US Patent 7894321 Laminated wave plate and optical pickup using the same

A laminated plate having a wider bandwidth at a desired retardation is provided. A laminated wave plate 1 includes a first wave plate 2 and a second wave plate 3 that are laminated to each other so that respective optical axes of the first wave plate and the second wave plate intersect each other at an angle of 51.5 degrees when the first wave plate has a retardation Γ1 of 360 degrees and an in-plane azimuth of −8 degrees, while the second wave plate has a retardation Γ2 and an in-plane azimuth of 43.5 degrees. Thus, the laminated wave plate 1 functions as a desired retardation Γ2 in a wavelength from 600 nm to 800 nm as a whole.