Patent ID: 7558162

Claim:
An optical information apparatus, comprising: an optical pick-up head including: a light source emitting a light beam; a condensing unit receiving a beam from the light source and condensing the beam onto an optical recording medium; a beam splitter receiving the beam reflected from the optical recording medium and splitting the beam; and a photodetector receiving the beams split by the beam splitter and outputting signals in accordance with amounts of the received light beams; wherein the photodetector has a plurality of light-receiving portions, a tracking error signal generator generating a tracking error signal for irradiating a desired track with a beam; wherein the optical recording medium has an information recording surface for recording information, the optical recording medium has a reflective surface for reflecting the beam when the beam is condensed onto the information recording surface, the beam splitter has a plurality of regions, a size of the beam on the beam splitter is D, a numerical aperture of the condensing unit is NA, a lateral multiplication of an optical system in the optical pick-up head from the optical recording medium to the photodetector is α, an interval between the information recording surface and the reflective surface is d, and a refractive index present in the interval d between the information recording surface and the reflective surface is n 2 , the tracking error signal generator performs a differential arithmetic operation with respect to the signals output from the light-receiving portions to generate a push-pull signal, and when the beam splitter splits the beam in a direction different from that of the light-receiving portion outputting a signal for generating the tracking error signal over a width h of a region in a vicinity of a center to be irradiated with the beam, a width S of the light-receiving portion outputting a signal for generating the tracking error signal has a relationship S≦2·h·α·NA·d/(D·n 2 ).