JP2002083426A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium suitable for multi-level recording. SOLUTION: A plurality of virtual recording cells each having prescribed length are defined consecutively in the direction of the relative displacement of this optical recording medium which can record information by being irradiated with a laser. When an irradiation time necessary to change 20% of a reflectance variation width X-Y defined by the initial reflectance X and the marginal lowest reflectance Y of the virtual recording cell from the initial reflectance X by irradiating with a laser beam having fixed power is defined as A, and an irradiation time necessary to change 80% of the reflectance variation width X-Y from the initial reflectance X by irradiating with a laser beam is defined as B, a recording layer is set so as to be 1.8<(B-A)/A<11. Thus, the irradiation time of the beam having fixed power is changed at five or more steps to enable the multi-level recording.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of performing multilevel recording of data by irradiating a laser beam by switching the irradiation time in multiple stages according to data to be recorded.

[0002]

2. Description of the Related Art In contrast to a conventional optical recording medium, in which data is recorded by changing the length of a reproduction signal (the length of a reflection signal modulation section) in multiple steps, the depth of the reproduction signal (the depth of the reproduction signal) is reduced. Many studies have been made on a method of recording a plurality of data in each signal of the same length by switching the modulation degree of the reflection signal) in multiple stages.

According to this optical recording method, a plurality of data can be recorded in a depth direction as compared with a case where binary data is simply recorded based on the presence or absence of a pit. The amount can be increased, and therefore, the linear recording density can be improved. As a method of switching the depth of the reproduction signal in multiple stages, generally, the power of the laser beam is switched in multiple stages to form some kind of different recording marks. At present, as a recording medium, a recording medium utilizing holography and a recording medium having a multilayer recording layer have been proposed.

[0004] Here, recording each data so that the modulation degree of the reflected signal changes in multiple steps is called multi-level recording.

[0005]

On the other hand, in these multi-level recordings, the signal quality at the time of reproduction deteriorates as the power of the laser beam at the time of recording increases, that is, as the depth of the reflected signal to be formed increases. There was a problem of doing. Although the reason for this has not been clarified, the present inventor's expectation is thought to be that the area of the recording mark (recording mark area) increases due to an increase in the laser power.

For example, when recording marks are shortened in order to increase the amount of information recorded on an optical recording medium, and the power of the laser is switched in multiple stages, multi-level recording is performed.
The deterioration of the signal quality becomes remarkable, and as a result, the advantage of multi-level recording cannot be utilized.
In other words, in order to adopt multi-level recording, the interval between recording marks must be widened so that data detection can be performed to some extent even if signal quality is deteriorated.

Further, under the concept of achieving multi-level recording by switching the laser power stepwise as in the prior art, the recording mark length must be larger than the diameter of the focused beam (beam waist) during recording. Will be. Generally, the diameter of a focused beam is represented by Kλ / NA (K: constant, λ: laser wavelength, NA: numerical aperture of a lens).
For a pickup used in a CD, λ = 780 nm,
Generally, NA = 0.45, and the diameter of the focused beam is about 1.6 μm. In this case, the recording mark length is 1.6 μm
In the vicinity, the above-mentioned problem of signal deterioration became apparent, and it was difficult to perform multi-level recording in five or more steps by changing the laser power.

[0008] The above problem is considered to be the result of complicated intertwining of all factors such as the power setting of the laser beam and the characteristics of the optical recording medium. To the best of the inventor's knowledge, the cause is not clear at present. In fact, high-density multi-level recording has not been achieved, including its optical recording medium and recording method.

The present invention has been made in view of the above problems, and has as its object to achieve high-density multi-level recording by setting the characteristics of an optical recording medium to a predetermined state.

[0010]

Means for Solving the Problems The present inventor has conducted intensive studies on an optical recording medium, and has found a recording method for performing multi-step recording on the optical recording medium.
It has been confirmed that high-level multilevel recording of five or more steps can be performed.

That is, the above object can be achieved by the present invention described below.

(1) An optical recording medium capable of recording information by irradiating a recording layer formed on a light-transmitting substrate with a laser beam, wherein the information is relative to the laser beam in the optical recording medium. In the moving direction, a plurality of virtual recording cells having a predetermined unit length and a predetermined unit width in a direction orthogonal to the predetermined unit length are continuously defined, and the initial reflectivity of the virtual recording cell in the laser beam non-irradiated state. X / 100% -Y / X / 100-Y /
When 100, the irradiation time necessary for changing the initial reflectance X% by the laser beam irradiation of a constant power is A, and the irradiation time required for changing 20% when the entire fluctuation width is 100% is set to A, and Reflectance fluctuation width X / 100-Y
The irradiation time required to change 80% of / 100 from the initial reflectance X% by the laser beam irradiation is B
In this case, the virtual cell is 1.8 <(BA) / A
<11 (... relational expression (1)) The multi-level recording can be performed by switching the irradiation time of the laser beam having a constant power to the virtual recording cell in five or more stages. An optical recording medium, comprising:

(2) The irradiation time of the laser beam is 5
It is characterized in that at least a part of the recording marks of a plurality of sizes formed by performing multi-level recording by switching to more than one step includes recording marks having a length equal to or less than the diameter of the focused beam waist of the reading laser. The optical recording medium according to (1).

