A New Type of Etched Fiber Grating Hydrophone

Abstract

We propose a new type of fiber hydrophone composed of an etched fiber Bragg grating and a special packaging structure for detecting acoustic waves in the low-frequency band under water. The operating mechanism is based on the mechanical vibration of the fiber Bragg grating from the induced vibrating stress of acoustic pressure. The induced pressure of acoustic waves pushes the silicone rubber thin film, causing its vibration and then stretching the fiber Bragg grating, thus resulting in the grating wavelength shift which is overlapped with a tunable laser. The variation in the overlapped light intensity is transferred to an electrical signal by using a photodetector. From the experimental results, we can determine that the smaller the fiber diameter, the higher the sensitivity and frequency response. In order to confirm that this FBG hydrophone has the ability to work in high-frequency acoustic waves, this fiber grating hydrophone and a standard piezoelectric hydrophone are experimentally compared to in the same test conditions in the frequency range from 4 to 10 kHz. According to the experimental results, the fiber grating hydrophone has better responsivity than that of the conventional hydrophone. Due to the unique sensing structure design, this wide-band fiber hydrophone can be useful in long-term continuous monitoring of acoustic waves.