| 摘要 |
<P>PROBLEM TO BE SOLVED: To correct spherical aberration generated by a difference in substrate thickness between 1st and 2nd optical recording media. <P>SOLUTION: As to a phase optical element 20, after obtaining 1st and 2nd phase function curves, respectively, from 1st and 2nd phase functions using a design wavelength λ of the same wavelength value as the reference wavelength λ1 of 1st laser light L, an inner circumferential side stepped phase difference pattern 20a1 is formed annular in the inner circumferential area on one surface based on the 1st phase function curve, and also an outer circumferential side stepped phase difference pattern 20a2 is formed annular based on the second phase function curve in the outer circumferential area outside the inner circumferential stepped phase difference pattern, also, a pitch of steps of the inner circumferential side stepped phase difference pattern is set to a height corresponding to about a 1λ phase difference, on the other hand, a pitch of steps of the outer circumferential side stepped phase difference pattern is set to a height corresponding to about an mλ phase difference (m is a natural number excluding 0) or set to a height corresponding to about an mλ phase difference by varying the value of m for each step. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
