High-sensitive all-fiber fabry-perot interferometer gas refractive index sensor based on lateral offset splicing and Vernier effect

A high sensitivity all-fiber open-cavity Fabry-Perot interferometer gas refractive index (RI) sensor based on lateral offset splicing and Vernier effect is proposed and demonstrated. The sensor is fabricated by splicing a short section of single mode fiber (SMF) between the lead-in SMF and a section of SMF with a specific length, ensuring that the sensor consists of an open-cavity FPI and a silica-cavity FPI. The reflection beam from the last end face of the sensor is used to generate the Vernier effect, which significantly improves the sensitivity of the sensor. The sensor was successfully used to monitor changes of air RI as a function of pressure and provided a high sensitivity of -11368.5 nm/RIU with good linearity by tracing the shift of the reflection spectrum envelope caused by Vernier effect. This sensor has potential applications in fields such as gas composition detection, environmental monitoring, and biological sensing.