| 摘要 |
PURPOSE:To rapidly perform the measurement of focus deviation, by impressing a pulse signal on a reproducing signal, measuring the change of the quantity of jitter in the amplitude of the reproducing signal, and measuring the offset quantity of an impressed pulse signal at a point where the change is minimized. CONSTITUTION:By impressing the output pulse of a pulse signal generator 10 on a bias voltage (b), shifting the offset quantity by controlling the pulse signal by an offset adjusting circuit 11, and finding the point where the change of the quantity of the jitter is minimized, the focus dislocation can be measured from the offset quantity at that time. For example, in an offset adjuster, a focus point can be found by impressing the pulse signal having a focused offset on a focus servo system, and adjusting the position of a cylindrical lens in a Z direction, or the Y direction of a photodetector so as to minimize the change of the quantity of the jitter. Also, the change of the quantity of the jitter can be detected by the amplitude of a RF signal, a signal amplitude with a cycle of 3T, and the amplitude of a radial error signal as well. |
