloration of butterfly scales play a crucial role in regulating their biological behavior. Accurate three-dimensional imaging of these structures is essential for understanding their functional mechanisms. Traditional imaging techniques usually may suffer from limitations such as sample damage， slow imaging speed， and inaccurate three-dimensional reconstruction. To address these issues， this study employed Fourier Light Field Microscopy （FLFM） to image the three-dimensional structural details of butterfly scales. This imaging method requires no slicing or mounting of samples， thereby preserving their native structural integrity， avoiding damage during imaging， allowing repeated use of the same specimen， and significantly reducing sample consumption. In principle， it can perform the three-dimension imaging in real time by taking the same advantage of single shot three-dimensional imaging and image reconstruction of light field microscopy. Moreover， compared to the conventional light field microscopy， the FLFM can increase the lateral spatial resolution thus the reconstruction quality of the three-dimensional image. We found that FLFM is particularly suitable for delicate biological samples such as butterfly wings and provides reliable technical support for studying their color and structural characteristics.

Here， the representative samples including pigmentary scales， structural color scales， and scale-free areas of different kinds of butterflies were imaged under 10X and 50X objectives with a consistent lighting condition. After introducing the optical system and the imaging mechanism of the FLFM， the three-dimensional reconstruction method based on refocusing and deconvolution algorithms is described. The experimental FLFM setup consisted of a DOIT3DMicro Fourier light-field module mounted on an Olympus IX73 inverted microscope， and the illumination was provided in both transmission and reflection modes depending on the sample type. The refocusing algorithm adopts a shift-and-sum procedure exploiting the conjugate relation between aperture stop and MLA， while the deconvolution algorithm models the system point spread function via wavefront propagation theory for high-resolution reconstruction.

The method is verified by imaging with a resolution target sample and another sample of distributed beads　the resolution target image demonstrates the lateral spatial resolution about 8 μm and the beads sample image demonstrate the depth differentiation capability around 60 μm. Finally， the imaging results for the butterfly scales demonstrate that FLFM can clearly reveal morphological characteristics， angle-dependent color variations， and spatial distribution patterns of different scale types. Imaging at 10X magnification verified the feasibility of this technology for visualizing scale structures： the Papilio wing sample shows the relative wide black and white stripes with the boundary somewhat smeared， the Morpho helenor wing sample shows the fine well-organized colorful structures and the color can change from the green blue tone to the blue violet tone， and the Haetera piera wing sample shows shrunk scales and sparsely distributed cilia. Imaging at 50X magnification further revealed significant differences in scale morphology， color formation mechanisms， and optical properties between Catopsilia pomona and Morpho helenor： the color of the Catopsilia pamona wing sample appears mainly due to the pigment structures and does not change when viewing from different angles， while the Morpho helenor wing sample show typical structured color and the hue change apparently by varying the incident light angles or the viewing perspectives.

Therefore， this study demonstrates the advantage and potential wide application prospect of the FLFM in imaging the samples with large depth-of-field. Through careful examination and comparison analysis， we observed the various fine details of the three-dimensional structures of the butterfly wing scales which is very helpful for understanding the different color formation mechanism of the scales. We expect that the FLFM not only can find important applications for studying the structured color of the butterfly wings， but also can provide the experiment support for the further exploration and investigation of biomimetic materials.

Event cameras are a novel type of visual sensor inspired by the biological retina， capable of asynchronously capturing pixel brightness changes with microsecond-level temporal resolution. Unlike traditional cameras that capture frames at fixed intervals， event cameras only trigger an event when pixel brightness exceeds a preset threshold. This unique mechanism endows event cameras with an ultra-wide dynamic range of up to 140 decibels and exceptional temporal resolution， granting them significant advantages in high-speed， high-dynamic-range scenarios such as object tracking， motion detection， and Simultaneous Localization and Mapping （SLAM）. These capabilities enable event cameras to capture rapid movements and subtle changes in dynamic scenes that conventional cameras might miss. However， event cameras have a significant limitation： they can not directly capture grayscale images in static scenes. This is because when a scene is stationary and light intensity remains constant， the camera detects no change in light intensity， failing to meet the conditions for event triggering. These characteristics restrict their application in scenarios requiring complete brightness information， such as static object or scene recognition and measurement in traditional image processing tasks. Consequently， despite their ultra-high dynamic range， temporal resolution， and exceptional performance in dynamic environments， event cameras still face challenges in applications demanding detailed， continuous brightness data acquisition under static conditions.

