| 摘要 |
PROBLEM TO BE SOLVED: To expose a regular position of a light receiving element with a light spot irrespective of optical recording media by carrying out tracking using three-spot method to a laser light source corresponding to a plurality of wavelengths. SOLUTION: The optical head optics 1 is provided with diffraction areas 12b, 12a differing in grid spacing and grid angle from each other, and a diffraction-grating 12 with which the diffraction region 12a is arranged on both sides of the diffraction region 12b at two symmetrical positions between these two diffraction regions is arranged between a semiconductor laser component 11 and an objective lens 15. Especially, when the grid spacing and grid angle of the diffraction region 12a are expressed by P<SB>1</SB>,θ<SB>1</SB>, those of the diffraction region 12b are expressed by P<SB>2</SB>,θ<SB>2</SB>, and the wavelengths used are expressed byλ<SB>1</SB>,λ<SB>2</SB>, a grid pitch is set satisfying P<SB>2</SB>/P<SB>1</SB>=ε*λ<SB>2</SB>/λ<SB>1</SB>(0.9≤ε≤1.1) considering various errors such as dimensional tolerances. COPYRIGHT: (C)2005,JPO&NCIPI
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