JPH08129778A - Optical recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to improve the number of times of repetitive recording / reproducing of an optical disc having both a mask layer and a recording layer. A mask layer 3, a recording layer 4 made of an optically recordable / reproducible substance, a reflection layer 5, and a protective film layer 6 are formed on a light-transmissive substrate 2 having a concentric or spiral guide groove 2A. Are laminated and configured. The light absorption wavelength range of the recording layer 4 is set to a shorter wavelength side than the light absorption wavelength range of the mask layer 3, and the mask layer 3 becomes substantially transparent to the light in the absorption wavelength range of the recording layer 4. Thus, the light absorption wavelength range of the mask layer 3 is set.

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 in which information is recorded at high density or information recorded at high density is reproduced, and in particular, a mask layer whose light transmittance changes with temperature change or the like. The present invention relates to an optical recording medium for reproducing information by reducing the effective spot diameter of irradiation laser light by using.

[0002]

2. Description of the Related Art In recent years, a large capacity optical disc has been studied,
Various proposals have been made. An optical disc can form a recording mark smaller than the light spot diameter by controlling the laser light power at the time of recording, and therefore there is no limit in principle to the improvement of the density at the time of recording. However, the diameter of the light spot when the laser light is narrowed down by a lens has a limit value that cannot be narrowed down to a certain value or less, and the densification of an optical disk depends on how to reduce the reproduction laser spot. The repetition wavelength (recording wavelength) of the recording mark at the reproduction limit is given by λ / 2NA. Here, λ is the wavelength of light and NA is the numerical aperture of the lens.

It is understood that in order to identify and reproduce a recording mark having a shorter recording wavelength, it is sufficient to reproduce with a light having a short wavelength λ or use a lens having a large numerical aperture NA. However, it is technically difficult to shorten the wavelength of a semiconductor laser used for reproduction, and it is not easy to incorporate a lens having a large numerical aperture NA into an optical disk device.

Therefore, as shown in FIG. 4, the temperature (light intensity) is higher than the threshold value I _s due to the temperature rise caused by the irradiation of light.
Absorbance decreases as increases, the light transmittance is high, also increased again absorbance by being cooled below the threshold I _s by the laser light passes is, a material that the light transmittance is low in the optical disk A method of recording information on an optical disc with high density or reproducing information recorded with high density by providing the layers is conventionally known.

The light intensity distribution of the laser light used for recording / reproducing information is normally a Gaussian distribution (see FIG. 6), and the temperature distribution is also a distribution close to this. When such a laser beam is irradiated onto the variable light transmittance medium, as shown in FIG. 5, only the portion A where the temperature inside the irradiation spot B has risen becomes light-transmitting, and the other portion inside the light spot is masked. , The so-called mask effect occurs. At this time, the effective spot diameter of the laser light transmitted through the portion A where the temperature has risen is smaller than the irradiation spot diameter of the irradiation laser light, as shown in FIG. By providing such a substance that causes a mask effect on the optical disc in a layered manner (hereinafter, such a layer is referred to as a mask layer), only the light having a high light transmittance in the irradiated laser beam spot passes through. Since the light in the irradiation spot having a low light transmittance is masked, crosstalk between adjacent tracks and adjacent pits can be eliminated.

[0006]

By the way, when the above mask layer is formed in an optical disk together with a recording layer capable of forming an optically readable recording mark, characteristic deterioration of the mask layer occurs during recording of the recording mark. Will end up. That is, most of the above-mentioned recording layers form recording marks by utilizing the fact that a predetermined amount or more of light is absorbed to change the optical characteristics. Laser light with a higher light intensity is used. Therefore, if the wavelength range of the laser light used for recording is near the absorption wavelength range of the mask layer, the mask layer may be damaged during recording mark formation, or the optical characteristics of the mask layer may deteriorate. is there. Further, since the mask layer is also made of a material that absorbs light and changes the light transmittance, the light intensity of the reproducing laser light needs to be a certain intensity. Therefore, when reproducing using the mask layer, the recording mark recorded according to the information may be destroyed or erased.

Therefore, the present invention has been made in view of the above points, and it is an object of the present invention to improve the number of times of repeated recording / reproduction of an optical disk having both a mask layer and a recording layer. .

