| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain a grid configuration in which, transmitted light flux does not cause wavefront degradation associated with a phase level difference, by forming a sub wavelength grid only in a designated area. <P>SOLUTION: An optical element, in which an incident optical beam having vertical polarization is transmitted in an optical recording medium A for a blue light optical beam and an optical beam of horizontal polarization is transmitted in an optical recording medium B of the same kind, is divided into an annular zone area 6b formed with a sub wavelength grid and a central area 6a not formed. In order for the optical beam for the optical recording medium A to transmit the annular zone area 6b of an opening restriction element 6, a phase difference δ of the optical beam of the vertical polarization direction is the integral multiple of 2π. On the other hand, the optical beam of the optical recording medium B is diffracted by the horizontal polarization. Because aberration occurs when a difference in an optical path length is caused in the optical beam of the optical recording medium A which transmits the annular zone area 6b and the a central area 6a of the opening restriction element 6, an average optical path length L1 of the optical beam which transmits the concavo-convex part in a shape of a cross section for the diffraction grid having a pitch longer than the wavelength of the annular zone area 6b is made to match optical path length L2 which transmits the central area 6a where the diffraction grid is not formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
