| 摘要 |
PURPOSE:To perform the recording and reproduction with high reliability by allowing a photodiode to change rapidly the wavelength/sensitivity characterisitcs in a use wavelength range so as to cancel the offset due to the wavelength fluctuation and always focusing the objective lens on the optical disk surface. CONSTITUTION:A luminous flux reflected by a beam splitter 4 is guided to a photodiode 16 for wavelength fluctuation monitoring use. The output of a photodiode 16 is normalized with the output of a power monitor photodiode incorporated in a semiconductor laser 1 of a dividing circuit 17. The output of the dividing circuit 17 is inputted in a offset superimposed circuit 18 and the offset superimposed circuit 18 outputs an offset portion generated due to the wavelength fluctuation to a substractor 19. Hence the original focus sensor signal with the canceled offset due to the wavelength fluctuation is obtaiend from the substractor 19. |
