Accession Number : ADD011603

Title :   Phase-Lock Fiber Optic Interferometer.

Descriptive Note : Patent,

Corporate Author : DEPARTMENT OF THE NAVY WASHINGTON DC

Personal Author(s) : Bush,I J

Report Date : 04 Dec 1984

Pagination or Media Count : 9

Abstract : A fiber optic acoustic sensing system for tracking a phase shift linearly over a wide range thereby allowing accurate tracking in the presence of temperature induced phase fluctuation. In one embodiment, light from a laser is split and coupled into both legs of a fiber interferometer. One leg is phase modulated by the acoustic signal while the other leg is phase modulated by a first and second piezoelectric cylindrical modulators. The second modulator is driven at omega sub m to effectively shift the acoustic information up in frequency into the sidebands of the carrier omega sub m. The light signals in the two legs are combined, detected, cross-correlated with the carrier omega sub m to produce an error signal, and then low pass filtered. This filtered error signal is fed back to control the first modulator. The first modulator keeps the interferometer locked in phase by effectively cancelling out the phase produced by temperature and acoustic pressure fluctuations. To effect this cancellation, the first modulator must inversely duplicate the phase shift thereby producing the desired output signal.

Descriptors :   *PATENTS, *OPTICAL INTERFEROMETERS, *PHASE LOCKED SYSTEMS, *FIBER OPTICS, *ACOUSTIC DETECTION, DEMODULATION, PHASE MODULATION, SCHEMATIC DIAGRAMS, ACOUSTIC DATA, LASERS, SIDEBANDS, ACOUSTIC SIGNALS

Subject Categories : Acoustic Detection and Detectors
      Fiber Optics and Integrated Optics

Distribution Statement : APPROVED FOR PUBLIC RELEASE