WO2002099793A1

WO2002099793A1 - Multi-level optical recording medium

Info

Publication number: WO2002099793A1
Application number: PCT/JP2002/005520
Authority: WO
Inventors: Hiroyuki Arioka; Syuji Tsukamoto; Takashi Horai
Original assignee: Tdk Corporation
Priority date: 2001-06-05
Filing date: 2002-06-04
Publication date: 2002-12-12
Also published as: TW588342B; JP2002367182A

Abstract

A multi-level optical recording medium (1) having a groove (11a) provided along a recording layer (12) mainly composed of an organic coloring matter for guiding recording or reproducing laser beam and enabling multi-level recording in five or more stages. In the groove (11a), during recording and reproduction, there are virtually provided a plurality of virtual record cells (S) having a predetermined unit length in the moving direction relative to the laser beam and a predetermined unit width in the direction orthogonally intersecting that direction, and the light reflection ratio of the laser beam in the portion including a virtual record cell (S) not yet recorded is adjusted to be not smaller than 40% and not greater than 80%. Thus, it is possible to produce the multi-level optical recording medium (1) which assures a sufficient difference of absolute light reflection ratios of the virtual record cells (S) in each of the recording stages and has a significantly small bit error rate when performing multi-level recording of high density in five or more stages.

Description

Akitoda

Multi-level optical recording medium

Technical field

The present invention relates to a multi-level optical recording medium capable of performing multi-level recording on one virtual recording cell. Background art

At present, as an optical recording medium, binary data is recorded by irradiating a recording laser beam to form pits, and the binary data can be reproduced based on the presence or absence of the pits. Optical recording media are widely used. In recent years, in response to a request for an increase in the recording density of an optical recording medium, a study for adjusting the focused beam diameter of a recording laser beam to perform high-density recording has been advanced. On the other hand, unlike the method of adjusting the focused beam diameter, the development of a multi-level optical recording medium that can record one of a plurality of different meaningful marks in one virtual recording cell is underway. In this multi-level optical recording medium, for example, by changing the irradiation amount of the recording laser beam to multiple stages, the deterioration of light transmittance of a part of one virtual recording cell to be recorded in the optical recording medium is reduced. A part (hereinafter, also referred to as a “recording mark”) appears, and the characteristic that the ratio of one recording mark to the entire virtual recording cell varies depending on the irradiation amount of one recording laser beam. In other words, in this multilevel optical recording medium, when the reproduction laser beam is irradiated, the light transmittance of the virtual recording cell where the recording mark is formed is affected, and as a result, the light of the reproduction laser beam is irradiated. The reflectance is multi-step (for example, 5 steps or more). Therefore, by associating each of the plurality of data contents with each of the multi-stage light reflectivities, one of the plurality of data is recorded in one virtual recording cell. In this case, the light transmittance refers to the ratio of the laser beam that has passed through the virtual recording cell to the reproduction laser beam irradiated to the virtual recording cell. The reproduction laser beam applied to the virtual recording cell passes through the portion including the virtual recording cell, is reflected by the reflective layer of the multi-level optical recording medium, and then passes through the portion including the virtual recording cell again. The ratio of one laser beam emitted to the outside of the multi-level optical recording medium is determined.

