Apparatus and method for detecting defocus error signal for optical pickup and seek direction detecting apparatus and method adopting the same

摘要

A defocus error signal detecting apparatus includes a photodetector (10) having first, second and third light receiving regions (A, B, C)arranged in a radial direction of a recording medium, each of the light receiving regions independently performing photoelectric conversion with respect to incident light which is reflected/diffracted by the recording medium, and a subtractor (30) for subtracting a sum signal of detection signals from the first and third light receiving regions (A, C) and a detection signal of the second light receiving region (B) and outputting a defocus error signal, so that defocus and/or a change in thickness of the recording medium can be detected. Thus, since a defocus error signal is not affected by a relative tilt of the recording medium with respect to an objective lens, detrack and a shift of the objective lens, by using the defocus error signal, defocus can be precisely controlled and a change in thickness of the recording medium can be detected. Also, when the defocus error signal and the push-pull tracking error signal according to the present invention are briefly compared in a state in which a predetermined amount of defocus is applied to a light spot, a seek direction of the recording medium having a land/groove structure can be detected.