[0008]

In a recording / reproducing apparatus for a recordable optical disk, if the wavelength regions of the output light of the recording laser beam and the output light of the reproducing laser beam are the same, the light source can be one and the device configuration can be improved. Although there is a merit that it can be simplified, an optical disk provided with a mask layer has problems such as the durability of the mask layer and erroneous erasure during reproduction as described above. Therefore, in the present invention, the mask layer is configured so that the recording laser light and the reproducing laser light are made to have different wavelength ranges, and the mask layer is configured to be substantially transparent to the recording laser light. It is intended to improve the durability of the. Furthermore, the light absorption wavelength range of the recording layer is set to a wavelength range shorter than the light absorption wavelength range of the mask layer. This is because the wavelength of the recording laser light is shorter than that of the reproducing laser light, so that the spot can be made smaller than the focused spot of the reproducing laser light, and the portion where the laser light intensity is high during recording. It is possible to record a minute recording mark even if there is no masking effect on the recording laser light, because the writing is performed with the writing tip. Therefore, the invention for achieving the above-mentioned object is to provide, on a light-transmissive substrate, a recording layer on which a recording mark that is optically readable is formed by absorbing light in a specific wavelength range, and a specific wavelength. For reading the recording mark by using at least a mask layer which changes the light transmittance by absorbing the light in the region and returns the light transmittance to the original state by stopping the irradiation of the light. In the optical recording medium for reducing the effective spot diameter of the reproduction laser light, the light absorption wavelength range of the recording layer is set to a shorter wavelength side than the light absorption wavelength range of the mask layer, and To provide an optical recording medium characterized in that a light absorption wavelength range of the mask layer is set so that the mask layer is substantially transparent to a laser beam for forming a recording mark on the layer. Is.

[0009]

The light intensity of the laser light for recording and reproducing on the optical recording medium usually has a Gaussian distribution as shown in FIG.
When the mask layer is irradiated with such a laser beam,
This mask layer is light-transmissive only in a portion of the laser beam spot where the temperature or the light intensity is high, the other portion of the spot is masked, and the spot diameter ( The effective spot diameter) becomes smaller, and minute marks can be optically identified. Since the irradiation spot moves relatively to the optical disc, the place delayed by the time until the transmittance changes due to light irradiation becomes brighter, and as shown in FIG. 5, the mask effect is further enhanced. It will work.

Further, since the mask layer has no absorption for the recording laser light, damage to the mask layer due to the laser light having high light intensity is reduced. Further, the recording layer does not absorb the reproduction laser beam, so that the information recorded during reproduction is not erased. Further, because the wavelength of the recording laser light is shorter than that of the reproducing laser light and the writing tip recording at the time of recording, a minute recording mark is recorded without using the mask effect for the recording laser light.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the structure of an optical disc according to an embodiment of the present invention. FIG. 1A shows the first embodiment and FIG. 1B shows the second embodiment. The optical disc shown in the figure is a sectional view in the track direction.
The optical disc 1 shown in FIG. 1A has a mask layer 3 and a recording layer 4 made of an optically recordable / reproducible material on a light-transmissive substrate 2 having concentric or spiral guide grooves 2A. The reflective layer 5 and the protective film layer 6 are laminated in this order. The optical disc 11 shown in FIG. 1B has a structure in which the recording layer 4 is laminated on the substrate 2, and the mask layer 3 is laminated on the recording layer. The stacking order of the mask layer 4 and the mask layer 3 is opposite to that of the optical disc 1. The optical discs 1 and 11 shown in FIG. 1 may be a light transmissive type that does not include the reflection layer 5, and may be further provided with a heat insulating layer, an enhancement layer, a dielectric layer, or the like.

As the substrate 2, a light-transmitting resin such as polycarbonate, polymethacrylic acid ester resin, or epoxy resin, glass, or the like used as a substrate for an ordinary optical disk can be used, and the guide groove 2A can be used. The forming method is not particularly limited, and the known method is used.

