Ultrasonic microfiber sensor based on tapered multi-core fiber

In this study, a compact fiber-optic ultrasonic sensor based on a tapered multi-core fiber (TMCF) is proposed and experimentally demonstrated. Comparative analysis and measurements are performed between the tapered four-core fibers and tapered seven-core fibers. Multiple modes are easily excited and coupled in the tapered region of the TMCF, which leads to highly sensitive inter-mode interference. According to the evanescent field interaction between the surrounding water and the transmitting light, the transmission spectrum of the TMCF is modulated periodically owing to the change in the refractive index of the water by ultrasonic waves. The sensor is packaged on a polyurethane rod as an ultrasonic probe. High signal-to-noise voltage signals are obtained, and the profile of a trapezoidal physical model is clearly imaged using scanning detection.