High performance extended fiber optic hydrophone

Abstract

An acceleration insensitive interferometric hydrophone sensor having increased sensitivity comprises a rigid cylindrical support mandrel that is coaxial with and between thin walled sense and reference mandrels. Flanges on the reference and support mandrels form air filled cavities above and below optical reference and sense fiber windings, respectively, that are symmetrically wound on associated mandrels. The walls of the sense and reference mandrels are thin so that they both respond to the same incident acoustic wave signal although 180.degree. out-of-phase. A central collar on the support mandrel provides an acceleration insensitive location for making attachment to the hydrophone. In another embodiment, the reference mandrel is much thicker than the sense mandrel and cavities supporting the sense fiber are caused to operate as acoustic impedance mismatches for rendering the reference fiber winding substantially insensitive to and acoustically decoupling it from an incident acoustic pressure wave signal. In yet another embodiment which does not employ a reference mandrel, the reference fiber is wound around the support mandrel in cavities above the latter that are caused to operate as acoustic mismatches. The junctions of the mandrels are preferably sealed for isolating the wound length of reference fiber and cavities from fluid in which the hydrophone sensor is located.