# Dual Interferometric Interrogation for DFB Laser-Based Acoustic Sensing

## TL;DR

This paper introduces a new method for fiber-optic hydrophones that improves their performance in detecting underwater sounds.

## Contribution

A dual interferometric setup is proposed to enhance the dynamic range of DFB laser-based acoustic sensing.

## Key findings

- The dynamic range of the system increased from 125 dB to 139 dB at 1 kHz.
- The noise floor was not degraded despite the performance improvement.
- The method supports applications like underwater surveillance and marine monitoring.

## Abstract

Acoustic sensing has many applications in engineering, one of which is fiber-optic hydrophones (FOHs). Conventional piezoelectric hydrophones face limitations related to size, electromagnetic interference, corrosion, and narrow operating bandwidth. Fiber-optic hydrophones, particularly those employing distributed feedback (DFB) lasers, offer a compelling alternative due to their mechanical flexibility, resistance to harsh conditions, and broad detection range. DFB lasers are highly sensitive to external perturbations such as temperature and strain, enabling the precise detection of underwater acoustic signals by monitoring the resultant shifts in lasing wavelength. This paper presents an enhanced interrogation mechanism that leverages Mach–Zehnder interferometers to translate wavelength shifts into measurable phase deviations, thereby providing cost-effective and high-resolution phase-based measurements. A dual interferometric setup is integrated with a standard demodulation algorithm to extend the dynamic range of these sensing systems. The experimental results demonstrate a substantial improvement in performance, with the dynamic range increasing from 125 dB to 139 dB at 1 kHz without degrading the noise floor. This enhancement significantly expands the utility of FOH-based systems in underwater environments, supporting applications such as underwater surveillance, submarine communication, and marine ecosystem monitoring.