(3) The optical recording medium according to (1) or (2), wherein the recording layer of the optical recording medium comprises an organic dye component.

(4) The virtual reflectivity of the virtual recording cell before recording is 40% or more, and the minimum reflectivity Y after recording is (X-10)% or less. The optical recording medium according to (1), (2) or (3).

(5) The optical recording medium according to (4), wherein the minimum reflectance is 30% or less.

The inventor paid attention to both the reflectance fluctuation characteristics and the multi-level recording method in an optical recording medium. In particular, with regard to the optical recording medium, attention is paid to the relationship between the irradiation time of the laser beam and the change in the reflectance due to the laser beam irradiation. It has been found.

According to the analysis of the inventor, the change in the reflectance is
As schematically shown in FIG. 5, the laser beam irradiation time is not completely proportional to the irradiation time. The entire reflectance variation starts with the initial reflectance X%, and the reflectance variation is small in the initial time region H until it reaches about 20% of the reflectance variation width P, and is about 80% of the reflectance variation width P. , The variation in the intermediate time region I is relatively large, and the variation in the reflectance is small in the final time region J, and finally converges to the limit minimum reflectance Y%.

From this characteristic, it is considered that the relationship between the time A required to escape from the initial time area H and the time B required to escape from the intermediate area I thereafter becomes an important point in multi-level recording. Was made by the present inventor.
This is because the multi-level recording requires setting and recording the reflectivity in multiple steps between the initial reflectivity X% and the limit minimum reflectivity Y%, and the above-described intermediate time region I is effectively used. It is necessary. That is, the balance between time A and time B has a very important significance for the recording laser.

In fact, according to the analysis of the present inventor, it was possible to perform multi-level recording in five or more steps within the range of the above relational expression (1).
It has been confirmed that even if it is too small (1.8 or less), multi-level recording is hindered. For example, in the relational expression (1), when (B−A) / A is 1.8 or less, an appropriate recording power cannot be set because the change in reflectance due to the recording power is steep. In such a case, it is considered that the reflectance fluctuation with respect to the recording power is too small, so that an appropriate recording power cannot be set. These can be said to be optical recording media that are not suitable for multi-level recording because the balance between the initial time A and the intermediate time B is poor.

In order to satisfy this condition, the material of the recording layer, the thickness of the recording layer, the material of the reflection layer, the material and thickness of the substrate, and the shape of the groove cut on the substrate for laser guide, etc. Is set as appropriate. In addition to this method, it is also possible to appropriately adjust the laser power at the time of recording. This set laser power is the recommended recording power for the optical recording medium. For example, ATI of optical recording medium
It is recorded in advance in P or the like. For example, it is known that (BA) / A increases when the recommended recording power is set high, and (BA) / A decreases when the recommended recording power is set low.

Note that, within the range of the above relational expression (1),
Particularly, 2 ≦ (BA) / A ≦ 9 is preferable.

Further, if an optical recording medium set within the above range is used, it is possible to include a recording mark below the converging beam waist of the reading laser (which was conventionally considered impossible). Signal degradation at the time is greatly reduced. Incidentally, if the laser beam is actually irradiated by the power control, it is difficult to generate a recording mark below the focused beam waist. The present inventor does not modulate the power, but uses a constant power that generally uses only a threshold value that indicates a constant intensity of the laser light having the Gaussian distribution, and sets the irradiation “time” (for the unit virtual recording cell) in five steps. By controlling the laser beam by switching as described above, it was confirmed that a recording mark below the focused beam waist could be generated. From the above-described elements, if the optical recording medium of the present invention is used, an optical recording medium having an extremely high recordable density including marks of five or more steps and a focused beam waist or less can be obtained.

In the above invention, it is preferable that the recording layer of the optical recording medium contains an organic dye component. In fact, the inventor has achieved the above-mentioned multi-level recording by a method of producing a recording mark by a reaction of an organic dye component.

Further, in the above invention, the virtual reflectivity of the virtual recording cell before recording is 40% or more, and the minimum reflectivity Y after recording is (X-10)% or less. preferable. By doing so, it is possible to secure a sufficient fluctuation range of the reflectance, and it is possible to generate recording marks in more stages.

The optical recording medium of the present invention may be configured as follows.

(6) The unit length of the virtual recording cell is set substantially equal to the length of a recording mark formed by laser beam irradiation for the maximum irradiation time (1) to (5). An optical recording medium according to any of the above.

(7) A groove for laser beam guide is provided along the recording layer, the virtual recording cell is set in the groove, and the unit width matches the width of the groove. The optical recording medium according to any one of (1) to (6), wherein

(8) The optical recording medium according to any one of (1) to (7), wherein information is multi-level recorded in advance on a part of the recording layer.

(9) Specific information indicating that the medium is a multilevel optical recording medium is recorded on at least one of the virtual recording cell and the multilevel recorded part (1) to (8). An optical recording medium according to any of the above.

(10) A laser beam guide groove is provided along the recording layer, and the groove is
(1) to (9) characterized by being partially interrupted
An optical recording medium according to any of the above.

[0032]

Embodiments of the present invention will be described below in detail with reference to the drawings.