To address the challenge of capturing static scenes with event cameras， this paper introduces a novel approach using mechanical shutter mapping for imaging. The core innovation lies in modulating brightness variations in static scenes through the rotation of a mechanical shutter， triggering events even in the absence of light intensity changes. By adjusting the shutter's rotation speed at varying rates， discrete events are generated， which are then reconstructed into High Dynamic Range （HDR） grayscale images. This technique overcomes a significant limitation of traditional event cameras， which struggle to capture static scenes due to the lack of natural light variations. A key aspect of this method is the calibration process， which ensures that the generated event data is accurately aligned with the actual light intensity of the scene， enabling precise and accurate grayscale image reconstruction. In this setup， the mechanical shutter acts as an active driving mechanism， inducing event generation by modulating the scene's brightness. This allows the event camera to capture dynamic information in static scenes， where traditional event cameras would otherwise fail to register changes. As a result， this method significantly enhances the imaging capabilities of event cameras， broadening their potential applications in static environments with minimal or no natural light variations.

Experimental results show that the reconstructed HDR images achieve a dynamic range of up to 112 dB. This range allows the event camera to capture fine details in both dark and bright areas of the scene， overcoming the limitations of conventional cameras with fixed dynamic ranges. The calibration process further improves the accuracy of grayscale image reconstruction. Our experimental results demonstrate that shutter-based techniques successfully reconstruct grayscale images of static scenes under extreme lighting conditions. Compared to prior methods， this approach significantly improves image quality， reduces grayscale distortion， and preserves details often lost in conventional event reconstruction techniques. By generating events through controlled brightness variations， this method enhances the imaging capabilities of event cameras in static environments. Furthermore， the mechanical shutter mechanism facilitates portability， enabling adaptation to multiple event camera models and enhancing the system's versatility and practical applicability. Beyond expanding event cameras' capabilities in static scenes， this approach also provides a solution for event cameras operating under complex lighting conditions. Our shutter mapping technology offers a controlled event triggering mechanism， enabling event cameras to function in scenarios where traditional methods fail. This opensnew possibilities for event cameras in fields requiring high-quality grayscale images， such as industrial inspection.

This paper proposes and validates a shutter-mapped event camera method for grayscale imaging in high-dynamic-range static scenes. The core innovation of this approach lies in introducing a mechanical shutter as an active driving mechanism， which effectively overcomes the limitation that event cameras cannot generate event streams in static scenes due to the absence of brightness changes. By modulating the scene's brightness using controlled shutter rotations， the event camera can trigger events even in stationary conditions. Experimental results demonstrate that this method successfully reconstructs grayscale images of high-dynamic-range static scenes， achieving a dynamic range of up to 112 dB under extreme illumination conditions， all using a frameless event camera. Compared to existing methods， our approach significantly improves reconstruction quality， reduces grayscale distortion， and preserves fine details. Additionally， the proposed mechanical shutter triggering mechanism offers versatility and portability， providing a controllable active refresh mechanism that is compatible with various event camera models. In summary， the shutter mapping method extends the capabilities of event cameras in static scenes， enabling high-quality HDR grayscale image reconstruction. By inducing brightness variations through mechanical shutter actuation， event cameras can generate event streams and reconstruct HDR images， even in static scenes with extreme lighting conditions.

