JP4136713B2 - Multilayer recording medium and multilayer recording system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a writable or rewritable multilayer recording medium and a multilayer recording system that performs writing or rewriting using the same.
[0002]
[Prior art]
In recent years, the increase in the capacity of optical disks has been achieved mainly by increasing the recording surface density by shortening the recording wavelength and improving the shortest recording wavelength by increasing the NA of the objective lens. On the other hand, attempts to achieve high-capacity recording by effectively using the entire recording medium by utilizing light transmission have originated in hologram memory and have continued to three-dimensional optical recording by bit recording. .
[0003]
The three-dimensional optical recording by bit recording can increase the capacity by the number of layers in the depth direction as compared with the optical recording with one recording layer, and the capacity of recording that is 100 times larger than the current recording capacity. Realization is expected. In order to multiplexly record in the depth direction, it is basically necessary to write or read only to the intended layer of the multiplexed recording layers having the same properties. Therefore, it is necessary to introduce some non-linearity to give selectivity.
[0004]
One method of imparting this nonlinearity is writing using a two-photon absorption reaction. The normal absorption process is a one-photon absorption process corresponding to the energy of the absorption band, but a similar reaction can be caused by a two-photon absorption process that simultaneously absorbs two photons having half the energy. . A characteristic of this two-photon absorption process is that the amount of absorption is proportional to the square of the light intensity (energy density). As a result, absorption occurs only in the vicinity of the focus of the writing light where the energy density of light increases. However, the two-photon absorption process is generally much less probable than the one-photon absorption process, and so far these experiments have been performed in a darkroom to avoid competing one-photon absorption effects (eg, non-patented Reference 1).
[0005]
Some materials that can be erased and written are known depending on the material used for the recording layer. However, the reaction probability of the two-photon absorption process is lower than that of writing with one photon, and it was also performed at the experimental level in the dark room to retain the writing information. In the erasing process, it has been shown that only a specific write bit can be erased using a two-photon absorption process. However, a short pulse light source having a wavelength different from that of writing is required, which is large and expensive. This has hindered the miniaturization and spread of the apparatus, such as the need for two short-pulse light sources (for example, see Non-Patent Document 2).
[0006]
[Non-Patent Document 1]
Yoshishima Kawata et al., “Applied Optics” (USA), 1995, 34, 20, p. 4105-4110
[Non-Patent Document 2]
A. Toriumi et al., “Optics Letters” (USA), 1998, Vol. 23, No. 24, p. 1924-1926
[0007]
[Problems to be solved by the invention]
As described above, in the multi-layer recording method using the two-photon absorption reaction, in order to avoid the one-photon absorption reaction, an environment at a dark room level is necessary, and recording and holding of recorded information are performed in a general use environment. It was difficult. Furthermore, the rewritable type requires two wavelengths of large and expensive short pulse light sources for recording and erasing, and there are problems in terms of downsizing and cost of the apparatus.
[0008]
The present invention has been made in view of this point, and an object of the present invention is to provide a multilayer recording medium and a multilayer recording system that are excellent in long-term storage and capable of recording data with a high S / N ratio.
[0009]
Another object of the present invention is to provide a rewritable multilayer recording medium and multilayer recording system that do not require an erasing short pulse light source.
[0010]
[Means for Solving the Problems]
Book invention Multi-layer recording medium Comprises at least two recording layers, Above In a multilayer recording medium that performs recording by a multiphoton absorption process on the recording layer, Each recording layer has grooves and lands formed on at least one surface, The recording layer is provided with a blocking layer that blocks light in a wavelength region where external one-photon absorption occurs.
Also book invention Other multilayer recording media Is A multilayer recording medium comprising at least two or more recording layers and performing recording by a multiphoton absorption process on the recording layer, comprising a recording layer holding substrate on which at least one of the recording layers is provided, and the recording layer The holding substrate has grooves and lands formed on the surface on which each recording layer is provided, and includes a blocking layer that blocks light from a wavelength region in which one-photon absorption from the outside occurs with respect to the recording layer. It is characterized by that.
[0011]
The multilayer recording medium described here is a recording medium having recording layers multiplexed in the depth direction and does not need to have a physical multilayer structure. For example, as a medium structure, even if it is a uniform material, if it has a recording layer multiplexed in the depth direction by being formatted by a method such as light, the multilayer described here Included in the category of recording media.
[0012]
In addition to the multiphoton absorption process used for recording, the recording material of the recording layer has a one-photon absorption process recording and an erasing process depending on the recording material. This one-photon absorption process is generally more sensitive than the multi-photon absorption process, and in order to ensure recording stability, it is necessary to sufficiently suppress the reaction due to the one-photon absorption process. In the present invention, as a method for suppressing the one-photon absorption process, the recording layer in the recording medium is protected from light exposure in the wavelength region where one-photon absorption occurs by blocking the wavelength region where one-photon absorption occurs. The stability of the recorded information by the photon absorption process is measured. By blocking the one-photon absorption band corresponding to recording, it is possible to prevent fogging on the recording properties before and after recording and maintain a good S / N ratio. By blocking the one-photon absorption band corresponding to erasure, the recording mark can be prevented from fading, and good recording information storage characteristics can be obtained.
[0013]
In this case, many Includes a dielectric multilayer designed to transmit light in the wavelength range corresponding to the photon absorption process and to reflect light in the wavelength range where single photon absorption occurs Is preferred .
[0014]
The dielectric multilayer film is a structure composed of two or more layers having different refractive indexes and controlling the wavelength range of reflection. It is formed by vapor deposition or coating.
[0015]
In this case, The fault includes an absorption layer containing a dye that absorbs light in a wavelength region where one-photon absorption occurs. Is preferred .
[0016]
The absorption layer is formed by dispersing an absorption dye that absorbs light in the wavelength band to be blocked in the resin, and is not limited to being provided exclusively by coating or the like, such as a recording layer in the medium or an intermediate layer that separates the recording layers. The layer constituting the medium may contain an absorbing dye to form an absorbing layer. A configuration combined with a dielectric multilayer film that reflects light in the wavelength band to be blocked is also possible.
