Optical pickup device

Details Optical pickup device Optical pickup device

2000-06-12

2003-01-14

Hindi, Nabil (Department: 2653)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S053100

Reexamination Certificate

active

06507548

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup device for writing and reading information on and from a recording medium by emitting light to the optical recording medium.
2. Description of the Related Art
A typical optical pickup device is for writing and reading information on and from an optical recording medium in a non-contact manner. The optical pickup device is adopted in compact disk players (CDPs), CR-ROM drives, digital versatile disk players (DVDs) and DVD-ROMs.
FIG. 1
shows the optical arrangement of an optical pickup device manufactured by Sony, a Japanese corporation, as an example of the conventional technology. Referring to the drawing, an optical pickup device includes a light source
10
, an objective lens
13
for focusing a main light ray emitted from the light source
10
and branched at a beam splitter
11
in one direction at an optical disk
1
, a main photodetector
15
for receiving a light ray reflected by the optical disk
1
and passing the beam splitter
11
, and a monitoring photodetector
17
for receiving a sub-light ray branched at the beam splitter
11
in another direction. A collimating lens
12
for focusing an incident light is disposed on an optical path between the beam splitter
11
and the objective lens
13
. Also, a holographic optical element
14
for diffracting and transmitting an incident light is installed on the optical path between the beam splitter
11
and the main photodetector
15
.
The main photodetector
15
reproduces the input light as a signal. The reproduced signal is determined in proportion to the amount of change in the amount of light output from the light source
10
. Thus, to obtain a reproduced signal of high quality, the amount of output light must be maintained constantly. For this purpose, the monitoring photodetector
17
detects the amount of sub-light which is not reflected by the beam splitter
11
and passes through it without change. The information on the detected amount of sub-light is used for control of the amount of output light of the light source
10
.
However, in the conventional optical pickup device, the light emitted from the light source
10
diverges at a predetermined angle after being branched at the beam splitter
11
whereas the size of a surface for detecting light of the monitoring photodetector
17
where the divergent light is detected is limited. Thus, the monitoring photodetector
17
cannot detect an amount of sub-light enough to obtain information to effectively control the output light of the light source
10
.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an optical pickup device having an improved structure by which the light emitted from a light source is focused to proceed to a monitoring photodetector.
Accordingly, to achieve the above objective, there is provided an optical pickup device which comprises a light source for emitting light, a beam splitter installed on an optical path of the light emitted from the light source for splitting the light, an objective lens for focusing a main light split by the beam splitter at an optical disk, a monitoring photodetector for receiving a sub-light split by the beam splitter and monitoring the amount of light output from the light source, a main photodetector for receiving the light emitted from the light source and reflected by the optical disk and passing through the beam splitter and detecting an error signal and an information signal, and a collimating lens installed on the optical path between the light source and the beam splitter for condensing both the main light and sub-light split by the beam splitter, so that the amount of light received by the monitoring photodetector increases.
It is preferred in the present invention that a radiation angle of the main light and sub-light passing through the collimating lens is 4°-6°, preferably, 5°.
Also, it is preferred in the present invention that the optical pickup device further comprises a collimating lens, installed between the beam splitter and the optical recording medium, for condensing the main light passing through the beam splitter.
According to another aspect of the present invention, there is provided an optical pickup device which comprises a first light source module for emitting first light having a predetermined wavelength, a second light source module for emitting second light having a wavelength different from that of the first light, a first beam splitter for changing a proceeding path of the first light emitted from the first light source module, a second beam splitter for splitting the second light emitted from the second light source module into a main light and a sub-light and transmitting the first light, an objective lens for focusing the main light split by the second beam splitter and the first light on an optical recording medium, a main photodetector for receiving the light emitted from each of the light source modules, reflected by the optical recording medium, and passing through the beam splitters, and detecting an error signal and an information signal, a monitoring photodetector for receiving the sub-light split by the second beam splitter and monitoring the amount of light output from the second light source module, and a first collimating lens installed on the optical path between the second light source module and the second beam splitter for condensing both the main light and the sub-light split by the second beam splitter by a predetermined angle.
It is preferred in the present invention that the optical pickup device further comprises a second collimating lens installed on the optical path between the second beam splitter and the objective lens for condensing the main light and the first light proceeding toward the objective lens.
Also, it is preferred in the present invention that the first collimating lens condenses the incident second light by a radiation angle of 5°.


REFERENCES:
patent: 6026071 (2000-02-01), Kimura
patent: 6222814 (2001-04-01), Ichimura
patent: 6304533 (2001-10-01), Toda et al.
patent: 5-314529 (1993-11-01), None
patent: 7-65400 (1995-03-01), None
patent: 7-26912 (1995-05-01), None
patent: 7-230628 (1995-08-01), None
patent: 8-153336 (1996-06-01), None

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