| 摘要 |
<P>PROBLEM TO BE SOLVED: To form satisfactory spots in recording surfaces of optical recording media different in substrate thickness, and to improve a luminous flux of a light receiving element by suppressing diffraction of reflected light from an optical recording medium. <P>SOLUTION: In order to suppress diffraction of reflected light from the optical recording medium, a concentric circular diffraction grating having a pitch larger than the wavelength of a luminous flux is disposed in an optical axis perpendicular plane on the substrate of an aberration correction element 105, and a cyclical sub-wavelength structure having a pitch smaller than the wavelength of the luminous flux is superimposed on the convex part of the diffraction grating. In the diffraction grating having the sub-wavelength structure superimposed thereon, diffraction efficiency varies depending on polarization direction of an incident light, and a 1/4 wavelength plate is disposed between the aberration correction element 105 and the optical recording medium. Thus, the polarization directions of an incident luminous flux from a light source to the optical recording medium and a reflected light reflected on the optical recording medium to enter a diffraction element cross each other. In the incident luminous flux of a polarization direction parallel to the groove direction of the sub-wavelength structure, a zero-order transmission light and a +first order diffracted light are generated, the zero-order transmission light becomes a main luminous flux in the reflected luminous flux of the polarization direction orthogonal to the groove direction. Thus, the luminous flux of the light receiving element is improved. <P>COPYRIGHT: (C)2009,JPO&INPIT |
