| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical head which never causes a large change of a focus error signal according as a condensing spot is on a group or a land on the recording surface of a recording medium and also to provide an optical information recorder-reproducer and a focal error detecting method. SOLUTION: The substantial numerical aperture NA of the ±1-order light generated by an optical diffraction element 34 is limited to a level where no modulation is caused by a track (land or group) of the signal recording surface of an optical disk 30. At the same time, the signal recording surface of the disk 30 is irradiated by the ±1-order light having its limited NA and a focus error is detected by means of a side spot that is produced on a photodetector 9 by the diffracted light produced on the signal recording surface of the disk 30. The track crossing noises are not caused in principle and accordingly, a stable focus servo is attained. |
