Fiber optic hydrophone: improved strain configuration and environmental noise protection.

It is shown that the pressure sensitivity of a fiber-optic hydrophone is strongly dependent on the fiber's strain configuration. Longitudinal strain is found to be much more effective than uniform strain, and consequently modifications to the sensor's design are proposed. Environmental noise sources such as ocean motion and mechanical vibrations are then discussed, and a new double-cavity configuration, which is unaffected by those perturbations, is presented. A tunable-cavity detection method is finally proposed, and it is shown how this method can overcome problems related to drift of the point of operation, laser intensity fluctuations, and nonlinearity for high dynamic ranges.

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