Ammonia （NH₃） is a fundamental chemical agent extensively utilized in industrial synthesis， agricultural fertilizer production， and large-scale refrigeration systems. However， its leakage poses severe threats to both human physiological health and the atmospheric environment， necessitating the development of high-precision， real-time concentration monitoring techniques. Currently， Tunable Diode Laser Absorption Spectroscopy （TDLAS） combined with Wavelength Modulation Spectroscopy （WMS） is the preferred method for trace gas detection due to its high selectivity and sensitivity. Nevertheless， traditional TDLAS-WMS systems typically employ a low-frequency sawtooth wave for wavelength scanning. This conventional approach faces two critical technical bottlenecks： first， the inherent non-linearity and discontinuous nature of the sawtooth waveform lead to spectral energy dispersion and significant baseline fitting inaccuracies； second， the sawtooth scanning often overlaps with low-frequency environmental noise and mechanical vibrations， which expands the noise integration bandwidth of the lock-in amplifier and consequently limits the Signal-to-Noise Ratio （SNR） in complex industrial scenarios.

To overcome these limitations， this paper proposes an optimized detection method based on dual-sinusoidal compound modulation for second-harmonic signal extraction. The core innovation lies in the simultaneous application of a low-frequency sinusoidal scanning signal （f_s） and a high-frequency sinusoidal modulation signal （f_m） to achieve precise control of the laser frequency. Unlike the abrupt transitions of a sawtooth wave， the smooth and continuous nature of the dual-sinusoidal waveform effectively eliminates time-domain non-linearities， thereby suppressing baseline drifts at the source. Theoretically， this compound modulation concentrates the signal energy more efficiently near the specific harmonic sidebands （\mathrm{2}{f}_m）， which significantly reduces the bandwidth requirements for the detection system and enhances its immunity to \mathrm{1}/f noise. By utilizing narrow-band lock-in amplification to extract the normalized second-harmonic （2f/1f） signal， the proposed method ensures a more robust and stable representation of the gas absorption line shape， providing a theoretical foundation for higher detection accuracy and lower cost.

The experimental validation was conducted using a 1 512 nm Distributed Feedback （DFB） laser and a 100 cm quartz gas cell under controlled laboratory conditions. A comprehensive platform based on a high-speed data acquisition card （NI-USB6363） and LabVIEW was established to compare the performance of the dual-sinusoidal method against the traditional sawtooth-plus-sine modulation. Precision calibration was performed using a combination of spatial cavity and fiber etalons to optimize the modulation depth. The experimental results demonstrate a substantial performance enhancement： the linear fitting degree （R^{\mathrm{2}}） between NH₃ concentration and the second-harmonic amplitude improved from 0.991 9 to 0.997 8. Quantitatively， the detection sensitivity was enhanced from 0.089 ppm to 0.053 ppm， representing a significant improvement of approximately 40.5%. Furthermore， Allan variance analysis confirms that the system achieves its optimum detection limit within a shorter integration time of 81.5 seconds， exhibiting superior long-term stability and a more concentrated Gaussian distribution of measurement data compared to the traditional scanning mode. These results quantitatively confirm that the dual-sine approach ensures higher repeatability， lower detection limits， and faster convergence to optimal precision.

In conclusion， this research successfully demonstrates that dual-sinusoidal compound modulation is a highly feasible and stable approach for high-precision trace gas detection. By circumventing the intrinsic flaws of sawtooth scanning-specifically baseline fitting errors and high sensitivity to low-frequency noise—this method provides a new technical pathway for the robust， real-time monitoring of NH₃ industrial emissions. The findings verify that the optimized system can maintain high accuracy and stability even in environments with significant physical disturbances. Future research will focus on further refining the modulation parameters and integrating advanced digital signal processing algorithms， such as adaptive filtering or artificial neural networks， to address multi-component gas interference in even more complex scenarios. Additionally， the development of integrated， FPGA-based hardware platforms and the incorporation of multipass cells will be explored to further enhance the detection limits and promote the widespread application of this technology in portable environmental monitoring and industrial safety systems.