An optical recording medium (disk) 10 according to an embodiment of the present invention has a recording layer
R, a substrate 14 made of a transparent substrate,
The recording layer 12 made of a dye applied to cover the laser beam guide groove 16 formed on one surface (the upper surface in FIG. 1) of the recording layer 12 and gold formed on the upper side of the recording layer 12 by sputtering or the like. Alternatively, it is formed to include a reflective film 18 of silver or the like and a protective layer 20 covering the outside of the reflective film 18.

Dyes used in the recording layer 12 are organic dyes such as cyanine, merocyanine, methine dyes and derivatives thereof, benzenethiol metal complexes, phthalocyanine dyes, naphthalocyanine dyes, and azo dyes.

The multi-level recording on the optical recording medium 10 is executed by the optical recording device 30 shown in FIG.

The optical recording apparatus 30 is a CD-R recorder, and drives the optical recording medium (disk) 10 to rotate at a constant linear velocity by a spindle motor 32 via a spindle servo 31. This records information on the optical recording medium (disc) 10.

According to the information to be recorded, the laser 36 is irradiated by a laser driver 38 with a laser beam irradiation time for one virtual recording cell (detailed later) 40 shown in FIGS. The number is controlled.

Reference numeral 42 in FIG. 2 denotes a recording optical system including an objective lens 42A and a half mirror 42B. Focus tracking of the objective lens 42A is controlled by the focus tracking servo 44 so that the laser beam is focused on the recording layer 12 of the disk 10. The movement of the objective lens 42A and the half mirror 42B is controlled by the feed servo 46 from the inner peripheral side to the outer peripheral side at a predetermined speed in synchronization with the rotation of the disk 10.

The spindle servo 31, laser driver 38, focus tracking servo 44, and feed servo 46 are controlled by a control device 50. Recording layer 1
The data (information) to be recorded in 2 is input to the control device 50.

Next, the virtual recording cell 40 and recording marks recorded in the virtual recording cell 40 will be described.

As shown in FIG. 1, the virtual recording cells 40 are continuously defined in the groove 16 in the rotation direction of the disk 34, that is, the circumferential direction S. As shown in FIG. 3, the length L of each virtual recording cell 40 in the circumferential direction S is set to be shorter than the beam diameter (diameter of the beam waist) D. Is irradiated, recording marks 48A to 48G schematically illustrated are formed in accordance with information to be recorded.

More specifically, recording marks 48A to 48G having different diameters are formed in the center of the laser beam by appropriately changing the laser irradiation time of the laser beam emitted from the laser 36 (the laser beam is Although it is circular, since the laser beam is irradiated while rotating the disk 10, the recording mark becomes oblong according to the irradiation time.)

The reason for this is that the focused laser beam generally has a Gaussian distribution, but the recording layer 12
In, since recording is performed only in a portion where the irradiation energy of the laser beam exceeds a certain threshold, the recording layer 12 is changed by changing the irradiation time of the laser beam.
It is considered that the spot size of the laser beam that can be recorded on the spot changes. As a result, for example, seven levels of recording marks 48A to 48G as shown in FIG. 3 can be formed.

In this case, the size of each of the recording marks 48A to 48G is set so that the light reflectance of the reflected light when the virtual recording cell 40 is irradiated with the read laser beam becomes seven levels. The light reflectance increases as the recording mark becomes smaller, and becomes maximum reflectance in a virtual recording cell where no recording mark is formed, and becomes minimum reflectance in a virtual recording cell where the maximum recording mark 48G is formed. More specifically, the light reflectance is set in consideration of the area ratio of each of the recording marks 48A to 48G to the virtual recording cell 40 and the light transmittance of the recording mark itself.

The light transmittances of the recording marks 48A to 48G themselves are determined by the case where the material constituting the recording layer 12 is decomposed and deteriorated by the irradiation of the laser beam to change its refractive index, or the change in the thickness direction of the recording layer 12. Depends on quantity. If the light transmittance of the formed recording mark portion is zero, this need not be considered.

Next, the characteristics of the disk 10 will be described.

In this disk 10, a virtual recording cell 40
The initial reflectance in the laser beam non-irradiation state is X%, and the reflectance (minimum reflectance) which has reached the limit by irradiating the laser beam (for some time) is Y.
%, And the reflectance variation width (X-Y)% is defined from these values.

In this case, the irradiation time required to reduce the reflectance of the virtual recording cell 40 from the initial reflectance X% by 20% of the reflectance variation range by the laser beam irradiation of a predetermined power is A, The irradiation time required to continue the irradiation and reduce the reflectance fluctuation width by 80% is B.

Here, the characteristics of the disk 10 are represented by a reflectance fluctuation balance T = (BA) /
A is set so that 1.8 <(BA) / A <11 (... relational expression (1)). This is the substrate 14, the recording layer 1
2. It is achieved by appropriately adjusting the thickness and material of the reflection layer 20 and the like.

With this setting, the irradiation time of the laser beam of a constant power (recommended recording power) to the virtual recording cell 40 is set to five or more stages (seven stages in the above example) as described above. Multi-level recording is possible by switching, and in particular, even if the length of the recording marks 48A to 48G of the multi-level recording is set to be equal to or less than the diameter D of the condensing beam waist of the reading laser, data can be detected reliably Becomes

As a result, it is possible to generate an extremely small recording mark of not more than the focused beam waist by changing the reflectivity in five or more steps, so that an optical recording medium having an extremely high recordable density can be produced. can get.

