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In general, an operational sonar system will require an anti-aliasing low-pass filter if any high frequency components are
present in the sensor phase information. A mechanical filter must be used in the sensor since anti-aliasing filtering must
be performed before sampling. Fiber-optic hydrophones with mechanical anti-aliasing filter, which consists of soft
closed-cell sponge rubber, have been reported, but they have poor ability of resistance to hydrostatic pressure due to the
softness of the rubber. Furthermore, the theoretical analysis and design of the hydrophone are difficult due to the
uncertainty of the rubber's mechanical properties. To effectively eliminate the aliasing in a practical sonar system based
on interferometric fiber-optic hydrophones, a novel mechanical anti-aliasing filtering fiber-optic hydrophone with a
cylindrical Helmholtz resonator has been proposed. The low frequency lumped parameters model of the fiber-optic
hydrophone is given based on the theories of electro-acoustic analogy, and the acoustic properties are analyzed using the
standard circuit analysis methods. The acoustic sensitivity frequency response is measured in a standing-wave tube using
a comparative measurement method. Experimental results show that this new type of fiber-optic hydrophones has good
acoustic low-pass filtering performance. The low frequency response, as determined by the sensing mandrel and the fiber
optical interferometer, is very flat and the average acoustic phase sensitivity is about -140 dB re 1rad/μPa with a
fluctuation within ±1.0 dB. The response curve has a resonant frequency determined by the hydrophone structure. Apart
from the resonant frequencies and the high frequency responses, the measured response curves are well in agreement
with the simulation results, which show the correction of the model and the theories. It is expected that this new type of
mechanical anti-aliasing fiber-optic hydrophone will have wide potential applications in modern sonar systems.
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