| 摘要 |
PURPOSE:To keep a read-in spot on an objective track without being subjected to the effect of change in the reflected light amount of an auxiliary spot, by obtaining a tracking error signal in accordance with the compared output of reflected light amount signal of each spot between the read-in and the auxiliary. CONSTITUTION:The beam sent from a laser light source 4 is converged on an information recording plane 8 and the reflected beam sent from the plane 8 is made incident to a photodetector 10. The reflected light amount signal of spoots 12, 13 being detected is differentiated at 16, 17 via LPFs 14, 15 the sign of the differentiation output of the auxiliary spot 13 is detected at 18, and the differentiation output of the read-in spot 12 and the sign detection output are multiplied at 19. The outputs of the LPFs 14, 15 are compared at 20, and either one of the multiplication output and the output A of the specified level generator is switched at 21 in accordance with the compared output, and the switching output is fed back to a control circuit of servo system as a tracking error signal. |
