Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: The invention is intended to solve the problem of a phase shift by the incidence angle dependence of a composite wave plate which is caused when divergent light is incident directly thereon because of occurrence of a phase shift in addition to a desired phase difference of the composite wave plate.

Abstract: As a ½ wave plate constituted by laminating two wave plates, a wave plate where temperature dependence of a phase difference is reduced is provided. In a wave plate constituted by laminating a first wave plate having a phase difference ?1 (deg.) and an optical axis azimuth ?1 (deg.), and a second wave plate having a phase difference ?2 (deg.) and an optical axis azimuth ?2 (deg.), the phase difference ?1 (deg.) of the first wave plate and the phase difference ?2 (deg.) of the second wave plate are set to 360n+180 (n=0, 1, 2 . . . ), and an angle formed by polarization planes of incident light and emitted light is ? (deg.). In this case, the first wave plate and the second wave plate are laminated so as to satisfy ?1=(90+?/2)/2 and ?2=?1+90+?/2.

Abstract: 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.

Abstract: 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 ? and a wave plate whose phase difference is ? 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 ? satisfies the following condition: ?=?n ?=?m/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.

Abstract: As a 1/2 wave plate constituted by laminating two wave plates, a wave plate where temperature dependence of a phase difference is reduced is provided. In a wave plate constituted by laminating a first wave plate having a phase difference &tgr;1 (deg.) and an optical axis azimuth &thgr;1 (deg.), and a second wave plate having a phase difference &tgr;2 (deg.) and an optical axis azimuth &thgr;2 (deg.), the phase difference &tgr;1 (deg.) of the first wave plate and the phase difference &tgr;2 (deg.) of the second wave plate are set to 360n+180 (n=0, 1, 2 . . . ), and an angle formed by polarization planes of incident light and emitted light is &thgr; (deg.). In this case, the first wave plate and the second wave plate are laminated so as to satisfy &thgr;1=(90+&thgr;/2)/2 and &thgr;2=&thgr;1+90&thgr;/2.