Measurement of RI and Temperature Using Composite Interferometer With Hollow-Core Fiber and Photonic Crystal Fiber

Abstract

A novel, highly sensitive double-parameter sensor based on the composite interference structure has been designed and implemented in this paper. It can be regarded as a cascade of the traditional single-mode fiber (SMF)–hollow-core fiber (HCF)–photonic crystal fiber (PCF)-SMF structure, which forms a reflected Fabry–Perot interferometer and a transmitted Mach–Zehnder interferometer at the same time. The HCF is filled with ethanol, which is sensitive to temperature. Then the simultaneous measurement of the temperature and the refractive index (RI) can be achieved by monitoring the reflected spectrum and transmitted spectrum. The fact that these two spectrums do not interfere with each other makes it easier to obtain a demodulation method for simultaneous temperature and RI measurement that does not involve complex fast Fourier transform and matrix computation. The sensitivities of the temperature and the RI can reach up to 0.454 nm/°C and 178.7 nm/RIU, respectively.