A distributed-feedback fiber-laser-based optical fiber hydrophone system with very high sensitivity

Abstract

This paper reports the development of a very compact and very-high sensitivity optical fibre hydrophone system using a distributed-feedback fibre laser with a cavity length of 10cm. A theoretical system design making use of a Mach-Zehnder interferometer, homodyne demodulation scheme and digital signal processing is described. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the distributed-feedback fibre laser sensor head. Results for noise spectrum below 100kHz are presented, as well as discussions on some key issues with designing such hydrophone systems. Although not the intention for the system, initial results also indicate the suitability of the DFBFL for intensity modulated sensing.

Investigation on a pressure-gradient fiber laser hydrophone

“…The length of the FLH is 32 mm (figure 3). The interrogation of a fiber laser sensor can be achieved by using phase-generated carrier (PGC) demodulation [9]. A piezoelectric fiber stretcher in one of the unbalanced fiber Michelson interferometer (FMI) arms in the demodulator induces a phase-shift carrier signal on the sensor output signals that enables passive recovery of dynamic phase-shift information.…”

“…Most of the proposed configurations are based on polymer coating on a bare fiber laser [8][9][10][11], or shielded polymer coating on a fiber laser [12]. However, if the FLH operates in deep water, the wavelength of the fiber laser will shift a lot due to the hydrostatic pressure, which will induce severe problems when using a dense wavelength division multiplexer (DWDM) technique [13].…”

A 4-element fiber laser hydrophone towed linear array

“…Using optical fiber as sensitive element, all electronics parts can be removed from the underwater portion of the array, and the sensor array is less prone to water-induced failures than existing systems [1] .Fiber grating can be used as ideal narrow spectral reflective end to form in-fiber resonance cavities of fiber lasers [2] , which provides a new technical way to study the fiber-optic-based hydrophone. The hydrophone which use DFB fiber laser as sensing element has many advantages such as thin diameter, high sensitivity, easy to multiplex array, wide dynamic range, immunity to electromagnetic interference and no need of impedance matching [3][4][5][6][7] .…”

Liquid Crystal-Based Hydrophone Arrays

“…The idea of using an optical fiber as a hydrophone was first published by Bucaro [2]; since then, various fiber-based sensors have been developed [3][4][5][6][7]. These rely either on (1) some interferometric approach including the use of fiber coils and distributed feedback (DFB) fiber-lasers or (2) one of a number of intensity modulation mechanisms, the latter involving physical motion or mechanical effects such as micro bending.…”