Residential gas leaks, vehicle exhaust, and industrial emissions all contain carbon monoxide (CO), a colorless, odorless, and extremely poisonous gas produced by the incomplete combustion of fuels containing carbon. Public safety, industrial production, and environmental quality are all seriously threatened by CO, which can cause acute poisoning or even death in humans at very low amounts. Therefore, it is crucial to create ultra-sensitive CO detection technology to protect human health, industrial operations, and environmental monitoring. Researchers have recently focused a lot of attention on anti-resonant hollow-core fiber (AR-HCF) because of its special benefits, which include low transmission loss, large core diameter, small optical stripe amplitude, compact structure, and the ability to enable long-distance continuous interaction between single-mode radiation and the target gas.These features give AR-HCF a lot of potential for use in gas sensing applications. In order to achieve high sensitivity, high stability, and compact trace CO detection, this study proposes an all-fiber gas detection system based on AR-HCF for CO monitoring employing fiber loop ring down spectroscopy.

In this work, an all-fiber CO detection system based on fiber ring cavity decay spectroscopy was built, using a continuous wave (CW) laser with a central wavelength of 1567 nm as the light source and AR-HCF as the gas chamber sensing element. The AR-HCF' transmission characteristics were first examined using the finite element approach, with an emphasis on its limiting loss at the operating wavelength of 1567 nm.The ideal length of the AR-HCF gas chamber was then determined by methodically examining the link between the sensitivity of the hollow-core gas chamber and the optical path length. Erbium-doped fiber amplifier (EDFA) with varying gain values were incorporated into the fiber ring cavity to boost the effective number of laser cycles and offset the intrinsic cavity loss in order to further improve the detection sensitivity. In order to thoroughly assess the detection performance of the developed system, a number of performance tests were carried out, including stability testing through repeated measurements and concentration detection tests in the range of 0-0.02%.

The research using the finite element approach showed that the AR-HCF' limiting loss at 1567 nm was roughly 0.92 dB/km.A 1-meter-long AR-HCF was chosen as the gas chamber structure after research into the relationship between optical path length and sensitivity revealed that the detection sensitivity increased with the length of the optical path. This was done while taking system compactness and practical applicability into full consideration. The findings of the experiment showed that increasing the EDFA gain greatly increased the system's sensitivity: the system's sensitivity with a 2 dB gain ring cavity was 16.7 times greater than that of the system without EDFA. With a correlation value (R²) of 0.99989, concentration detection experiments verified a strong linear relationship between the decay time and CO concentration in the range of 0%-0.02%. The greatest average relative error was only 0.4%, according to stability tests with ten repeated measurements for various CO concentration gradients. In the end, the developed system demonstrated outstanding detection performance and reliability with a minimum detection limit of 3.0757×10⁻¹¹, a sensitivity of 0.795 s, and a stability of 0.82%.

This work effectively creates an all-fiber CO detection system using fiber loop ring down spectroscopy in conjunction with AR-HCF. The system achieves ultra-high sensitivity and stability in trace CO detection by utilizing the superior performance of AR-HCF and the gain compensating effect of EDFA. The system offers a new and efficient technical method for trace gas detection thanks to its benefits of strong anti-interference ability, compact structure, high detection sensitivity, and dependable performance.It not only improves the technical methods of CO detection but also has great potential for use in areas including public health protection, environmental quality monitoring, and industrial safety early warning. In order to increase the detection limit and broaden the system's application scope to more trace gas detection scenarios, future research can concentrate on improving the fiber cavity construction and EDFA gain control.