Microfiber Bragg Grating Bonded Using Tapered Cantilever for High-Sensitivity Ultrasonic Detection

A microfiber Bragg grating (MFBG) bonded using tapered cantilever was designed to improve ultrasonic sensitivity, and was investigated using experimental, theoretical, and numerical methods. The ultrasonic signal was amplified by the tapered structure while the influences of the static strain and evanescent field were eliminated by the cantilever. Compared with the cantilevered fiber Bragg grating, the sensitivity of the sensor presents an upward trend with the descent of the diameter as there are 331% and 108% sensitivity increment by MFBGs with 20 and 40 μm diameters, and the improvement is apparent when the frequency of the ultrasonic signal is high.