A fiber-optic hydrophone with a mechanical anti-aliasing filter

Two fiber-optic hydrophones which use high birefringence fiber have been constructed and tested. The hydrophone sensitivity, as determined by optical interferometry, was 93.5 mrad/Pa at 100 Hz. One of the hydrophones tested had an integral low-pass filter which had a break point near 200 Hz and a measured roll-off of 26 dB/octave. This hydrophone transducer is a prototype device for a class of sensors that can be optically sampled. Fiber sensors that are optically sampled require mechanical anti-aliasing filters to remove high frequency components. Optical frequency multiplexing of a number of fiber sensors which are connected in series is expected to be an important application for this type of sensor.