Simultaneous Measurement of the Refractive Index and Temperature Based on a Hybrid Fiber Interferometer

Abstract

A simple and compact sensor based on a hybrid interferometer, which is composed of a cascaded single-mode-multimode-single-mode (SMS) and bending single-mode fiber (BSF) structure, is proposed and investigated. By carefully designing the multimode fiber length of the SMS and the bending diameter of the BSF, the transmittance spectrum features two kinds of dips simultaneously, which show different responses to the surrounding refractive index (RI) and temperature. The SMS structure is only sensitive to the temperature, while the BSF structure is sensitive to both the RI and temperature. Therefore, the simultaneous measurement of the RI and temperature can be achieved by monitoring the two dips induced by the SMS and the BSF, respectively. According to this principle, a cascaded SMS-BSF hybrid sensor is designed, fabricated, and tested. Experimental results show that the sensor possesses an RI sensitivity of 331.71 nm/RIU (from 1.333 to 1.404) and a temperature sensitivity of -1.053 nm/°C (from 30 °C to 70 °C), which is outstanding among the reported results.