With the rapid development of precision manufacturing， semiconductor lithography， and aerospace engineering， ultra-precision machining and metrology have placed higher demands on micro-displacement measurement systems that combine nanometer-level precision with high-bandwidth real-time performance. In dynamic， high-speed motion scenarios， such systems not only need to achieve extremely high resolution but also provide low-latency data processing at high sampling rates. As a fundamental technology in modern length metrology， laser interferometry has inherent advantages in terms of accuracy and stability. However， traditional software-based processing architectures rely on CPUs and sequential execution models， often encountering severe computational bottlenecks when processing high-speed interferometric signals. These limitations make it difficult to simultaneously meet the conflicting demands of large measurement range， high resolution， and real-time detection. To overcome these challenges， this paper proposes a single-frequency laser displacement measurement system based on FPGA， which integrates an FPGA platform and a high-performance point-by-point phase calculation algorithm. By transferring the signal processing algorithm from software to a dedicated hardware logic platform and employing parallel computing and a pipelined approach， the system significantly improves real-time performance while maintaining nanometer-level measurement accuracy.

First， this paper establishes a four-channel orthogonal laser interferometry structure and develops a real-time phase demodulation method based on the phase difference between adjacent sampling points. By introducing phase jump correction and cumulative phase compensation mechanisms， the algorithm effectively solves the problems of phase unwrapping ambiguity and displacement direction discrimination under high-speed motion conditions， thereby ensuring the continuity and robustness of displacement measurement. Meanwhile， to analyze the impact of non-ideal optical elements on nonlinear errors， this paper constructs a systematic error model using Jones matrix theory. This model quantitatively analyzes the effects of waveplate angle misalignment and Polarization Beam Splitter （PBS） splitting ratio imbalance on the interference signal， revealing their roles in introducing DC offset， amplitude mismatch， and non-orthogonality between orthogonal channels. Based on this analysis， this paper designs a vector-based error compensation algorithm to correct these defects， thereby significantly improving phase linearity and overall measurement accuracy. Based on the proposed algorithm， a complete experimental test platform was established， and a host-computer-based multi-threaded displacement measurement software was developed to evaluate the system performance. Experimental results demonstrate that， within a measurement range of 200 μm， the system achieves a statistical measurement accuracy better than 10 nm while supporting millisecond-level data update rates， thereby validating the effectiveness and practicality of the proposed method.

Based on the validated theoretical and software framework， this paper further develops an FPGA hardware system integrating a high-speed multi-channel ADC to comprehensively enhance real-time processing capabilities. By employing a fully pipelined architecture and dedicated parallel processing units， key algorithms such as error compensation and phase demodulation are transformed into hardware logic. This hardware-oriented design ensures stable and predictable computational latency， which is crucial for real-time measurement. Experimental comparisons show that the results of the FPGA-based hardware processing are in high agreement with the results of the host multi-threaded software algorithm， with a Root Mean Square Error （RMSE） of only 9.16 nm and statistical accuracy consistently maintained within 10 nm. Real-time performance evaluation further validates the advantages of the proposed system. The initial processing latency is reduced to 10.4 μs， and the displacement data update cycle reaches 100 ns. Therefore， the system can reconstruct complete micrometer-level motion trajectories in real time within 1 millisecond， representing a significant performance improvement compared to traditional CPU-based processing architectures. These performance characteristics make the system particularly suitable for applications such as high-speed motion， dynamic vibration monitoring， and real-time feedback control.

In summary， this paper proposes a laser interferometric real-time displacement measurement system by deeply integrating a point-by-point phase demodulation algorithm and FPGA-based hardware acceleration technology. This system simultaneously achieves high precision， high stability， and ultra-fast real-time performance. It provides a reliable and high-performance metrology solution for closed-loop motion control， dynamic vibration analysis， and nanometer-level precision positioning in ultra-precision engineering applications， demonstrating significant practical value and broad application prospects.

The purpose of this study is to develop a robust and accurate Phase Unwrapping （PU） algorithm that can reliably recover continuous phase information from noisy wrapped phase data while preserving structural details. In many practical measurements， noise and local phase disturbances degrade the accuracy of gradient estimation， which leads to error amplification and structural distortion during the unwrapping process. To address this challenge， this work proposes a new PU framework based on gradient consistency detection and adaptive noise correction. The main objective is to accurately identify noise-corrupted pixels in the wrapped phase map and selectively suppress their influence without altering reliable phase information. By combining localized complex-domain filtering with efficient phase reconstruction， the proposed method aims to improve both reconstruction accuracy and robustness while maintaining computational efficiency suitable for practical imaging systems.

