Catadioptric optical system, optical pickup and optical disk...

Details Catadioptric optical system, optical pickup and optical disk... Catadioptric optical system, optical pickup and optical disk...

1998-11-20

2001-07-24

Tran, Thang V. (Department: 2752)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S118000

Reexamination Certificate

active

06266315

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catadioptric optical system, an optical pickup and an optical disk drive employing the optical focusing system, and a digital data storage medium on which information is recorded and from which information is read by the optical pickup and the optical disk drive.
2. Description of the Related Art
Various methods for increasing a recording capacity in an optical recording and/or reproducing apparatus have been studied. Those basic approaches are to reduce the wavelength of used light and to heighten a numerical aperture (NA) of a used objective lens, thereby reducing the size of a focused light spot. An optical focusing system for reducing the size of a focused light spot by heightening the numerical aperture is described with reference to FIG.
1
.
The optical focusing system shown in
FIG. 1
which reduces the size of a focused light spot using a near field, includes an aspherical lens
1
and a spherical lens
2
called a solid immersion lens. When the optical focusing system is used as an objective lens for an optical disk
4
, a slider
3
carries the spherical lens
2
over the surface of the disk
4
, and maintains the distance between the spherical lens
2
and the disk
4
to be less than 100 nm. The aspherical lens
1
refracts a laser light beam emitted from a light source (not shown), and the spherical lens
2
focuses the laser light beam refracted by the aspherical lens
1
on the inside of its surface faced to the disk
4
. The surface of the spherical lens
2
on which the laser light beam is focused forms a near field, and thus information is recorded on or read from the disk
4
via the near field.
In the case that a material constituting the spherical lens
2
has a refractive index “n”, in the inside of the spherical lens
2
, the converging angle of a laser light beam becomes large and momentum of the laser light is reduced. Consequently, a wavelength of the laser light beam is reduced to &lgr;
. The numerical aperture (NA) is also increased to NA/&lgr;. Thus, a size of the light spot which is finally formed in the inside of the surface of the spherical lens
2
is proportional to NA/&lgr;. As a result, the size of the spot can be reduced using the refractive index “n” of the medium of the spherical lens
2
.
However, the optical focusing system of
FIG. 1
includes the aspherical lens
1
and the spherical lens
2
which are separately manufactured. Accordingly, it is hard to assemble or adjust the optical focusing system so that a desired optical characteristic is obtained. Since the optical focusing system requires incident laser light having a beam diameter more than or equal to 3 mm, the size of all optical components including a light reception unit are enlarged. As well, in the case where the inclination of incident beam that a laser beam deviates from a normally used angle with respect to an optical disk occurs due to sway of a moving optical pickup or a rotating optical disk, it is difficult to record or reproduce a signal normally.
Further, the shortest wavelength of light of a currently available laser diode light source is about 600 nm.
Also, the numerical aperture of the objective lens is approximately 0.6 at present. Thus, in the case where a numerical aperture of 0.6 or more is required, performance of an optical pickup is much sensitive to inclination of an incident beam. Accordingly, it is difficult to use the existing optical focusing system in order to commercialize an optical recording and/or reproducing apparatus.
SUMMARY OF THE INVENTION
Thus, it is a first object of the present invention to provide an optical focusing system for focusing a light beam using a novel optical system, to thereby have an excellent performance with respect to an incident beam inclination, make optical components compact and reduce the size of a focused light spot.
A second object of the present invention is to provide an optical pickup employing the above optical focusing system.
A third object of the present invention is to provide a method for fabricating the above optical focusing system.
A fourth object of the present invention is to provide an optical disk driver employing the above optical focusing system.
A fifth object of the present invention is to provide an optical pickup including a readout layer for amplifying a light beam containing information recorded on an optical disk.
A sixth object of the present invention is to provide an optical disk to allow more precise read of recorded information.
To accomplish the first object of the present invention, there is provided an optical focusing system for use with a light beam for forming a focused beam spot. The optical focusing system comprises, a refractive surface on one side of the optical focusing system and having a first radius of curvature; a first reflection surface on said one side, surrounding the refractive surface and having a second radius of curvature being different from the first radius of curvature; a transparent beam focusing surface on the other side of the optical focusing system; and a second reflection surface on said other side and surrounding the beam focusing surface,
wherein the refractive surface refracts an incident light beam, the second reflection surface reflects a light beam refracted by the refractive surface toward the first reflection surface, and the first reflection surface focuses a laser light beam reflected from the second reflection surface on the beam focusing surface, as a focused beam spot.
The second object of the present invention is accomplished by an optical pickup for an optical disk. The optical pickup which records and/or reads information to an optical disk using a focused beam spot, comprises,
a light source;
optical detection means;
an optical head comprising,
a refractive surface on one side of the optical head and having a first radius of curvature;
a first reflection surface on said one side, surrounding the refractive surface and having a second radius of curvature being different from the first radius of curvature;
a transparent beam focusing surface on the other side of the optical head; and
a second reflection surface on said other side and surrounding the beam focusing surface,
wherein the refractive surface refracts an incident light beam, the second reflection surface reflects a light beam refracted by the refractive surface toward the first reflection surface, and the first reflection surface focuses a laser light beam reflected from the second reflection surface on the beam focusing surface as a focused beam spot,
optical path altering means for transferring a light beam emitted from the light source to the refractive surface of the optical head and transferring a light beam outgoing from the refractive surface to said optical detection means; and
a supporting means to which the optical head is attached, elastically supporting the optical head so that the optical head moves in the direction perpendicular to said loaded optical disk, within a predetermined distance from said loaded optical disk.
The third object of the present invention is accomplished by a method for manufacturing an optical focusing system which use with a light beam for forming a focused beam spot and comprises, a concave refractive surface on one side of the optical focusing system and having a first radius of curvature, a convex first reflection surface on said one side, surrounding the refractive surface and having a second radius of curvature being different from the first radius of curvature, a transparent beam focusing surface on the other side of the optical focusing system, and a second reflection surface on said other side and surrounding the beam focusing surface, wherein the refractive surface refracts an incident light beam, the second reflection surface reflects a light beam refracted by the refractive surface toward the first reflection surface, and the first reflection surface focuses a laser light beam reflected from the second reflection surface on the beam focu

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