| 摘要 |
PURPOSE:To prevent a track jump of a beam spot by separating a laser beam into 9 beams by a pair of diffraction gratings to form spots on a disk surface, detecting the dropout out of the reflected light of the bean spot via a 8-split photodetecting element and switching a pair of tracking servo circuits. CONSTITUTION:Nine spots (a)-(i) are formed on a disk via a pair of diffraction gratings 12 and 13. The reflected light of the spot (b), the reflected light of spots (a) and (c) and the reflected light of spots (e) and (h) are received by a 4-split photodetecting element 19b, photodetecting elements 19a and 19c and photodetecting 19e and 19h respectively. The outputs of elements 19a and 19b and the outputs of elements 19e and 19h are supplied to differential amplifiers 31 and 32 respectively. The differential signals of both amplifiers are supplied to a switch 24 as tracking error signals T1 and T2. An amplifier 21 adds the sum of diagonal line signals of those photoelectric elements. When the dropout is detected out of an RF signal R by a dropout detecting circuit 22, a pair of tracking servo circuits are switched via a switch signal generating circuit 23 and the switch 24. This prevents the track jump of beam spots. |
