Fiber optic hydrophone sensor arrays using low reflectance internal mirrors

Abstract

A new design of fiber optic hydrophone sensor arrays phics. using low reflectance internal mirrors in optical fibers is investigated. The mirrors are produced by fusion arc splicing of two fibers, one of which has a thin film of TiO2 on the end. A magnetron sputtering machine was used for producing a coating on a cleaved fiber end. Three different coating thicknesses of the TiO2 material [(150 i, 250 h, and 300 i)] for the low reflectance internal mirrors were tested. For the controllable low reflectance range less than 1.0%, the range [0.034% '-' 0.054% (150 i)], the range [0.13%- 0.38% (250 i)], and the range [0.44%-0.97% (300 i)] were obtained by varying the parameters of the splicing process. The measured optical excess loss was 0.3dB-0.4dB for the 3001 coating. Two perturbations are applied to fiber optic hydrophone sensor arrays in the water tank. A six hydrophone array using the internal mirrors was tested in a water tank using two forms of acoustic excitation, one generated by a speaker in air and the other by a wave in the tank. The hydrophones were monitored using a pulsed semiconductor laser light source and a photodiode. The feasibility of time division multiplexing of the hydrophones was confirmed in these tests.