OPTICAL DISC DEVICE

摘要

Light emitted from a radiation light source (1) passes through a diffraction grating (3a) and is separated into a transmitting light "a", a +1 degree diffracted light "b", and a -1 degree diffracted light "c". The transmitting light "a", the +1 degree diffracted light "b", and the -1 degree diffracted light "c" which are partially overlapped pass through an objective lens (7) and are focused on a track on a signal plane (8a) of an optical disc (8).The light reflected from the track on the signal plane (8a) passes through the objective lens (7) and comes into light branching means (13a). According to the incident position, the light corresponding to the transmitting light "a" is branched into two lights, which come into light detection regions (A1, A2), respectively. The light corresponding to the +1 degree diffracted light "b" is branched into two lights, which come into light detection regions (B1, B2), respectively. The light corresponding to the -1 degree diffracted light "c" is branched into two lights, which come into light detection regions (C1, C2), respectively. By combining the detection signals from the light detection regions (A1, A2, B1, B2, C1, C2), a tracking error signal is generated for the track of the optical disc (8). With this configuration, it is possible to cancel the affect of the off-track accompanying the lens shift without damaging the tracking error signal detection output even without adjusting rotation of the rectilinear grating.