Patent ID: 6714306
Filing Date: 2004-03-30
Classification: G01B,G01H,G01N,G08B

Abstract:
A sensor for optically sensing air borne acoustic waves from a remote source, comprising:(a) means for producing mutually coherent optical sampling and reference beams, which may be combined to form a heterodyne or homodyne intermediate frequency carrier, said sampling beam having a cross section which is small in relation to the acoustic wave lengths of interest, (b) optical means for defining a path for said sampling beam including an aperture through which the sampling beam enters the air in which acoustic waves are borne, and through which any light from said sampling beam passes after reflection, said aperture having a cross section which is small in relation to the acoustic wave lengths of interest, (c) light reflective means arranged in said path for reflecting significant sampling beam energy back via said aperture, said sampling beam path being oriented with a substantial component parallel to the acoustic wavefronts of interest, so that the sampling beam is exposed to an acoustic wave induced density variation of like amplitude over a substantial portion of said path, said density variation producing a variation in the index of refraction, and thereupon phase modulation of the sampling beam in proportion to the accumulated variation in the index of refraction over said beam path, (d) an optical detector including optical means for coherently combining said reflected sampling beam with said reference beam to form an electrical carrier, phase modulated as a result of said variation in the index of refracton and (e) a phase detector coupled to the output of said optical detector for detecting the acoustic wave induced phase variation of said sampling beam and thereby recovering an electrical signal representative of the acoustic waves.