Sensitivity-Improved Sensor for Ultrasound Detection and Imaging of Seismic Physical Model

A sensitivity-improved fiber-optic ultrasonic sensor is proposed and employed for ultrasonic imaging of seismic physical models. The sensor consists of a single mode fiber (SMF) embedded into the hollow-core-fiber (HCF) bubble. Using gas pressure assisted arc discharge, the diameter of the bubble can be larger than $430 \mu \mathrm{m}$ with a wall thickness of approximately $0.48 \mu \mathrm{m}$. Besides, by using the coating technique, the optical reflectivity and extinction ratio of the ultra-thin bubble are further improved. Fiber tails of SMF and the HCF are partly bonded to form an open-cavity sensor. When applied with ultrasonic waves, the compact bubble can balance the difference of air pressure between inside and outside. The fault topography is designed and the proposed sensor is used for ultrasonic detection and imaging.