Refractive index and temperature measurement by cascading macrobending fiber and a sealed alternated SMF-MMF structure

Abstract

A simple and low-cost optical fiber sensor is proposed for simultaneous measurement of refractive index (RI) and temperature. The sensor is constructed by cascading a sealed long period fiber grating (LPFG) structure and a macrobending fiber with a certain bending radius. The LPFG structure is fabricated by fusing the single-mode and multimode fiber sections in series and sealed in a thermal shrinkable tube to increase its temperature sensitivity. Two obvious resonance dips in the transmission spectrum are observed for the sensor, which could realize the simultaneous measurement of RI and temperature. Experimental results show that the proposed sensor has a high RI sensitivity of 165.04 nm/RIU in the RI range of 1.335–1.38, and a high temperature sensitivity of −255.52 pm/∘C for the temperature range of 35–80 °C.