The proposed method consists of three main stages　dual wrapped phase generation， gradient consistency-based noise detection， and integral phase reconstruction. First， two wrapped phase maps are obtained from the same group of fringe patterns through forward and reverse phase-shifting demodulation. Specifically， phase extraction is performed using five fringe images in the sequences I_{\mathrm{1}}\to I_{\mathrm{5}} and I_{\mathrm{5}}\to I_{\mathrm{1}}， respectively. These two wrapped phase maps represent the same underlying phase distribution but contain opposite phase-shift directions introduced during demodulation. Under ideal noise-free conditions， the spatial gradients of the two wrapped phase maps should be identical at each pixel location. Based on this property， the proposed algorithm detects noise by evaluating the gradient consistency between the primary wrapped phase and the auxiliary wrapped phase. The gradients of the two maps are computed and compared pixel-wise， and pixels whose gradient difference exceeds a predefined threshold are classified as noisy pixels. This detection strategy enables accurate localization of noise while avoiding unnecessary processing of reliable regions. Once the noisy pixels are identified， localized filtering is applied only to these pixels in the complex domain. The wrapped phase is first transformed into a complex representation to eliminate discontinuity issues caused by the 2π periodicity. A local mean filtering operation is then iteratively performed to suppress noise while maintaining phase continuity. To prevent excessive smoothing and loss of structural details， a gradient-based stopping criterion is introduced. The filtering process for each pixel terminates once the corrected gradient becomes sufficiently consistent with the reference gradient or when the maximum number of iterations is reached. This selective filtering mechanism effectively reduces noise while preserving reliable phase structures. After the noise suppression stage， the continuous phase is reconstructed through gradient integration. Instead of solving large optimization problems， the proposed method employs a fast integral reconstruction strategy. Starting from a reference point， the unwrapped phase is obtained by accumulating the denoised gradient values across the image. This approach avoids nonlinear optimization and large matrix operations， thereby significantly improving computational efficiency.

Extensive experiments were conducted using both simulated datasets and real measurement data to evaluate the performance of the proposed method. In the simulation experiments， wrapped phase maps with different noise levels were generated to analyze the robustness of the algorithm under controlled conditions. The proposed method was compared with several representative phase unwrapping techniques， including the Total Variation （TV） based method， the Least-Squares （LS） method， and the Transport-of-Intensity Equation （TIE） method. Quantitative evaluation was performed using multiple performance metrics， including Root Mean Square Error （RMSE）， Structural Similarity Index （SSIM）， and computational time. The results show that the proposed method consistently achieves lower RMSE values and higher SSIM scores across all noise levels. When the noise level is low， the proposed algorithm produces highly accurate phase reconstructions comparable to existing approaches. As the noise level increases， the advantages of the proposed method become more evident. Traditional LS and TIE methods exhibit significant error amplification due to inaccurate gradient estimation， while TV-based methods tend to oversmooth phase structures and blur sharp edges. In contrast， the proposed method effectively suppresses noise while preserving phase discontinuities and structural details. To further evaluate the stability of the algorithm， repeated experiments were performed under identical experimental conditions. Ten independent runs were conducted with different random noise realizations. The results show that the RMSE values obtained by the proposed method remain consistently low with minimal variation， indicating strong robustness and stability. In contrast， the TV method exhibits noticeable fluctuations in reconstruction error across different runs. Real-world experiments were also carried out using fringe images captured from physical samples. The test object consisted of stacked wafer surfaces forming a discontinuous phase structure. The proposed method successfully reconstructed the phase distribution and preserved sharp structural boundaries. Two-dimensional profile comparisons further demonstrate that the reconstructed phase closely matches the reference phase and maintains accurate edge information. Additionally， the computational time of the proposed method is significantly shorter than that of the TV-based method， demonstrating its efficiency advantage.

