| 摘要 |
A conventional broadband quarter-wave plate has not completely solved the wavelength dependence and has different efficiencies of shifting the phase by 90° depending on the wavelengths, and therefore has a problem that it cannot fulfill the strict specifications on the optical characteristics which are demanded of a wave plate from a viewpoint of the optical efficiency and the like in an optical pickup device compatible with a plurality of different wavelengths. To provide a wave plate which completely functions as a quarter-wave plate with respect to a plurality of different wavelengths and an optical pickup using that wave plate to solve the problem, the present invention provides a laminated wave plate, wherein a wave plate with a phase difference alpha and a wave plate with a phase difference beta with respect to monochromatic light with a wavelength lambda are laminated in such a way that directions of optical axes of said plates intersect each other, so that the laminated wave plate, as a whole, functions as a quarter-wave plate, and which is characterized in that a relationship between the alpha and the beta satisfies the following formulas: <?in-line-formulae description="In-line Formulae" end="lead"?>(3/2)xpi<>alpha=2xpix(m-1)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>pi<>beta=2xpix(n-1)<?in-line-formulae description="In-line Formulae" end="tail"?> wherein: each of m and n is a positive integer.
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