Optical pickup apparatus and method

Details Optical pickup apparatus and method Optical pickup apparatus and method

1998-08-31

2002-02-05

Tran, Thang V. (Department: 2651)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S044240, C369S112010

Reexamination Certificate

active

06345029

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No.97-44707, filed Aug. 30, 1997, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup apparatus and method for optical pickup, and more particularly, to an optical pickup apparatus and method therefor which can perform optical pickup on disks having different thicknesses.
Recently, disk type recording media have become popular for recording and reproducing information containing video, audio, data, etc. The most popular disk types are a standard recording-density recordable compact disk (CD-R) and a high recording-density digital versatile disk (DVD). Characteristics of CD-Rs and DVDs are shown in table 1.
TABLE 1
Thickness
Track pitch
Wavelength
(mm)
(&mgr;,m)
(nm)
NA
CD-R
1.2
1.6
780
0.4~0.45
DVD
0.6
0.74
635
0.6
As can be seen from table 1, CD-Rs and DVDs have different thicknesses and different information recording surfaces on which different track pitches are formed. Therefor to perform optical pickup on both CD-Rs and DVDs, light beams having different specific wavelengths must be used. For example, if optical pickup is performed on a DVD using an apparatus for optical pickup on a CD-R, spherical aberrations are generated due to the difference in thickness between the DVD and the CD-R. Accordingly, separate apparatus and methods are currently used for optical pickup of a CD-R and a DVD.
Various optical pickup apparatuses compatible with both CD-Rs and DVDs have recently been proposed. These proposed optical pickup apparatuses: (1) use a separate objective lens for disks having different thickness, (2) use an expensive holographic optical element, and (3) use a liquid crystal diode (LCD) shutter. Several applications relating to an optical pickup apparatus and/or an optical pickup method compatible with CD-Rs and DVDs have been filed by the same applicant, including: U.S. Pat. No. 5,743,304 and U.S. patent application Ser. No. 09/031,541.
However, these proposed optical pickup apparatuses compatible with a conventional CD-Rs and DVDs use relatively high-priced components such as holographic optical elements and LCD shutters, increasing production cost. Further, when employing an objective lens, the proposed optical pickup apparatus should form a “finite optical system,” requiring a relatively complicated structure to focus light beams on a disk.
SUMMARY OF THE INVENTION
In order to solve the above noted problems, an object of the present invention is to provide an optical pickup apparatus and method compatible with disks having a different thickness.
It is another object of the present invention to provide an optical pickup apparatus and method having a reduced production cost utilizing a relatively simple construction process.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
To accomplish the above objects of the present invention, there is provided an optical pickup apparatus having a disk supporter for selectively loading at least two types of optical disks, each having a different thickness on which information recording surfaces are formed, a plurality of light sources, respectively maintaining different spaced distances from the disk supporter, for emitting light beams of respectively different wavelengths for optical pickup of the disks loaded on the disk supporter, and a plurality of photodetection units.
Each photodetection unit includes an optical path alteration unit for altering a path of a light beam so that the light beam emitted from each light source proceeds toward the disk; a numerical aperture adjustment unit, including an annular shielding region which is disposed concentrically about an optical path axis between the optical path alteration unit and the disk supporter, for providing a different numerical aperture according to a characteristic of a light beam to be incident; and an objective lens for respectively focusing the light beams passed through the numerical aperture adjustment unit, onto the information recording surfaces of the disks, forming a beam spot.
The plurality of light sources include a first light source and a second light source. It is preferable that the shielding region maintains a predetermined reference numerical aperture with respect to the light beam in a horizontal direction from any one side of the first light source and the second light source, and maintains a predetermined numerical aperture or below with respect to the light beam in the form of a divergent beam from other side thereof.
The first light source emits a light beam having a wavelength of 790 nm~800 nm, and the second light source emits a light beam having a wavelength of 600 nm~800 nm. In order to effectively perform optical pickup, the shielding region has an inner diameter of 1.2 mm and an outer diameter of 1.45 mm centering the optical axis.
To achieve another object of the present invention, there is provided an optical pickup method for selectively performing optical pickup with respect to at least two types of optical disks having a different thickness on which information recording surfaces are formed, the optical pickup method including: forming an optical path of light beams having different wavelengths capable of performing optical pickup with respect to the respective disks; providing an annular shielding region disposed concentrically about an optical axis of the optical path, providing different numerical apertures according to a characteristic of a light beam to be incident; loading a disk to be picked-up on the disk supporter; and emitting light beams capable of performing optical pickup with respect to the loaded disk, forming a beam spot on the information recording surface of the disk via the numerical aperture adjustment unit, and detecting the light beam containing information obtained from the disk.


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