High Sensitivity Balloon-Like Interferometer for Refractive Index and Temperature Measurement

Abstract

An all-fiber high-sensitivity modal interferometer formed by a bent standard single-mode fiber (SMF) has been presented and demonstrated, which can be used to measure refractive indexes (RIs) of solutions and temperature. The interferometer has a simple and compact structure built with a bent bare SMF mimicking a balloon shape. Because of the curvature of bent fiber sensor, modal interference effect would occur when light propagates from the fiber core into the cladding. The measurement is achieved by monitoring the spectral shift of the modal interference. The performances of the interferometers with different bending diameters and sensitive lengths are experimentally investigated concluding the optimal bending radius as 4 mm and sensitive length 16 mm. In the RI range of 1.3493–1.3822, the corresponding sensitivity and detection limit are 225.95 nm/RIU (refractive index unit) and $3.2\times 10^{-4}$ , respectively. The temperature sensitivity and detection limit of 0.418 nm/°C and 0.173 °C are achieved, respectively.