[0017]
In this case, The fault is formed on the medium surface Is preferred .
The blocking layer on the surface of the medium may be one that absorbs or reflects a wavelength region in which one-photon absorption occurs, and may be any method as long as light in the wavelength region is not transmitted inside the medium. In the case of blocking a plurality of wavelength bands, it may be constituted by a plurality of coatings corresponding to each wavelength band, and a combination of a reflective coating and an absorption coating may be used.
[0018]
In this case, many Provided with a fluorescent layer that emits fluorescence in the one-photon absorption band corresponding to erasure by the photon absorption process Is preferred .
In this case, firefly The optical layer contains a fluorescent dye that emits fluorescence in a one-photon absorption band corresponding to erasure by a multiphoton absorption process. Is preferred .
[0019]
Conditions for the fluorescent layer or fluorescent dye are: 1. It can be excited by a two-photon absorption process with a laser used for writing. The recording material of the recording layer emits fluorescence in a wavelength region that can be erased by a one-photon absorption process. Since this fluorescent layer is excited by two-photon absorption, it is excited only at the condensing point of the writing light (the probability of two-photon absorption is proportional to the square of the light intensity), so writing to other layers is possible. It is not excited when it is running, but only when the fluorescent layer is scanned with writing light. That is, the fluorescence from the fluorescent layer can be controlled by the writing light. In the multilayer recording medium of the present invention, light in the erasable wavelength region is blocked by an external one-photon absorption process. However, the presence of the fluorescent layer allows writing light only when necessary (only during erasing operation). When excited, the recording layer can be erased.
[0020]
In this case, firefly Provided with a fluorescence reflection layer that reflects fluorescence emitted by the light layer and transmits light in the wavelength range corresponding to the multiphoton absorption process Is preferred .
In this case, firefly The light reflecting layer is made of a dielectric multilayer film. Is preferred .
[0021]
Thereby, the fluorescence emitted from the fluorescent layer during the erasing operation can be confined in the medium by being reflected by the fluorescent reflecting layer, and the fluorescence can be efficiently used as the erasing light.
[0022]
In this case, A plurality of recording layer groups each including a combination of at least one recording layer, a fluorescent layer, and a fluorescent reflecting layer; Is preferred .
The recording layer group described here refers to a combination of at least one recording layer, a fluorescent layer for erasing the recording layer, and a fluorescent reflecting layer that confines fluorescence used for erasing in the structure of the recording layer and the fluorescent layer. . A single recording layer or a plurality of recording layers can be set according to the purpose. Thereby, it is possible to erase each recording layer group.
[0023]
Many of the present invention Layer recording system Is , Above multilayer The recording layer is written on the recording medium using a recording light source in which multiphoton absorption occurs.
This the above This multi-layer recording medium can be favorably recorded by the multiphoton absorption process.
[0024]
The other of the present invention Multi-layer recording system Is , Above multilayer For a recording medium, writing is performed on the recording layer by using a recording light source in which multiphoton absorption occurs during recording, and at the time of erasing, fluorescence is emitted from the fluorescent layer by using the recording light source to erase recorded information in the recording layer. It is characterized by that.
[0026]
If the multilayer recording medium has a fluorescent reflective layer, The recording information can be erased only by the recording light source without the need for the erasing light source separately from the recording purpose, and the downsizing and cost reduction of the recording / reproducing apparatus for the rewritable multilayer recording medium can be realized. be able to.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows an example of a process for producing a multilayer recording medium according to the first embodiment of the present invention, and FIG. 2 shows an example of the configuration of a multilayer recording system for recording on the multilayer recording medium of the present embodiment. As shown in FIG. 1, the multilayer recording medium of the present embodiment includes a plurality of recording layers 103 formed by stampers 101 and 102, a protective layer 104 that protects the recording layer 103, a protective layer 104, and a plurality of recording layers. An adhesive layer 105 containing a dye that absorbs ultraviolet rays, and a support substrate 106 that sandwiches the recording layer 103 laminated via the adhesive layer 105 together with the protective layer 104; a protective layer 104; The dielectric multilayer film 107 is formed on the outer surface of the support substrate 106 and blocks the wavelength band for erasing by one-photon absorption.
[0029]
The recording layer 103 is formed by injection molding or the like using the stampers 101 and 102. At this time, a mixture of a photochromic material and a binder is used. For example, diarylethenes can be used as the photochromic material, but other photochromic materials, photopolymers, and the like can be widely used. Examples of the binder include polycarbonate resin, and other optical grades may be used as long as the combination of ensuring the strength of the material and the refractive index difference with the adhesive layer 105 filled between the recording layers 103 takes a desired value. Resins can be widely used. Note that the formation of the recording layer 103 is not limited to injection molding, and other molding methods such as thermal polymerization or ultraviolet curing in a stamper can be employed.
[0030]
The protective layer 104 and the support substrate 106 are disposed outside the recording layer 103 having a multilayer structure in order to protect the recording layer 103 against humidity, gas, mechanical shock, and the like. Used.
[0031]
The adhesive layer 105 is formed between the support substrate 106, the plurality of recording layers 103, and the protective layer 107. In order to obtain a desired reflectance of, for example, less than 1% at the interface with the recording layer 103, the adhesive layer 105 is formed. A resin having a different refractive index from the resin to be formed, for example, an acrylic thermosetting resin when the recording layer 103 is a polycarbonate resin can be used. The reflectance at the interface with the recording layer 103 is obtained by the difference in refractive index between the two layers, and the difference in refractive index can be arbitrarily set according to the number of recording layers constituting the medium. The adhesive layer 105 contains a dye that absorbs ultraviolet rays, that is, an ultraviolet absorber. Thereby, the ultraviolet ray which is a wavelength region in which one-photon absorption from the outside occurs is blocked, and the recording layer 103 is protected from fogging due to the one-photon absorption by the ultraviolet ray.
