Temperature-Compensated Refractive Index Measurement Using a Dual Fabry–Perot Interferometer Based on C-Fiber Cavity

We demonstrate a simple-to-fabricate, temperature-compensated refractive index sensor using a dual Fabry-Perot optical fiber interferometer using C-fiber. The sensor device is formed by combining two types of in-fiber interferometers, including a C-fiber Fabry-Perot interferometer and a single mode fiber (SMF) Fabry-Perot (FP) interferometer. The C-fiber is a silica capillary with an open side, which allows external liquid to directly enter the internal hole. The C-fiber interferometer is sensitive to external refractive index (1704 nm/RIU) as well as temperature (-0.196 nm/°C) due to the thermo-optic effect and thermal expansion of the C-fiber cavity, while the SMF interferometer is only sensitive to ambient temperature (0.0118 nm/°C). Thus, temperature-compensated refractive index measurement can be achieved by examining the phase shift responses of the two FP interference peaks with transfer matrix approach, solving the problem of temperature sensitivity of RI sensors due to the relatively large thermo-optic coefficient of colloidal materials and aqueous samples.