On the other hand, multi-level recording is possible only after the multi-level optical recording medium controls the light reflectivity of each virtual recording cell in multiple steps. For example, the light reflectivity of the unrecorded portion and the recording laser beam If the light reflectivity dynamic range corresponding to the difference from the light reflectivity of the recording portion where the irradiation amount is the largest is large to some extent, multi-level recording becomes difficult. In this case, the unrecorded portion means a portion including the unrecorded virtual recording cell and irradiated with the reproducing laser beam, and the recorded portion includes the recorded virtual recording cell and irradiated with the reproducing laser beam. Means the part to be done. Further, even if this dynamic range of light reflectance can be secured and multi-level recording can be performed, data cannot be accurately reproduced unless the bit error rate is good. In this case, the bit error rate fluctuates due to various factors, and the influence between adjacent virtual recording cells is one of the factors. In other words, when a reproducing laser beam is irradiated to one of the adjacent virtual recording cells to reproduce the recorded data based on the light reflectance, the peripheral portion of the reproducing laser beam is moved to the adjacent virtual recording cell. It is also irradiated to the other side. As a result, the reflected light of one virtual recording cell includes the reflected light of the other virtual recording cell, so that the light reflectance of one virtual recording cell is affected by the other virtual recording cell. . Regarding the influence between the adjacent virtual recording cells, if the influence exceeds a predetermined level, the bit error rate deteriorates. For this reason, the components of a multi-level optical recording medium that are considered to affect light reflectance, specifically, the material and thickness of the recording layer, the material of the reflective layer, the material and thickness of the light transmitting layer, and Specific criteria are set for components such as group structure (groove depth, width or shape), and when manufacturing multi-level optical recording media, the characteristics of multi-level optical recording media can be obtained by manufacturing according to these standards. To meet the above conditions You need to take care. Disclosure of the invention

However, for example, the recording layer, the reflective layer and the light transmitting layer described above may be made of a very large number of materials, and the thickness of the recording layer and the light transmitting layer and the structure of the groove are variously defined. Could be done. In addition, there are components other than these components that are considered to affect the light reflectance. For this reason, the number of combinations of materials, thicknesses, structures, and the like of all these components is enormous. Therefore, setting individual standards specifically and unambiguously may hinder improvement of the characteristics of a multi-level optical recording medium capable of performing multi-level recording and multi-level reproduction more stably. Absent. Therefore, the inventor has asked whether a multi-level optical recording medium capable of performing stable multi-level recording and multi-level reproduction as a whole can be manufactured only by setting standards for specific characteristics of specific components. We worked hard on the issues. At the same time, the inventor has performed multi-level recording and multi-level reproduction in a stable manner as a whole by using another manufacturing method instead of a manufacturing method in which a specific standard is set for each of these components. We also conducted intensive research on the issue of whether media could be manufactured.

The present invention has been made to solve the above-described problem, and has as its main object to provide a multi-level optical recording medium capable of reliably performing multi-level recording of five or more steps.

The multi-level optical recording medium according to the present invention is provided with a group for guiding a recording or reproducing laser beam along a recording layer mainly composed of an organic dye, so that multi-level recording of five or more levels is possible. A multi-level optical recording medium manufactured in accordance with claim 1, wherein said group includes a predetermined unit length with respect to a direction of relative movement with respect to said laser beam during recording and reproduction and a direction with respect to a direction perpendicular to said unit length. A plurality of virtual recording cells defined in a fixed unit width are continuously imagined, and the light reflectance for the laser beam in a portion including the virtual recording cell in an unrecorded state becomes 40% or more and 80% or less. It is configured as follows.

In this multi-level optical recording medium, the multi-level optical recording medium is configured so that the light reflectance of the laser beam in the portion including the virtual recording cell in the unrecorded state becomes 40% or more and 80% or less. However, a sufficient difference between the absolute light reflectance of the virtual recording cell in each recording step can be ensured, and the density of five or more steps is high regardless of the type of element that defines the light reflectance for the reproducing laser beam. The bit error rate at the time of performing multi-level recording is extremely low, and a multi-level optical recording medium can be manufactured.

In this case, it is preferable that the unit width of the virtual recording cell is set to be the same as the width of the group. With this configuration, virtual recording cells can be efficiently arranged in the radial direction of the multi-level optical recording medium. The multi-level optical recording medium according to the present invention is provided with a group for guiding a recording or reproducing laser beam along a recording layer mainly composed of an organic dye, so that multi-level recording of five or more levels is possible. A multi-level optical recording medium manufactured in accordance with claim 1, wherein the light reflectance for the laser beam for recording or reproduction is 40% or more and 80% or less in a state where the laser beam for recording or reproduction is focused on the group. It is configured to be.

