METHOD FOR ADJUSTING DIFFRACTION GRATING

PURPOSE:To facilitate the adjustment of the diffraction grating by radiating two or over of laser beams in the direction of pin orientation of an optical disk, detecting the radiated point by a preceding light sensor and a succeeding light sensor, comparing the retarded preceding light sensor output with the succeeding light sensor output so as to obtain maximum value of the correlation. CONSTITUTION:The post-stage of the preceding light sensor 1 and the succeeding light sensor 2 is provided respectively with amplifiers 6, 7. A delay circuit 3 is provided to the post-stage of a preceding light sensor amplifier 6A, required time difference DELTAt is set for the preceding light sensor and the succeeding light sensor to detect one and same pit. In tracing the same pits by the two preceding/succeeding sensors, the output signal of the delay circuit 3 is the same as that of the amplifier 7. In giving the two signals to the X and Y axes of an oscilloscope of a correlation detecting circuit 4, the waveform becomes linear. It is possible to adjust the diffraction grating quickly and accurately to retard the signal of the preceding light sensor by DELTAt so as to obtain the maximum value of the correlation of the succeeding light sensor in this way.