A Dual-Parameter Sensor Using a Long-Period Grating Concatenated With Polarization Maintaining Fiber in Sagnac Loop

In this paper, a novel dual-parameter measurement scheme using a long-period grating (LPG) concatenated with polarization maintaining fiber (PMF) in a Sagnac loop was proposed and experimentally demonstrated to measure temperature and refractive index (RI) simultaneously. There are two types of dips in the output spectrum of the proposed sensor, which are formed by the LPG and Sagnac loop. Compared with the traditional Sagnac loop sensors using PMF only, the birefringence induced by the LPG changes the phase difference and makes the dips of the Sagnac loop sensitive to surrounding RI. Due to different interference mechanisms, the dual-parameter measurement is realized by Sagnac loop and LPG with different sensitivities to temperature and RI. Experiments show that in the output spectrum of the sensor, the dip of the LPG has the sensitivities of 0.201 nm/degrees C and -8.36 nm/RIU, and the dip of the Sagnac loop has the sensitivities of -1.06 nm/degrees C and -23.068 nm/RIU. The proposed sensor has a simple structure and great potential in biological, chemical, and ocean fields.