| 摘要 |
PURPOSE:To make accurate tracking possible by cutting the intensity asymmetrical part of diffracted light to reduce the deviation of the phase of a tracking signal. CONSTITUTION:If the quantity of intercepted light of the luminous flux made incident on a focus detecting photodetector is 80%, a deviation of the phase of the tracking signal is generated because of asymmetry of the intensity distribution; but when the quantity of light approximately equal to that used for focus detection is intercepted as shown by oblique lines, a track detecting photodetector 6 receives only the light in a region between lines A and B in a figure, and asymmetry is eliminated to reduce the deviation of the phase of the tracking signal. In an actual device, an oblique line part 12 is not used as a light receiving area as shown in the figure when the photodetector is used as a knife edge also. |
