Highly sensitive refractive index sensor with fiber in-line Fabry-Perot interferometers based on vernier effect

A highly sensitive refractive index (RI) sensor with fiber in-line Fabry-Perot interferometers based on vernier effect is proposed and experimentally demonstrated. The sensor is fabricated by splicing a short segment of capillary to a commercial single mode fiber (SMF) and then splicing a tiny large mode area fiber to the capillary. There are two micro-channels in the lateral wall of the tube. The sensor exhibits a compact size of less than 1 mm in total length and has the highest RI sensitivity of ~10189.2 nm/RIU within the range of 1.32846 to 1.33327.