Variable sensitivity acoustic transducer

Abstract

The gauge length of an acoustic signal detector is dynamically variable by adjusting the location of an induced light reflection interface within a section of optical waveguide to which an acoustic stimulus is coupled. In an interferometer based architecture, a light beam is applied to each of an 'acoustic signal detection' optical waveguide and a 'reference' optical waveguide. The ‘acoustic signal detection’ waveguide is coupled to an acoustic energy transmission element. The acoustic input modifies the index of refraction of the optical waveguide and modulates the light passing through the waveguide. Since the index of refraction of the optical waveguide section is modified by the acoustic stimulus, the signal beam has a phase delay dependent upon the acoustic signal and the distance between one end of the signal waveguide section and an induced reflection interface. The ‘reference’ optical waveguide section also contains a reflection interface, the induced location of which is ganged with that of the signal optical waveguide section. The ‘signal’ path and ‘reference’ path beams reflected by their reflection interfaces are combined and applied to a photo-detector. The index of refraction of the material of the signal optical waveguide section is modified by the acoustic stimulus is the ‘signal path’. This ‘signal’ path light beam is combined out of phase with ‘reference’ light beam at the photo-detector.