Ultrasonic imaging of seismic physical models using an ultra-thin open-cavity microbubble sensor

A sensitivity-improved fiber-optic ultrasonic sensor is proposed and employed for ultrasonic imaging of seismic physical models (SPMs). 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 um with a wall thickness of approximately 0.48 um. 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 (UWs), the compact bubble can balance the difference of air pressure between inside and outside. Eventually, a side-band filter technique is used for UWs interrogation. Compared with enclosed uncoating fiber bubble, the sensor shows an enhanced response to pulsed ultrasound. The SPMs of rugged topography and reservoir type are both designed and the proposed sensor is used for ultrasonic imaging of the two specific models.