An ultra-high sensitivity methane gas sensor based on Vernier effect in two parallel optical fiber Sagnac loops

Methane gas sensing has attracted great interest for its applications in agriculture production, industrial manufacturing, medical diagnosis, and environmental monitoring. In this paper, we proposed an ultra-high sensitivity methane gas sensor based on Vernier effect in two parallel optical fiber Sagnac loops. The reference arm contained a polarization maintaining photonic crystal fiber (PM-PCF), while sensing arm consists of a methane gas sensitive film coated PM-PCF. Vernier effect (VE) was generated and as a result the sensitivity was improved by multiple times. The finite element method (FEM) was used to assess the methane gas sensor’s sensing capabilities. According to the numerical simulation, the average sensitivity based on two parallel Sagnac loops in the methane gas concentration of 0-3.5% was 197.775 nm/%, which was 5.5 times in contrast to a single Sagnac loop. To our best knowledge, we presented the methane gas sensor based on VE in two parallel optical fiber Sagnac loops for the first time. The designed optical fiber methane gas sensor possessed the merits of ultra-high sensitivity, providing helpful guidelines for the fabrication of high-performance methane gas sensors.