| 摘要 |
PURPOSE:To correct the deviation of a scanning spot, by providing a conductive film on a rotary hologram disc and adjusting the angle of incidence to the disc in accordance with the deflection quantity of the surface of the disc which is detected on a basis of the electrostatic capacity between this conductive film and a fixed electrode facing this conductive film. CONSTITUTION:A hologram disc 1 is provided with a hologram recording layer 3 and a light-transmissive conductive film 5 on a glass substrate 2 and is fixed to a rotating shaft 7 of a motor 6. The conductive film 5 is grounded through the rotating shaft 7 of the motor 6, and an electrode 14 for detecting an electrostatic capacity is provided in a fixed position facing to this conductive film 5 and is connected to an electrostatic capacitive displacement measuring circuit 15. The output terminal of this measuring circuit 15 is connected to a mirror controlling circuit 16 which controls the turning of a mirror 10, and the angle of incidence to the hologram 1 is so adjusted as to correct the positional deviation of a scanning spot based on the rotation positional deviation of the hologram disc 1. |
