Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-12-14
2003-09-02
Hindi, Nabil (Department: 2655)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044240
Reexamination Certificate
active
06614742
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head, a magneto-optical head, a disk apparatus, and a manufacturing method of the optical head, and in particular, relate to an optical head, a magneto-optical head, and a disk apparatus, that have high light efficiency, can realize a high-density recording medium and perform high-speed recording and reproduction, and can prevent erroneous record or erroneous reproduction, and a manufacturing method of the optical head.
2. Discussion of the Related Art
Recently, in order to perform high-density recording on a magneto-optical disk or a magnetic disk which records data with light and a magnetic field, and an optical disk which records data only with light, minimization of near field light spot used for recording or reproduction has been investigated.
As conventional disk apparatuses using this miniaturized near field light, there are what are shown in, U.S. Pat. No. 5,883,872, Japanese Patent Laid-Open No. 11-176007 (1999), and a reference “Applied Physics Letters, vol. 65(6), p. 658(1994)”.
FIG. 20
shows a disk apparatus shown in the above-described U.S. Pat. No. 5,883,872, and Japanese Patent Laid-Open No. 11-176007. This disk apparatus
1
has a laser source
2
emitting a laser beam, an objective lens
5
converging the laser beam emitted from the laser source
2
, a solid immersion lens (SIL)
6
condensing the converged beam from the objective lens
5
and forming a light spot
9
on a light-condensed surface
6
b
of a bottom surface, a shade
7
that is provided on the light-condensed surface
6
b
of the SIL
6
and has a micro aperture
7
a
with the size smaller than that of the light spot
9
, a beam splitter
13
separating the reflected light, derived from light emitted to a disk
12
through the micro aperture
7
a,
from emitted light from the laser source
2
, and a photo detector
15
detecting the reflected light separated by the beam splitter
13
. This aperture
7
a
is formed by coating the shade
7
on an entire surface of the light-condensed surface
6
b
of the SIL
6
and thereafter milling the shade
7
by using a focused ion beam method.
In the disk apparatus
1
configured in this manner, a laser beam emitted from the laser source
2
is converged by the objective lens
5
to be condensed on the light-condensed surface
6
b
of the SIL
6
. Since the size of this aperture
7
a
is sufficiently smaller than that of the light spot
9
, propagation light does not pass through this aperture
7
a,
and hence only near field light
10
leaks out on a surface of the aperture
7
a
of the light-condensed surface
6
b.
When a recording layer of the disk
12
is brought close to this near field light
10
, this near field light
10
propagates into the recording layer, then recording and reproduction of information is performed. Since the size of the near field light
10
is determined with the size of the aperture
7
a,
minute recording and reproduction light that is a fraction of one or smaller than the size by only the SIL
6
can be obtained. Therefore, it is possible to increase recording density by using this for recording.
FIG. 21
shows a near field light microscope disclosed in the above-described reference. This near field light microscope
80
uses the near field light, whose light intensity is increased by plasmon resonance, for observation of a minute substance. This microscope
80
has an argon ion laser
83
emitting a blue laser beam
83
a
in an oblique direction, a hemispherical lens (SIL)
81
condensing the blue laser beam
83
a,
emitted from the argon ion laser
83
, in a central part of a light-condensed surface
81
a
of a bottom surface, a micro metal particle
82
made of Ag with the diameter of 30 nm that is coated on the central part of a flat surface
81
b
of the hemispherical lens
81
, and a photo multiplier (PM)
89
detecting reflected light
87
from an optical disk
125
through an objective lens
88
. In the near field light microscope
80
configured in this manner, the blue laser beam
83
a
is made to enter a hemispherical incident surface
81
a
of the hemispherical lens
81
from an oblique angle so that the blue laser beam
83
a
emitted from the argon ion laser
83
is totally reflected on the flat surface
81
b
of the hemispherical lens
81
. Furthermore, the blue laser beam
83
a
is condensed at and emitted to a position of a micro metal particle
82
. Then, the plasmon resonance is generated in the micro metal ball
82
, and near field light
84
generated therefrom is made to enter a recording film
86
of the optical disk
125
. Moreover, reflected light
87
from the recording film
86
is condensed on the PM
89
by the objective lens
88
on the hemispherical lens
80
and is detect. In addition, the optical disk
125
is scanned in the X-Y direction with a piezo element, and recording marks in the recording film
86
are displayed by inputting an output signal of the PM
89
into a luminance signal of a monitor TV (not shown) in performing synchronization with the scanning. Although being a near field light microscope, this device can also be used for optical recording. Since it is possible to obtain the near field light
84
with the minute size, which is a fraction of the size in the case of only the hemispherical lens
81
; it is possible to increase recording density by using this for recording.
FIG. 22
shows a metal structure described in the Dig. of the 6th Int. Conf. on Near-Field Optics and Related Tech. 2000, No. MoOI3 (2000). As shown in
FIG. 22
, the metal structure consists of small metal bodies
91
a
and
91
a
′ faced each other with a small gap
91
c
between them. The width of apexes
91
b
and
91
b
′ of the metal bodies and the gap
91
c
are about 20 nm and far less than the wavelength of incident laser beam
92
.
By arranging the polarization direction of the incident laser beam
92
to cross over the gap, a surface plasmon is excited in the metal bodies
92
a
and
92
a
′ and vibrated in the direction parallel to the polarization direction, and electric charges having opposite polarities with each other in the apexes
92
b
and
92
b
′ causes dipole and the dipole generates the plasmon effectively. The induced electric charges which constitute an electric dipole, generate a strong near-field light
93
effectively, the size of which is nearly equal to that of the gap
92
c.
The simulation result shows that the dipole excited emits a near-field light which intensity is 2300 times larger than that of the incident light and is emitted only around the gap
91
c.
An experimental result about micro wave radiation with a dipole antenna (R. D. Grober et al.: Appl. Phys. Lett, Vol.70, No.11, (1997) p.1354) shows that the radiation occurs only around the gap region. The reason is that the antenna acts as a shield for the incident microwave because the conductivity of the metal antenna is so high enough to induce a strong dipole and the dipole has a strong shield effect.
But in the case of the optical frequency region (FIG.
22
), the most of the incident wave passes side of the metal shade without coupling to the metal shade and is emitted out from the bottom surface of the transparent condensing medium, because the conductivity of the metal shade is not high enough to shield the incident wave, and the spot size of the incident is fairly larger than the size of the metal shade and its gap. The passed beam
92
b
irradiates and affects a recording medium when the medium is placed just under the metal bodies
92
a
and
92
a
for applying the near-field light for recording, which prevents the near-field light to make small recorded marks even if the size of the near-field light could be small enough.
According to a conventional disk apparatus shown in
FIG. 20
, light contributing to recording and reproduction is only the near field light
10
leaking out from the micro aperture
7
a,
and most of a laser beam condensed on the light-condensed surface
6
b
is reflected.
Fuji Xerox, Ltd.
Hindi Nabil
Oliff & Berridg,e PLC
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