Fiber-optic Michelson interferometer fixed in a tilted tube for direction-dependent ultrasonic detection

• A fiber-optic Michelson interferometer is proposed and demonstrated experimentally for ultrasonic detection.
• Two arm end-faces of the MI are coated with gold films for improving the reflectivity, and the sensing arm is etched for improving sensitivity.
• The signal is detected with high-sensitivity, and the sensor presents strongly direction-dependent ultrasonic sensitivity.

A fiber-optic interferometer is proposed and demonstrated experimentally for ultrasonic detection. The sensor consists of a compact Michelson interferometer (MI), which is fixed in a tilted-tube end-face (45°). Thin gold films are used for the reflective coatings of two arms and one of the interference arms is etched serving as the sensing arm. The spectral sideband filter technique is used to interrogate the continuous and pulse ultrasonic signals (with frequency of 300 KHz). Furthermore, because of the asymmetrical structure of the sensor, it presents strong direction-dependent ultrasonic sensitivity, such that the sensor can be considered a vector detector. The experimental results show that the sensor is highly sensitive to ultrasonic signals, and thus it can be a candidate for ultrasonic imaging of seismic physical models.