The mask layer 3 absorbs light in a specific wavelength range, has a light transmittance characteristic as shown in FIG. 4 with respect to the light intensity, and has a temperature (light intensity) below the threshold value I _s. in a low light transmission state having absorption and transmittance absorbance by being heated to a temperature higher than the threshold value I _s is reduced is increased becomes high light transmittance state, even more threshold I _s When cooled to a low temperature, it has the property of increasing the absorbance and returning to the original low light transmittance state. That is, it is in a low light transmittance state before the laser light irradiation, becomes a high light transmittance state due to the temperature rise due to the laser light irradiation, and returns to the low light transmittance state by cooling after passing the laser light. This mask layer 3
The light absorption wavelength range of is set to a wavelength range longer than the light absorption wavelength range of the recording layer 4, absorbs the reproducing laser light, and is substantially transparent to the recording laser light. Composed.

Various materials having the above-mentioned properties can be used as the material of the mask layer 3, and examples thereof include a thermochromic substance, a saturable absorptive substance, a phase change substance, and a photochromic substance. As the thermochromic substance, for example, an electron-donating color-forming compound,
Examples thereof include a mixture of an electron-accepting color developing agent and an organic compound, and a mixture of an electron-donating color developing compound and a phenol type color developing agent. Examples of the electron-donating color-forming compound include fluorane compounds, phthalide compounds, and lactam compounds. Further, as the saturable absorbent substance, various dye materials can be applied, as the phase change substance, there are metal and non-metal compounds (eg, germanium, antimony, tellurium alloy), and as the photochromic substance, various substances are available. Photochromic dye materials can be used.

The recording layer 4 is made of a material capable of absorbing light in a specific wavelength range and recording optically readable information. As the material forming the recording layer 4, various materials such as a phase change material, a magneto-optical material, and a dye material can be used. Further, these optical recording materials are formed by using a spin coating method, a vapor deposition method, a sputtering method, or the like. Here, in the optical discs 1 and 11 of this embodiment, since the light absorption wavelength range of the mask layer 3 and the absorption wavelength range of the recording layer 4 are largely different, the recording layer 4 is made of an organic dye having good wavelength selectivity.
Is composed. When the recording layer 4 is composed of an organic dye, it is preferable to form the recording layer by a spin coating method in view of downsizing of a manufacturing apparatus and running cost. The light absorption wavelength range of the recording layer 4 is set to a wavelength range shorter than the light absorption wavelength range of the mask layer 3, absorbs the recording laser light, and is substantially transparent to the reproducing laser light. Is configured to be.

The reflection layer 5 is similar to the metal reflection layer generally used in optical disks, and is formed of a thin film of metal or alloy such as gold or aluminum. The protective layer 5 provided on the reflective layer 5 is provided as necessary for the purpose of protecting the medium. The protective layer 6 can be easily formed by providing an ultraviolet curable resin by spin coating.

As described above, in the optical discs 1 and 11, the light absorption wavelength range of the mask layer 3 is different from that of the recording layer 4, and the light absorption wavelength range of the recording layer 4 is different from that of the mask layer 3. It is set to a position shorter than the light absorption wavelength range. Here, since the wavelength of the recording laser light is shorter than that of the reproducing laser light, the spot diameter can be made smaller than in the case of condensing the laser light used for the reproducing laser light, and the recording on the recording layer 4 is Since the writing is done with the laser beam (the recording mark is recorded at the portion having the light intensity equal to or higher than the threshold value within the laser beam spot), the masking effect by the mask layer 3 is not necessary for the recording laser beam. Of.
Further, at the time of reproduction, a reproduction laser beam having a wavelength longer than that of the recording laser beam is used, and the focused spot diameter thereof is larger than that of the recording laser beam, but as shown in FIG. The recording mark can be detected by the mask effect of 3.

Further, in the optical disc 11, in order to further improve the durability of the mask layer as compared with the optical disc 1, the recording layer 4 is provided on the substrate 2 and the mask layer 3 is provided on the recording layer 4. Therefore, the recording laser light that is pulse-modulated and emitted according to 0 and 1 of the information is recorded on the recording layer 4.
Therefore, most of them are absorbed and almost never reach the mask layer 3, and it is possible to reduce the characteristic deterioration of the mask layer 3 due to the recording laser light having a high light intensity.

