Optical: systems and elements – Lens – With support
Reexamination Certificate
2002-05-29
2004-03-09
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C359S641000, C359S216100, C369S044230, C369S044320, C250S201400, C372S038060
Reexamination Certificate
active
06704152
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a light irradiating device, optical pickup device with the same, and method of adjusting the light irradiating device, which is suitably used in various recording apparatuses having a function of recording information in optical information recording media, such as digital versatile discs, etc.
2. Description of the Prior Art
Recently, there has been realized a digital versatile disc (DVD) that allows an image quality higher than that of a laser disc and a running time longer than 130 minutes on a single side. Such a DVD has a capacity of about 4.7 GB on a single side, which is seven times greater than that of a compact disc-read only memory (CD-ROM).
For recording/reproducing of an optical information recording medium such as the optical disc, an optical pickup device is used having the construction in which optical devices such as a semiconductor laser (LD: light emitting device), a polarization beam splitter, a collimating lens, a ¼&lgr; plate, an object lens and a PIN-photo diode (PIN-PD: light receiving device) are arranged along an optical axis.
The optical pickup device narrows light emitted from the semiconductor laser to a predetermined diameter by the collimating lens and the object lens, and then condenses the narrowed light onto an optical information recording medium. In this case, in order to maximally increase energy of a light spot condensed onto the optical recording medium, the light emitted from the semiconductor laser must be used as efficiently as possible, and a numerical aperture (NA) of the collimating lens must be set to as large as possible.
However, on a plane perpendicular to an optical axis of light emitted from the semiconductor laser, a light intensity distribution is represented by a Gaussian distribution in which light intensity is high at its center, and becomes rapidly lower from the center to the sides. Therefore, parallel light obtained by converting the emitted light using the collimating lens, or diffused light with a predetermined radiation angle, also has the same light intensity distribution as the Gaussian distribution. In this case, since the size of the spot of light condensed onto the optical information recording medium by the object lens is increased, various problems such as a decreased recording density of the optical information recording medium, a deterioration of reproduced signals, etc., may occur.
Therefore, in order to solve the above problems, an optical pickup device using a beam shaping prism is proposed and provided practically.
FIG. 12
is a view showing the construction of a conventional optical pickup device using a beam shaping prism. Referring to
FIG. 12
, reference numeral
1
designates a semiconductor laser (LD: light emitting device), reference numeral
2
a collimating lens, reference numeral
3
a beam shaping prism in which a pair of prisms
3
a
and
3
b
are arranged facing each other, reference numeral
4
an object lens, and reference numeral
5
an optical disc (optical information recording medium).
The semiconductor laser
1
emits light, for example, blue light having a wavelength of 430 nm, or red light having a wavelength of 635 nm. A radial diffusion angle of the emitted light has radiation properties different in the horizontal and vertical directions with respect to a plane of polarization. For example, a diffusion angle in a vertical direction is about 30 to 40 degrees, and a diffusion angle in a horizontal direction is about 10 degrees.
In the optical pickup device, light radially emitted from the semiconductor laser
1
is converted into parallel light by the collimating lens
2
. Intensity distribution of light sequentially transmitted through and diffracted by the respective prisms
3
a
and
3
b
constituting the beam shaping prism
3
is converted from the Gaussian distribution to a flat distribution. Then, the transmitted and diffracted light is narrowed to a predetermined diameter by the object lens
4
, such that it is condensed onto a recording surface of the optical disc
5
.
Light reflected from the recording surface of the optical disc
5
is converted into parallel light by the object lens
4
, sequentially transmitted through the beam shaping prism
3
and the collimating lens
2
, and then received by the PIN-PD (light receiving device) via an optical system such as a polarizing beam splitter (not shown). The received light can be obtained as reproduced signals.
FIG. 13
is a graph showing light intensity distributions before and after light is transmitted through the beam shaping prism
3
. In the graph, a curve A is a light intensity distribution before light is transmitted through the beam shaping prism
3
, and a curve B is a light intensity distribution after light is transmitted through the beam shaping prism
3
.
Referring to
FIG. 13
, the light intensity distribution A before light is transmitted through the beam shaping prism
3
is a Gaussian distribution. However, as light is transmitted through and refracted by the beam shaping prism
3
, the light intensity distribution is converted into the light intensity distribution B, in which the light intensity is lower in its center than that of the Gaussian distribution, and becomes gradually lower from the center to the sides, that is, flatter than the Gaussian distribution.
As described above, the light emitted from the semiconductor laser
1
has the light intensity distribution B flatter than the Gaussian distribution over the entire range of a valid diameter Dc of the collimating lens
2
by the transmission of light through the beam shaping prism
3
. Therefore, if the recording density of an optical information recording medium is decreased, there is a little concern about deterioration of reproduced signals, or other problems.
Meanwhile, in the conventional optical pickup device using a beam shaping prism, the beam shaping prism
3
is constructed such that the pair of prisms
3
a
and
3
b
are arranged facing each other. Therefore, an optical axis is apt to be refracted and be eccentric, so it is difficult to adjust the assembly of the optical pickup device using a beam shaping prism. Further, the conventional optical pickup device is problematic in that it employs the pair of prisms
3
a
and
3
b
, so it is difficult to miniaturize the optical pickup device. Further, the conventional optical pickup device is problematic in that the number of optical parts is increased, thus causing the manufacturing process of the optical pickup device to be lengthened, and increasing manufacturing costs thereof.
Moreover, the conventional optical pickup device using a beam shaping prism is problematic in that astigmatism occurs if light transmitted through and refracted by the beam shaping prism
3
is not parallel light.
Further, a light emission wavelength of emitted light can be adjusted within ±5 nm of a desired wavelength by the semiconductor laser
1
, while deviation of a radiation angle of the emitted light cannot be adjusted.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a light irradiating device, optical pickup device with the same, and method of adjusting the light irradiating device, which can obtain light use efficiency required for recording/reproducing of an optical information recording medium, achieve a uniform light intensity distribution in a plane perpendicular to an optical axis, prevent refraction and eccentricity of the optical axis, simplify assembly and adjustment of the light irradiating device, minimize generation of astigmatism, and adjust deviation of a radiation angle of light emitted from a semiconductor laser.
In order to accomplish the above object, the present invention provides a light irradiating device, optical pickup device with the same, and method of adjusting the light irradiating device.
In accordance with a first aspect of the pr
Kaiho Naoki
Morishita Ichiro
Takeya Noriyoshi
Togashi Mitsuhiro
Ben Loha
Birch & Stewart Kolasch & Birch, LLP
Samsung Electro-Mechanics Co. Ltd.
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