On the mechanism of transduction in optical fiber hydrophones

The receiving sensitivity of optical fiber hydrophones is determined in part by the rate of change in the optical path length of the sensing fiber with respect to changes in the external pressure on the fiber. These changes in the optical path length are a result of the induced changes in index of refraction of the fiber (photoelasticity) and changes in the physical length of the fiber (elasticity). These two properties are analyzed to determine their individual impacts on the hydrophone sensitivity. It is shown that both of these two effects act to increase the optical path length of the fiber as it is subjected to an increasing external pressure. Therefore, the two effects act in concert with one another, not against one another, in their effect on hydrophone sensitivity.