Optical Fiber Hydrophone Using Polymer-Coated Fiber Bragg Grating

Abstract

In this work, new fiber optic hydrophone based on the intensity modulation of the laser light in a FBG (Fiber Bragg Grating) under the influence of the sound pressure is experimental proved. In order to increase the sensitivity, the FBG has been coated with a proper material, characterized by an elastic modulus much lower than the fiber one. In comparison with conventional fiber optic hydrophones based on bare FBGs, an increase of sensitivity is obtained. In particular, the minimum detectable acoustic pressure is found to be ~10Pa in the investigated frequency range, with excellent performances in terms of linear response and wide dynamic range. Furthermore, in order to analyze the behaviour of the hydrophone in terms of sensitivity and bandwidth, FBGs have been coated with different materials and dimensions. The experimental results show that by proper design of the coating features such as damping, Young's modulus, acoustic impedance and thickness, bandwidth and sensitivity can be tailored for specific applications. Thanks to the simplicity of its operating principle, geometry and interrogation scheme, these hydrophones can provide an alternative to the current state of the art in piezoelectric hydrophone technology.