In this multi-level optical recording medium, with the recording or reproducing laser beam focused on the group, the multi-level optical recording medium is adjusted so that the light reflectance for the laser beam is 40% or more and 80% or less. With this configuration, it is possible to sufficiently secure the difference between the absolute light reflectivities of the virtual recording cells in each recording stage, and regardless of the type of element that defines the light reflectivity for the reproduction laser beam. It is possible to manufacture a multi-level optical recording medium with an extremely low bit error rate when performing high-density multi-level recording of five or more steps. Further, the factors that define the light reflectivity to the laser beam include a material and a thickness of the recording layer, a material of a reflection layer that reflects the laser beam for reproduction irradiated through the recording layer, It is preferable that the material is at least one of the material and thickness of the light transmitting layer through which the reproducing laser beam passes before reaching the recording layer, and the structure of the group. With such a configuration, the light reflectance in the unrecorded state in the portion including the virtual recording cell can be reliably satisfied from 40% to 80%.

This disclosure is related to the subject matter included in Japanese Patent Application No. 2001-169699, filed on June 5, 2001, All are expressly incorporated herein by reference. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a partially cutaway perspective view showing the configuration of an optical recording medium 1 according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram conceptually showing the recording marks M a to M g recorded on the optical recording medium 1.

FIG. 3 is a characteristic diagram showing a characteristic of a light reflectance dynamic range with respect to a film thickness of the recording layer 12.

FIG. 4 is a characteristic diagram showing the influence of adjacent cells on the thickness of the recording layer 12. FIG. 5 is a characteristic diagram showing the characteristic of the bit error rate with respect to the film thickness of the recording layer 12 in the upper part, and the absolute light in the unrecorded part of the optical recording medium 1 with respect to the film thickness of the recording layer 12 in the lower part. FIG. 4 is a characteristic diagram showing a characteristic of a reflectance. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a multilevel optical recording medium according to the present invention will be described with reference to the accompanying drawings. First, the configuration of the multi-level optical recording medium 1 (hereinafter, also referred to as “optical recording medium 1”) will be described with reference to FIG.

The optical recording medium 1 is a CD-R type optical recording medium (write-once optical recording medium). As shown in FIG. 1, a substrate (light transmitting layer) 11, a recording layer 12, a reflective film 13 And a protective layer 14. The substrate 11 is formed in a disk shape using a transparent resin as a base material, and transmits one laser beam for reproduction before the laser beam for reproduction reaches the recording layer 12. On one surface (upper surface in FIG. 1) of the substrate 11, a group 11 a for laser beam guide and a land 11 b are spirally formed from near the center to the outer edge. ing. The recording layer 12 is composed of cyanine, merocyanine, methine dye and its derivative, benzenethiol metal complex

It is formed by using an organic dye such as a phthalocyanine dye, a naphthalocyanine dye, or an azo dye, and is formed by applying the organic dye so as to cover the group 11a and the land 11b. The recording layer 12 is decomposed and deteriorated by irradiating a recording laser beam with a recording device, and its absolute light reflectance changes according to the irradiation amount of the laser beam. In this case, the absolute light reflectance is obtained by replacing the value of the light reflectance of a disk having a thin surface made of gold or the like by a sputtering method or the like with a reference light reflectance (100%). It means the light reflectance at an unrecorded portion (unrecorded virtual recording cell S) in the recording layer 12 of each optical recording medium 1 compared to the reference light reflectance. The reflective film 13 is a thin film layer for reflecting a reproducing laser beam that has passed through the substrate 11 and the recording layer 12 when reproducing the recorded data recorded on the optical recording medium 1. It is formed by, for example, sputtering on the recording layer 12 using a metal as a main raw material. The protective layer 14 is a layer that protects the reflective film 13 and the recording layer 12 and is formed so as to cover the outer surface of the reflective film 13.

Next, the recording principle of the optical recording medium 1 will be described with reference to the drawings.