[0032]
The dielectric multilayer film 107 transmits the writing and reading wavelengths by the two-photon absorption, but has a characteristic of blocking the erasing band (450 to 550 nm) by the one-photon absorption. A film is formed on each surface of the support substrate 106. Such a dielectric multilayer film 107 is made of, for example, TiO. ₂ And SiO ₂ It can be obtained by laminating a plurality of pairs of laminated films.
[0033]
An example of a method for producing a multilayer recording medium according to the present embodiment will be described with reference to FIGS. FIG. 1 shows an enlarged cross section of the recording surface of the recording medium, and any shape such as a chucking portion of the disk can be adopted.
[0034]
As shown in FIG. 1A, stampers 101 and 102 with lands and grooves are prepared. In this embodiment, since both surfaces are used as recording layers, lands and grooves are engraved on both stampers 101 and 102, but it is also possible to adopt a configuration in which lands and grooves are formed only on one surface.
[0035]
In FIG. 1B, the recording layer 103 is formed by injection molding using stampers 101 and 102 and using, for example, a mixture of diarylethenes that are photochromic materials and polycarbonate resin that is a binder.
In FIG. 1C, the recording layer 103 is obtained by releasing from the stamper.
[0036]
In FIG. 1D, a recording layer 103 is laminated between a support substrate 106 and a protective layer 104 via an ultraviolet absorber-containing thermosetting resin spin-coated as an adhesive layer 105, heated and solidified to be integrated. In this embodiment, the recording layer 104 is protected from fogging due to one-photon absorption by ultraviolet rays by mixing an ultraviolet absorber with the adhesive layer 105. Also, by using acrylic as the thermosetting resin and setting the difference in refractive index from the recording layer 103 of polycarbonate resin to about 0.1, a reflectance of about 0.1% can be obtained at the interface between the two layers. The refractive index difference can be arbitrarily set depending on the number of recording layers constituting the medium, and is not limited to this. In FIG. 1, only three layers are shown for simplification, but the number of recording layers is not limited to this.
[0037]
In FIG. 1 (e), TiO on both sides ₂ / SiO ₂ A dielectric multilayer film 107 is stacked. The layer structure is, for example, TiO ₂ 51nm / SiO ₂ 19 pairs of 84 nm are stacked. With this layer structure, a dielectric multilayer film having a cutoff characteristic exceeding 99.8% at 450 to 550 nm (erasing band by one-photon absorption) and hardly affecting transmission at a writing and reading wavelength of 780 nm is obtained. be able to.
[0038]
Through the steps as described above, a multilayer recording medium having a long-term storage characteristic with a high S / N ratio can be produced. Note that this embodiment is an example of the configuration of the present invention, and the configuration of each layer responsible for the constituent materials and functions, the stacking order, and the like can be appropriately changed depending on the application. Further, the shape of the medium can take other forms such as a card in addition to the disk.
[0039]
The multilayer recording medium is recorded using the recording / reproducing system shown in FIG. 2, the multilayer recording system for recording / reproducing the multilayer recording medium 201 according to the first embodiment includes an objective lens 202, a quarter-wave plate 203, a polarizing beam splitter (PBS) 204, a non-polarizing beam splitter 205, Coupling lens 206, reproducing semiconductor laser (780 nm) 207, beam expander 208, recording pulse laser (780 nm) 209, quadrant avalanche photodiode (4D-APD) 210, cylindrical lens 211, condenser lens 212, pin It is composed of a hole 213 and a condenser lens 214. This system has two systems of lasers (reproducing semiconductor laser 207 and recording pulse laser 209).
[0040]
The operation of the multi-layer recording system having the above configuration will be described first from the optical system of a reproducing laser related to reproducing and focus / tracking servos. The light emitted from the reproducing semiconductor laser 207 having a wavelength of 780 nm is converted into parallel light by the coupling lens 206, the optical path is changed by the non-polarizing beam splitter 205, and the light composed of the polarizing beam splitter (PBS) 204 and the quarter wavelength plate 203. It passes through an isolator and is converted into circularly polarized light. A part of the light condensed on one of the recording surfaces of the multilayer recording medium 201 by the objective lens 202 is reflected by the difference in the refractive index of the different interface constituting the recording surface (in the production example of this embodiment, about 0). .1%). The reflected light has a reverse optical rotation direction, passes through the quarter-wave plate 203, is converted into linearly polarized light orthogonal to the incident light, and is guided to the detection system by the PBS 204. In the detection system, the light is condensed by the condensing lens 214, and reflected / scattered light from other than the focal point is removed by the pinhole 213. The light is condensed again by the condenser lens 212, passes through the cylindrical lens 211, and is guided to the four-divided avalanche photodiode (4D-APD) 210. Tracking / focus servo is applied by a signal detected with high sensitivity by the 4D-APD 210. Needless to say, the recorded information can also be read by the sum signal from the 4D-APD 210. The output light from this light source has a weak output for two-photon absorption to occur in the recording layer, and the reproduction signal cannot be degraded by reading.
[0041]
Next, the recording system will be described. Light emitted from a recording pulse laser 209 having a wavelength of 780 nm passes through a beam expander 208, a non-polarizing beam splitter 205, a PBS 204, and a ¼ wavelength plate 203, and is focused on the multilayer recording medium 201 by the objective lens 202. At this time, the emitted light of the recording pulse laser 209 needs to be adjusted to be coaxial with the emitted light of the reproducing semiconductor laser 207. At this time, since the focal points in the multilayer recording medium coincide with each other, tracking / focus servo during recording is also possible. By the mechanism as described above, information is written by two-photon absorption by the large peak power that is characteristic of the pulse laser.
[0042]
As described above, in the present embodiment, good recording is possible using the multilayer recording system, and writing due to a one-photon absorption reaction can be prevented by an adhesive layer containing an ultraviolet absorber. In addition, since the dielectric multilayer film can prevent erasure due to a one-photon absorption reaction, there is no fogging on the recording layer and no fading of the recording mark. As a result, the multilayer recording medium has a high S / N ratio and excellent long term storage Can be obtained.
