JP2007242227A - Optical information recording and reproduction system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system capable of performing mass optical information recording by satisfactorily controlling an optical recording medium that can perform satisfactory recording and reproduction and tracking when a track pitch is made small. <P>SOLUTION: In the optical information recording and reproduction system, the recording medium 1 has tracking grooves on one surface of a recording layer, a metal needle is caused to get closer to the one surface with the tracking grooves, evanescent photons generated by emitting light to the surface of the recording layer at a part where the needle is caused to get closer are made to fly to the point of the needle to shine the point, tracking control is performed by detecting a change in light emitting strength of the light at the point, and an optical head for performing tracking control and an optical head for recording and reproduction are combined and united into a single body to be used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is an optical information recording medium capable of optically recording or reproducing information as typified by an optical disk, and is excellent in recording and reproducing information on an ultra-large capacity optical information recording medium using near-field light. The present invention relates to a recording / reproducing system that realizes large-capacity recording by using a tracking control method.

As an optical recording medium, a disk-shaped information recording medium is well known as represented by a compact disk, but in the era of multimedia and information networks, a recording medium having a larger capacity is required. .
There are read-only, write-once, and rewritable optical disk memories, but read-only CD-ROM, DVD-ROM, write-once CD-R, etc., rewritable phase change recording method, magneto-optical recording method, etc. Things are in practical use.

  The methods for increasing the capacity can be roughly divided into two methods: reducing the recording pit and recording a plurality of information at the same place. In order to reduce the recording pits, there is a report that even in a phase change type disk and a magneto-optical type optical disk currently in practical use, it is possible to write a small pit with a pit diameter of about 60 to 100 nm. is there. However, since reproduction involves a plurality of pits in the reproduction light spot, it is difficult to read out each piece of information. In order to read out small pits, it is necessary to make the light smaller and the aperture spot size smaller, but the limit of the optical spot size depends on the wavelength of the light and the numerical aperture of the lens. For this reason, the conventional method of condensing recording / reproducing light using an optical system has a limit in reducing the spot size due to the diffraction limit of light, which is a limit in improving the recording density. Therefore, super-resolution reproduction has been proposed as a method for reading out pits having a spot size or less, centering on the magneto-optical method. This is a method in which a mask layer is provided on a recording layer and pits smaller than the spot diameter are reproduced by utilizing the temperature distribution in the spot of the reproduction light.

  There is another proposal to apply near-field light. Unlike normal light propagating in the air, it uses light localized in a region smaller than the wavelength of light on the surface of the material. This is an application of a recording / reproducing head that applies a scanning probe microscope such as a scanning tunneling microscope or a scanning atomic force microscope. Light is introduced into the scanning probe and the proximity that emerges from the narrowed tip. A method using field light has been proposed (see Patent Document 1: Japanese Patent Laid-Open No. 8-160564). Since the spot size possible with this method is determined only by the aperture diameter at the tip of the probe regardless of the wavelength of light, recording and reproduction can be performed in a small area.

In addition, near-field light allows a minute spot, so even if the pit interval and track pitch are reduced, recording and playback can be performed without crosstalk. In this case, it is necessary to perform tracking stably.
That is, when trying to reduce the recording pits and increase the recording capacity, it is necessary to reduce the recording interval, increase the capacity, reduce the track pitch, and further increase the capacity. However, there is a problem that tracking control during recording / reproduction becomes difficult by reducing the track pitch. When near-field light is used, the light intensity is relatively small, so that a tracking control method is particularly problematic.

JP-A-8-160564

  The present invention improves the above-mentioned problems and can perform good recording / reproduction by using the optical recording medium of the present invention. Also, the tracking when the track pitch is reduced is well controlled, and the large capacity light It aims to provide an information recording system.

