This work describes the progress in the developing of a hydrophonic sensors array, based on fiber laser
technology, tailored for underwater acoustic surveillance of harbors, naval forces, and, in general, of maritime areas of
strategic relevance; the same apparatus can also find application for marine mammals coastline surveying, simply
addressing a suitable frequency detection band. The sensors are Distributed Bragg Reflectors Fiber Lasers. The laser
active medium is an Er+ doped fiber included between two Bragg mirrors that are photo-imprinted through UV radiation
on the fiber. The acoustic water pressure variations produce a longitudinal strain on the fiber laser structure with a
consequent modulation of the emission wavelength. An in-fiber un-balanced Michelson interferometer transforms the
wavelength modulation into phase modulation, enhancing the detection sensitivity. An acousto-optic modulator,
mounted on one arm of the interferometer, generates a frequency carrier to allow conventional demodulation techniques.
This apparatus has demonstrated a noise-equivalent level of less than 1 mPa/(Hz)1/2 in the 0.5-5 kHz frequency band.
Experimentations in marine environment of sensor arrays are in progress, and the first results obtained on a couple of
sensors written on a same fiber are presented.