OBJECTIVE LENS FOR OPTICAL DISK, AND OPTICAL HEAD APPARATUS USING IT

摘要

PROBLEM TO BE SOLVED: To provide an objective lens in which the off-axis property of the lens is improved not only by improving the use efficiency of light by providing a diffraction element at a part but also by suppressing limited magnification for a second optical disk, and to provide an optical head apparatus using it.

SOLUTION: This optical head apparatus is constituted so that temperature compensation is performed by forming the diffraction element at only the outer circumferential part of the objective lens, an optical disk for CD is used with smaller magnification than that the third order spherical aberration is made 0 and residual aberration is compensated by phase level difference.

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