  As a result of intensive studies by the inventor, the above-mentioned problem is recorded by providing unevenness corresponding to the information signal on the substrate or providing a recording layer whose optical characteristics change corresponding to the information signal. The information is reproduced by using the optical recording medium that reproduces the information using light as the recording medium, irradiating the recording medium with light, and reading the characteristic change of the reflected light according to the recording information from the optical recording medium. A recording medium having a tracking groove on one surface of a recording layer, a metal needle approaching the one surface having the tracking groove, and the recording medium By detecting evanescent photons generated by irradiating light on the surface of the recording layer in the vicinity of the needle, flying to the tip of the needle to shine the tip, and detecting a change in light emission intensity at the tip What is achieved by an optical information recording / reproducing system that performs racking control and uses an optical head for controlling tracking and an optical head for recording / reproducing in combination. I found it.

According to the optical information recording / reproducing system of the present invention, a metal needle is brought close to the surface of the recording medium opposite to the light-irradiated surface, and tracking control is performed by detecting a change in light intensity generated at the tip. Thus, a large-capacity optical memory can be realized.
Further, according to the optical information recording / reproducing system of the present invention, a large-capacity optical memory can be realized by using a phase change recording medium without greatly changing the conventional system.
Further, according to the optical information recording / reproducing system of the present invention, a large-capacity optical memory can be realized by using a magneto-optical recording medium without greatly changing the conventional magneto-optical memory system.
Further, according to the optical information recording / reproducing system of the present invention, the resolution increases by using a recording medium that performs recording / reproducing in the photon mode, so that an optical memory having a larger capacity can be realized.
In addition, according to the optical information recording / reproducing system of the present invention, a large-capacity optical memory can be realized without greatly changing the conventional system by using a recording medium using an organic dye material.
Further, according to the optical information recording / reproducing system of the present invention, the sensitivity resolution of the medium can be increased by using a recording medium containing elements of Ag, In, Sb, Te as the optical recording medium, and further in the heat mode. A large-capacity optical memory can be realized.
Further, according to the optical information recording / reproducing system of the present invention, by using a mechanism using a piezoelectric element as a tracking control mechanism, good responsiveness and good tracking can be achieved.
Further, according to the optical information recording / reproducing system of the present invention, by using a mechanism using a magnetostrictive element as a tracking control mechanism, accurate alignment can be performed at high speed, and good tracking can be performed.
Further, according to the optical information recording / reproducing system of the present invention, a small and lightweight head can be realized by combining and using an optical head for controlling tracking and an optical head for recording / reproducing. .
Also, according to the optical information recording / reproducing system of the present invention, an array type laser is included as a constituent element as an optical head used for recording / reproducing, thereby enabling high-speed recording / reproducing of a large-capacity optical memory.

  As a recording medium used in the optical information recording / reproducing system, a recording medium provided with irregularities corresponding to an information signal on a substrate, such as a read-only disk such as a CD-ROM, and a recording medium such as a CD-R are used. Recordable recording media that can be recorded only once, or magneto-optical recording that reproduces using the magneto-optical effect due to the magnetization of the recording part, recording by the difference between crystalline phase and amorphous phase, utilizing the difference in optical characteristics Any rewritable recording medium such as a phase change recording method for reading can be used.

  In the case of a read-only disc, recording is performed by providing irregularities directly on the substrate by fine processing. For reproduction, near-field light is used to read minute pits. In the case of a write-once type or rewritable type medium, it is preferable to use near-field light capable of recording smaller pits in a recording method using the temperature distribution in the spot. It is also preferable to use near-field light for reproduction.

  Tracking control during recording and reproduction is performed by irradiating light from the opposite surface of the recording medium and bringing a metal needle close to the surface. When light is irradiated from the back surface of the sample (here, a recording medium), evanescent light is present on the surface. By bringing a metal needle close to it, non-radiative photons called evanescent photons fly to the tip of the needle and make it light. Since the unevenness of the medium can be detected based on the intensity of light at the needle tip, tracking control is performed by detecting an error signal that is likely to be off the track.

