Temperature-Independent Fiber Bending Sensor Based on a Superimposed Grating

Abstract—A compact fiber bending sensor has been presented by superimposing a uniform fiber Bragg grating (FBG) into a tilted fiber Bragg grating (TFBG). The reflection of FBG is modulated by the same bandwidth of the cladding modes of TFBG, which is sensitive to the bending of fiber. By monitoring the differential Bragg reflection between FBG and TFBG, the sensor is insensitive to ambient temperature changes and power fluctuations from light source or fiber link during the measurement. The sensitivity of the sensor is also doubled because the signal from FBG passes through the TFBG twice. Index Terms—Bending measurement, fiber-optic sensor, super-imposed grating, tilted fiber Bragg grating (TFBG). I