The optical grating hydrophone

An optical hydrophone has been developed having an output which is a direct intensity modulated representation of an incident acoustic field. The principle of operation involves the relative displacement induced by an acoustic field of two optical gratings which lie between a constant optical source and an optical receiver. The received light intensity is a function of the relative displacement of the two optical gratings. The optical source may 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, comparab...