Hybrid Sagnac interferometer with high measurement resolution for simultaneous measurement of ambient index and temperature

Abstract

A simple technique for simultaneous measurement of the concentration of ethylene glycol and temperature by using a hybrid Sagnac interferometer is proposed and experimentally demonstrated. The hybrid Sagnac interferometer is configured by inserting a long-period fiber grating (LPFG) and a D-shaped polarization-maintaining fiber (PMF) into a Sagnac interferometer. By partially removing the cladding of the PMF, we make the Sagnac interferometer sensitive to ambient index by exposing the core region of the D-shaped PMF to external circumstance. The determinant of the sensitivity matrix of the proposed sensing probe is improved by using the negative temperature sensitivity of the LPFG.