Objective lens for optical disc

Details Objective lens for optical disc Objective lens for optical disc

2006-04-25

2006-04-25

Hindi, Nabil (Department: 2655)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S112080

Reexamination Certificate

active

07035193

ABSTRACT:
An objective lens for recording data to and/or reproducing data from first and second optical discs. The objective lens is provided with at least one surface including a plurality of annular zones divided by steps. The steps has functions of phase shifting a wavefront of light passing through the plurality of annular zones so that a beam spot formed at a converging point of an average wavefront of the wavefront phase shifted by the steps is used for the first and second optical discs. The plurality of annular zones of the at least one surface includes at least one annular zone structure which includes first and second annular zone groups, each of which has at least three steps for phase shifting the wavefront in a first direction, and a first return step which is a step formed at a boundary between the first and second annular zone groups. The first return step phase shifts the wavefront in a second direction opposite to the first direction. An absolute value |Δψ1| of a phase shifting amount of the first light beam given by the first return step satisfies a condition: 6π<|Δψ1|<14π . . . (1). The absolute value |Δψ1| of the phase shifting amount of the first light beam given by the first return step is smaller than larger one of an absolute value of a sum of phase shift amounts given by the first annular zone group and an absolute value of a sum of phase shift amounts given by the second annular zone group.

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