The experimental results demonstrate that the proposed phase unwrapping algorithm achieves high reconstruction accuracy， strong robustness， and efficient computational performance under various noise conditions. The method effectively suppresses noise while preserving structural details， providing a reliable solution for phase reconstruction in practical measurement environments.

High-efficiency solar cells based on nanostructures are a research hotspot in the photovoltaic field today. On the one hand， there is the research on new types of solar cells such as perovskite cells. On the other hand， silicon-based solar cells remain the most widely studied and applied type of cell. How to further improve the efficiency of silicon-based solar cells and reduce their cost still requires in-depth research. Silicon is an indirect bandgap semiconductor material， and its absorption of incident light in the near-infrared band is very weak. Only when the thickness of the absorption layer exceeds 200 µm can the cell achieve full absorption in a wide band （300~1 100 nm）. Reasonable light-trapping nanostructure design can enhance the light absorption performance of silicon thin-film solar cells. The morphology， size， material and spatial layout of these light-trapping nanostructures have a significant impact on the surface anti-reflection characteristics and light-trapping performance of silicon thin-film solar cells.

In this paper， a double-layer conformal grating silicon thin-film solar cell structure was designed. The influence of different grating shapes on the light-trapping performance of silicon thin-film solar cells was systematically studied by using the concept of super-quadratic subwavelength gratings. By changing the degree of the grating’s profile function， the profile shape of the grating can be adjusted. Five representative grating profile curves （n=1， 2， 4， 10， ∞） were selected. As n increases， the grating profile shape can be gradually changed from triangular （n=1）， parabolic （n=2）， to rectangular （n→∞）. The silicon thin-film solar cells with the above five grating structures were optimized by using the finite-difference time-domain method. By comparing and analyzing the short-circuit current density， absorption spectrum， and light absorption enhancement spectrum of the five grating structures and the planar structure， the light-trapping effect law of the double-layer conformal grating silicon thin-film solar cell was explored. The internal light-trapping mechanism was analyzed using the electromagnetic field intensity distribution diagrams. In addition to qualitatively analyzing the light-trapping performance of each grating structure silicon thin-film solar cell， the concept of integral absorption was also introduced to quantitatively analyze their light absorption characteristics over the entire wavelength range. Moreover， the optimization calculation of the silicon thin-film solar cells with four types of bottom metal grating materials （Ag， Au， Cu， and Al） was carried out. A comparative analysis was conducted on the short-circuit current densities and absorption spectra of four types of bottom metal grating structures， and the light absorption enhancement effect of different bottom metal grating materials was explored. The mechanism was analyzed from the perspective of optical constants.

The research results indicate that as n increases， the overall light-trapping performance of silicon thin-film solar cells decreases as the grating profile shape transforms from triangular （n = 1） to rectangular （n→∞）. Among them， the parabolic （n = 2） grating structure has superior light absorption performance in both the 300~750 nm and 750~1 100 nm bands. Because the n = 2 grating structure has excellent anti-reflection performance in the visible light band， and the LSPRs mode is excited on the surface of the bottom Ag grating in the near-infrared band， while optical waveguide mode coupling is achieved in the c-Si absorption layer. The triangular （n = 1） grating structure has better light-trapping performance in the 750~1 100 nm band， but its light absorption performance in the 300~750 nm band is poor. The results also show that the J_sc values of the silicon thin-film solar cells with the bottom metal gratings of Ag， Au， Cu and Al decrease in sequence， among which the bottom Ag grating structure has the best light-trapping performance and the bottom Al grating structure has the worst. The research results of this paper can provide theoretical guidance for the structural design of thin-film solar cells based on nano-grating structures.

Silicon nitride （Si₃N₄） photonic integrated circuits are promising for next-generation optical communications due to their low loss and wide transparency window. However， efficient coupling between submicron Si₃N₄ waveguides and standard optical fibers remains challenging due to mode-field mismatch. Existing solutions like inverse tapers or polymer claddings involve trade-offs among bandwidth， loss， and manufacturability. This work proposes a taper-straight-taper edge coupler， where the straight section acts as a mode stabilizer and reflection suppressor. The optimized device achieves sub-decibel coupling loss across the S+C+L bands with high alignment tolerance， offering a compact and fabrication-friendly solution for Si₃N₄ photonic integration.