In this optical recording medium 1, as shown in FIG. 1, along the rotation direction (circumferential direction). The virtual recording cells S 1, S 2 ··· that are obtained by virtually dividing the group 11 a are defined as recording units (virtual). Here, as shown in FIG. 2, the length along the groove 11a of the virtual recording cell S (the circumferential direction of the optical recording medium 1, the direction of relative movement with respect to the laser beam in the present invention) ( The unit length, for example, 0.6 111) is specified to be shorter than the focused beam diameter (beam waist diameter) D (for example, 1.5 μΐη). On the other hand, the length (unit width) in the direction (radial direction of the optical recording medium 1) orthogonal to the direction along the group 11a of the virtual recording cell S is also specified to be equal to or smaller than the beam waist diameter D of the laser beam. . In this case, the track pitch of the optical recording medium 1 and the width of the group 11a can be arbitrarily selected. In this optical recording medium 1, the unit width of the virtual recording cell S is, as shown in FIG. It is defined to be the same as the width of a (for example, 0.6 μπι). Therefore, the virtual recording cells S are efficiently arranged in the radial direction of the optical recording medium 1. It should be noted that the virtual recording cell s is merely a virtual one, and does not have an entity like the rectangle shown in the figure, but is used by the multi-level recording / reproducing apparatus during signal processing during multi-level recording / reproducing. is assumed.

In this case, by controlling the irradiation time of the recording laser beam emitted from the pickup of the recording device (that is, the irradiation amount of the laser beam) in multiple stages according to the value of the recording data, as shown in FIG. In the virtual recording cell S, recording marks M a to M g (hereinafter, also referred to as “recording marks M” when no distinction is made) with different degrees of decomposition and alteration of the recording layer 12 (mainly organic dye) are formed. In the figure, the degree of decomposition and deterioration is conceptually shown by the size of the recording mark M. Further, the virtual recording cell S in which the recording mark M is formed becomes a recording portion in the recording layer 12. When recording data is recorded by the recording laser beam, the recording laser beam is irradiated while rotating the optical recording medium 1, so that the recording mark M has an oval length according to the irradiation time. .

When multi-level recording is performed on the optical recording medium 1, the virtual recording cell S is included. The degree of degradation of each of the recorded marks Ma to Mg is adjusted so that the absolute light reflectance when the reproduction laser beam is irradiated to the recorded area is, for example, 7 steps (8 steps including the unrecorded area). Light transmittance change). In this case, the absolute light reflectance increases as the degree of degradation of the recording layer 12 decreases. Therefore, the portion including the virtual recording cell S where the recording mark M is not recorded has the characteristic of the maximum absolute light reflectance, and the portion including the virtual recording cell S where the largest recording mark Mg is formed is the smallest. It has the characteristic of absolute light reflectance. In the present invention, the “portion including the virtual recording cell S” means an irradiated portion on the surface of the optical recording medium 1 where a recording or reproducing laser beam is focused. Therefore, this does not mean the number of virtual recording cells S. In other words, the irradiated portion of the focused recording or reproduction laser beam has a specific portion in one virtual recording cell S and one or more virtual portions in accordance with the focused beam diameter of the laser beam. This is a concept that includes a part including the recording cell S. Therefore, by controlling the irradiation amount of the recording laser beam to the portion including the virtual recording cell S and appropriately setting the area ratio of the degraded and deteriorated portions (that is, the light transmittance of the recording layer 12), This makes it possible to form recording marks Ma to Mg having an absolute light reflectance of seven levels when irradiated with a laser beam.

Next, the characteristics of the recording layer 12 using an organic dye will be described with reference to the drawings.