In the above invention, it is preferable that the recording layer of the optical recording medium contains an organic dye component. In fact, as described in the examples below,
The above-described multi-level recording has been achieved by a method of generating a recording mark by a reaction of an organic dye component.

In this disk 10, a virtual recording cell 40
Is set to 40% or more, and the minimum minimum reflectivity Y is set to (X-10)% or less. This is because it is not suitable for multi-level recording of five or more steps unless the reflectivity has a certain fluctuation width. Further, according to the experiment of the present inventors, multi-level recording was possible when the initial reflectance X was 40% and the variation width of the reflectance was 10% or more.

In the example of the present embodiment, the optical recording medium 10 is configured as a CD-R disk as described above, but the present invention is not limited to this. It is generally applied to other optical recording media including R, and is not limited to a disk-shaped rotating body.

In the above embodiment, the recording layer 12 uses an organic dye such as cyanine. However, the present invention is not limited to this. Sufficient properties are sufficient, and organic or inorganic dyes other than those described above may be used, and other materials may be used as appropriate. However, when an organic dye as described above is used, it is possible to record by changing the size of the recording mark without fail, corresponding to the irradiation time of five or more steps of the laser beam, and it is possible to read with extremely high accuracy. Was.

Further, in the above embodiment, the optical recording medium 1 includes an unrecorded area in which information such as data is not recorded.
However, the present invention is not limited to this, and is also applicable to an optical recording medium in which information is recorded in multi-levels in five or more steps.

Furthermore, the size of the virtual recording cell 40 set on the recording layer 12 when forming a recording mark by the optical recording device 30 is not limited to the embodiment. In particular, if the beam waist diameter of the laser beam can be further reduced, the length becomes larger than the groove 16.
Should be equal to the width of On the other hand, when recording marks are recorded in further multiple steps such as eight steps, the recording mark may be set to be equal to or larger than the laser beam waist. In that case,
Some recording marks can be larger than the beam waist. Of course, the present invention is not limited to the structure of the present embodiment, but can be applied to discs having various structures that have been put into practical use. Further, the present invention can be applied to an optical recording medium having no groove 16. Applicable.

The recording laser beam is applied to the recording layer 1.
The shape of the optical recording medium 1 is circular at the position 2 as shown in FIG. 4, for example, by using a beam shaping prism 42C instead of the objective lens 42A, as shown in FIG.
An oval or linear shape that is short in the feed direction of 0 and long in the direction perpendicular to this direction may be used. In this case, since the recording mark 49 is shortened, the virtual recording cell can be further shortened. That is, the recording density can be improved.

Further, as shown by reference numeral 52 in FIG. 1, the optical recording medium 10 may have a plurality of pits having different reflectivities in advance corresponding to the number of signal modulation stages. Multilevel recording may be performed in advance on a part of the optical recording medium as described above. The plurality of pits 52 and / or the recording marks 54 of the multi-level recorded portion include information for individually identifying the optical recording medium, information for identifying the optical recording medium for multi-level recording, and information for identifying the optical recording medium for multi-level recording. Specific information such as information for determining a recommended recording power of a laser beam for recording / reproducing a medium may be recorded. The specific information is read at the time of reproduction and / or recording of the optical recording medium, thereby reliably identifying the optical recording medium for multi-level recording, further identifying them individually, or recording them in advance. The irradiation time of the laser beam can be determined according to the number of pit stages, and more reliable multi-level recording / reproduction can be performed.

Alternatively, as shown by reference numeral 56 in FIG. 1, the same effect can be obtained by providing a groove interruption portion for partially interrupting the groove for laser beam guide. These methods can be used alone or in combination.

[0061]

Examples of the present invention will be described below. The specific conditions in this embodiment are as follows.

A multi-level recording experiment was performed using a CD-R using a dye for the recording layer as the optical recording medium 10.

As a recording method, a DDU manufactured by Pulstec (used laser wavelength =
784 nm) with a high-frequency signal generator connected.

The reproduction was evaluated by connecting a digital oscilloscope to the DDU.

In multi-level recording, recording is performed by changing the laser beam irradiation time in 6 steps at a clock frequency of 4 MHz while rotating at a constant linear speed of 4.8 m / sec. Reproduction was performed by irradiating a 1 mW laser beam while detecting the difference in the amount of reflected light.

Further, the jitter value of the reproduced signal at this time is referred to as “Le Croy digital oscilloscope L”.
C-534EL ". The jitter value depends on the shape of a recording mark formed by irradiating a recording layer with a laser beam, and the smaller the jitter value, the more reliably the recording mark is formed. This is synonymous with the fact that information can be reliably recorded, and therefore, the reproduction can also be performed reliably.

Considering the case of recording by the conventional binary recording / reproducing method, if the jitter value is measured to be 10% or less by the evaluator used this time, it can be determined that good recording has been performed.

