Objective lens for optical discs

Details Objective lens for optical discs Objective lens for optical discs

2006-04-04

2006-04-04

Tran, Thang V. (Department: 2653)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

Reexamination Certificate

active

07023788

ABSTRACT:
An objective lens for two or more types of optical discs of different standards is provided. A surface of the objective lens is formed with a diffracting structure, and has an inner area including an optical axis and an outer area. The outer area is configured such that part of a first beam (having a first wavelength for a first optical disc of relatively lower data density) passed through the zones will be substantially in phase (within a prescribed phase difference) with part of the first beam that passed through the inner area. A convergence angle θ of part of the first beam incident on the outermost part of the inner area measured after emerging from the objective lens and a design numerical aperture NAreffor the first optical disc satisfy:in-line-formulae description="In-line Formulae" end="lead"?0.9<sin θ/NAref<1.0,in-line-formulae description="In-line Formulae" end="tail"?while the effective NA is substantially equal to the design numerical aperture NAref.

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