| 摘要 |
PURPOSE:To attain high density optical disk by providing an astigmatism to a light spot on a reflected face, detecting a return light with split and using its difference as a reproduction signal. CONSTITUTION:A photodetector 19 is split into four areas 19A-19D by a split line 19L in parallel with the disk drive direction and a split line 19m orthogonal thereto and the cross point between the split lines 19L, 19m is coincident with the center of a return light 20. Summing amplifiers 21A-D and respectively detected outputs of photodetectors 19A, 19C, photodetectors 19A, 19B, photodetectors 19C, 19D, and photodetectors 19B, 19D and differential amplifiers 22A, 22B take respectively difference of outputs of the summing amplifiers 21A, 21B and summing amplifiers 21C, 21D. Then an output of the differential amplifier 22A is used as a tracking error (TE) signal and the output of the differential amplifiers 22B is used as a reproduction signal. Thus, the difference signal is used for the reproduction signal to cancel crosstalk and high density optical disk is formed. |
