| 摘要 |
<P>PROBLEM TO BE SOLVED: To perform stable recording and reproducing by converging with required numerical aperture (NA) at a recording plane of three kinds of optical recording media with a single plastic objective lens, and by correcting good spherical aberration due to temperature change without losing the efficiency of using light. <P>SOLUTION: A region ψt to turn in which caused phase difference of an aberration correcting element 501 is a reverse direction of the same shape as phase distribution of spherical aberration of the objective lens 106 and a direction of difference in level at which caused phase difference in a phase shifter plane 503 becomes the maximum is replaced in order to correct spherical aberration caused in the objective lens 106 is within a range satisfying 0.6×ra≤ψt≤0.8×ra, in the case of an effective diameter ra of the aberration correcting element 501. The region ψt of this phase difference in level is formed in a range satisfying ψd≤ψt for the effective range ψd of a diffraction plane 502, difference in level in the region ψt is a difference in level shape being approximate to a function indicated by α×r<SP>2</SP>. Thereby, convergence is performed with required numerical aperture (NA), spherical aberration is corrected, recorded, and reproduced without loss of the efficiency of using light. <P>COPYRIGHT: (C)2011,JPO&INPIT |
