Pressure sensitivity amplification in interferometric fiber optic hydrophones

Abstract

The induced optical phase change when a pressure is applied to a fiber optic hydrophone is examined both theoretically and experimentally. The induced phase change is calculated both with and without a plastic jacket around the glass fiber. It is shown that the phase change predicted from a detailed three‐dimensional analysis can be adequately described in terms of the much simpler two‐dimensional generalized plane strain approximation. Sensitivities calculated assuming hydrostatic boundary conditions are shown to correspond closely in value with static pressure‐sensitivity measurements. The application of a plastic jacket can substantially increase the pressure sensitivity of the fiber. The increased phase shift is due primarily to the tendency of the jacket to increase the axial strain experienced by the glass fiber. It is predicted that maximum pressure sensitivity (up to 30 times that of the bare fiber) will be achieved by jacketing with Teflon.