[0068]

Example 1 A cyanine dye was dissolved in a fluorinated alcohol as a coating solvent to prepare a dye solution for forming a recording layer having a concentration of 2 wt%, and this solution was coated on a spiral pregroove (track pitch: 1.6 μm, pre-groove width: 0.35 μm, pre-groove depth: 0.18 μ
m) on the pre-groove side surface of a light-transmitting substrate having a diameter of 120 mm and a thickness of 1.2 mm made of polycarbonate (manufactured by Teijin Chemicals Ltd .: Panlite AD5503) formed by injection molding. The organic dye recording layer having a thickness of about 200 nm from the bottom in the pre-groove was formed while spin coating was performed.

Next, on the organic dye recording layer, about 100
The light reflecting layer was formed by sputtering to a thickness of nm. Further, an ultraviolet curable resin (Dainippon Ink and Chemicals, Inc .: SD318) is applied on the light reflecting layer at a rotation speed of 300.
The coating was performed by a spin coating method while changing the rotation speed from rpm to 4000 rpm. After the application, the coating was cured by irradiating ultraviolet rays from above the coating with a high-pressure mercury lamp to form a protective layer having a thickness of 10 μm.

Multi-level recording was performed on this optical recording medium by setting the laser beam power during recording to 14 mW.
At this time, the recording linear velocity was 4.8 m / s, the recording clock frequency was 4 MHz (250 nsec), and the laser irradiation time during recording was (1) 50 nsec, respectively.
(2) 80 nsec, (3) 110 nsec, (4) 1
40 nsec, (5) 170 nsec, (6) 200 n
sec. Note that each single signal is
Recorded over the lap.

The initial reflectance of this optical recording medium is 72%.
(0.72), and the minimum minimum reflectance was 20% (0.20) when the laser was irradiated for 250 nsec or more. Therefore, the reflectance fluctuation range is 0.52 (= 0.72−
0.20).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.72 by 20% (approximately 0.1) of the reflectance variation width is 50 nsec. The irradiation time B required to reduce the fluctuation width by 80% (about 0.42) was 200 nsec. Therefore,
The reflectance variation balance T = (BA) / A = 3.

In this optical recording medium, six levels of multi-level recording were achieved, and the recorded data could be read reliably. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in the following table. It can be seen that good evaluation of 10% or less was obtained for all the recording marks.

[0074]

Example 2 A dye solution was prepared by changing the cyanine in Example 1 to phthalocyanine and changing the coating solvent to methylcyclohexane. Otherwise, an optical recording medium was manufactured in exactly the same manner as in Example 1.

The laser beam power during recording is 13 mW
Set to. The recording linear velocity at this time was 4.8 m /
s, and the recording clock frequency is 4 MHz (250 n
sec), and the laser irradiation time during recording is (1) 50 nsec, (2) 70 nsec, and (3) 90
nsec, (4) 110 nsec, (5) 130 nsec
c, (6) 150 nsec. Each single signal was recorded over one round of the disk.

The initial reflectance of this optical recording medium is 68%.
(0.68), and reached a critical minimum reflectance of 22% (0.22) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance fluctuation width is 0.46 (= 0.68−
0.22).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.68 by 20% of the reflectance variation width (about 0.92) is 50 nsec.
The irradiation time B required to reduce the reflectance fluctuation width by 80% (about 0.37) was 150 nsec. Therefore, the reflectance variation balance T = (BA) / A = 2.

In this optical recording medium, six levels of multi-level recording were achieved, and the recorded data could be reliably read. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in the following table. It can be seen that good evaluation of 10% or less was obtained for all the recording marks.

[0079]

Example 3 An optical recording medium was produced in the same manner as in Example 1, except that the dye solution was changed to a mixture of cyanine and an azo metal complex. The compounding ratio of cyanine and azo metal complex is 5
0: 50 wt%.

During recording, the laser beam power was 14 mW
Set to. The recording linear velocity at this time was 4.8 m /
s, and the recording clock frequency is 4 MHz (250 n
sec), and the laser irradiation time during recording is (1) 20 nsec, (2) 56 nsec, and (3) 92
nsec, (4) 128 nsec, (5) 164 nsec
c, (6) 200 nsec. Each single signal was recorded over one round of the disk.

The optical recording medium has an initial reflectance of 70%.
(0.70), and reached a critical minimum reflectance of 21% (0.21) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance variation width is 0.49 (= 0.70−
0.21).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance 0.70 by 20% of the reflectance variation width (about 0.10) is 20 nsec.
The irradiation time B required to reduce the reflectance fluctuation width by 80% (about 0.39) was 200 nsec. Therefore, the reflectance variation balance T = (BA) / A = 9.

In this optical recording medium, six levels of multi-level recording were achieved, and the recorded data could be reliably read. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in the following table. It can be seen that good evaluation of 10% or less was obtained for all the recording marks.

[0084]

Comparative Example 1 An optical recording medium was manufactured in the same manner as in the dye solution of Example 2. At that time, the dye film thickness was changed to 250 nm by adjusting the rotation speed of the spin coating method,
Further, the reflection film was changed to gold.

The laser beam power at the time of recording was 13 mW
The recording linear velocity at this time is 4.8 m / s, and the recording clock frequency is 4 MHz (250 ns
c), and the laser irradiation time during recording is (1)
50 nsec, (2) 70 nsec, (3) 90 nsec
c, (4) 110 nsec, (5) 130 nsec,
(6) 150 nsec. Each single signal was recorded over one round of the disk.