[0043]
(Second Embodiment)
As shown in FIG. 3, the multilayer recording medium of the second embodiment includes a plurality of recording layer holding substrates 303 formed by stampers 301 and 302, and a recording layer 304 formed on each recording layer holding substrate 303. A protective layer 305, a recording layer holding substrate 303 on which each recording layer 304 is formed, an adhesive layer 306 that joins the protective layer 305 to each other, and a support substrate that supports the multi-layered recording layer 304 via the adhesive layer 306 307, an ultraviolet absorbing layer 308 formed on both sides of the medium, a protective multilayer 305, and a dielectric multilayer film 309 formed on the outer surface of the support substrate 307.
[0044]
The recording layer holding substrate 303 holds the recording layer 304 formed on the surface thereof, and is formed by ultraviolet curing, thermal polymerization, injection molding or the like using the stampers 301 and 302. As the material, for example, an acrylic resin can be used. However, other optical grade resins can be used as long as the refractive index difference with the resin that fills the recording layer between ensuring the strength of the substrate takes a desired value. Can be adopted.
[0045]
The recording layer 304 is formed by coating the recording layer holding substrate 303 with a resin mixed with a recording material. As the recording material, for example, diarylethenes can be used. Examples of the resin include acrylic resin and polycarbonate resin.
[0046]
The protective layer 305 and the support substrate 307 are disposed outside the recording layer 304 having a multilayer structure to protect the recording layer 304 against humidity, gas, mechanical shock, and the like, and are equivalent to those in the first embodiment. Is used.
[0047]
The adhesive layer 306 is filled and solidified by coating between the substrates in order to stack and integrate a plurality of recording layer holding substrates 303 on which the recording layer 304 is formed between the support substrate 307 and the protective layer 305. . The material of the adhesive layer 306 may be a thermosetting or ultraviolet curable resin, and a material having a difference in refractive index so that the reflectance at the interface with the recording layer 304 has a desired value is selected. The For example, when the recording layer 304 is an acrylic resin, an ultraviolet curable resin containing fluorine is used.
[0048]
The ultraviolet absorbing layer 308 is for blocking ultraviolet rays, which is a wavelength region in which one-photon absorption from the outside occurs, and protecting the recording layer 304 from fogging by one-photon absorption by ultraviolet rays. It consists of a resin containing an absorbent and is coated on both sides of the medium.
[0049]
Similar to the first embodiment, the dielectric multilayer film 309 transmits the write and read wavelengths by two-photon absorption, but has a characteristic of blocking the erase band (450 to 550 nm) by one-photon absorption. Then, a film is formed on each surface of the protective layer 305 and the supporting substrate 307 which are stacked with the recording layer 304 having a multilayer structure interposed therebetween.
[0050]
An example of a method for producing a multilayer recording medium according to the present embodiment will be described with reference to FIGS. FIG. 3 shows an enlarged cross section of the recording surface of the recording medium, and any shape such as a chucking portion of the disk can be adopted.
[0051]
As shown in FIG. 3A, stampers 301 and 302 with lands and grooves are prepared. In the present embodiment, lands and grooves are carved only on the stamper 301 in order to form a recording layer on one side. However, as in the first embodiment shown in FIG. 1, lands and grooves are formed on both sides. It is also possible to take a configuration.
[0052]
In FIG. 3B, an ultraviolet curable resin is poured between the stampers 301 and 302, and the recording layer holding substrate 303 is formed by exposing and solidifying ultraviolet rays. For example, an acrylic resin can be used as the ultraviolet curable resin.
[0053]
In FIG. 3C, the recording layer holding substrate 303 released from the stamper is coated with an acrylic resin added with diarylethenes as a recording material by spin coating to form a recording layer 304.
[0054]
In FIG. 3D, a recording layer holding substrate 303 integrated with the recording layer 304 is laminated between the support substrate 307 and the protective layer 305 through an ultraviolet curable resin spin-coated as the adhesive layer 306, and ultraviolet rays are irradiated. Irradiate to cure and integrate. After the integration, the photosensitive recording material is irradiated with light having a wavelength of about 520 nm and initialized. As the ultraviolet curable resin, a resin containing fluorine is used, and the difference in refractive index from the recording layer 304 of acrylic resin is set to about 0.1, so that the reflectance at the interface between both layers is set to about 0.1%. The refractive index difference can be arbitrarily set depending on the number of recording layers constituting the medium, and is not limited to this example. In FIG. 3, only three layers are shown for simplification, but the number of recording layers is not limited to this.
[0055]
In FIG. 3 (e), TiO on both sides ₂ / SiO ₂ A dielectric multilayer film 309 is stacked. The layer structure is, for example, TiO ₂ 51nm / SiO ₂ 19 pairs of 84 nm are stacked. This structure has a blocking characteristic exceeding 99.8% at 450 to 550 nm (erasing band by one-photon absorption), and hardly affects transmission at a writing and reading wavelength of 780 nm. Further, in order to prevent the recording layer 304 from being exposed to light by absorption of one photon by ultraviolet rays, the ultraviolet absorbing layer 308 is formed by coating a resin containing an ultraviolet absorber on both sides.
[0056]
Through the above-described steps, a multilayer recording medium having a long-term storage characteristic with a high S / N ratio can be manufactured in the same manner as in the first embodiment. Note that this embodiment is an example of the configuration of the present invention, and the configuration of each layer responsible for the constituent materials and functions, the stacking order, and the like can be appropriately changed depending on the application. Further, the shape of the medium can take other forms such as a card in addition to the disk.
