Optical pickup device with tracking and focusing utilizing a photodetector having four regions

Claim 1

An optical pickup device comprising: a light source; an objective lens for focusing a light beam from said light source on a disk; a photodetector for detecting a light beam reflected from said disk, said photodetector being divided into inner first and second regions and outer third and fourth regions by three parallel division lines; optical means for astigmatizing a reflected portion of said light beam incident on said photodetector; means for adding outputs of said first and second regions; means for adding outputs of said third and fourth regions; a first differential amplifier receiving an output signal produced by said means for adding said outputs of said first and second regions and an output signal produced by said means for adding outputs of said third and fourth regions for thereby producing a focus error signal; and a second differential amplifier receiving at least one of said outputs of said first and third regions and at least one of said outputs of said second and fourth regions for thereby producing a tracking error signal, and wherein the sum of the widths of said first and second regions is such that said focus error signal is zero when said light beam is focused on said disk, the direction of movement of a track relative to said pickup is inclined with respect to said division lines at an angle such that the difference between components of diffracted light from said track in said first and third regions and the difference between components of diffracted light from said track in said second and fourth regions are a minimum, and the direction of movement of said light beam during tracking is parallel to said division lines.