As described above, the characteristic of the light reflectivity dynamic range with respect to the film thickness of the recording layer 12 is, as shown in FIG. 3, as the film thickness of the recording layer 12 becomes thinner, the dynamic range becomes narrower (poor). Become. In this case, the smaller the dynamic range of the light reflectivity, the smaller the light reflectivity difference between the stages, and the lower the bit error rate. Further, as shown in FIG. 4, the influence between adjacent virtual recording cells S on the film thickness of the recording layer 12 (the degree of influence of the adjacent cells) decreases as the film thickness of the recording layer 12 decreases. Specifically, if the film thickness of the recording layer 12 is reduced, the recording laser beam The amount of organic dye that decomposes and changes can be accurately controlled by the irradiation amount of the recording laser beam because the heat radiation effect of the heat generated in the recording layer 12 when receiving Decomposition and deterioration of the organic dye can be avoided. Accordingly, when the recording laser beam is focused on one of the adjacent virtual recording cells S, the decomposition and alteration of the other adjacent virtual recording cell S can be prevented, and as a result, the film thickness of the recording layer 1 2 The thinner the bit error rate, the better the bit error rate. For this reason, based on the above two characteristics of the recording layer 12, the inventor has set the recording layer 12 between the film thickness and the bit error rate as shown in the upper part of FIG. When the film thickness of 1 2 is somewhat thick, the bit error rate is large, and as the film thickness of the recording layer 12 decreases, the bit error rate gradually decreases. We found that there is a correlation that the error rate increases again. On the other hand, the organic dye constituting the recording layer 12 has an optical dependency on the wavelength of the laser beam, and the other components (the group 11a and the reflection film 13 except for the recording layer 12) In the state where the material and the structure of) are constant, the absolute light reflectance in the unrecorded portion shows a predetermined characteristic with respect to the film thickness of the recording layer 12. As described above, since there is a correlation between the film thickness of the recording layer 12 and the bit error rate as shown in the upper part of FIG. 5, when manufacturing the optical recording medium 1, the film thickness itself is controlled. (Management) to keep the bit error rate low, that is, a method in which the film thickness of the recording layer 12 is specified to be within a predetermined range A, and a method of manufacturing so as to satisfy this specification is also considered. It is. According to this method, the bit error rate of the optical recording medium 1 can be suppressed to the reference value B or less. However, it is not easy to manufacture the film thickness of the recording layer 12 formed on the optical recording medium 1 with high accuracy, and moreover, the quality of the recording layer 12 is determined at the time of quality inspection for each production lot of the manufactured optical recording medium 1. It is also difficult to apply the evaluation based on the film thickness. Therefore, the inventors focused on the optical dependence of the organic dye constituting the recording layer 12 on the wavelength of the laser beam, and focused on the absolute light reflectance (specific characteristics) of the laser beam. It has been found that a predetermined correlation exists between the bit error rate and the bit error rate. Hereinafter, the absolute light reflectance of the reproducing laser beam in the optical recording medium 1 and

, The bit error rate will be described.

As described above, there is a correlation between the film thickness of the recording layer 12 and the bit error rate as shown in the upper part of FIG. On the other hand, as shown in the lower part of the figure, a predetermined correlation exists between the film thickness of the recording layer 12 and the absolute light reflectance. The correlation is represented by a solid line or a broken line in the lower part of the figure, based on the material of the organic dye constituting the recording layer 12 and the structure and material of the components other than the recording layer 12 constituting the optical recording medium 1. It changes variously as shown. However, if the structures and materials of these components are determined, the absolute light reflectance of the recording layer 12 is uniquely determined. Further, as is clear from the upper and lower parts of the figure, there is a uniquely determined correlation between the bit error rate and the absolute light reflectance. That is, when the absolute light reflectance is within the predetermined range, there is a correlation in which the bit error rate is equal to or less than the reference value B. According to the experiment of the inventor, in the optical recording medium 1, as long as the absolute light reflectance falls within a range of 40% or more and 80% or less, finally, the structure and material of the above-mentioned constituent elements are finally determined. Regardless of the type, it has been confirmed that the bit error rate of the optical recording medium 1 is equal to or lower than the reference value B. Further, when multi-level recording of seven or more levels is performed on the optical recording medium 1, a sufficient difference in absolute light reflectance in the virtual recording cell S in each recording step can be sufficiently ensured, and each recording step can be reliably performed. It has been confirmed that it can be identified.

