Coupling Model And Application Of Ultra-small GRIN Fiber Probe And Hollow-core Photonic Crystal Fiber

All-fiber gas sensor based on hollow core photonic crystal fiber(HC-PCF)with spectral absorption method has the advantages of small size,strong anti-interference ability,high stability,so it has been favored by scholars in recent years.However,the existing gas sensors of this type often use single mode fiber(SMF)to couple with HC-PCF,which has problems such as short coupling distance and low efficiency.In this paper,the ultra-small self-focusing(Gradient-index,GRIN)fiber probe is used to couple with HC-PCF,and the good focusing characteristics of GRIN fiber probe are used to achieve longer working distance and higher coupling efficiency with HC-PCF.The main tasks and innovations completed are as follows:1.The development of micro-optical probes and fiber gas sensors is discussed.In order to improve the working performance of the spectral absorption gas sensing measurement system,the idea of using ultra-small GRIN fiber probes to replace traditional single-mode optical fibers is proposed.The ultra-small GRIN fiber probes coupled with HC-PCF are used to study new fiber gas sensors.2.Based on the optical characteristics of the GRIN fiber probe,the optimization design method of the structure parameters of the GRIN fiber probe is studied and a software for the design and performance analysis of GRIN fiber probes is developed using the programming language C#.By analyzing the influence of different structural parameters on the optical performance parameters of GRIN fiber probes,the software can design the structural parameters of GRIN fiber probes with superior focusing performance.This software can provide support for the production and testing of GRIN fiber probes.3.The coupling model of the GRIN fiber probe and HC-PCF is established,the coupling efficiency is calculated theoretically and analyzed numerically.The effect of different GRIN fiber probes on the coupling efficiency was studied.4.An experimental system for measuring the coupling efficiency of the GRIN fiber probe and HC-PCF was constructed.Five different GRIN fiber probes were developed for the measurement of coupling efficiency experiments.The experimental comparison with a single mode fiber as the coupling probe was performed.The results demonstrate that when the GRIN fiber probe is coupled with HC-PCF,a longer working distance and higher coupling efficiency can be obtained than the single-mode fiber probe.5.The coupling model of GRIN fiber probe and HC-PCF was used in the research of a new fiber gas sensor that uses the spectral absorption gas detection method.The corresponding physical model of gas sensors was established,and a preliminary experimental verification system was set up.