A laser cavity hydrophone of the type comprising an active optical fiber element with Bragg gratings inscribed in the optical fiber forming the laser cavity, having a mechanical structure defining a cavity filled with a fluid, inside which the optical fiber element is placed along the longitudinal axis of the cavity, the mechanical structure further comprising: - a hollow rigid body defining the cavity inside which is placed the optical fiber element, the rigid body being substantially cylindrical and/or rotationally symmetrical about the longitudinal axis; - two end caps (14, 15) configured and designed to seal the ends of the rigid body traversed by the optical fiber element, said optical fiber element being fixed to the end caps (14, 15) at the level of the points of traversal so as to be permanently under tension; the hydrophone being characterized in that: the two end caps (14, 15) each exhibit a part rigidly tied to the rigid body and a mobile part having a deformable wall able to be deformed when it is subjected to variations in the pressure exerted by the exterior medium in which the hydrophone is immersed; the deformation of the end caps giving rise to a variation of the length of the optical fiber element, each of the two end caps exhibiting a hollow body shape open at one end being inserted into the cavity defined by the rigid body so as to seal the end thereof, the hollow body exhibiting a side-wall defining an internal cavity and the deformable wall perpendicular to the longitudinal axis of the cavity, and sealing the end of the internal cavity, the side-wall comprising a segment C distant from the internal wall of the rigid body so as to deform freely in the longitudinal direction under the action of the temperature variations of the exterior medium in which the hydrophone is immerged, giving rise to a variation of the length of the optical fiber element which at least partially compensates the variations of the emission frequency of the laser cavity as a result of these temperature variations, the mechanical structure further having a through orifice configured to allow communication between the cavity and the exterior medium and to achieve equilibration of the static pressure between the exterior medium and the fluid contained in the cavity. - a hollow rigid body defining the cavity inside which is placed the optical fiber element, the rigid body being substantially cylindrical and/or rotationally symmetrical about the longitudinal axis; - two end caps (14, 15) configured and designed to seal the ends of the rigid body traversed by the optical fiber element, said optical fiber element being fixed to the end caps (14, 15) at the level of the points of traversal so as to be permanently under tension; the hydrophone being characterized in that: the two end caps (14, 15) each exhibit a part rigidly tied to the rigid body and a mobile part having a deformable wall able to be deformed when it is subjected to variations in the pressure exerted by the exterior medium in which the hydrophone is immersed; the deformation of the end caps giving rise to a variation of the length of the optical fiber element, each of the two end caps exhibiting a hollow body shape open at one end being inserted into the cavity defined by the rigid body so as to seal the end thereof, the hollow body exhibiting a side-wall defining an internal cavity and the deformable wall perpendicular to the longitudinal axis of the cavity, and sealing the end of the internal cavity, the side-wall comprising a segment C distant from the internal wall of the rigid body so as to deform freely in the longitudinal direction under the action of the temperature variations of the exterior medium in which the hydrophone is immerged, giving rise to a variation of the length of the optical fiber element which at least partially compensates the variations of the emission frequency of the laser cavity as a result of these temperature variations, the mechanical structure further having a through orifice configured to allow communication between the cavity and the exterior medium and to achieve equilibration of the static pressure between the exterior medium and the fluid contained in the cavity. the two end caps (14, 15) each exhibit a part rigidly tied to the rigid body and a mobile part having a deformable wall able to be deformed when it is subjected to variations in the pressure exerted by the exterior medium in which the hydrophone is immersed; the deformation of the end caps giving rise to a variation of the length of the optical fiber element, each of the two end caps exhibiting a hollow body shape open at one end being inserted into the cavity defined by the rigid body so as to seal the end thereof, the hollow body exhibiting a side-wall defining an internal cavity and the deformable wall perpendicular to the longitudinal axis of the cavity, and sealing the end of the internal cavity, the side-wall comprising a segment C distant from the internal wall of the rigid body so as to deform freely in the longitudinal direction under the action of the temperature variations of the exterior medium in which the hydrophone is immerged, giving rise to a variation of the length of the optical fiber element which at least partially compensates the variations of the emission frequency of the laser cavity as a result of these temperature variations, the mechanical structure further having a through orifice configured to allow communication between the cavity and the exterior medium and to achieve equilibration of the static pressure between the exterior medium and the fluid contained in the cavity.