[0057]
(Third embodiment)
As shown in FIG. 4, the multilayer recording medium of the third embodiment is formed on a plurality of recording layer holding substrates 403 formed by stampers 401 and 402 and on each recording layer holding substrate 403 except for one part. Recording layer 404, a fluorescent layer 405 formed on a part of the recording layer holding substrate 403, a protective layer 406, a recording layer holding substrate 403 and a protective layer 406 on which the fluorescent layer 405 or the recording layer 404 is formed. An adhesive layer 407 formed between the layers, a support substrate 408 that supports the laminated structure via the adhesive layer 407, an ultraviolet absorption layer 409 formed on both sides of the medium, a protective layer 406, and a support substrate 408. The dielectric multilayer film 410 is formed on the outer surface.
[0058]
The recording layer holding substrate 403 is formed by ultraviolet curing, thermal polymerization, injection molding or the like using stampers 401 and 402 in the same manner as in the second embodiment. As the material, for example, an acrylic resin can be used. However, other optical grade resins can be used as long as the refractive index difference with the resin that fills the recording layer between ensuring the strength of the substrate takes a desired value. Can be adopted.
[0059]
The recording layer 404 is formed by coating a resin mixed with a recording material on the recording layer holding substrate 403 in the same manner as in the second embodiment. As the recording material, for example, diarylethenes can be used. Examples of the resin include polycarbonate resin and acrylic resin.
[0060]
The fluorescent layer 405 contains a fluorescent dye that emits fluorescence in the erasing band by two-photon absorption. Similarly to the recording layer 404, a fluorescent dye is used instead of the recording material on one part of the recording layer holding substrate 403. It is formed by coating the mixed resin. An example of the fluorescent dye is Coumarin 522, which is an example of a usable fluorescent dye, and it goes without saying that other fluorescent dyes can be selected depending on the characteristics of the recording material, excitation light source, and the like. As the resin, the same resin as that of the recording layer 404 is used. The fluorescent layer 405 formed on the recording layer holding substrate 403 is laminated together with the recording layer 404 formed on another recording layer holding substrate 403.
[0061]
The protective layer 406 and the support substrate 408 are disposed outside the recording layer 404 having a multilayer structure to protect the recording layer 404 against humidity, gas, mechanical shock, and the like, and the first and second embodiments. An equivalent is used.
[0062]
The adhesive layer 407 has a recording layer 404 formed between the support substrate 408 and the protective layer 406, with the recording layer holding substrate 403 on which the fluorescent layer 405 is formed at the bottom (support substrate 408 side). In order to stack and integrate a plurality of holding substrates 403, each substrate is filled with a coating and solidified. The material of the adhesive layer 407 includes a thermosetting or ultraviolet curable resin, and a material having a difference in refractive index so that the reflectance at the interface with the recording layer 404 becomes a desired value is selected. The For example, when the recording layer 404 is a polycarbonate resin, an acrylic thermosetting resin is used.
[0063]
Similar to the second embodiment, the ultraviolet absorbing layer 409 is formed by coating a resin containing an ultraviolet absorber on both sides of the medium.
[0064]
The dielectric multilayer film 410 has a film configuration similar to that of the first and second embodiments, and is formed on the surface of each of the laminated protective layer 406 and support substrate 408. As described above, the dielectric multilayer film 410 transmits the writing and reading wavelengths by the two-photon absorption, but reflects the erasing band (450 to 550 nm) by the one-photon absorption. The erasing light generated in the fluorescent layer 405 has a function of confining in the medium.
[0065]
An example of a method for producing a multilayer recording medium according to the present embodiment will be described with reference to FIGS. FIG. 4 shows an enlarged cross section of the recording surface of the recording medium, and any shape such as a chucking portion of the disk can be adopted.
[0066]
As shown in FIG. 4A, stampers 401 and 402 with lands and grooves are prepared. In this embodiment, lands and grooves are carved only on the stamper 401 in order to form a recording layer on one side as in the second embodiment. However, as in the first embodiment shown in FIG. It is also possible to take a configuration in which lands and grooves are formed.
[0067]
In FIG. 4B, as in the second embodiment, an acrylic ultraviolet curable resin, for example, is poured between the stampers 401 and 402, and ultraviolet rays are exposed and solidified, whereby a recording layer holding substrate 403 is obtained. Create
[0068]
In FIG. 4C, the recording layer holding substrate 403 released from the stamper is coated with a polycarbonate resin added with diarylethenes as a recording material by spin coating to form a recording layer 404.
[0069]
In FIG. 4D, a part of the recording layer holding substrate 403 is coated with a polycarbonate resin added with a fluorescent dye (for example, Coumarin 522) by spin coating to form a fluorescent layer 405.
[0070]
In FIG. 4E, a recording layer holding substrate 403 integrated with the recording layer 404 via an acrylic thermosetting resin spin-coated as an adhesive layer 407 is provided between the support substrate 408 and the protective layer 406. A recording layer holding substrate 403 integrated with the fluorescent layer 405 is laminated on the lower portion and heated and cured. The difference in refractive index between the adhesive layer 407 and the polycarbonate resin recording layer 404 is about 0.1, and the reflectance at the interface between the two layers is about 0.1%. The refractive index difference can be arbitrarily set depending on the number of recording layers constituting the medium, and is not limited to this example. In the figure, only three layers are shown for simplification, but the number of recording layers is not limited to this.
[0071]
In FIG. 4 (f), TiO on both sides ₂ / SiO ₂ A dielectric multilayer film 410 is laminated. The layer structure is, for example, TiO ₂ 51nm / SiO ₂ 19 pairs of 84 nm are stacked. This structure has a reflectivity of over 90% at 450 to 550 nm (erasing band by one-photon absorption), a blocking characteristic of over 99.8%, and hardly affects transmission at a write and read wavelength of 780 nm. Absent. Therefore, the dielectric multilayer film 410 also has a function of confining the erasing light generated in the fluorescent layer 405 in the medium. Further, the ultraviolet absorbing layer 409 is formed by coating a resin containing an ultraviolet absorber on both sides. Thereby, it is possible to prevent the recording layer 404 from being exposed to light by one-photon absorption by the ultraviolet rays.
