The optical grating hydrophone

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Abstract
Receiver. The received light intensity is a function of the relative displacement of the two optical gratings. The optical sourcmay be coherent or incoherent light, and a simple pin-photodiode detector affords adequate receiver sensitivity. Large, multimode optical fibers can be used to carry the light to and from the hydrophone. Since the device is photon-noise limited, arbitrarily high sensitivities can be obtained by increasing the optical power, and/or increasing the spatial frequency of the optical gratings. The direct intensity-modulated output eliminates the need for more sophisticated detection techniques that are often applied to phase modulating optical hydrophones. However, comparable sensitivities can be realized with the optical grating approach. Fabrication of the device is straightforward, without any advanced optical techniques required. Several prototypes have been built and have already demonstrated dynamic ranges as high as 160 dB, with the ability to detect acoustically induced displacements of less than 0.01,.

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