Compact dual wavelength optical pickup head

Details Compact dual wavelength optical pickup head Compact dual wavelength optical pickup head

1998-10-16

2001-10-16

Huber, Paul W. (Department: 2651)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S112100

Reexamination Certificate

active

06304542

ABSTRACT:

FIELD OF THE INVENTION
Cross Reference to Related Application
The present invention relates to a dual wavelength optical pickup head which may be used in an optical disk reading and/or writing device.
BACKGROUND OF THE INVENTION
The dual wavelength optical pickup head allows to use light of different wavelengths in order to process disks of different thickness and/or different reflectivity of a reflecting layer. The dual wavelength optical pickup head may be used in most recent optical disk reading and/or writing devices, e.g. in DVD-ROM reading devices, in order to preserve a backward compatibility with older optical disk formats, e.g. a CD-R disk format. At least two characteristics of disks have to be taken into account to preserve the backward compatibility, namely a thickness and a reflectivity of the disks. DVD optical disks use a 0.6 mm thick substrate and may be read out using light with a wavelength of about 650 nm. CD-R optical disks use a substrate as thick as 1.2 mm and may be read out using light with a wavelength of about 780 nm. The CD-R optical disk has the drawback that it may not be read using light with a wavelength of about 650 nm because a special dye recovering its surface absorbs light of the latter wavelength.
A publication
Dual Wavelength optical Head
for 0.6 mm and 1.2 mm
Substrate Thicknesses
, R. Katayama, Y. Komatzu and Y. Ono, Jpn. J. Appl. Phys. Vol. 36 (1997) pp. 460-466, Part 1, No. 1B, January 1997, discloses an optical head which uses either holographic optical element type optics or variable magnification type optics. The optical head may be used with 0.6 and 1.2 mm substrate thicknesses and contains 635 nm and 785 nm laser diodes. The optical head comprises a single polarizing beam splitter and a set of signal detection optics for each 635 nm and 785 nm light beam.
Consumer product industries strive to reduce the size of their products in order to make them portable and cheaper. These efforts impose a miniaturization and/or a reduction of the number of parts in components making up the products. This would apply e.g. to the optical head of a portable and/or cheaper optical disk reading and/or writing device. On the other hand small components should be just as reliable as their more voluminous equivalents.
One aim of the present invention is to find a solution to reduce the size of an optical head without increasing its cost.
SUMMARY OF THE INVENTION
The present invention provides a dual wavelength optical pickup head for use in an optical disk writing and/or reading device which comprises at least optical means for directing light beams of a first and a second wavelength emitted by a first and a second light source to an optical disk. The optical means comprise at least a wavelength selective beam splitter which allows to at least partially change the direction of a light beam of the first wavelength and is transmissive for a light beam of the second wavelength. The optical pickup head further comprises focusing means for focusing the light beams on a layer of the optical disk, photodetection means for detecting with a single detector light of each one of the first or the second wavelength reflected by the layer of the optical disk, and further optical means for directing a reflected light beam reflected by the layer to the photodetection means.


REFERENCES:
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patent: 5703856 (1997-12-01), Hayashi et al.
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* Patent Abstracts of Japan, vol. 097, No. 001, Jan. 31, 1997, (Mitsubishi Electric Corp.).
R. Katayama, Y. Komatsu, and Y. Ono, “Dual Wavelength Optical Head for 0.6mm and 1.2mm Substrate Thicknesses”, Jpn. J. Appl. Phys., vol. 36 (1997) Pt. 1, No. 1B, pp. 460-466.
EPO Search Report dated: Apr. 1, 1998.

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