Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-12-12
2004-10-05
Young, W. R. (Department: 2652)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112250, C359S731000
Reexamination Certificate
active
06801492
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2000-76492 filed Dec. 14, 2000, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid immersion mirror (SIM) type objective lens and an optical pickup device adopting the same, and particularly, to a modified SIM type objective lens for far field recording/reproducing, and an optical pickup device adopting the same.
2. Description of the Related Art
In general, information recording/reproducing density increases as a size of a light spot formed on an optical disc by an optical pickup device is decreased. The size of a light spot decreases as a wavelength of a light beam in use becomes shorter and an NA of an objective lens which focuses the light spot becomes greater. A relationship of the size of a light spot to wavelength and NA is shown in equation (1).
Size of light spot∝&lgr;/NA (1)
Thus, an optical pickup device for high density should adopt a light source emitting a light beam having a shorter wavelength and an objective lens having a high NA. To realize a stable system, the objective lens should have a working distance (a distance from a light exit surface of an objective lens to a light input surface of an optical disc) which is large. An optical pickup device for recoding/reproducing information on/from an optical disc of a next generation DVD family, or a so-called HD-DVD (high definition digital versatile disk) family, may adopt, for example, a light source for emitting a light beam having a wavelength of 405 nm and an objective lens having an NA of 0.85 and a large working distance.
However, due to a limit in manufacture, it is difficult to manufacture an objective lens formed of a single lens having an NA of 0.7 or more and satisfying an allowance condition of optical aberration. Thus, to realize an NA of 0.7 or more and satisfy an allowance condition of optical aberration, an objective lens
10
formed of two lenses as shown in
FIG. 1
has been suggested.
Referring to
FIG. 1
, a conventional objective lens
10
includes a first condensing lens
11
for condensing incident light and a second condensing lens
13
arranged between the first condensing lens
11
and an optical disc
1
for increasing an NA of the objective lens
10
. In the objective lens
10
, for example, where a 0.6 NA is secured by the first condensing lens
11
, the NA may be increased by the second condensing lens
13
. For the objective lens
10
to have a 0.85 NA, a light input surface of each of the first and/or second condensing lenses
11
and
13
, facing a light source (not shown), is formed to have a large curvature, or at least one of the first and second condensing lenses
11
and
13
is formed of a material exhibiting a high refractive index, to produce a sharp refraction of light.
Thus, the objective lens
10
as shown in
FIG. 1
is sensitive to decenter, being off an optical axis, and coma is greatly generated according to an amount of the decenter. Also, the objective lens
10
is difficult to manufacture because processing a lens surface having a large curvature is difficult.
Also, the working distance WD1 of the objective lens
10
is short, for example, about 0.15 mm due to a sharp refraction of light. It is difficult to design the objective lens
10
to have a working distance of 0.15 mm or more. For reference, the working distance of an objective lens in an optical pickup device for DVD is about 1.8 mm.
Since the objective lens
10
realizes a high NA by the structure of two lenses, where the first and second condensing lenses
11
and
13
are inclined to each other, it is impossible to maintain a small optical aberration. Thus, allowance of distance and inclination between the first and second condensing lenses
11
and
13
is very strictly obeyed.
Referring to
FIG. 2
, a conventional solid immersion mirror
20
includes a first transmission surface
21
for diverging and transmitting incident light, a second transmission surface
23
disposed to face the first transmission surface
21
, a first reflection surface
25
formed around the second transmission surface
23
, for reflecting incident light passing through the first transmission surface
21
and a second reflection surface
27
, formed around the first transmission surface
21
, for reflecting incident light reflected by the first reflection surface
25
to proceed toward the second transmission surface
23
.
The solid immersion mirror
20
as described above may realize an NA of 0.7 or more with a single lens structure. In the solid immersion mirror
20
, since a blocking area, indicated by a hatched area
29
in
FIG. 2
, exists where the light input to the first transmission surface
21
is relatively near the optical axis, some of the input light is not focused on a recording surface of the optical disc
1
and is lost. Here, the light lost by not being focused on the recording surface of the optical disc
1
is light directly input to the second transmission surface
23
from the first transmission surface
21
, and light which is lost at a boundary between the first transmission surface
21
and the second reflection surface
27
among the light from the fist transmission surface
21
, reflected by the first reflection surface
25
, and proceeding toward the second reflection surface
27
. In
FIG. 2
, to show the blocking area, only a proceeding path of the light input to the first transmission surface
21
is shown. Light reflected by the recording surface of the optical disc
1
and input to the second transmission surface
23
proceeds in the reverse order along the light proceeding path shown in FIG.
2
.
The solid immersion mirror
20
can realize a high NA of 0.7 or more with a single lens. Since the solid immersion mirror
20
has a structure in which light is condensed after reflected from the two reflection surfaces
25
and
27
, curvature may be small so that the solid immersion mirror
20
may be insensitive to the decenter, exhibit relatively superior chromatism quality, and be manufactured easily.
However, since the blocking area exists due to the structure of the solid immersion mirror
20
, as shown in
FIG. 2
, all of the incident light is not used, and the efficiency of light is reduced. About {fraction (
1
/
3
)} of the incident light is blocked in the conventional solid immersion mirror
20
.
Also, since the quantity of the blocked light depends on the size of the first transmission surface
21
, the diameter of the first transmission surface
21
is made less than ¼ of an overall effective diameter of the solid immersion mirror
20
to minimize reducing the light efficiency. To maximize efficiency in an optical pickup device employing the solid immersion mirror
20
as an objective lens, an incident light beam having a diameter slightly greater than that of the first transmission surface
21
is input to the first transmission surface
21
. Accordingly, the quantity of light input to the first transmission surface
21
is greatly affected by movement of the solid immersion mirror
20
for tracking in a radial direction perpendicular to the optical axis.
FIG. 3
shows a light beam intensity profile of light focused by the solid immersion mirror
20
. As can be seen from
FIG. 3
, since a side lobe S
1
which amounts to 5-6% of a peak value of the light intensity is relatively great, where the solid immersion mirror
20
is adopted as an objective lens of an optical pickup device, a great amount of jitter is generated during reproduction of information recorded on the optical disc
1
and a cross erasure problem of removing signals recorded on adjacent tracks may occur during recording. The conventional solid immersion mirror
20
used to generate the light intensity profile shown in
FIG. 3
has an NA of 0.85, an overall effective diameter of 4.5 mm, and the first transmission surface
21
has a diameter of 1.0 mm. Thus, where a
Jung Seung-tae
Kim Dae-sik
Lee Chul-woo
Lee Ki-won
Battaglia M. V.
Samsung Electronics Co,. Ltd.
Young W. R.
LandOfFree
Solid immersion mirror type objective lens and optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solid immersion mirror type objective lens and optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid immersion mirror type objective lens and optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3266644