A Hybrid Fiber Interferometer for Simultaneous Refractive Index and Temperature Measurements Based on Fabry–Perot/Michelson Interference

A hybrid fiber interferometer sensing configuration for ambient refractive index (RI) and high temperature measurements is proposed and experimentally demonstrated, which is constructed by splicing a short section of photonic crystal fiber to one output port of a 2 × 2 50:50 fiber-optics coupler with controllable offset. The reflected spectrum pattern of the proposed interferometer presents two obvious interference fringes with different frequencies caused by Fabry-Perot and Michelson interferences. Experimental results show that the two output port probes of the unique hybrid interferometer can be applied, respectively, in measuring ambient RI and temperature simultaneously by monitoring the spatial frequency change and the resonance wavelength shift. The RI and temperature sensitivities are approximate -102048.3 a.u/RIU in the range of 1.33-1.38 and 13 pm/^°C in the range of 35 ~ 500^°C, respectively.