# A Novel Two-Dimensional Hydrophone Based on Fiber Bragg Gratings

## TL;DR

This paper introduces a high-sensitivity 2D hydrophone using fiber Bragg gratings for detecting and locating underwater sound sources.

## Contribution

A novel hydrophone design with enhanced sensitivity and localization using FBGs and a pyramidal acoustic concentrator.

## Key findings

- The hydrophone achieved a peak sensitivity of −210.59 dB re 1 V/μPa.
- The system demonstrated a figure of merit (FOM) up to 3.64 dB/Hz and an SNR of 26 dB in the dominant band.
- The device successfully localized acoustic sources with high accuracy in underwater environments.

## Abstract

This paper presents a high-sensitivity two-dimensional fiber-optic hydrophone designed for the detection and localization of underwater acoustic sources. The device comprises two sensing heads, each incorporating a fiber Bragg grating (FBG) embedded within a customized 3D-printed encapsulation. To enhance acoustic sensitivity, the design utilizes a silicone thin-film coupled with a pyramidal channel that spatially concentrates acoustic energy from the base to the apex, where the FBG is positioned. Incident acoustic pressure induces vibrations in the film, which are amplified by the channel structure, imparting strain on the FBG and resulting in a shift in the Bragg wavelength. The acoustic frequency response is demodulated by converting the overlapping optical power between the sensing and reference gratings into an electrical signal via a photodetector. By arranging the two sensing heads orthogonally, the system effectively determines the direction and angle of the acoustic source. Experimental results show a peak sensitivity of −210.59 dB re 1 V/μPa, with a FWHM of 57.92–66.27 Hz and a figure of merit (FOM) up to 3.64 dB/Hz. In addition, the acoustic-field SNR is approximately 26 dB in the dominant band, and the LOD is 64.19 dB re 1 μPa (10–400 Hz). Experimental validation confirms the hydrophone’s high sensitivity and localization accuracy, demonstrating its significant potential for underwater acoustic sensing applications.