With the evolution of optical communication from 5G to 6G, core optical devices face the increasing performance demands. Electro-optic (E-O) materials have attracted much attention due to their fast modulation speed, wide bandwidth, and good stability. Conventional materials such as KDP single crystals are hygroscopic and possess a low E-O coefficient, while LN single crystals have a limited damage threshold, thus hindering their suitability for high-power applications. Binary PMN-PT relaxor ferroelectrics exhibit excellent E-O properties, but suffer from a poor temperature stability. In contrast, the ternary PIN-PMN-PT system combines a high Curie temperature with outstanding ferroelectric and piezoelectric performance. However, the related research on its E-O properties remains limited. Previous studies mostly focused on strong ferroelectric materials exhibiting the primary E-O (Pockels) effect, which typically show low extinction ratios (<30 dB), insufficient for optical communication devices that require high extinction ratios (>30 dB). This work fabricated a series of transparent E-O ceramics with a weakened ferroelectricity in the xPIN-(85-x)PMN-15PT ceramics (i.e., x=0, 5, 10, 15, 20), to achieve both a high extinction ratio and good E-O performance through composition design. The results demonstrated that the composition with 5% PIN could exhibit optimal overall performance (i.e., a quadratic EO coefficient of 51.0×10^-16 m²/V², an extinction ratio of 31.87 dB, and a transmittance of 66.87% at 1550 nm). A modulation system based on this material was constructed, verifying its potential for applications such as optical switch. This study was to systematically investigate the influence of PIN content on the phase structure, transmittance, ferroelectric properties, and E-O performance, providing valuable insights for the future design of ternary PIN-PMN-PT E-O materials.

The ternary PIN-PMN-PT transparent electro-optic ceramics were prepared by a columbite precursor method with high-purity oxide raw materials (MgO, Nb₂O₅, In₂O₃, PbO, TiO₂, and La₂O₃, purity ≥ 99.9%). First, MgO, In₂O₃, and Nb₂O₅ were mixed by grinding in a high-energy ball mill and then calcined at 1100 ℃ to synthesize MgNb₂O₆ and InNbO₄. Subsequently, these precursors were mixed with La₂O₃, PbO and TiO₂ by milling and calcined at 850 ℃ to obtain PIN-PMN-PT powder. After dry pressing into green bodies, sintering was carried out in oxygen atmosphere at 1235 ℃ for 10 h to achieve densification. This was followed by hot-press sintering at 1200 ℃ and 100 MPa for 3 h to further eliminate pores, ultimately yielding highly dense transparent ceramics.

A systematic characterization was performed on the 0.5La-xPIN-(85-x)PMN-15PT (x=0, 5, 10, 15, 20) transparent electro-optic ceramics. After cutting and polishing, the transmittance, refractive index were measured by ultraviolet-visible-near infrared spectroscopy and spectroscopic ellipsometry, respectively. The quadratic electro-optic coefficient of the material was determined by a single-beam compensation method with a 632.8 nm He-Ne laser. The phase structure and microstructure were analyzed by X-ray diffraction and scanning electron microscopy. Finally, the ferroelectric properties were investigated via measuring the polarization-electric field hysteresis loops by a ferroelectric test system after depositing gold electrodes on the samples.

A series of 0.5La-xPIN-(85-x)PMN-15PT (x=0, 5, 10, 15, 20) transparent ceramics are fabricated. The effect of PIN solid-solution ratio on the transmittance, phase structure, microstructure, ferroelectricity, and electro-optic properties of the samples is systematically investigated. The transmittance of the ceramic sintered at 1235 ℃ gradually increases at a higher PIN content. The 0.5La-20PIN-65PMN-15PT transparent ceramic exhibits the optimum transmittance of 69.11% at 1550 nm, approaching a theoretical upper limit of 69.38%. All the compositions display a pseudocubic phase structure, allowing optical losses due to the birefringence to be neglected. The samples show dense microstructures with relative densities of 99.8%, 99.84%, 99.85%, 99.88%, and 99.95%, respectively, nearly eliminating scattering losses caused by internal pores. The average grain sizes are 6.63, 5.98, 6.41, 7.33 μm and 7.54 μm, respectively. The coercive field and remnant polarization of the samples both increase with increasing PIN content, indicating an enhanced ferroelectricity, which is attributed to the stronger ferroelectric nature of PIN, compared to PMN. The T_m also gradually increases, benefiting from a higher Curie temperature of PIN (90 ℃) relative to PMN (-10 ℃). The maximum and room-temperature dielectric constants both show a monotonic decreasing trend, which is related to a reduction in the relaxor behavior of the samples. The measured electro-optic coefficients at room temperature first increase and then decrease with PIN content, reaching a maximum value of 51.0×10^-16 m²/V² for the 0.5La-5PIN-80PMN-15PT ceramic. This is likely associated with domain sizes constrained by grain dimensions. The extinction ratios of the samples are 33.47, 31.87, 28.77, 23.87 dB and 22.08 dB, respectively, showing a gradual decrease influenced by the variation in ferroelectricity.

Based on the PIN-PMN-PT transparent electro-optic ceramics, an electro-optic modulation system is designed and constructed. Modulation experiments are conducted using a 250 kHz high-frequency AC signal and an audio signal. The modulated optical signal closely matches the original input signal, confirming a feasibility of applying PIN-PMN-PT transparent electro-optic ceramics in the field of optical communications.

La-doped PIN-PMN-PT transparent electro-optic ceramics were fabricated by a two-step sintering method, and the influence of PIN content on the transmittance and electro-optic coefficient was investigated. The 0.5La-20PIN-65PMN-15PT composition exhibited the optimum transmittance of 69.11% at 1550 nm, approaching the theoretical limit, which could be attributed to its pure perovskite phase, pseudocubic structure, and dense microstructure. The 0.5La-5PIN-80PMN-15PT composition demonstrated an optimal electro-optic performance with a transmittance of 66.87% and a high extinction ratio (31.87 dB), while exhibiting a significantly high electro-optic coefficient of 51×10^-16 m²/V², surpassing most reported PMN-PT-based ceramics. Its fine-grained structure facilitated domain switching. An electro-optic modulator based on this ceramic system achieved 200 kHz sinusoidal signal modulation and radio-frequency signal transmission, confirming its promising potential for optical communication applications.