Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-11-23
2001-10-02
Psitos, Aristotelis M. (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
Reexamination Certificate
active
06298029
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information recording and reproducing method and apparatus capable of recording or reproducing FM-modulated analog codes, such as image and voice signals and digital information, for example, data used in computers, facsimile signals and digital audio signals, using a recording beam, such as laser light, in real time.
Recently, a high-density optical recording technique with increased capacity has been developed. However optical recordings have the limitation that a diameter of a recording bit is about 500 nm due to the diffraction of light. The diffractive limitation is directly proportional to the wavelength of light and inversely proportional to a numerical aperture (NA) of a lens. Accordingly, an orientation for high-density recording is to shorten the wavelength of light and increase the numerical aperture of an objective lens. Alternatively, it is possible to utilize the optical phenomenon independent of the diffractive limitation. One method for manufacturing a recording medium involves forming a super-resolution film on a recording film. Further, in an optical head, an attention is paid to a near-field in light recently as a method of pushing forward the above methods. For example, as described in U.S. Pat. No. 5,121,256, a solid immersion lens (SIL) is used to attain a large numerical aperture, so that a smaller spot diameter is obtained as compared with that of a conventional optical lens. The principle thereof is now described. The solid immersion lens is provided by polishing a spherical lens made of transparent material and having a large refractive index n into a hemisphere, for example. Laser light concentrated by an objective lens then becomes focused on the polished surface or flat surface. The velocity of laser light in the solid immersion lens slows by the refractive index and the wavelength thereof is shortened to 1
. That is, the diffractive limitation in the solid immersion lens reduces to 1
as compared with a usual value. From a different viewpoint, it may be stated that the numerical aperture (NA) of the objective lens can increase by n times. In this time, the numerical aperture increases within the solid immersion lens, although when the laser light passes through the solid immersion lens into air, the diameter of the beam spot thereof returns to the former diameter again. However, when the distance between the flat surface corresponding to a bottom surface of the solid immersion lens and a sample (such as a recording film of a disk) is shortened to 200 nm or less (near-field), the laser light is transmitted to the sample, while the wavelength thereof stays at 1
as compared with the wavelength &lgr; of incident light and accordingly the resolution increases with n times. That is, the diffractive limitation reduced to 1
, as compared with the usual value, can be obtained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an information recording and reproducing method and apparatus capable of realizing higher-density recording or reproducing.
According to the present invention, a super resolution film is formed in an optical head to thereby attain higher-density recording. Further, the super resolution film is formed in a solid immersion lens (SIL) to thereby attain higher-density recording. The super resolution film is a film that functions to make the diameter of a beam spot emitted from the super resolution film smaller than the diameter of an incident beam when the incident beam entering the super resolution film emits therefrom. The degree that the diameter of the beam spot is made small is different depending on kinds of the super resolution film used. In addition, the super resolution film is often formed in a flat portion (for example, a polished bottom surface) of the solid immersion lens. In present invention, photochromic material is mainly used as the super resolution film and the multiphoton absorption, photobleaching, saturated absorption and the like are utilized. For multiphoton absorption, material may be used having no light absorption for a wavelength of a one-photon and having light absorption in an energy region of a two-photon (a half of a wave-length of the one-photon). Since the reaction of the two-photon absorption is effected with a square of the light intensity, an optically changed area is a squared shape of a spot size of the irradiation light. From a different viewpoint, the wavelength may be replaced with the light intensity and the absorption may be replaced with the transmission. For example, the transmissivity of the multiphoton absorption film does not change in a weak light intensity, while the two-photon absorption occurs in a sufficiently strong light intensity and the transmissivity increases in that area. The multiphoton absorption film involves a film containing DANS (4-dimethylamino-4′-nitrostilbene) or N-methylaniline or P-nitroaniline or the like or acrylic resin or the like. Furthermore, the photobleaching film produces the optical reaction to effect photobleaching progressively so that light transmits the film at the irradiation portion of light having a strong intensity and does not effect photobleaching progressively so that light does not transmit the film at the irradiation portion of light having the weak intensity. Water-soluble diazonium salts or fluorine diarylethene (FC-124) or the like may be used for the photobleaching film. In addition, the photo-bleaching film may use material having the characteristic hat when laser light is irradiated thereto a degree of exceeding a certain threshold, the coloring matter or pigment in the base level disappears, so that the material does not absorb light any longer as a saturable absorption film. The material involves phthalocyanine or naphthalocyanine pigment or the like. As described above, since the transmissivity in the middle portion of the irradiation beam increases, the beam transmits only this area. Consequently, the diameter of the beam spot is made small apparently (super resolution phenomenon).
Further, even when a pin hole film having a hole formed therein and smaller than a diameter of an incident beam is disposed on a bottom surface of the solid immersion lens instead of the super resolution film, similar effects can be attained. As document JP-A-5-234117 discloses the similar technique with respect to utilization of the pin hole, while in the present invention the film having the pin hole formed therein must be used in order to dispose the pin hole film on the bottom surface of the solid immersion lens.
The super resolution film has been disposed on the side of the sample (recording medium) and used for the super resolution reproduction mainly. In the present invention, the super resolution film is disposed on the side of the lens to thereby be able to apply the present invention to the super resolution recording without limitation to the super resolution reproduction. It is a matter of course that the super resolution film is formed on the solid immersion lens to thereby attain higher density recording and furthermore the super resolution film is also disposed on the side of the sample (recording medium) to thereby attain still higher density recording.
When the super resolution film is used in the present invention, a film (reversible film) having the transmissivity in the middle portion, to which an energy beam is irradiated, of the super resolution film, the transmissivity is increased when the energy beam is irradiated thereto and is reduced when the irradiation is stopped; it is preferable that the transmissivity in the middle portion of the super resolution film to which the energy beam is irradiated is always increased even if any positional shift of the beam occurs. However, the film (non-reversible film) having the transmissivity in the middle portion increased even when the irradiation of the beam is stopped may be used if necessary. In the case of the pin hole film, when the beam is deviated from the pin hole, recording and reprodu
Miyauchi Yasushi
Nakamura Kimio
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Psitos Aristotelis M.
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