| 摘要 |
PURPOSE:To eliminate unstable operation of tracking control loop so as to obtain an optical head which generates no offset of tracking operation point due to the movement of tracking drive element by shifting the reflected light by the amount proportional to the shifting amount of objective lens in an optical recording and reproducing device. CONSTITUTION:The reflected light from a disc 7 is separated into a luminous flux other than for tracking control by means of a half mirror and the luminous flux is received by a detector (d3, d4) 22 composed of halves. At this time, the beam is formed elliptical by using an astigmatism means between the mirror 23 and a photodetector. The output of d1 and d2 are detected by a differential amplifier 1, and are synthesized into a tracking signal to form a tracking control loop. Thus, the tracking control loop with excellent tracking follow-up accuracy and stability can be obtained. |