This optical recording medium has an initial reflectance of 70%.
(0.70), and reached a critical minimum reflectance of 20% (0.20) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance fluctuation width is 0.50 (= 0.70−
0.20).

The irradiation time A required to reduce the reflectance of the optical recording medium by 20% (0.10) of the variation range of the reflectance from the initial reflectance 0.70 is 50 nsec. The irradiation time B required to reduce the width by 80% (0.40) was 140 nsec. Therefore, the reflectance variation balance T = (BA) /A=1.8.

With this optical recording medium, it was not possible to reliably read the recording data in six stages. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in the following table.
0% or more, indicating that the evaluation was insufficient.

[0089]

Comparative Example 2 An optical recording medium was produced by changing the mixing ratio of the dye solution in Example 3. Specifically, the mixing ratio of cyanine and azo metal complex was set to 30:70 wt%.

The laser beam power at the time of recording was 15 mW
The recording linear velocity at this time is 4.8 m / s, and the recording clock frequency is 4 MHz (250 ns
c), and the laser irradiation time during recording is (1)
20 ns, (2) 64 ns, (3) 108 ns
ec, (4) 152 nsec, (5) 196 nsec,
(6) 240 nsec. Each single signal was recorded over one round of the disk.

This optical recording medium has an initial reflectance of 70%.
(0.70), and reached a critical minimum reflectance of 20% (0.20) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance fluctuation width is 0.50 (= 0.70−
0.20).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.70 by 20% (0.10) of the variation range of the reflectance is 20 nsec. The irradiation time B required to reduce the width by 80% (0.40) was 240 nsec. Therefore, the reflectance variation balance T = (BA) / A = 11.

In this optical recording medium, recording data (4)
(5) could be read with a certain probability, but other recorded data could not be read reliably. Incidentally, the above-mentioned (1) to (6) in this optical recording medium
The jitter values of the recording marks are shown in the table below, and some recording marks are 10% or more, indicating that the evaluation is insufficient.

[0094]

Comparative Example 3 An optical recording medium was manufactured in exactly the same manner as in Example 1.

Here, the laser beam power at the time of recording was set to 17 mW. The recording linear velocity at this time is 4.8 m / s, and the recording clock frequency is 4 MHz (25
0), and the laser irradiation time during recording is (1)
10 nsec, (2) 40 nsec, (3) 70 nsec
c, (4) 100 nsec, (5) 130 nsec,
(6) 160 nsec.

The initial reflectance of this optical recording medium is 72%.
(0.72), and reached a critical minimum reflectance of 20% (0.20) when irradiated with a laser for 200 nsec or more. Therefore, the reflectance fluctuation range is 0.52 (= 0.72−
0.20).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.72 by 20% of the reflectance variation width (about 0.10) is 10 nsec.
The irradiation time B required to reduce the reflectance fluctuation width by 80% (0.42) was 160 nsec. Therefore,
The reflectance variation balance T = (BA) / A = 15.

With this optical recording medium, all the recorded data could not be read reliably. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in the following table.
% Or more, and the value is in the above Comparative Example 2 (T = 1
It turns out that it is worse than 1).

[0099]

Comparative Example 4 An optical recording medium was manufactured in the same manner as in Example 1.

Here, the laser beam power at the time of recording was set to 11 mW. The recording linear velocity at this time was 4.8 m
/ S, the recording clock frequency is 4 MHz (250 ns
c), and the laser irradiation time during recording is (1)
100 nsec, (2) 130 nsec, (3) 160
nsec, (4) 190 nsec, (5) 220 nsec
c, (6) 250 nsec.

The initial reflectance of this optical recording medium is 72%.
(0.72), and reached a critical minimum reflectance of 20% (0.20) when irradiated with a laser for 300 nsec or more. Therefore, the reflectance fluctuation range is 0.52 (= 0.72−
0.20).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.72 by 20% of the reflectance variation width (about 0.10) is 100 nsec. The irradiation time B required to reduce the fluctuation width by 80% (0.42) was 250 nsec. Therefore, the reflectance variation balance T = (BA) /A=1.5.

In this optical recording medium, all the recorded data could not be read reliably. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in the following table.
% Or more, and the value is in Comparative Example 1 (T = 1.
It turns out that it is worse than 8).

Table 1 shows the above results.

[0105]

[Table 1]

[0106]

Example 4 An optical recording medium was produced in the same manner as in Example 1 except that the cyanine in Example 1 was changed to another cyanine. The laser beam power during recording was set to 14 mW. The recording linear velocity at this time was 4.8 m /
s, the recording clock frequency is 4 MHz (250 ns
c), and the laser irradiation time during recording is (1)
50 ns, (2) 75 ns, (3) 100 ns
ec, (4) 125 nsec, (5) 150 nsec,
(6) 175 nsec. Each single signal was recorded over one round of the disk.