[0072]
Through the steps as described above, a multilayer recording medium having a long-term storage characteristic with a high S / N ratio can be produced. Note that this embodiment is an example of the configuration of the present invention, and the configuration of each layer responsible for the constituent materials and functions, the stacking order, and the like can be appropriately changed depending on the application. Further, the shape of the medium can take other forms such as a card in addition to the disk.
[0073]
Next, a recording / reproducing system using the multilayer recording medium will be described with reference to FIG. 5, the multilayer recording system for recording / reproducing the multilayer recording medium 501 according to the third embodiment includes an objective lens 502, a quarter-wave plate 503, a polarization beam splitter (PBS) 504, and a non-polarized beam. Splitter 505, coupling lens 506, semiconductor laser for reproduction (780 nm) 507, beam expander 508, pulse laser for recording (780 nm) 509, four-divided avalanche photodiode (4D-APD) 510, cylindrical The lens 511, the condensing lens 512, the pinhole 513, and the condensing lens 514 are comprised. This system has two systems of lasers (reproducing semiconductor laser 507 and recording pulse laser 509).
[0074]
The operation of the multi-layer recording system having the above configuration will be described first from the optical system of a reproducing laser related to reproducing and focus / tracking servos. The light emitted from the reproducing semiconductor laser 507 is converted into parallel light by the coupling lens 506, the optical path is changed by the non-polarizing beam splitter 505, and passes through the optical isolator composed of the polarizing beam splitter (PBS) 504 and the quarter wavelength plate 503. , Converted to circularly polarized light. A part of the light condensed on one of the recording surfaces of the multilayer recording medium 501 by the objective lens 502 is reflected by a difference in refractive index between different interfaces constituting the recording surface (in the creation example of the third embodiment). About 0.1%). The reflected light has a reverse optical rotation direction, passes through the quarter-wave plate 503, is converted into linearly polarized light orthogonal to the incident light, and is guided to the detection system by the PBS 504. In the detection system, the light is condensed by the condenser lens 514, and the reflected / scattered light from other than the focal point is removed by the pinhole 513. The light is condensed again by the condensing lens 512, passes through the cylindrical lens 511, and is guided to a four-divided avalanche photodiode (4D-APD) 510. Tracking / focus servo is applied by a signal detected with high sensitivity by the 4D-APD 510. Needless to say, the recorded information can also be read by the sum signal from the 4D-APD 510. The output light from this light source has a weak output for two-photon absorption to occur in the recording layer, and the reproduction signal cannot be degraded by reading.
[0075]
Next, the recording system will be described. Light emitted from the recording pulse laser 509 passes through the beam expander 508, the non-polarizing beam splitter 505, the PBS 504, and the ¼ wavelength plate 503, and is focused on the multilayer recording medium 501 by the objective lens 502. At this time, the emitted light of the recording pulse laser 509 needs to be adjusted to be coaxial with the emitted light of the reproducing semiconductor laser 507. At this time, since the focal points in the multilayer recording medium coincide with each other, tracking / focus servo during recording is also possible. By the mechanism as described above, information is written by two-photon absorption by the large peak power that is characteristic of the pulse laser.
[0076]
In the erasing operation, the focus servo is applied to the fluorescent layer 405 by the same focus servo as at the time of recording, and the fluorescent dye is excited by two-photon absorption by the pulse laser to emit fluorescence. Since the fluorescence is confined in the medium by the dielectric multilayer film 410, erasing of the recording is efficiently performed.
[0077]
As described above, in the present embodiment, good recording is possible using the multilayer recording system, and writing due to a one-photon absorption reaction can be prevented by the ultraviolet absorbing layer. Can prevent erasure due to a one-photon absorption reaction, so that a multi-layer recording medium having a high S / N ratio and excellent long-term storage stability without fogging on the recording layer and fading of the recording mark can be obtained. . In addition, it is possible to erase recorded information efficiently with a fluorescent layer that emits fluorescence in the erasing band with a writing light source and a dielectric multilayer film that confines the fluorescence in the medium, and rewritable without a dedicated pulse light source. A multilayer recording medium can be obtained.
[0078]
(Fourth embodiment)
As shown in FIG. 6, the multilayer recording medium of the fourth embodiment is formed on a plurality of recording layer holding substrates 603 formed by stampers 601 and 602 and one surface of each recording layer holding substrate 603. Recording layer 604, fluorescent layer 605 formed on the other surface of each recording layer holding substrate 603, dielectric multilayer film 606 formed on fluorescent layer 605, support substrate 607, recording on one surface A plurality of recording layer holding substrates 603 on which the layer 604 is formed and the fluorescent layer 605 and the dielectric multilayer film 606 are formed on the other surface are stacked on the supporting substrate 607 and adhered to each other; The protective layer 609 is stacked on the opposite side of the support substrate 607 of the stacked structure, the ultraviolet absorbing layer 610 containing the UV absorber formed on both surfaces of the medium, and the film is formed on the outer surface of the support substrate 607. Dielectric It is composed of a film 611.
[0079]
The recording layer holding substrate 603 is formed by ultraviolet curing, thermal polymerization, injection molding or the like using the stampers 601 and 602 in the same manner as in the second and third embodiments. As the material, for example, an acrylic resin can be used. However, other optical grade resins can be used as long as the refractive index difference with the resin that fills the recording layer between ensuring the strength of the substrate takes a desired value. Can be adopted.
[0080]
The recording layer 604 is formed by coating a resin mixed with a recording material on one surface of the recording layer holding substrate 603 in the same manner as in the second and third embodiments. As the recording material, for example, diarylethenes can be used. Examples of the resin include polycarbonate resin and acrylic resin.
[0081]
The fluorescent layer 605 has the same function as that of the third embodiment, and is formed by coating the other surface of the recording layer holding substrate 603 with a resin mixed with a fluorescent dye. An example of the fluorescent dye is Coumarin522. As the resin, the same resin as that of the recording layer 604 is used.
[0082]
The dielectric multilayer film 606 has a film configuration similar to that of the first and second embodiments, and is formed on each fluorescent layer 605. As described above, the dielectric multilayer film 606 transmits the writing and reading wavelengths by two-photon absorption, but reflects the erasing band (450 to 550 nm) by one-photon absorption.
