All-optical hydrophone insensitive to temperature and to static pressure

A optical hydrophone comprising:

• an active optical fiber element with Bragg gratings inscribed in the active optical fiber element forming the laser cavity;
• a mechanical structure forming a cavity filled with a fluid, and inside which the active optical fiber element is placed along a longitudinal axis of the cavity, the mechanical structure comprising:
• a substantially cylindrical hollow rigid body forming the cavity inside which the optical fiber element is placed;
• two end caps configured and designed to seal the ends of the substantially cylindrical hollow rigid body and traversed by the active optical fiber element, said active optical fiber element being fixed with a prestrain to the end caps at a level of points of traversal to be permanently under tension,
• wherein the two end caps each comprise a part rigidly tied to the substantially cylindrical hollow rigid body, and a mobile part able to expand or contract along the longitudinal axis under the effect of a temperature variations, the mobile part comprising a deformable wall deformed when subjected to variations in a pressure exerted by an exterior medium in which the optical hydrophone is immersed, the deformation of the end caps giving rise to a variation of a length of the active optical fiber element,
• the deformable wall comprising an internal face directed toward an interior of the cavity and an external face directed toward an exterior of the cavity and the internal face being translated with respect to the substantially cylindrical hollow rigid body along the longitudinal axis of the cavity by expansion or contraction of the respective mobile part under an effect of temperature variations of the exterior medium in which the optical hydrophone is immersed, giving rise to a variation in the length of the active optical fiber element, such that the variation in the length at least partially compensates the variations of an emission frequency of the laser cavity as a result of the temperature variations;
• and
• a through orifice configured to allow communication between the cavity and the exterior medium and to achieve equilibration of a static pressure between the exterior medium and the fluid contained in the cavity.