Optical information recording/reproducing apparatus based on tracking control of irradiated light

Claim 1

An optical information recording/reproducing apparatus for optically recording/reproducing information by irradiating a track on a recording medium with a light comprising: detecting means for selectively detecting an area of a reflected light beam smaller than a beam cross-section of a light beam reflected from the recording medium and obtaining an output signal corresponding to the area; tracking error signal producing means for producing, from the output signal of the detecting means, a tracking error signal indicating a shift in a position of the light beam irradiated on the recording medium in a track width direction; and tracking control means for controlling an irradiation position of a light beam irradiated on the recording medium in the track width direction based on the tracking error signal, wherein the detected area has a width that is from 0.2 times to less than 1.0 times the beam diameter of the light beam reflected from the recording medium, said track has a land area and a groove area which are alternately disposed, and information is recorded on both of the land area and the groove area and wherein, when a track pitch Tp, provided in micrometers, on the recording medium, a wavelength λ, provided in micrometers, of a light beam for recording/reproducing information on the recording medium and NA of an objective lens for condensing the light beam in a very small beam spot on the recording medium satisfy the rational expression, 0.62≦Tp/λ×NA≧0.66, the detecting means selectively detects a circular area having a diameter whose size is 0.23 to 0.86 times the beam diameter of the light beam reflected from the recording medium and obtains an output signal corresponding to the circular area.