Object lens and optical head for reproducing data from optical disks in different thickness of substrate
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United States of America Patent
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-
Mar 30, 1999
Grant Date -
N/A
app pub date -
Dec 26, 1996
filing date -
Dec 28, 1995
priority date (Note) -
In Force
status (Latency Note)
Importance
Abstract
The objective lens has a numerical aperture NA=0.6 when reproducing a DVD having a thickness of 0.6 mm and NA=0.42 when reproducing a CD having a thickness of 1.2 mm. At a boundary of NA 0.42, a slight stepped portion is formed so as to establish a phase difference. In this case, a designed wavelength is 0.635 .mu.m, and an optimum designed substrate thickness of a central portion is approximately 0.8 mm. While the DVD is reproduced, wave front aberration is on the order of 0.025.lambda., and jitter contained in the reproduction signal of the CD is equivalent to the present jitter. As a consequence, such an objective lens and an optical head with employment of this objective lens are provided, which precisely reproduce signals from the CD having the substrate thickness of 1.2 mm, and the DVD having the substrate thickness of 0.6 mm.
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