In this case, as another reason that the absolute light reflectance within the range of 40% or more and 80% or less is preferable, the inventor conducted experiments and studies on various materials and found the following facts. I have. In other words, in order to use the absolute reflectance in multiple stages during multi-level recording / reproduction, a certain level of reflectance is required. When an experiment supporting this was performed, the recording / reproducing characteristics of the optical recording medium 1 having a reflectance of 40% or less were deteriorated. Conversely, in the optical recording medium 1 having a reflectance of 80% or more, the recording layer 12 has an insufficient absorptivity of the recording laser beam, and the recording sensitivity is reduced. Was. Therefore, in order to enhance the recording / reproducing characteristics, as described above, the absolute light reflectance within the range of 40% or more and 80% or less is preferable. The optical recording medium 1 does not need to consider compatibility with an optical recording medium for general-purpose binary recording / reproduction, and the recording / reproduction method is different from the optical recording medium for general-purpose binary recording / reproduction. Clearly different. For this reason, the fact that the inventor has found that the use with an absolute light reflectance within the range of 40% or more and 80% or less is optimal for the optical recording medium 1 is due to the fact that the optical recording medium for general-purpose It is not easily derived based on the absolute light reflectance values already used in the recording medium.

Therefore, in order to manufacture the optical recording medium 1 capable of multi-level recording at five or more levels of high density, the absolute light reflectance of the optical recording medium 1 should be 40% or more and 80% It is preferable to define the following. In addition, since the measurement of the absolute light reflectance is easy, by manufacturing the optical recording medium 1 with the above-described specification, the inspection of the production lot becomes extremely easy. Furthermore, as long as the absolute light reflectance of the optical recording medium 1 is in the range of 40% or more and 80% or less, the structure and material type of the above-described components can be appropriately selected. This can further improve the bit error rate of the optical recording medium 1, that is, the recording / reproducing performance of the optical recording medium 1.

As described above, by manufacturing the optical recording medium 1 with the absolute light reflectance specified to be 40% or more and 80% or less, the optical recording medium 1 capable of performing stable multi-level recording and multi-level reproduction can be obtained. Mass production is now possible. In addition, when performing a non-defective inspection of the optical recording medium 1, it is possible to use a conventionally used binary evaluation device. In this case, since the binary evaluation device can be used, it is not necessary to newly purchase or manufacture an evaluation device dedicated to multi-level recording, so that the manufacturing cost can be reduced. Further, since the measurement of the absolute light reflectance is easy, it is possible to accurately and easily perform the quality inspection for each production lot in the production of the optical recording medium 1,

It should be noted that the present invention is not limited to the above-described embodiment of the invention, and can be appropriately modified. For example, in the embodiment of the present invention, the optical recording medium 1 is a CD-R type optical recording medium. The present invention is not limited to this, but is generally applied to other optical recording media, and is limited to a disk-shaped rotating body. is not. Further, in the embodiment P of the present invention, the optical recording medium 1 is configured to irradiate the recording and reproducing laser beams from the substrate 11 side, but the reflection layer, the recording layer, and the recording layer are formed on the substrate. The present invention can also be applied to an optical recording medium having a structure in which a protective layer as a light transmitting layer in the invention is sequentially laminated, and a recording and reproducing laser beam is irradiated from the protective layer side.

Further, in the embodiment of the present invention, the recording layer 12 using an organic dye such as cyanine is exemplified. However, the present invention is not limited to this, and has a characteristic satisfying the above light reflectance. Any organic dye or inorganic material other than those described above may be used, and other materials may be used as appropriate. However, in the optical recording medium 1 using the above-mentioned organic dye, the recording mark M can be recorded with the light transmittance changed in accordance with the irradiation time of the recording laser beam in seven or more steps, and extremely high accuracy is achieved. Could be played. Further, the unit length and unit width of the virtual recording cell S are not limited to the above-described example, and can be appropriately changed. For example, for the unit length H, when the numerical aperture of the objective lens in the reproduction laser is NA and the wavelength of the reproduction laser beam is given, it is appropriate to change the unit length appropriately within the range expressed by the following formula. It is good.

