Dual-wavelength optical pickup head

Details Dual-wavelength optical pickup head Dual-wavelength optical pickup head

1999-01-08

2001-04-03

Epps, Georgia (Department: 2873)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C250S216000, C369S103000, C369S109010

Reexamination Certificate

active

06211511

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 87117841, filed Oct. 28, 1998, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical pickup head device used for accessing data, and more particularly to a laser light source, which can produce two laser lights with different wavelengths, suitable for various uses such as compact disk (CD), CD-recordable, or digital versatile disk (DVD).
2. Description of Related Art
A DVD device was successfully developed and became a commercial product at the end of 1996. The DVD device is a highlight product of computer peripheral products because the DVD with its extremely large memory capacity is able to store image, sound, information, and multimedia, for example, in just one format. The DVD has a memory capacity of about 4.7 GB, which is much larger than the 650 MB of a typical compact disk read-only memory (CD-ROM). The DVD is predicted to be a most promising product in the upcoming years. Manufacturers are now devoting a lot of effort to further developing DVD player technology. Since the main purpose of the DVD player is to include all various media in one storage format, the DVD player should have the capability to read all currently existing types of optical disks, which includes compact disk (CD), CD-read only memory (CD-ROM), and CD-recorder (CD-R). In a CD optical pickup head, the laser light source has a wavelength of 780 nm, and the numerical aperture (NA) of the objective lens is about 0.45. However, DVD players use a laser light source with a wavelength of 635 nm or 650 nm. In order to satisfy the requirement of reading CD's as well as DVD's, several efforts were made to design an objective lens system with two different NA's, NA 0.6 for DVD and NA 0.38 for CD. The early-stage DVD player could therefore accurately focus the light to a small spot both through the 0.60 mm DVD substrate thickness and the 1.2 mm CD substrate thickness. So, early-stage DVD players could also read CD's, and thus was both DVD and CD compatible.
However, it still could not read a CD-R optical disk. Generally, the recording material on the CD-R optical disk has very low reflectivity to a laser light with a wavelength of 635 nm or 650 nm so that the CD-R can only be read by an optical pickup head having a laser light with a wavelength of 780 nm. This resulted in the inability of the early-stage DVD players to read information stored on CD-R media. Nowadays, since the CD-R optical disk is extremely popular, it has become necessary to create a DVD player that is compatible with the CD-R media. Current DVD-ROM pickup head designs usually include two lasers having wavelengths of 650 nm and 780 nm respectively, in order to also read all of the CD system products. As a result, the DVD-ROM player needs to include one more light path for a laser light with a wavelength of 780 nm. This not only increases the dimensions and complexity of the optical pickup head but also increases the fabrication cost.
FIG. 1A
is a schematic drawing, illustrating a conventional structure of an optical pickup head with a single light source. In
FIG. 1A
, a laser light emitted from a laser diode
102
passes a diffraction grating
104
and is incident on beam splitter
106
. The beam splitter
106
reflects the laser light through a collimator lens
108
. The laser light is collimated and then is focused by an objective lens
110
to reach an optical disk
112
so as to read information stored on the optical disk
112
. The laser light is reflected by the optical disk
112
and travels back to the beam splitter
106
through the same light path. The laser light continuously travels through a cylindrical lens
114
and finally reaches a photodetector
116
.
FIG. 1B
is a schematic drawing, illustrating another conventional structure of an optical pickup head with a single light source, which uses a holographic laser module to replace a number of the traditional components used in the pickup at FIG.
1
A. In
FIG. 1B
, a holographic laser module
120
is applied. A laser light emitted from a laser diode
122
passes a holographic optical element (HOE)
124
and then enters a collimator lens
126
. After the laser light is collimated, the laser light continuously travels through an objective lens
128
and is focused onto an optical disk
130
to read information stored on the optical disk
130
. The laser light follows the same light path and travels back to the HOE
124
. The HOE
124
deflects the laser light onto a photodetector
132
.
In summary, current DVD optical pickup heads carrying a single light source with wavelength 650 nm is not compatible with the CD-R disk medium. Moreover, although the current DVD dual-wavelength optical pickup heads can read different types of optical disks like DVD, CD, CD-ROM, and CD-R, their design is too complex and fabrication cost is too high.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a dual-wavelength holographic laser module to produce two laser lights with different wavelengths so as to have a capability to read all optical disk products used in, for example, a DVD system, a CD system, or a CD-R system.
It is another objective of the present invention to provide a dual-wavelength holographic laser module, which is designed to have a single light path and can be applied in an optical pickup head. In the optical pickup head, an objective lens unit is also included to have two changeable numerical aperture (NA) parameters. The optical pickup head including the dual-wavelength holographic laser module is much less complex.
It is still another objective of the present invention to provide a dual-wavelength holographic laser module, which produces laser light with two different wavelengths so as to fit any kind of system that needs two laser lights with different wavelengths.
In accordance with the foregoing and other objectives of the present invention, a dual-wavelength holographic laser module is provided. The dual-wavelength holographic laser module includes a holographic optical element (HOE), a photodetector, and a laser light source, which can produce a laser light with two different wavelengths. The laser light emitted from the laser light source with a desired wavelength travels through the HOE and an objective lens unit, which is used to focus the laser light onto an optical disk of the DVD system, the CD system, or the CD-R system, depending on which wavelength quantity is chosen. The objective lens unit includes a single lens with a changeable NA quantity or a two-lens system that can be switched to utilize one lens at a time. The optical disk reflects the laser light back to the HOE along the same light path. The reflected laser light is diffracted by the HOE to reach the photodetector. The photodetector receives the reflected laser light to obtain a signal, which is used for focusing and tracking, and further reads the information in the DVD system, the CD system, or the CD-R system. The laser light has a single light path even though the laser light can have two different wavelengths.
Using this dual-wavelength holographic laser module with its single light path and the objective lens unit, an optical pickup head is formed. The objective lens unit can be designed to have, for example, two NA quantities of 0.65 and 0.45 to be accordingly chosen. The optical pickup head can therefore read a disk of the DVD system, the CD system, or the CD-R system without an extra light path in the design. The structure of the optical pickup head of the invention is effectively simplified. The fabrication cost is also reduced.


REFERENCES:
patent: 5898722 (1999-04-01), Ramdani et al.
patent: 6016300 (2000-01-01), Takeda et al.
patent: 6043911 (2000-03-01), Yang

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