Laminated half-wave plate, optical pickup device, polarization converter, and projection display apparatus

A laminated half-wave plate comprising:

• a first wave plate;
• and
• a second wave plate in which the first wave plate and the second wave plate are arranged so that optical axes thereof intersect each other,
• wherein when phase differences of the first wave plate and the second wave plate with respect to a wavelength λ are represented by Γ1 and Γ2, in-plane bearing angles formed by a polarization plane of a linearly-polarized beam incident on the laminated half-wave plate and optical axes of the first and second wave plates are represented by θ1 and θ2, an angle formed by a polarization direction of the linearly-polarized beam incident on the laminated half-wave plate and a polarization direction of the linearly-polarized beam emitted from the laminated half-wave plate is represented by φ, and an optical axis adjustment amount is represented by a, the following expressions are satisfied:
• Γ1=180°+n×360°;
• Γ2=180°+n×360° (where n in Γ1 and Γ2 is a non-negative integer);
• θ1=φ/4+a;
• and
• θ2=3φ/4−a.