  Although there is no restriction | limiting in particular as a light source, It is preferable to use a semiconductor laser from the surface of size reduction and weight reduction, and also considering compatibility with the present optical memory. Since the spot size of the near-field light depends on the aperture diameter of the probe, a sufficiently small spot can be obtained without using a short wavelength laser such as blue. For this reason, even light such as infrared light can be used, and the light source becomes cheaper.

  In addition, the system of the present invention uses a phase change recording medium that performs recording by changing the amorphous-crystalline phase by light irradiation and reproduces a signal by utilizing the difference in the reflectance of light by different phases. be able to. Examples of the phase change recording medium include chalcogenide compounds and chalcopyrite compounds, which are used for rewritable and write-once types. GeSbTe, AgInSbTe, and the like are particularly excellent in their rewritable and erasable performances, and are used in the system of the present invention. It is particularly preferred.

  Among them, it is very effective to use a recording medium containing Ag, In, Sb, and Te elements. AgInSbTe is known to be a highly sensitive material. Therefore, it is possible to sufficiently write the recording pits even with a relatively small output light. Moreover, since high contrast is shown, reproduction can be performed well. When erasing the recorded information, complete erasure is possible, so that the overwrite characteristic is excellent and the recording signal does not disappear, so that a good overwriting is possible. Further, since no coarse particles appear as seen with GeSbTe around the recording mark, small pits can be recorded and reproduced stably.

  A magneto-optical medium can also be used as the recording medium of the present invention. By using the magneto-optical recording medium, there is an advantage that the present magneto-optical recording system can be partially used as it is, and the system can be easily realized. Examples of the magneto-optical material used in the present invention include compounds of rare earth elements and transition metal elements. For example, amorphous films such as TbFeCo, GdFeCo, and TbFe can be used because their Kerr rotation is relatively large and medium noise is low. Other magneto-optical recording films that can be used in the present invention include, for example, GdTbCo, GdTbFe, GdDyCo, GdDyFe, GdTbDyFe, GdTbDyCo, GdHoCo, GdTbErFe, GdTbErCo, DyFeCo, GdTbFeCo, GdTbFeCo, GdTbFeCo, GdTbFeCo, However, these magneto-optical recording films may be a single layer film or a multilayer film such as a two-layer film of GdFeCo / TbFeCo. Further, as a medium for light having a short wavelength, a multilayer film of a noble metal or a noble metal alloy layer and a transition metal or a transition metal alloy layer is effective. Examples of the noble metal include Pt, Pd, Au, Ag, Rh, Nd, Pr, and alloys thereof. Examples of the multilayer film include Pt / Co, Pt / Fe, Au / Co, and Pd / Co.

Also, a photon mode material can be used as the recording medium material of the present invention. When a material capable of performing photon mode recording is used as a recording medium, it is preferable to make use of the advantages of the photon mode by performing near-field optical recording. Photon mode recording materials that can be used are silver halides that use photochemical reactions, and photopolymers that are photosensitive compounds that absorb and excite light and react with the polymer. The polymer itself is photosensitive. And those that cause a photopolymerization reaction by light irradiation. There is also a so-called photo doping phenomenon. This phenomenon is, for example, a phenomenon in which when a chalcogenide amorphous semiconductor thin film and a two-layer structure of a metal such as Ag or Cu are irradiated with light, the metal diffuses into the chalcogenide film. A photochromic phenomenon in which the absorption spectrum of crystals, glass, molecules, etc. reversibly changes by light irradiation can also be used. Photochromic materials include inorganic and organic materials. Inorganic materials include oxides such as SrTiO ₃ doped with transition metal elements, fluorides such as CaF ₂ doped with rare earth elements, silicate glass and the like silver. There are those in which halides are dispersed. For example, Fe / Mo or Ni / Mo is used as a dopant for SrTiO ₃ , CaTiO ₃ , TiO ₂ , BaTiO ₃ or the like is used, and Fe or the like is used as a dopant. As a photochromic material, an inorganic material is often used in a form in which a reaction is diluted with a crystal or glass, whereas an organic material can change the molecule itself, thereby increasing the resolution. Materials that use bond cleavage such as spiropyran, photooxidation reduction reaction such as methylene blue, free radical formation reaction by photodissociation reaction such as β-tetrachloro-1-ketodihydronaphthalene, saltylideneaniline Those utilizing reactions such as tautomerization with intramolecular hydrogen transfer, cis-trans photoisomerization reaction such as azobenzene, and photopolymerization reaction such as anthracene are used.

