| 摘要 |
PROBLEM TO BE SOLVED: To focus light at two wavelengths onto the recording faces of respective optical recording media having different disk thickness while satisfying the requirement for a compact and low-cost optical pickup device without making the structure of the device complicated by separately applying zone plates having a step-like cross section having different wavelength selectivity and converging effects from each other on the top and back faces of a lens. SOLUTION: Zone plates 12A, 12B having a step-like cross section (with the step height h1, h2 of the unit step) are formed on both faces of a diffraction lens 8. The number of the steps is three. When a CD-R is recorded and reproduced, the laser beams at 780 nm wavelength (λ2) in almost parallel beams incident to the diffraction lens 8 are focused by the zone plate 12B on the face of the lens 8 in the light source side onto the recording face of the CD-R. When a DVD is recorded and reproduced, the laser beams at 634 nm wavelength (λ1) in almost parallel beams incident to the diffraction lens 8 are focused by the zone plate 12A formed on the face of the lens 8 in the disk side onto the recording face of the DVD. |
