| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical head apparatus used for compatibility with three wavelengths and to provide a wide band phase plate and a polarization diffraction element used for the optical head apparatus. <P>SOLUTION: In the optical head apparatus provided with semiconductor lasers 401, 402 and 403, the polarization diffraction element 411, the wide band phase plate 412, and photo detectors 404, 405 and 406, the semiconductor lasers 401, 402 and 403 emit luminous fluxes of linearly polarized beams having a 410 nm wavelength band, a 660 nm wavelength band and a 780 nm wavelength band, respectively, the polarization diffraction element 411 transmits a linearly polarized beam in a prescribed polarization direction straight and diffracts a linearly polarized beam in the direction orthogonal to the prescribed polarization direction and the wide band phase plate 412 generates phase differences of nearly (2m<SB>a</SB>-1)λ/4, nearly (2m<SB>b</SB>-1)λ/4, and nearly m<SB>c</SB>λ (λ denotes wavelength and m<SB>a</SB>, m<SB>b</SB>and m<SB>c</SB>each denotes a natural number) to the beams having the 410 nm wavelength band, the 660 nm wavelength band and the 780 nm wavelength band, respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
