Optical head, lazer diode module and optical recording-reproducing apparatus
AssigneeTDK Corporation
InventorGiichi Shibuya
Life of this patent
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Abstract
The spot diameter D3 of a side beam 21 imaged on a disc 5 is set to at least 2.5 times as large as that of a main beam. Via this configuration, an output signal from a detector detecting a reflected light via a side beam, that is, a signal representing a different in the output from photo-detection devices split by split lines in the radial contains a negligible track cross component caused by a beam spot crossing a track. The signal substantially contains a DC offset component alone caused by the shift of an objective lens in the radial direction under tracking control. Thus, by subtracting the output signal of the detector from the push-pull signal of the main beam, a tracking signal substantially containing no DC offset.
Claims12
An optical head comprising:
- a light source for radiating a single laser beam;
- a diffraction element which splits said single laser beam into a plurality of sub-beams and radiates the plurality of sub-beams on a disc for tracking control;
- wherein a diameter of said sub-beam on a disc is set to at least 2.5 times as large as that of the main beam.
A laser diode module comprising:
- a optical head including:
- a light source for radiating a single laser beam;
- and
- a diffraction element which splits said single laser beam into a plurality of sub-beams and radiates the plurality of sub-beams on a disc for tracking control;
- wherein said diffraction element enlarges a diameter of said sub-beam on a disc to at least 2.5 times as large as that of the main beam.
An Optical recording/reproducing apparatus comprising:
- an optical head including a light source for radiating a single laser beam;
- and a diffraction element which splits said single laser beam into a plurality of sub-beams and radiates the plurality of sub-beams on a disc for tracking control, in that a diameter of said sub-beam on a disc is set to at least 2.5 times as large as that of the main beam,
- detectors which receive disc-reflected lights of a main beam and sub-beams respectively, each of said detector being split by split line in the tracking direction,
- wherein arithmetic operation processing on output signals from each detector split by said split line to obtain a tracking signal.
Dependencies are inferred from the claim text.