A photorefractive material can also be used. A material exhibiting a photorefractive effect, and the photorefractive effect is a property in which a refractive index changes when irradiated with light. Materials exhibiting this property are both inorganic and organic. Examples of inorganic materials include LiNbO ₃ , BaTiO ₃ , SrBaNbO, and Bi ₁₂ SiO ₂₀ . Recently, organic materials have been actively studied, and organic crystals, photoconductive polymer films, and materials using nematic liquid crystals have been reported.

  When near-field light is used, a photon mode material system is particularly preferable as the recording material. As a photon mode material, a photochromic material is typical, but among the photochromic materials, when an inorganic material is used as a recording medium, it is used by being dispersed in a polymer or the like, so the density does not increase. On the other hand, organic photochromic materials have recently attracted attention. Since organic photochromic materials react with each molecule, a medium with high sensitivity and excellent resolution can be realized. Therefore, when recording / reproducing with near-field light, recording is possible even with minute near-field light, which is particularly preferable when near-field light is used.

  In the present invention, an organic coloring material can also be used. Examples of organic dyes include cyanine dyes, phthalocyanines, and azo metal materials used in CD-R, but dye materials that exhibit a photochromic reaction can also be used.

  The access mechanism is moved and tracking control is performed in accordance with the tracking error signal so that tracking can be controlled satisfactorily. A tracking error is detected by a change in the intensity of the near-field light detected from the tip of the tracking control needle. A piezoelectric element is used as the access mechanism. A change in the intensity of the near-field light for tracking is detected as a voltage change by a photodiode or the like, and a voltage is applied to the piezoelectric element in accordance with the voltage to perform tracking control. By using a piezoelectric element, it can be performed at higher speed and higher accuracy than those using electromagnetic induction.

  A magnetostrictive element can be used as an access mechanism for tracking control. A near field height intensity change detected from the tip of the tracking control needle is detected by a photodiode or the like, and a current is applied to the coil for driving the magnetostrictive element in accordance with the voltage to expand and contract the magnetostrictive element. Thus, tracking control is performed. The magnetostrictive element can be increased with the sensitivity of material expansion and contraction, and the amount of expansion and contraction can be increased. Therefore, the magnetostrictive element can be performed at a higher speed and with higher accuracy than those using electromagnetic induction.

  In order to reduce the size and weight of the system of the present invention, it is possible to incorporate and use the system in an integrated form by designing the optical head for tracking control and the optical head for recording / reproducing in combination. A semiconductor laser and a tracking needle can be integrally formed by using a micromachine technique that has become popular in recent years.

  Further, it can be used in a configuration using an array type laser as a head used for recording and reproduction. As the recording density increases, it is necessary to improve the data transfer speed of the recording / reproduction. As a method, instead of performing recording / reproduction by a single track as in the current optical memory, a plurality of tracks are used simultaneously. A recording / reproducing system can be used. By using this method, an optical head for recording / reproducing can be configured in an array, and simultaneous writing and reading can be performed on the same number of tracks as the number of lasers arranged in the array. Tracking can be performed by providing several metal needles on the arrayed head. A plurality of tracks are recorded / reproduced at the same time, but by using an array head, it is not necessary to perform tracking for each track, and it is only necessary to track at several points.

