We proposed a kind of fiber-optic gradient hydrophone based on interferometer. Two arms of the interferometer are
sensing fibers, each of which can be regard as a scalar pressure sensing element, and then the phase gradient between the
two elements is transformed into the light intensity modulated output by the coupler. In this paper, a suit of analytical
models for researching the sensor performance are developed. The theoretical and experimental research was carried out
to demonstrate this kind of gradient hydrophone's phase sensitivity as the function of the measure frequency and the "8"