An air-coupled ultrasonic sensor based on cascaded fibre Bragg grating and Fabry-Perot interference cavity

Abstract In this paper, we proposed and demonstrated experimentally an air-coupled fiber-optic ultrasonic sensor, based on cascaded fibre Bragg grating (FBG) and Fabry-Perot interference (FPI) cavity. Because of the modulation effect of FPI cavity, the sensor’s responses to ultrasonic wave (UW) have been improved. With side-band filtering technology-based intensity interrogation, the voltage responses of 1.2 V and 1.34 V to the continuous and pulse UW at 1 MHz respectively are obtained in air, and its SNR is about 37 dB. Further results of the directivity and stability of the sensor indicate that the sensor has the potential of imaging in air.