Detector for an optical-fiber acoustic sensor using dynamic holographic interferometry

It is shown that the acoustically induced phase modulation of coherent light propagating within a multimode optical fiber may be linearly detected by an interferometer employing an unmodulated replica of the fiber beam as the reference. It is proposed that a dynamic hologram provide such a reference. This technique allows a performance comparable with that of a monomode interferometric sensor to be obtained, but with considerably relaxed alignment tolerances.