| 摘要 |
It is an object of the present invention to provide a wave plate which functions as a 1/4 wave plate where wave front aberration, temperature characteristics, and incident angle dependence are improved with respect to a plurality of wavelengths of an optical pickup unit or the like compatible with DVD and CD, and an optical pickup using the wave plate. In the laminated wave plate where a wave plate whose phase difference is a with respect to a monochromatic light of a wavelength lambda and a wave plate whose phase difference is beta are laminated so that their optical axes cross, and which the laminated wave plate functions as the 1/4 wave plate, a relationship between the phase difference a and the phase difference beta satisfies the following condition: alpha=pin beta=pim/2 however, n>1, and m>1 a material of one wave plate is a film having birefringence characteristics and a material of the other wave plate is quarts.
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