Optical pickup having catadioptric objective lens

Details Optical pickup having catadioptric objective lens Optical pickup having catadioptric objective lens

1998-10-27

2002-03-19

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

C369S112230

Reexamination Certificate

active

06359850

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of Korean Application No. 98-13317 filed Apr. 14, 1998, in the Korea Industrial Property Office, the disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup having a catadioptric objective lens.
There are various methods under study for increasing recording capacity of an optical recording and reproducing apparatus through reducing the size of a focused spot by decreasing the wavelength of light and increasing a numerical aperture (NA) of an objective lens.
FIG. 1
is a conceptual diagram of a conventional optical focusing system which is used as an objective lens for an optical disk
4
and generates a near field to reduce the size of a focused spot on the disk
4
. The conventional optical focusing system includes a conventional aspherical lens
1
and a spherical lens
2
. The spherical lens
2
is typically called a solid immersion lens. A slider
3
is located between the spherical lens
2
and the disk
4
to load and move the objective lens thereon. The slider
3
moves the spherical lens
2
with respect to the surface of the disk
4
while maintaining a set distance between the spherical lens
2
and the disk
4
of less than 100 nm.
The aspherical lens
1
refracts the laser light emitted from a light source (not shown). The spherical lens
2
focuses the laser light refracted by the aspherical lens
1
on an inner surface (that surface located toward the disk
4
) of the spherical lens
2
. The inner surface of the spherical lens
2
, on which the laser light is focused, forms a near field. As a result, information may be recorded on the disk
4
or read from the disk
4
, via the near field.
When the spherical lens
2
is formed of a material having a refractive index “n,” an angle at which the laser light is focused on the inner surface of the spherical lens
2
becomes large, and the momentum of the laser light is reduced. As a result, an effect of reducing the wavelength of the laser light to &lgr;
is generated. Thus, the NA is increased to NA/&lgr;. Therefore, the size of the focused spot which is finally formed in the surface of the spherical lens
2
is proportional to 1

2
. Accordingly, the size of the spot can be reduced by fabricating the spherical lens
2
using a material having a refractive index different from the refractive index “n.”
However, as the aspherical lens
1
and the spherical lens
2
are separately manufactured, it is difficult to assemble and adjust an optical focusing system having the desired optical features. Since the optical focusing system needs an incident laser light having a beam diameter greater than or equal to 3 mm, the size of all optical components, including a light receptor, is quite large. When an incident laser beam slants off a normal angle with respect to the optical disk, due to vibration of a moving optical pickup or a rotating optical disk, it is difficult to accurately record or reproduce signals. The shortest wavelength of the light from currently available laser diode light sources is about 600 nm, while the NA of the objective lenses is approximately 0.6. Thus, when an NA greater than or equal to 0.6 is needed, the performance of the optical pickup is very sensitive to the incident beam slant. As a result, it is difficult to use conventional optical focusing systems in commercial optical recording and reproducing apparatus.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an optical pickup having a catadioptric objective lens having an excellent performance with respect to an incident beam slant.
It is also an object of the present invention to provide an optical pickup having a catadioptric objective lens enabling a reduction of the size of a focused spot.
It is yet a further object of the present invention to provide an optical pickup with lightweight compact optical components
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 for recording and reproducing information on a recording medium using a near field, the optical pickup having a unit for emitting laser light to a recording medium and detecting the light reflected from the recording medium, and a catadioptric objective lens including a first reflective area for reflecting the light incident from the unit, a focusing area on which the light incident from the unit is focused as a focused spot, and a second reflective area for reflecting the light reflected from the first reflective area toward the focusing area, in which the first reflective area and the focusing area forms a first surface of the catadioptric objective lens and the second reflective area becomes a part of a second surface of the catadioptric objective lens located in the vicinity of the unit, wherein the unit and the catadioptric objective lens are integrated and the light from the unit is incident to the catadioptric objective lens via the portions of the catadioptric lens other than the second reflective area of the second surface.


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