Patent ID: 7933023

Claim:
A displacement detection apparatus comprising: a light source which emits a light; an extinction ratio conversion means which raises an extinction ratio of the light emitted from said light source to 20 dB or more; a condenser lens which condenses the light having the extinction ratio made to be 20 dB or more by said extinction ratio conversion means, wherein the light source directly feeds into a collimator lens at first side of a polarization element operating as the extinction ratio conversion means and the condenser lens is located at the second side of the polarization element; a polarization maintaining type optical fiber which transmits the light condensed by said condenser lens; a depolarization element which depolarizes the light transmitted by said optical fiber, wherein the depolarization element cancels a polarization of a beam transmitted by and emitted from the optical fiber, the depolarization element being located between an exit end of the polarization maintaining optical fiber and a further condenser lens; a diffraction grating subjected to an irradiation of the light depolarized by said depolarization element, said diffraction grating attached to a measurement object; and light receiving means which receives the light diffracted by said diffraction grating, wherein: said displacement detection apparatus matches a polarization axis of the light to an optical axis of said optical fiber or an axis perpendicular to the optical axis to enter the light into said optical fiber, the light having the extinction ratio raised to 20 dB or more by said extinction ratio conversion means and being condensed by said condenser lens, and detects a displacement of the measurement object based on a magnitude of a received light quantity of the diffracted light received by said light receiving means.