Development of a high sensitivity DFB fibre laser hydrophone

Over the last three decades, extensive research has been carried out towards the development of fibre optic hydrophones. The initial designs focused on strain sensitivity enhancements through coatings and coiling long fibres on compliant mandrels. With the advent of fibre Bragg gratings and fibre lasers with ultra high sensitivity to strain, the interest has shifted towards employing these technologies in underwater acoustic sensing. In this work, we present the results from on-going development of Distributed Feedback Fibre Laser (DFB-FL) hydrophones at the Acoustic Research Laboratory (ARL), National University of Singapore in collaboration with Institute of Infocomm Research (I2R) under A*STAR (Science and Technology Agency for Research), Singapore. We also compare the sensitivities of Fibre Optic Hydrophones (FOH) encapsulated in three different configurations and present the results from Finite Element Analysis (FEA) and modelling. It is seen that an air-backed Teflon encapsulation provides a sensitivity enhancement as high as 15 dB from resin moulded one.