Hereinafter, embodiments of the present invention will be illustrated, but the present invention is not limited to these examples.
Example 1
Tracking is performed using a metal needle before and after the light for recording and reproduction. FIG. 1 shows a schematic diagram of a system corresponding to the present invention. As shown in this figure, light is applied from the back side of the recording medium (1), and the tracking metal needle (2) is brought close to the opposite side. An access mechanism in which the intensity of light from the tip of the metal needle is detected by a photodiode (5) through a lens, and a voltage signal corresponding to the intensity change is attached to the optical head (3) for recording and reproduction and the metal needle (2). Applied to (4) to perform tracking control. Thus, tracking is performed and recording / reproduction is performed.

Example 2
FIG. 2 shows an embodiment of the structure of an optical recording medium used in the system according to the present invention. The disc-shaped polycarbonate transparent substrate (6) has a center hole and a guide groove. There is an amorphous ZnS—SiO ₂ film (ZnS: SiO ₂ = 80: 20 mol%, film thickness 170 nm) as a lower protective layer (7) on the transparent substrate (6), and a Ge ₂ Sb ₂ Te ₅ alloy film. A recording layer (8) having a thickness of about 20 nm and an upper protective layer (9) on the upper surface thereof are amorphous ZnS—SiO ₂ (ZnS: SiO ₂ = 80: 20 mol%, film thickness 20 nm). A system was configured using this recording medium. The system configuration other than the above is the same as that of the first embodiment. As shown in FIG. 6, the system preferably includes a recording / reproducing head and a tracking metal needle integrally formed.

Example 3
An example in which a magneto-optical recording medium is used as a recording medium used in the optical recording system of the present invention will be described. As shown in FIG. 3, the magneto-optical recording medium of this example has a lower protective layer (7), a recording layer (8), and an upper protective layer (9) on one main surface side of the transparent substrate (6). It is formed by lamination.
As the transparent substrate (6), a disk-shaped polycarbonate transparent substrate is used, but any substrate can be used as long as it is used as a substrate of this type of magneto-optical recording medium such as transparent polycarbonate or glass.
The lower protective layer (7) is made of silicon nitride and has a thickness of 80 nm. However, the lower protective layer (7) may be made of a material used for the dielectric film of this type of magneto-optical recording medium, such as silicon nitride.
Furthermore, the upper protective layer (9) was made of silicon nitride and had a thickness of 20 nm. However, it may be formed of a material used for the dielectric film of this type of magneto-optical recording medium such as silicon nitride.
In the magneto-optical recording medium of this example, a Tb _0.2 Fe _0.64 Co _0.16 film was used as the recording layer (8). This recording layer may contain Gd.

Example 4
FIG. 4 shows an example of a recording medium using a photorefractive material. A system was constructed using LiNbO ₃ using Fe as a dopant as a recording medium. A LiNbO ₃ layer using a polycarbonate substrate as the transparent substrate (6) and Fe as a dopant as the recording layer (8) was formed thereon to obtain a recording medium. Otherwise, the system was the same as in Example 1.

Example 5
FIG. 4 illustrates a recording medium using, as the recording layer (8), a thin film in which diarylethene molecules, which are organic photochromic materials, are dispersed in a polymer. A thin film in which diarylethene molecules were dispersed as a recording layer (8) was formed to 20 nm on a polycarbonate substrate as a transparent substrate (6) to obtain a recording medium. Recording was performed by introducing a He-Ne laser beam into a probe having micropores at the tip of the medium that had been initialized so that the entire surface was irradiated with ultraviolet light and colored blue, thereby fading the recording layer. Was done. Otherwise, the system was the same as in Example 1.

