All-fiber Fabry-Perot interferometer gas refractive index sensor based on hole-assisted one-core fiber and Vernier effect

A novel high sensitivity all-fiber Fabry-Perot interferometer (FPI) gas refractive index (RI) sensor based on hole-assisted one-core fiber (HAOCF) and Vernier effect was proposed and demonstrated. The sensor is fabricated by splicing a section of HAOCF to a section of silica tube (ST) fused with the lead-in single-mode fiber (SMF), ensuring that the sensor is composed of an air-cavity FPI and a silica-cavity FPI. The cascaded dual-cavities generate the Vernier effect due to a similar free spectrum range (FSR), which significantly improve the sensitivity of the sensor. Owing to the air hole in the cladding of the HAOCF, gases with different RI can enter or leave the in-fiber air cavity, which makes the device usable as a gas RI sensor. The sensor was used to monitor the RI changes of air with different pressures and provided a high sensitivity of −9462.4 nm/RIU. The proposed sensor has a potential to find further applications in the fields of gas composition detection, medical diagnostics and environmental monitoring.