Fiber Fabry–Perot tip sensor based on multimode photonic crystal fiber

We propose a novel Fabry–Perot interferometer (FPI) sensor for simultaneous measurement of refractive index (RI) and temperature based on Fresnel reflection and the thermo-optic effect of silica. The sensor head consists of a short section of multimode photonic crystal fiber (MPCF) and a conventional single mode fiber (SMF), where two thin films are formed by collapsing the air holes of MPCF with a commercialized fusion splicer. Experimental results show that such a device has a linear RI sensitivity of ~21.52dB/RIU (RI unit) and a linear optical path difference (OPD) temperature sensitivity of ~25nm/°C. In addition, a high RI resolution of about ~1.7×10−5 is obtained by using the Fourier transformation to decompose the spectral response in different spatial frequencies. Low-cost, easy fabrication and high resolution make it appropriate for practical applications.