| 摘要 |
PURPOSE:To detect the sensitivity of focus error signals by providing the prescribed step in the optical information recording medium and to enable the focus control with high accuracy by correcting the loop gain in the focus control system in accordance with this. CONSTITUTION:The prescribed steps 5a, 5b for correcting the gain are provided on an optical information medium 5. When the objective lens passes this step 5a, it becomes defocus temporarily and a focus error signal v1 corresponding to the size of the step is generated. Similarly, a focus error signal v2 is generated also by the step 5b. If the focus error signals v1, v2 at the time of this defocus are compared with the preliminarily decided value at the time of the design, the detection sensitivity can be known. The fluctuation of the loop gain in the focus control system due to the secular change, etc., can be reduced by correcting this detected signal level by correction value corresponding to it and by correcting the gain in the control circuit by corrected value. |
