| 摘要 |
PURPOSE:To prevent the effect of the adverse influence to the motion of the lens barrel and to correctly detect the position of the objective lens by providing the reflecting means having a 1/4 wavelength plate and a reflection mirror in the lens- barrel as well as the objective lens. CONSTITUTION:At a glass plate 6 of a lens barrel 2, a 1/4 wavelength plate 7 and a reflection mirror 8 having the size of the extent that the information reading is not troubled are provided and a part of a main beam 3 is guided through the glass plate 6 and the 1/4 wavelength plate 7 to the reflection mirror 8. Since the luminous flux reflected by the reflection mirror 8 passes through the 1/4 wavelength plate 7 two times and the polarizing direction is rotated to 90 deg., the flux transmits a polarizing film 5a of a polarizing beam splitter 5. The reflecting light by the reflection mirror 8 to transmit the polarizing film 5a is received by a light receiving element 9 having light receiving areas 9a and 9b divided into two in the tracking direction, the output of respective light receiving areas 9a and 9b is supplied to a signal processing circuit 10 and in the signal processing circuit 10, the difference in the output of the complementarily changing light receiving areas 9a and 9b is detected. Thus, the position signal is obtained which shows the quantity and the direction of the dislocation from the neutral position of an objective lens 1 in the tracking direction. |
