| 摘要 |
An optical pick-up includes light sources for emitting light beams having different wavelength, the light sources being switched according to the kind of optical discs, a refractive lens element for converging the light beams from the light sources onto recording layer of the optical disc; and a spherical aberration correcting element on which a concentric phase grating structure is formed, the phase grating structure altering spherical aberration in response to change of wavelength to correct change of the spherical aberration due to change of the thickness of the cover layer. The spherical aberration correcting element has a wavelength dependence such that spherical aberration varies in the undercorrected direction as wavelength of incident light increases. |
