Patent ID: 7639587

Claim:
An optical information recording and reproducing apparatus for recording information on a recording medium by forming interference fringes generated by interference between an information beam and a reference beam on the recording medium, and reproducing the information by irradiating the recording medium with the reference beam, in which the interference fringes are formed, said apparatus comprising: a spatial light modulator for spatially modulating at least a portion of a light beam emitted from a light source into the information beam; a light sensing device that reads the information beam extracted from the recording medium by the reference beam irradiated on the recording medium; a shift amount detector that detects a shift of an irradiating position of the light beam entering said spatial light modulator; and a correction device that corrects a positional shift between a position of an area for modulating the information beam and a position of the light beam in said spatial light modulator, based on a positional shift amount detected by said shift amount detector, wherein said spatial light modulator comprises a plurality of pixels, and is configured such that effective pixels are allowed to function as pixels for the reference beam and pixels for the information beam, and the area of the effective pixels of said spatial light modulator is divided into the area for the reference beam and the area for the information beam, according to a position based on the detected positional shift amount.