Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-12-26
2004-03-02
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
C369S118000
Reexamination Certificate
active
06700856
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, relates to an optical head, a magneto-optical head, and a disk apparatus, that have high optical efficiency, can realize high-density recording media and perform high-speed recording and reproduction, and can prevent erroneous reproduction, and a manufacturing method of the optical head.
2. Related Art
Recently, to improve the recording density of a magneto-optical disk or a magnetic disk, which records data with light and a magnetic field, or an optical disk, which records data only with light, reducing a spot size of the near field light used for record or reproduction has been investigated.
As conventional disk apparatuses using this miniaturized near field light, there are what are shown in, for example, Japanese Patent Laid Open No. Hai 11-250460 (1999).
FIG. 16
shows the disk apparatus. This disk apparatus
80
has clear lens-like holding member
81
that is a transparent condensing medium, a laser source
83
emitting a laser beam
83
a
at an oblique angle to an incident surface
81
a
of the holding member
81
, a scattering member
82
that is provided on a bottom surface
81
b
of the holding member
81
and has the size that is equal to or smaller than a wavelength of the beam, and a photo detector
89
detecting reflected light
87
from an optical disk
85
through an objective lens
88
. In the disk
80
configured in this manner, the laser beam
83
a
from the laser source
83
is made to enter the incident surface
81
a
at an oblique angle so as to be totally reflected at the bottom surface
81
b
of the holding member
81
to be condensed and applied at a position of the scattering member
82
. The plasmon resonance is generated in the scattering member
82
, and a scattered light (near field light)
84
generated therefrom enters to a recording film
86
of the optical disk
85
. Then, reflected light
87
from the recording film
86
is guided to the photo detector
89
by the objective lens
88
and detected by the photo detector
89
. Since it is possible to obtain the near field light
84
with the minute size that is a fraction of one or less of the size in a case of only the holding member
81
, it is possible to increase recording density.
According to a conventional disk apparatus, since the laser beam
83
a
enters the holding member
81
at an oblique angle, the irradiated area with the laser beam
83
a
at the incident surface
81
a
of the holding member
81
, and so the numerical aperture of the incident laser beam becomes small. Hence optical efficiency becomes low. This causes a problem that a high-power light source becomes necessary, and a photo detector for reproduction becomes large.
On the other hand, if a laser beam is applied right above the holding member
81
, the surface
81
a
of the holding member
81
becomes wide. Although optical efficiency is increased in this case, there is a probability of erroneously reproducing another recording area caused by the propagation light leaking out from a light spot position of the light-condensed surface
81
b.
FIG. 17
shows a metal structure described in the Dig. of the 6th Int. Conf. on Near-Field Optics and Related Tech. 2000, No. MoO13 (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
9
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 rest shows that the dipole excited emit a near-field list 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.
In the case of the visible frequency region, 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 meal 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 and its gap. Further to incident beam of the prior art bodies vertically, so the component of the propagation light of the light leaking out from a light spot is much more than the component of the near field light. The propagation light becomes the background noise of the optical recording and reproducing the near field light. In
FIG. 17
, The poised beam
92
b
, i.e. propagation light, 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 recorded marks even if the size of the near-field light could be small enough.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and provides an optical head, a magneto optical head, and a disk apparatus that have high optical efficiency, and can realize high-density recording media and perform high-speed recording and reproduction, and a manufacturing method of the optical head.
In addition, the present invention also provides an optical head, a magneto-optical head, and a disk apparatus and a manufacturing method of the optical head that can prevent erroneous reproduction.
According to a first aspect of the present invention, an optical head includes: a laser emits a laser beam; an optical system that has a transparent condensing medium which condenses the laser beam from the laser source and forms a light spot on a light-condensed surface of the transparent condensing medium; a shade provided in an optical path of the laser beam from the laser to the transparent condensing medium and shields a central part of the laser beam and a micro metal member provided so that at least part of the micro metal member is in a position where the light spot is formed and the size of the part of the metal member is smaller than that of the light spot.
According to the above configuration, the laser beam emitted from the laser source enters the transparent condensing medium with its central part being shielded by the shade, and forms the light spot on the light-condensed surface. Since the central part of the laser beam emitted from the laser source is shielded, the propagation light can be prevented from leaking out from the light-condensed surface. When the laser beam is irradiated to the micro metal member provided at a position of the light spot being formed, the plasmon is excited in the micro metal member is excited and near field light having one-digit or higher of multiplication of intensity in comparison with an incident beam is generated. By irradiating a recording medium with this near field light, recording and reproduction becomes possible. Since the size of the near field light is almost the same as the size of the micro metal member, by reducing the si
Fuji 'Xerox Co., Ltd.
Hindi Nabil
Oliff & Berridg,e PLC
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