The initial reflectance of this optical recording medium is 65%.
(0.65), and reached a limiting minimum reflectance of 28% (0.28) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance fluctuation width is 0.37 (= 0.65−
0.28).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.65 by 20% (about 0.07) of the reflectance variation width is 50 nsec.
The irradiation time B required for reducing the reflectance fluctuation width by 80% (about 0.30) was 175 nsec. Therefore, the reflectance variation balance T = (BA) /A=2.5.

With this optical recording medium, six levels of multi-level recording were achieved, and the recorded data could be read reliably. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in Table 2 below, and it can be seen that good evaluations of 10% or less were obtained for all the recording marks. .

[0110]

Comparative Example 5 An optical recording medium was produced in the same manner as in Example 1, except that the cyanine in Example 1 was changed to another cyanine different from that in Example 4. The laser beam power during recording was set to 14 mW. At this time, the recording linear velocity was 4.8 m / s, and the recording clock frequency was 4M.
Hz (250 nsec), and the laser irradiation time during recording was (1) 15 nsec, and (2) 55 nsec, respectively.
c, (3) 95 nsec, (4) 135 nsec,
(5) 175 nsec and (6) 215 nsec.
Each single signal was recorded over one round of the disk.

The initial reflectance of this optical recording medium is 65%.
(0.65), and the minimum reflectance was 32% (0.32) when the laser irradiation was performed for 250 nsec or more. Therefore, the reflectance fluctuation width is 0.35 (= 0.65−
0.32).

The irradiation time A required to reduce the reflectivity of the optical recording medium from the initial reflectivity of 0.65 by 20% (approximately 0.07) of the fluctuation range of the reflectivity is 15 nsec.
The irradiation time B required for reducing the reflectance fluctuation width by 80% (about 0.28) was 215 nsec. Therefore, the reflectance fluctuation balance T = (BA) /A=13.3.
Met.

With this optical recording medium, six levels of recorded data could not be read reliably. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in Table 2 below. The jitter value of all the recording marks is 10% or more, which is an insufficient evaluation. You can see that there is.

[0114]

Comparative Example 6 An optical recording medium was produced in the same manner as in Example 1 except that the cyanine in Example 1 was changed to another cyanine which was different from those in Examples 4 and 5. The laser beam power during recording was set to 14 mW. The recording linear velocity at this time was 4.8 m / s, the recording clock frequency was 4 MHz (250 nsec), and the laser irradiation time during recording was (1) 10 nsec and (2) 5
5 ns, (3) 100 ns, (4) 145 ns
ec, (5) 190 nsec, and (6) 235 nsec. Each single signal was recorded over one round of the disk.

The initial reflectance of this optical recording medium is 71%.
(0.71), and the minimum reflectance was 38% (0.38) when the laser irradiation was performed for 250 nsec or more. Therefore, the reflectance variation width is 0.33 (= 0.71−
0.38).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance 0.71 by 20% of the reflectance variation width (about 0.07) is 10 nsec.
The irradiation time B required to reduce the reflectance fluctuation width by 80% (about 0.26) was 235 nsec. Therefore, the reflectance fluctuation balance T = (BA) /A=22.5
Met.

With this optical recording medium, it was not possible to reliably read the recording data in six stages. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in Table 2 below. The jitter value of all the recording marks is 10% or more, which is an insufficient evaluation. You can see that there is.

[0118]

Example 5 A dye solution was prepared by changing the phthalocyanine in Example 2 to another phthalocyanine. Otherwise, an optical recording medium was manufactured in exactly the same manner as in Example 2.

The laser beam power during recording was 13 mW
Set to. The recording linear velocity at this time was 4.8 m /
s, and the recording clock frequency is 4 MHz (250 n
sec), and the laser irradiation time during recording is (1) 50 nsec, (2) 75 nsec, and (3) 10 nsec, respectively.
0 ns, (4) 125 ns, (5) 150 ns
ec, (6) 175 nsec. Each single signal was recorded over one round of the disk.

The initial reflectance of this optical recording medium is 43%.
(0.43), and reached a critical minimum reflectance of 22% (0.22) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance fluctuation range is 0.21 (= 0.43−
0.22).

The irradiation time A required to reduce the reflectance of the optical recording medium from the initial reflectance of 0.43 by 20% of the reflectance variation width (about 0.04) is 50 nsec.
The irradiation time B required to reduce the reflectance fluctuation width by 80% (about 0.17) was 175 nsec. Therefore, the reflectance variation balance T = (BA) /A=2.5.

In this optical recording medium, six levels of multi-level recording were achieved, and the recorded data could be reliably read. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in Table 2 below, and it can be seen that good evaluations of 10% or less were obtained for all the recording marks. .

[0123]

Example 6 A dye solution was prepared by changing the phthalocyanine in Example 2 to another phthalocyanine different from Example 5. Otherwise, an optical recording medium was manufactured in exactly the same manner as in Example 2.

The laser beam power during recording was 13 mW
Set to. The recording linear velocity at this time was 4.8 m /
s, and the recording clock frequency is 4 MHz (250 n
sec), and the laser irradiation time during recording is (1) 43 nsec, (2) 67 nsec, and (3) 94
nsec, (4) 121 nsec, (5) 148 nsec
c, (6) 175 nsec. Each single signal was recorded over one round of the disk.

This optical recording medium has an initial reflectance of 52%.
(0.52), and reached a critical minimum reflectance of 22% (0.22) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance variation width is 0.3 (= 0.52-0.
22).