Example 6
FIG. 5 illustrates a recording medium using AgInSbTe, which is a phase change material.
FIG. 5 is an explanatory diagram showing a cross-sectional configuration of the phase-change optical recording medium according to the embodiment. This phase change type optical recording medium comprises a lower protective layer (7) (dielectric layer), a recording layer (8), and a 1.2 mm or 0.6 mm thick transparent substrate (6) made of polycarbonate resin. The upper protective layer (9) (dielectric layer) is laminated in order.
As a material of the lower protective layer (7) (dielectric layer), for example, a composite of ZnS and SiO ₂ is used, and its thickness is set to 200 nm.
The recording layer (8) contains a layer-changeable material, preferably Ag5.1 (silver), In9.2 (indium), Sb58.5 (antimony), Te27.2 (tellurium) as the layer constituent elements, The thickness is 20 nm.
As a material of the upper protective layer (9) (dielectric layer), for example, a composite of ZnS and SiO ₂ is used, and its thickness is set to 20 nm.
The system was the same as that of Example 1 except that the above recording medium was used.

Example 7
As an embodiment corresponding to the present invention, in an optical information recording / reproducing system in which a metal needle is formed at the tip of a piezoelectric element, a system that performs tracking by expanding and contracting the piezoelectric element in accordance with a change in tracking signal. An example of In FIG. 1, a piezoelectric element is used as an access mechanism for controlling a metal needle and a recording / reproducing head, and a voltage corresponding to a change in light intensity from the metal needle is applied to the piezoelectric element to perform expansion / contraction and tracking. .

Example 8
As an embodiment corresponding to the present invention, a system similar to that of Embodiment 7 is used except that a magnetostrictive element is used instead of the piezoelectric element.

Example 9
As shown in FIG. 6, the metal needle (2) is formed before and after the recording / reproducing optical head (3). FIG. 7 shows an enlarged view of the integrated head as an embodiment of the present invention. Light is irradiated from the opposite side of the recording medium (1), and light generated at the tip of the metal needle (2) is photodiode ( 5), the access mechanism (4) is moved according to the signal, tracking is performed, and recording / reproduction is performed. By integrating, recording / reproducing and tracking can be performed with near-field light.

Example 10
As an embodiment of the present invention, FIG. 8 shows a cross section of an array-type head and a view seen from an oblique upper surface. Using a photolithographic technique, the silicon substrate is anisotropically etched to form a microhole arrayed in an array. The head is irradiated with light, and near-field light generated at the tip of the fine hole (10) is used for recording and reproduction. A metal needle (2) is formed on the side of the arrayed hole, etc., tracking is performed, and recording / reproduction is performed with the arrayed optical head.

It is the schematic which showed the structure of the optical information recording / reproducing system of this invention. 1 is a configuration diagram illustrating an example of a recording medium of the present invention. It is the block diagram which showed another example of the recording medium of this invention. It is the block diagram which showed another example of the recording medium of this invention. It is the block diagram which showed another example of the recording medium of this invention. It is the block diagram which showed one example of the head of this invention. It is the block diagram which showed another example of the head of this invention. It is the block diagram which showed another example of the head of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording medium 2 Metal needle 3 Recording / reproducing optical head 4 Access mechanism 5 Photodiode 6 Transparent substrate 7 Lower protective layer 8 Recording layer 9 Upper protective layer 10 Fine hole

Claims (1)

An optical recording medium that uses light to reproduce information recorded by providing irregularities corresponding to an information signal on a substrate or providing a recording layer whose optical characteristics change corresponding to an information signal is used as a recording medium. A recording / reproducing system for reproducing information by irradiating the recording medium with light and reading out a change in characteristics of reflected light according to the recording information from the optical recording medium, wherein the recording medium is one of the recording layers; A tracking groove on the surface, a metal needle is brought close to the one surface having the tracking groove, and light is irradiated to the surface of the recording layer in the portion where the needle is brought close The generated evanescent photons fly to the tip of the needle to shine the tip, and tracking control is performed by detecting a change in light emission intensity at the tip. The optical information recording and reproducing system, characterized in that the optical head and the recording reproducing optical head for performing control is used in integrated combination.

Images