[0083]
The support substrate 607 and the protective layer 609 are disposed outside the recording layer 604 having a multilayer structure to protect the recording layer 604 against humidity, gas, mechanical shock, and the like, and are equivalent to the first to third embodiments. Is used.
[0084]
The adhesive layer 608 includes a plurality of recording layer holding substrates 603 each having a recording layer formed on one surface and a fluorescent layer 605 and a dielectric multilayer film 606 formed on the other surface between the support substrate 607 and the protective layer 609. In order to stack and integrate, each substrate is filled with a coating and solidified. The material of the adhesive layer 608 includes a thermosetting type or ultraviolet curable resin, and a material having a refractive index difference such that the reflectance at the interface with the recording layer 604 becomes a desired value is selected. The
[0085]
As in the second and third embodiments, the ultraviolet absorbing layer 610 is formed by coating a resin containing an ultraviolet absorber on both sides of the medium.
[0086]
The dielectric multilayer film 611 has the same characteristics as the dielectric multilayer film 606, and is formed on the outer surface of the support substrate 607 so that the recording layer 604 is sandwiched between the dielectric multilayer film 606.
[0087]
An example of a method for producing a multilayer recording medium according to the present embodiment will be described with reference to FIGS. FIG. 6 shows an enlarged cross section of the recording surface of the recording medium, and any shape such as a chucking portion of the disk can be adopted.
[0088]
As shown in FIG. 6A, stampers 601 and 602 with lands and grooves are prepared. In this embodiment, in order to apply servo to both surfaces of the recording layer holding substrate 603, lands and grooves are engraved on both stampers 601 and 602.
[0089]
In FIG. 6B, a recording layer holding substrate 603 made of, for example, an acrylic resin is formed by injection molding using stampers 601 and 602.
In FIG. 6C, the recording layer holding substrate 603 is released from the stamper.
[0090]
In FIG. 6D, a recording layer 604 is formed by coating one surface of the recording layer holding substrate 603 with a polycarbonate resin added with diarylethenes as a recording material by spin coating. The other surface is spin-coated with a polycarbonate resin added with a fluorescent dye (for example, Coumarin 522) to form a fluorescent layer 605. Further, on the fluorescent layer 605, for example, TiO ₂ 51nm / SiO ₂ A dielectric multilayer film 606 in which 19 pairs of 84 nm are stacked is formed. As described above, the dielectric multilayer film having this structure has a reflectivity exceeding 90% at 450 to 550 nm (erasing band by one-photon absorption), a blocking characteristic exceeding 99.8%, and writing and reading. It hardly affects transmission at a wavelength of 780 nm.
[0091]
In FIG. 6E, the recording layer 604, the fluorescent layer 605, and the dielectric multilayer film 606 are integrated with each other through an acrylic thermosetting resin spin-coated as an adhesive layer 608 between the support substrate 607 and the protective layer 609. The recording layer holding substrate 603 is laminated and cured by heating. The difference in refractive index between the adhesive layer 608 and the polycarbonate resin recording layer 604 is about 0.1, and the reflectance at the interface between the two layers is about 0.1%. The refractive index difference can be arbitrarily set depending on the number of recording layers constituting the medium, and is not limited to this example. In the figure, only three layers are shown for simplification, but the number of recording layers is not limited to this.
[0092]
In FIG. 6F, a dielectric multilayer film 611 having the same layer configuration as the dielectric multilayer film 606 is formed on the support substrate 607. Further, a resin containing an ultraviolet absorber is coated on both sides to form an ultraviolet absorbing layer 610.
[0093]
In the multilayer recording medium having the above configuration, each recording layer group composed of the recording layer 604 and the fluorescent layer 605 is separated from each other by dielectric multilayer films 606 and 611, and an ultraviolet absorbing layer 610 is formed on the outermost layer of the medium. Has been. Therefore, since the dielectric multilayer films 606 and 611 transmit the light of the writing light source, the recording layer 604 can be written by two-photon absorption, while the photosensitivity of the recording layer 604 by one-photon absorption is caused by the ultraviolet absorbing layer 610. In addition, since the erasing band light from the outside is blocked by the dielectric multilayer films 606 and 611, there is no fogging on the recording layer and no fading of the recording mark, resulting in long-term storage with a high S / N ratio. Excellent recording information can be obtained. In addition, since the erasing light can be generated in the fluorescent layer 405 by the writing light source, the erasing light source is not necessary, and the erasing light generated in the fluorescent layer 405 is confined in each recording layer group. Erasure for each group is possible. Note that the recording layer group can include a plurality of recording layers 604, and of course, a write-once portion in which the fluorescent layer 405 is not provided can be provided in some recording layer groups.
[0094]
Through the steps as described above, a multilayer recording medium having a long-term storage characteristic with a high S / N ratio and capable of erasing for each recording layer group can be manufactured. Note that this embodiment is an example of the configuration of the present invention, and the configuration of each layer responsible for the constituent materials and functions, the stacking order, and the like can be appropriately changed depending on the application. Further, the shape of the medium can take other forms such as a card in addition to the disk.
[0095]
【The invention's effect】
As mentioned above ,Book According to the invention, by providing a blocking layer that blocks the wavelength region where one-photon absorption from the outside occurs, writing by the one-photon absorption process competing with the multi-photon absorption process, and depending on the recording material, by the one-photon absorption process Erasure can be prevented. The prevention of writing by the one-photon absorption process prevents the recording layer from being fogged, and the prevention of erasure by the one-photon absorption process leads to the prevention of fading of the recording mark, resulting in long-term storage characteristics with a high S / N ratio. A multilayer recording medium can be obtained.
[0096]
Also, shield By using a dielectric multilayer film as a fault, the degree of freedom of design of transmission / cutoff characteristics is increased, and the deterioration of the S / N ratio due to the one-photon absorption process is prevented, and the high transmission efficiency of writing light and reading light is compatible. Can Can The S / N ratio of the recording / reproduction system as a whole can be improved.