The irradiation time A required to reduce the reflectivity of the optical recording medium from the initial reflectivity of 0.3 by 20% of the reflectivity variation width (about 0.06) is 43 nsec. The irradiation time B required to reduce the fluctuation width by 80% (about 0.24) was 175 nsec. Therefore,
The reflectance variation balance T = (BA) /A=3.07.

In this optical recording medium, six-level multi-level recording was achieved, and the recorded data could be reliably read. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in Table 2 below, and it can be seen that good evaluations of 10% or less were obtained for all the recording marks. .

[0128]

Comparative Example 7 A dye solution was prepared by changing the phthalocyanine in Example 2 to another phthalocyanine different from Examples 5 and 6. Otherwise, an optical recording medium was manufactured in exactly the same manner as in Example 2.

The laser beam power during recording was 13 mW
Set to. The recording linear velocity at this time was 4.8 m /
s, and the recording clock frequency is 4 MHz (250 n
sec), and the laser irradiation time during recording is (1) 15 nsec, (2) 57 nsec, and (3) 99
nsec, (4) 141 nsec, (5) 183 nsec
c, (6) 225 nsec. Each single signal was recorded over one round of the disk.

This optical recording medium has an initial reflectance of 37%.
(0.37), and reached a critical minimum reflectance of 22% (0.22) when irradiated with a laser for 250 nsec or more. Therefore, the reflectance fluctuation width is 0.15 (= 0.37−
0.22).

The irradiation time A required to reduce the reflectivity of the optical recording medium from the initial reflectivity of 0.37 by 20% (approximately 0.03) of the reflectivity variation range is 15 nsec.
The irradiation time B required to reduce the reflectance fluctuation width by 80% (about 0.12) was 225 nsec. Therefore, the reflectance variation balance T = (BA) / A = 14.

With this optical recording medium, it was not possible to reliably read the recorded data in six levels. The jitter values of the recording marks (1) to (6) in this optical recording medium are shown in Table 2 below. The jitter value of all the recording marks is 10% or more, which is an insufficient evaluation. You can see that there is.

[0133]

[Table 2]

[0134]

According to the present invention, it is possible to obtain an optical recording medium which can be applied to a new multi-level recording method of five or more stages and from which data can be detected reliably. In addition, since the length of the recording mark can be smaller than the diameter of the condensed beam (beam waist) of the reading laser, the recording density of information can be significantly increased.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view showing a main part of an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an optical recording apparatus for recording information on the optical recording medium using a laser beam.

FIG. 3 is a schematic diagram showing a relationship between the recording mark, a virtual recording cell, and its light reflectance when a recording mark is formed on a recording layer by the optical recording apparatus.

FIG. 4 is a schematic perspective view showing a case where a laser beam for irradiating a virtual recording cell has another shape.

FIG. 5 is a conceptual diagram schematically showing a change in reflectance in the optical recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Optical recording medium 12 ... Recording layer 14 ... Substrate 16 ... Groove 18 ... Reflective film 20 ... Protective layer 30 ... Optical recording device 32 ... Spindle 36 ... Laser 38 ... Laser driver 40 ... Virtual recording cell 42 ... Recording optical system 42A ... Objective lens 42B Half mirror 42C Beam shaping prism 44 Focus servo circuit 46 Feed servo circuit 48A to 48G, 49, 54 Recording mark 52 Pit 56 Groove interruption D D Beam

Claims (5)

[Claims] An optical recording medium capable of recording information by irradiating a recording layer formed on a light-transmitting substrate with a laser beam, wherein the optical recording medium moves relative to the laser beam in the optical recording medium. In the direction, a plurality of virtual recording cells having a predetermined unit length and a predetermined unit width in a direction orthogonal to the predetermined length are continuously defined, and the initial reflectance X of the virtual recording cell in the non-irradiated state of the laser beam. %, And the reflectivity variation range defined from the limit minimum reflectance Y% of the laser beam irradiated state is X
/ 100−Y / 100, the entire fluctuation range is 1
The irradiation time required to change the initial reflectance X% by irradiation of the laser beam with a constant power from 20% when the laser beam is irradiated at a constant power of 20% is A, and the reflectance variation width X / 100−Y / Assuming that the irradiation time required to change 80% of 100 from the initial reflectance X% by the laser beam irradiation is B, the virtual cell has 1.8 <(BA) / A <11. An optical recording medium which is set so as to have characteristics and is capable of multi-level recording by switching the irradiation time of the laser beam having a constant power to the virtual recording cell in five or more stages. 2. A condensed beam of a reading laser beam on at least a part of recording marks of a plurality of sizes formed by performing multi-level recording by switching the irradiation time of the laser beam to five or more stages. An optical recording medium comprising a recording mark having a length equal to or less than the waist diameter. 3. The optical recording medium according to claim 1, wherein the recording layer of the optical recording medium contains an organic dye component. 4. The virtual reflection cell according to claim 1, wherein the initial reflectance X of the virtual recording cell before recording is 40%.
And the minimum reflectance Y after recording is (X
-10)% or less. 5. The optical recording medium according to claim 4, wherein the minimum reflectance is 30% or less.