Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2003-02-14
2004-12-14
Heinz, A. J. (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
Reexamination Certificate
active
06831887
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a recording medium reproducible by utilizing near-field light and a near-field optical probe for reproducing information recorded on such a recording medium and, more particularly to a recording medium and near-field optical probe that enhances reproducing resolution for information recorded with density.
In recent years, remarkable development has been made in optical reproducing apparatuses (DVD players, etc.) for reproducing information on recording media by illuminating laser light. However, the information recording density has reached a limitation because of a presence of a diffraction limit of laser light. In an attempt to break through such diffraction limit, a proposal has been made on a near-field light reproducing apparatus using an optical head provided with a microscopic aperture having a diameter of less than a wavelength of laser light to be utilized in reproducing so that near-field light (including both near field and far field) produced at the microscopic aperture or on a surface of the recording medium can be utilized, thereby increasing reproducible information recording density.
Conventionally, the near-field microscopes using a probe (hereinafter referred to as a near-field optical probe) having a microscopic aperture as mentioned above as an apparatus utilizing near-field light have been utilized for observing sample microscopic surface textures. As one of schemes utilizing near-field light in the near-field microscopes, there is a scheme that the near-field optical probe microscopic aperture and the sample surface are approached in distance to nearly a diameter of the near-field optical probe microscopic aperture so that near-field light can be produced at the microscopic aperture by introducing propagation light through the near-field optical probe and toward the near-field optical probe microscopic aperture (illumination mode). In this case, scattering light caused by the interaction between the produced near-field light and the sample surface involving an intensity and phase reflecting a sample surface microscopic texture is detected by a scattering light detection system. Thus, high resolution of observation is made feasible that could not be achieved by the conventional optical microscopes.
There is another scheme of the near-field microscopes utilizing near-field light that propagation light is illuminated toward a sample to localize near-field light over the sample surface wherein a near-field optical probe microscopic aperture is approached to the sample surface to nearly a diameter of the near-field optical probe microscopic aperture (collection mode). In this case, scattering light cause by the interaction between the localized near-field light and the near-field optical probe microscopic aperture involving an intensity and phase reflecting a sample surface microscopic texture is guided to a scattering light detection system through the near-field optical probe microscopic aperture, thus achieving observation with high resolution.
As a near-field microscope, Japanese Patent Laid-open No. 174542/1995, for example, has been proposed disclosing a scanning near-field atomic force microscope. This scanning near-field atomic force microscope adopts as near-field optical probe an optical waveguide sharpened at a tip to perform probe access control-and scanning control for the atomic force microscope (AFM) thereby enabling observation of sample surface topology and optical characteristics.
FIG. 11
is a block diagram showing a schematic configuration of the scanning near-field atomic force microscope.
In
FIG. 11
, a scanning near-field atomic force microscope
80
has, above a probe
89
, a laser light source
83
, a focus lens
84
, a mirror
85
and a photoelectric conversion element
86
vertically divided into two. The light emitted from the laser light source
83
is collected by the focus lens
84
onto a probe top surface
82
so that the light reflected thereon is guided to the photoelectric conversion element
86
via the mirror
85
. Meanwhile, the light emitted from a light source
94
for light information measurement is illuminated through a collimate lens
95
to a backside of a recording medium
81
over a prism
92
having a slant face treated for total reflection. Then, the light is guided to the other end of the probe
89
(not-sharpened base) that is proximate to the recording medium
81
and introduced to the photoelectric conversion element
87
.
The prism
92
and recording medium
81
are set up on a rough movement mechanism
97
and fine movement mechanism
96
movable in XYZ directions. The signal detected by the photoelectric conversion element
86
is sent to a servo mechanism
93
. Based on the signal, the servo mechanism
93
controls the rough movement mechanism
97
and fine movement mechanism
96
so that the deflection on the probe
89
cannot exceed a prescribed value when approaching of the probe
89
to the recording medium
81
or reading out data. The servo mechanism
93
is connected with a computer
99
to control operation of the fine movement mechanism
96
in a planar directions and receive information about the recording medium from a control signal of the servo mechanism
93
. Meanwhile, when applying modulation to the light of the light source
94
or providing vibration by a vibration mechanism
88
to between the probe
89
and the recording medium
81
, the signal obtained in the photoelectric conversion element
87
is connected to an analog input interface of the computer
99
via a lock-in amplifier
98
to detect optical information in synchronism with planar action of the fine movement mechanism
96
. When no modulation or the like is applied to the light source
94
, the signal obtained in the photoelectric conversion element
87
is directly connected to the analog input interface of the computer
99
without being passed through the lock-in amplifier
98
.
The above near-field optical information reproducing apparatus utilizes the near-field microscope technology and observation scheme, and can reproduce information densely recorded on a recording medium by utilizing near-field light.
However, where the recording medium is increased in recording density by arranging data marks as information units in a close relationship, when conducting reproducing with the recording medium there encounters difficulty for the near-field optical probe used in the conventional near-field optical information reproducing apparatus to individually recognize and detect adjacent ones of the data marks. This problem is explained hereinbelow on an example of a near-field optical probe of a near-field optical information reproducing apparatus for information reproducing on the collection mode.
FIG. 12
shows a recording medium
100
arranged with data marks
101
to produce near-field light. Incidentally,
FIG. 12
shows one part of the recording medium
100
wherein the dotted circle
102
signifies a position that a data mark is possible to provide.
In
FIG. 12
the data marks
101
are different in optical transmittance or refractive index, for example, from a base member
103
of the recording medium
100
. The difference in optical property enables recognition of the presence or absence of a data mark
101
. That is, in the data mark
101
the near-field light produced on a surface of the recording medium
100
is different in intensity or the like from that of the base material
103
, which realizes to reproduce information configured by the data mark
101
. Here, the near-field light on the surface of the recording medium
100
is produced by illuminating incident light, such as laser light, at a backside (surface not having data marks) of the recording medium
100
under a condition of total reflection. Incidentally, recording onto the data mark
101
is possible to realize by a phase change recording method or the like in the currently-marketed rewritable recording mediums.
FIG. 13
shows a relationship between a sectional view of the recording medium
10
Chiba Norio
Kasama Nobuyuki
Kato Kenji
Mitsuoka Yasuyuki
Niwa Takashi
Adams & Wilks
Heinz A. J.
Le Kimlien
Seiko Instruments Inc.
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