Patent ID: 8873361

Claim:
An optical information recording/reproducing apparatus for recording and reproducing information in and from an optical recording medium using light, the optical information recording/reproducing apparatus comprising: an oscillator light generator which generates oscillator light that is made to overlap and interfere with reproduced light from the optical recording medium; an oscillator light modulator which adds a predetermined phase difference between the oscillator light and the reproduced light; a light detector which detects interference light in which the oscillator light and the reproduced light overlap each other; a wavefront deviation detector which detects an amount of wavefront deviation between the oscillator light and the reproduced light from an output of the light detector; and a compensation amount calculation unit which calculates a wavefront compensation amount from the amount of wavefront deviation; wherein the phase difference added at the oscillator light modulator is controlled based on the wavefront compensation amount; and the wavefront deviation detector detects the amount of wavefront deviation for an output from the light detector based on a signal passed through a low-pass filter that is designed to pass frequencies of interference fringes of the interference light.