Patent ID: 6813229
Filing Date: 2004-11-02
Classification: G11B

Abstract:
A multibeam type optical disc read apparatus comprising an optical system (2A) including an objective lens (8) for applying n light beams at the same time to respective n tracks on a signal plane of an optical disc, focus servo means (22, 23) for controlling the optical system by using a focus error signal (FE) to make the n light beams focus the signal plane of the optical disc by moving the objective lens to follow a surface vibration of the optical disc and signal processing means (20A) for generating a signal for each light beam from a detection output of the light beam reflected from the signal plane and reading data recorded on the tracks to which the light beams were applied, based upon the detection output of the light beam, characterized in that said focus servo means performs a focus bias adjustment by applying a first focus bias (Vf) to the focus error signal so that one of the n light beams focus on the signal plane of the optical disc, and then modifying the first focus bias with a predetermined focus bias (W1 or W2) so that the signal plane of the optical disc is positioned at the middle of respective in-focus points of the n light beams as viewed along an optical axis direction of the optical system.