| 摘要 |
PURPOSE:To correct always the optical axis of a spot light correctly by rotating and controlling a rotatable polarization mirror, which polarizes an irradiation light flux and irradiates it to an information recording face, by a servo signal generation means and by tracing accurately the track of the information recording face by the irradiation light flux. CONSTITUTION:Photoelectric conversion element 9 consists of elements 9a-9d divided into four to obtain a RF reproducing signal and control signal Ve for focus servo, and outputs of elements 9a and 9b are subjected to subtraction in 50 to obtain signal Va-Vb, and this signal is superposed to control signal Vg, and the superposed signal is inputted to amplifier 52 to drive driving coil 53 of tracking mirror 6. Then, outputs of elements 9c and 9d are subjected to subtraction in 54 to obtain signal Vc-Vd, and this signal is superposed to control signal Vf, and the superposed signal is inputted to driving amplifier 56 to drive driving coil 57 of tangential mirror 5. When the neutral point position, etc., of the polarization mirror are changed, center 31 of the spot light on light receiving element 9 is shifted from center 30 of the face, however, the spot light is analyzed into y components corresponding to output Va-Vb and x components corresponding to output Vc-Vd, and the neutral point position is corrected on a basis of these values. |