0.10 X (λ / ΝΑ) <H <1.0 0 X (λ / ΝΑ)

—Specifically, using an example, when ぇ = 0.785 μππ, NA = 0.5, the unit length Η is 0.15 7 / in! It is preferable to change within the range of ~ 1.57; um. In this case, when changing the wavelength λ of the reproducing laser beam, it is preferable to change the unit length Η within the above range according to the wavelength λ. Further, in the embodiment of the present invention, the optical recording medium 1 that can be recorded in eight steps including an unrecorded portion where no information is recorded is exemplified, but the present invention includes an unrecorded portion, or It is also applied to optical recording media on which information is recorded in multi-levels in five or more levels without being included. Industrial Available Individuals

As described above, according to the multi-level optical recording medium of the present invention, the multi-level optical recording medium is configured such that the light reflectance with respect to the laser beam in the portion including the unrecorded virtual recording cell is 40% or more and 80% or less. By configuring the level optical recording medium, it is possible to sufficiently secure a difference between the absolute light reflectances of the virtual recording cells in each recording stage. Therefore, the bit error rate when performing high-density multi-level recording of five or more steps can be extremely reduced, regardless of the type of element that defines the light reflectance for the reproduction laser beam. As a result, a multi-level optical recording medium in which multi-level recording of five or more steps can be reliably performed and obtained is realized.

Claims

The scope of the claims

1. Multi-level optical recording manufactured with a group for guiding a laser beam for recording or reproduction along a recording layer mainly composed of organic dyes, and capable of multi-level recording of five or more stages Medium,

The group includes a virtual recording cell defined to have a predetermined unit length in the direction of relative movement with respect to the laser beam and a predetermined unit width in the direction orthogonal to the direction of the laser beam during recording and reproduction. Are continuously imagined, and a portion including the virtual recording cell in an unrecorded state has a light reflectance for the laser beam of 40% or more and 80% or less. Multi-level optical recording medium.

2. Multi-level optical recording manufactured with a group for guiding a laser beam for recording or reproduction along a recording layer mainly composed of organic dyes, and capable of multi-level recording of 5 or more stages A medium,

A multi-level structure in which the light reflectance for the laser beam for recording or reproduction is 40% or more and 80% or less when the focus of the laser beam for recording or reproduction is adjusted to the group. Optical recording medium.

3. The multi-level optical recording medium according to claim 1, wherein the unit width of the virtual recording cell is set to be the same as the width of the group.

4. The factors that define the light reflectivity to the laser beam are the material and thickness of the recording layer, the material of the reflective layer that reflects the laser beam for reproduction irradiated through the recording layer, 2. The multi-layer optical system according to claim 1, wherein the reproducing laser beam is at least one of a material and a thickness of a light transmitting layer that transmits before reaching the recording layer, and a structure of the group. 3. Level optical recording medium.

5. The factors that define the light reflectivity to the laser beam include the material and thickness of the recording layer, the material of the reflective layer that reflects the laser beam for reproduction irradiated through the recording layer, and the reproduction. Laser beam reaches the recording layer 3. The multi-level optical recording medium according to claim 2, wherein the medium has at least one of a material and a thickness of a light transmitting layer which is transmitted prior to the formation, and a structure of the group.

6. The factors that define the light reflectivity to the laser beam are the material and thickness of the recording layer, the material of the reflective layer that reflects the laser beam for reproduction irradiated through the recording layer, 4. The multi-layer optical system according to claim 3, wherein the reproducing laser beam is at least one of a material and a thickness of a light transmitting layer transmitted before reaching the recording layer, and a structure of the group. Level optical recording medium.