Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-06-01
2001-05-15
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
C369S121000
Reexamination Certificate
active
06233217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup, and more particularly, to an optical pickup capable of performing a high-density recording or reproduction.
2. Description of the Related Art
In general, an optical pickup is adopted to a disk player to record or reproduce information such as image and sound on or from a disk type recording medium. To increase the recording density on a recording medium, the size of a light spot formed on the recording medium must be made as small as possible by an objective lens of an optical pickup. To this end, the optical pickup for recording or reproducing information on or from a digital versatile disk (DVD) adopts an objective lens having a large numerical aperture and a light source of 650 nm wavelength.
Referring to
FIG. 1
, a conventional optical pickup includes a semiconductor laser
10
, a grating
12
to detect a tracking error signal using a 3-beam method, an objective lens
25
for converging an incident light to form a light spot on a recording medium (DVD)
1
, a beam splitter
23
for changing an optical path of the incident light, and a photodetector
29
for detecting the incident light and generating a radio frequency (RF) signal and an error signal. The semiconductor laser
10
is a general edge emitting laser for emitting a light of 650 nm.
Also, a collimating lens
21
for collimating the divergent light emitted from the semiconductor laser
10
is placed on an optical path between the semiconductor laser
10
and the objective lens
25
. An astigmatism lens
27
is located between the beam splitter
23
and the photodetector
29
.
The light emitted from the semiconductor laser
10
passes the beam splitter
23
, and is then focused by the objective lens
25
to form a light spot on the recording surface of the recording medium
1
. The light reflected from the recording surface of the recording medium
1
travels toward the photodetector
29
via the objective lens
25
, the beam splitter
23
and the astigmatism lens
27
, and the photodetector
29
generates the RF signal and the error signal.
Here, the size of the light spot formed on the recording surface of the recording medium satisfies the following relationship (1).
size
of
light
spot
∼
λ
NA
(
1
)
where &lgr; represents the wavelength of the semiconductor laser
10
, and NA represents the numerical aperture of the objective lens
25
. Thus, in order to achieve high-density recording/reproduction, the size of the light spot must be made small by using the semiconductor laser
10
emitting a short wavelength light, and/or the objective lens
25
having a large numerical aperture.
However, when using the objective lens
25
having a large numerical aperture, aberration caused by the tilt of the recording medium increases, thereby lowering the stability of the light spot. Also, the semiconductor laser
10
capable of emitting a short wavelength light is expensive.
Due to the above reasons, the optical pickup of the DVD adopts an objective lens having a numerical aperture of 0.6 and a semiconductor laser emitting 650 nm wavelength light. In this case, the size of the light spot formed on the recording medium
1
becomes 1.08 &mgr;m in diameter. However, it is difficult to record 5 gigabytes of information or more on one side of a recording medium of a 120 mm-diameter disk by using an optical pickup forming such a light spot size.
Thus, the optical pickup cannot be adopted to record or reproduce large quantities of information, as in the case of a high definition (HD) television which requires processing of at least 10 gigabytes of information.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide an optical pickup capable of recording/reproducing a large amount of information at high density using a light-emitting diode (LED) whose cost is comparatively low.
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.
According to an aspect of the present invention which achieves the above and other objects, there is provided an optical pickup for recording/reproduction, including a light source unit having a light emitting diode (LED) to emit light and a waveguide to condense the light emitted from the LED; a collimating lens to collimate the light emitted from the waveguide; an objective lens to condense the light passed through the collimating lens to form a light spot on the recording surface of a recording medium; a light path changing unit arranged on an optical path between the waveguide and the objective lens, to change a traveling path of the incident light; and a photodetector to receive the light incident via the objective lens and the light path changing unit after being reflected from the recording medium.
According to another aspect of the object, there is provided an optical pickup for recording/reproduction, including a plurality of light-emitting diodes (LEDs) to emit light; a plurality of waveguides respectively coupled with the LEDs, to condense the light emitted from the LEDs; a coupler to couple the light emitted from the plurality of waveguides onto one optical path; an objective lens to condense the light passed through the collimating lens to form a light spot on the recording surface of a recording medium; a light path changing unit arranged on the optical path between the waveguide and the objective lens, to change the traveling path of the incident light; and a photodetector to receive the light incident via the objective lens and the light path changing unit after being reflected from the recording medium.
Preferably, each LED emits the light having an approximately 550 nm or less wavelength. Also, preferably, each waveguide has a conical shape, and is installed at a respective one of the LEDs.
The optical pickup may further include an optical filter installed between the LED and the light path changing unit, to pass the light of a predetermined wavelength of the light emitted from each LED.
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Cho Kun-ho
Lee Chul-woo
Yoo Jang-hoon
Chu Kim-Kwok
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
Tran Thang V.
LandOfFree
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