To overcome these limitations， this work proposes and demonstrates an innovative edge coupler architecture that combines two inverse tapers with an intermediate straight waveguide section. The straight section is introduced as a mode stabilizer and reflection suppressor， effectively filtering residual higher-order modes and eliminating parasitic reflections through phase-matching interference. This configuration allows the optical mode to evolve smoothly from the tightly confined on-chip waveguide to the expanded fiber mode， while maintaining high fundamental-mode purity and minimal spectral ripple. The design principle ensures adiabatic mode conversion without relying on extreme geometries or high-aspect-ratio structures， thus preserving compatibility with standard photolithography and etching processes.

Comprehensive electromagnetic simulations based on eigenmode expansion were employed to optimize the key design parameters， including the taper lengths， transition widths， and the straight section geometry. The optimized configuration exhibits an excellent balance between low coupling loss， wide operational bandwidth， and compact device size. The inclusion of the straight section significantly enhances the stability of the mode conversion process and mitigates the oscillations typically observed in conventional two-taper couplers. The simulation results predict broadband， flat coupling performance with high tolerance to fabrication deviations and fiber alignment errors， confirming the robustness of the proposed design.

Experimental characterization was performed on fabricated devices covering the S， C， and L communication bands. The measured results show broadband low-loss performance with minimal wavelength dependence and excellent alignment tolerance. Specifically， the coupler achieves sub-decibel coupling loss per facet over a wide spectral range， with the wavelength-dependent variation remaining below one decibel across the entire operational window. The measured results agree well with the theoretical predictions， confirming that the phase-matching mechanism in the straight section effectively suppresses reflection-induced interference and improves modal stability. Furthermore， the design maintains low loss under several micrometers of lateral or vertical fiber misalignment， demonstrating strong packaging robustness suitable for large-scale manufacturing.

The proposed edge coupler achieves these results without the need for complex processes such as electron-beam lithography or high-aspect-ratio etching. Its fully planar structure and moderate feature sizes ensure high yield and compatibility with commercial foundry processes. The broadband and low-loss characteristics make it particularly advantageous for integrated systems that require efficient chip-to-fiber interfaces， such as coherent transceivers， frequency comb sources， and integrated photonic sensors.

In summary， this study introduces a broadband， low-loss， and fabrication-tolerant silicon nitride edge coupler based on a taper-straight-taper configuration. By integrating a straight single-mode section between two inverse tapers， the design simultaneously achieves mode stabilization， reflection suppression， and efficient field expansion. Both simulation and experimental results demonstrate superior performance across a wide wavelength range， with low insertion loss， minimal wavelength sensitivity， and high alignment tolerance. The proposed structure provides a compact， manufacturable， and scalable coupling solution for silicon nitride photonic integrated circuits， enabling their deployment in next-generation high-speed optical communication and broadband photonic applications.

The performance and stability of underwater wet-mate connectors are of great significance for guaranteeing the long - term reliable operation and safety of subsea engineering systems. In recent years， while some domestic research institutions and enterprises have successfully developed prototype models based on relevant principles， domestic products still face the challenge of insufficient market recognition in the competition. This is due to the lack of efficient， low-cost， and full-life-cycle system testing methods， dedicated equipment， and a comprehensive sea-trial verification system. This paper commences from the perspective of enhancing the reliability of domestically-produced underwater electric-optical hybrid wet-mate connectors. A systematic series of tests were carried out on the self-developed connector prototypes， and a set of automatic connecting test devices suitable for underwater pressure environments was successfully developed， enabling automatic cyclic mating and demating operations of the connectors. The outcomes of sea trials indicate that the self-developed connectors successfully accomplished 100 consecutive mating and demating operations at a water depth of 2 960 meters， and all performance indicators met the technical requirements of relevant foreign standards， attaining an international advanced level.