A phase-modulating microphone utilizing integrated optics and micromachining in silicon

Abstract A proposed new integrated optical microphone, in which micromachining and integrated optics in silicon are combined, is described. It is an interferometric sensor with a hollow parallel-plate waveguide as the phase modulator. One of the walls of this hollow waveguide is the gold-coated silicon nitride diaphragm. If the membrane is displaced by sound pressure, the phase of a light wave propagating in the waveguide is modulated. All-silicon waveguides are used for good coupling of light between glass fibers and the modulator. The fabrication process will be very short and compatible to standard semiconductor technology. An equivalent noise level of 45 dB assuming a bandwidth of 10 kHz can be estimated for the microphone, which has not yet been realized. The sensor has dimensions of 10 mm×3 mm×0.56 mm with a 1 mm×1 mm membrane area.