| 摘要 |
There is provided, in an optical disk apparatus which is capable of recording data to or reading data from a plurality of types of optical disks, a wavelength plate and an optical pickup which can reduce deterioration in signal quality even in the presence of a large birefringence of the substrate of an optical disk. A wavelength plate 6 according to the present invention is a wavelength plate to be placed in an optical path through which rays of a plurality of wavelengths travel back and forth, the plurality of wavelengths including a ray having a wavelength λ. The wavelength plate includes a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first regions D1 and second regions D2 having different optic axis directions from each other. The relationship 240°≦̸&Dgr;1≦̸300° is true, where &Dgr;1 is a retardation of the wavelength plate 6 for the ray of the wavelength λ.
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