Patent ID: 8813571

Claim:
An optical microphone for detecting an acoustic wave by using a light wave, the acoustic wave propagating in an ambient fluid, comprising: a propagation medium section for the acoustic wave to propagate through; a light source for emitting a light wave to be transmitted through a diffraction region in the propagation medium section; and a photoelectric conversion section for detecting the light wave having been transmitted through the propagation medium section and outputting an electrical signal, wherein, the optical microphone is configured: to allow a first acoustic wave and a second acoustic wave to propagate in antiparallel directions in the propagation medium section so as to simultaneously arrive at the diffraction region and traverse the light wave being transmitted through the diffraction region, the first acoustic wave being a portion of the acoustic wave and the second acoustic wave being at least a portion of the remainder; and to generate, in the diffraction region, a +1 st order diffracted light wave and a −1 st order diffracted light wave of the light wave based on a refractive index distribution of a propagation medium composing the propagation medium section, the refractive index distribution occurring due to propagation of the first acoustic wave and the second acoustic wave; and the photoelectric conversion section detects at least one of: an interference component between a +1 st order diffracted light wave of the light wave ascribable to the first acoustic wave and a −1 st order diffracted light wave of the light wave ascribable to the second acoustic wave; and another interference component between a −1 st order diffracted light wave of the light wave ascribable to the first acoustic wave and a +1 st order diffracted light wave of the light wave ascribable to the second acoustic wave.