| 摘要 |
An optical pickup head device includes a diffraction grating for generating zero-order diffracted light and at least first-order diffracted light and provides a tracking error signal with a DPP method. The diffraction grating includes grating patterns with a nonuniform period or phase. The size of the first-order diffracted light converged on an optical recording medium is larger in the direction parallel to a tangent to the track than in the direction perpendicular to the tangent. P1/P0>PW2/PW1 is established, where PW1 represents the power that is required to record information on the optical recording medium, PW2 represents the maximum power that allows information recorded on the optical recording medium to be reproduced without being erased, P0 represents the light amount of the zero-order diffracted light converged on the optical recording medium, and P1 represents the light amount of the at least first-order diffracted light converged on the optical recording medium. This configuration makes it possible to detect a tracking error signal with reduced offset, even if a recordable optical recording medium having two information recording planes is used.
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