Fibre-optic hydrophone with internal filter

Abstract

A fibre-optic hydrophone comprising a substantially incompressible tubular body, the tubular body generally having a geometry of a cylindrical shell defining an axis, and a deflectable outer wall, arranged to surround the tubular body in a distance thereof, and defining an axis that is arranged to substantially coincide with the axis of the tubular body. The hydrophone further comprising an optical fibre coil arranged on an outer surface of the outer wall, and a first and a second end lid arranged to seal the tubular body and the outer wall at a first end and a second end thereof, respectively, the first end lid and the second end lid being substantially incompressible. Additionally, the hydrophone comprising an outer cavity defined by an inner surface of the outer wall, an outer surface of the tubular body, the first lid, and the second lid; and an inner cavity defined by an inner surface of the tubular body, the first lid, and the second lid. The outer cavity is in fluid communication with the inner cavity via one or more passages in the tubular body, the outer cavity and the inner cavity being filled with a fluid, wherein the passages are configured to contribute to a function as a filter defining a low pass filter response with high cut-off frequency. In some embodiments the deflectable outer wall is cylindrical.