Compact fiber-optic ultrasonic sensor using an encapsulated micro-cantilever interferometer.

ABSTRACT

A compact optical fiber Fabry-Perot interferometer is proposed and demonstrated for ultrasound wave (UW) measurement. The sensor consists of a suspended cantilever in a sealed hollow-core fiber, while the end-face of the leading-in fiber together with the end-face of the suspended fiber act as two reflection mirrors and form an air cavity. A short section of graded index fiber is also employed as a micro-lens to improve the fringe contrast of the interference spectral pattern. Due to the suspended fiber structure, the sensor presents high sensitivity to UW loading, which allows the freely suspended fiber to be stretched and compressed easily. By spectral side-band filtering technology, a simple intensity interrogation technology is used for UW demonstration. Moreover, the sealed sensor structure avoids disturbance from other environment parameters, thus presenting good stability for UW detection.