| 摘要 |
To permit reproduction of a CD-R and the reproduction of a DVD in a compatible manner, both the aberration introduced by a substrate of a DVD having a 0.6 mm thickness and the aberration introduced by a substrate of a CD having a 1.2 mm thickness are reduced by a lens shape design where corresponding substrate thicknesses of the inner and outer regions of the objective lens are made different, and providing, in the inner region thereof, a protruding circular phase shifter and, also in a verge of the inner region, an annular phase shifter. The aberration of the objective lens in the CD reproduction was further decreased and the NA was increased up to 0. S, so that the recording of the CD-R was made possible.
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