[0097]
Also, shield By using an absorption layer containing an absorption dye as a fault, a multilayer recording medium having a long-term storage characteristic with a high S / N ratio can be obtained at low cost.
[0098]
Also, shield By providing a fault on the surface of the medium, it is possible to easily obtain a multilayer recording medium having excellent blocking characteristics and thus having a long-term storage characteristic with a high S / N ratio.
[0099]
Fireflies By providing an optical layer, the medium has a erasing light source that can be controlled by writing light while preventing the recording mark from fading due to the one-photon absorption process from the outside. Thus, a rewritable multilayer recording medium can be obtained, and the cost of a multilayer recording system using this multilayer recording medium can be reduced.
[0100]
Fireflies By providing the light reflecting layer, the fluorescence generated from the fluorescent layer can be confined in the medium and the absorption efficiency thereof can be improved. As a result, the erasing characteristics are improved, and as a result, even if the erasing / writing cycle is repeated, the S / N Recording / reproduction characteristics with a high ratio can be obtained. Further, since there is no strong reflection of the reproduction light from the fluorescent reflection layer having the characteristic of transmitting the reproduction light, it is possible to reproduce a signal from a weak recording mark with a high S / N ratio, resulting in highly reliable recording / reproduction. A possible multilayer recording medium and a recording / reproducing system using the same can be realized.
[0101]
Fireflies By using a dielectric multilayer film as the light reflection layer, the transmission / reflection characteristics of the fluorescent reflection layer can be set sharply and the transmittance of the transmission band is high, so that a multilayer recording medium capable of more reliable recording / reproduction In addition, a recording / reproducing system using the same can be realized.
[0102]
Also small By providing a recording layer group in which a set of a fluorescent layer and a fluorescent reflecting layer is provided for at least one recording layer, erasing for each recording layer group can be performed.
[0103]
Also, above By using a multilayer recording medium, a large-capacity multilayer recording system having a long-term storage characteristic with a high S / N ratio can be obtained.
[0104]
In addition, the above-mentioned with a fluorescent layer Since the erasing light source can also be used as the recording light source by using the multi-layer recording medium, at present, only one system of pulse light source such as an expensive femtosecond laser is required. Cost reduction is possible.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an example of a manufacturing process of a multilayer recording medium according to a first embodiment of the invention.
FIG. 2 is a diagram showing a multilayer recording system using the multilayer recording medium according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating an example of a manufacturing process of a multilayer recording medium according to a second embodiment of the invention.
FIG. 4 is a cross-sectional view illustrating an example of a manufacturing process of a multilayer recording medium according to a third embodiment of the invention.
FIG. 5 is a diagram showing a multilayer recording system using a multilayer recording medium according to a third embodiment of the present invention.
FIG. 6 is a cross-sectional view illustrating an example of a manufacturing process of a multilayer recording medium according to a fourth embodiment of the invention.
[Explanation of symbols]
101, 102, 301, 302, 401, 402, 601, 602 ... Stamper
103, 304, 404, 604... Recording layer
104,305,406,609 ... protective layer
105, 306, 407, 608 ... adhesive layer
106,307,408,607 ... support substrate
107,309,410,606,611 ... dielectric multilayer film
303, 403, 603 ... Recording layer holding substrate
308, 409, 610 ... UV absorbing layer
405, 605 ... Fluorescent layer

Claims (12)

In a multilayer recording medium comprising at least two recording layers and performing recording by a multiphoton absorption process on the recording layer,
Each recording layer has grooves and lands formed on at least one surface,
A multilayer recording medium comprising a blocking layer that blocks light in a wavelength region where external one-photon absorption occurs with respect to the recording layer. In a multilayer recording medium comprising at least two recording layers and performing recording by a multiphoton absorption process on the recording layer,
  A recording layer holding substrate provided with each recording layer on at least one surface,
  In the recording layer holding substrate, grooves and lands are formed on the surface on which each recording layer is provided,
  A multilayer recording medium comprising: a blocking layer that blocks light in a wavelength region where external one-photon absorption occurs with respect to the recording layer. The blocking layer is transmitted through the wavelength area corresponding to the multiphoton absorption process, according to claim 1, characterized in that it comprises a dielectric multilayer film designed to reflect a wavelength region light of occurrence of one-photon absorption or 2 The multilayer recording medium described. The blocking layer is a multilayer recording medium according to any one of claims 1 to 3, characterized in that it comprises an absorbing layer containing a dye absorbing wavelength area of occurrence of one-photon absorption. The blocking layer is a multilayer recording medium according to claim 1 or 2, wherein the formed on the surface of the medium. 3. The multilayer recording medium according to claim 1, further comprising a fluorescent layer that emits fluorescence in a one-photon absorption band corresponding to erasure by a multiphoton absorption process. 7. The multilayer recording medium according to claim 6 , wherein the fluorescent layer contains a fluorescent dye that emits fluorescence in a one-photon absorption band corresponding to erasure by a multiphoton absorption process. The multilayer recording medium according to claim 6, further comprising a fluorescent reflection layer that reflects fluorescence emitted from the fluorescent layer and transmits light in a wavelength region corresponding to a multiphoton absorption process. 9. The multilayer recording medium according to claim 8, wherein the fluorescent reflection layer is made of a dielectric multilayer film. Multilayer recording medium according to claim 8, wherein the having a plurality of recording layer group composed of a combination of said at least one recording layer wherein the phosphor layer and the fluorescent reflective layer. Multilayer recording system characterized by writing to the recording layer with respect to multi-Symbol recording medium according to any one of claims 1 to 10, a recording light source of occurrence of multiphoton absorption. The multilayer recording medium according to any one of claims 6 to 10, wherein the recording layer is written using a recording light source in which multiphoton absorption occurs during recording, and the fluorescent light is used using the recording light source during erasing. A multilayer recording system, wherein fluorescence is emitted from a layer to erase recorded information in the recording layer.

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