Fiber laser hydrophones as pressure sensors

The development of hydro-phonic sensors for deep see acoustic detection is described. The sensitive element is an erbium-doped single mode fiber laser, with the cavity delimited by two Bragg grating reflectors. The variations of temperature and pressure perturb the cavity, inducing a wavelength shift. The very narrow emission band of the laser, together with the interferometric techniques, allows a dynamic pressure sensitivity in the mPa range. The devices have been characterized both optically and acoustically in a closed tub in laboratory. A resin coating of the fiber laser has been experimented: this technique improves the sensitivity by more than one order of magnitude. The high sensitivity makes these sensors suitable for the detection of the acoustic waves induced by Ultra High Energy Neutrinos.