Next, a recording / reproducing apparatus for the optical discs 1 and 11 will be described. FIG. 2 is a diagram showing a schematic configuration of a main part of the optical disc recording / reproducing apparatus in FIG. In the optical disk device 21 shown in FIG.
Is a condenser lens 23 for condensing the laser light outputted from the reproduction light source 28 or the recording light source 29 onto the recording layer 4 of the optical discs 1 and 11, and a condenser lens 23 for focusing and tracking. Actuator 2
4, the irradiation light to the optical disks 1, 11 and the optical disks 1, 1
A beam splitter 25 for separating the return light from 1
The beam splitter 24 includes a light receiver 26 that receives the return light separated from the irradiation light, and the like. The light receiver 26 converts the received return light into an electric signal,
An electric signal corresponding to the returned light is output to a signal demodulation circuit (not shown), a tracking servo circuit, or a focus servo circuit. The components of the optical head 22 are housed in a housing 27. The housing 27 is composed of the optical discs 1, 1
1 is configured to move in the radial direction of 1 (not shown), and the focused spot of the recording laser light or the reproducing laser light is largely moved in the radial direction from the inner circumference to the outer circumference of the optical discs 1, 11. You can Also, this optical head 2
The moving direction of 2 is the same as the direction of the optical axis R of the laser light incident on the optical head, and the incident laser light is always the beam splitter regardless of the radial movement of the optical head 22. 25 are incident on the same portion. An opening 27A is provided on the side surface of the housing 27 through which the optical axis R of the laser light incident on the optical head passes.

In the recording / reproducing apparatus 21, the reproducing light source 28 and the recording light source 2 having different output light wavelengths are used.
9 and 9. The reproduction light source 28 outputs reproduction laser light in the absorption wavelength range of the mask layer 3, and the recording light source 29
Is shorter than the output light of the reproduction light source 28 from the recording layer 4
The recording laser light in the absorption wavelength range of is output. The laser light output from each of the reproduction light source 28 and the recording light source 29 has the same traveling direction by the half mirror 30 and the like (in the figure, the traveling direction of only the output light from the reproduction light source 28 is a right angle). Bending in the same direction as the traveling direction of the output light from the recording light source 29). Either one or both of the reproduction light source 28 and the recording light source 29 may be provided in the housing 27.

The reproduction light source 28 and the recording light source 29
The drive of is controlled by the system control circuit 31. That is, when a recording operation command is input to the system control circuit 31 by an operating means (not shown), the system control circuit 31
Drives the recording light source 29 and outputs pulsed laser light modulated according to an information signal from the recording light source 29 to record information on the optical discs 1 and 11. When a reproduction operation command is input, reproduction laser light is output from the reproduction light source 28 to reproduce information. Note that circuits such as demodulation of information signals, tracking servo, and focus servo are performed by conventionally known methods. In addition, the recording / reproducing device 21 includes the reproducing light source 2
Reproduction-only machine equipped with only 8 or the above recording light source 2
It may be configured as a recording-only machine in which only 9 is mounted, and if laser lights of two wavelengths can be output from the light source, it is not necessary to provide two light sources.

Next, an optical disc based on the above embodiment,
An optical disk for comparison was prepared and an experiment was conducted to evaluate it. <Example> On a polycarbonate resin injection molded substrate 2 provided with grooves with a track pitch of 0.8 μm,
Rhodamine B, which is one of the organic dyes, as the recording layer
Was formed with a film thickness of about 50 nm by spin coating. The transmission spectral characteristic of this thin film was as shown in FIG. A mask layer 3 having a film thickness of 50 to 100 nm was formed on this. This mask layer 3 uses GN-169 (manufactured by Yamamoto Kasei) as an electron-donating color compound, and a bisphenol A (BPA) thermochromic dye as a color developer.
50 on the monitor at a ratio of about 1: 2 by the vacuum deposition method.
The film was formed to -100 nm. Aluminum is formed on the reflective layer 4 to a thickness of about 70 nm, and a UV curable resin SD-17 (manufactured by Dainippon Ink & Co., Inc.) is formed on the protective layer 5 to a thickness of about 7 μm.
The thickness was formed. The transmission spectral characteristics of the mask layer are also shown in FIG. The optical disc prepared above is recorded by a recording device equipped with an argon ion laser having a wavelength of 515 nm,
Reproduction was performed with a reproducing device equipped with a laser diode having a wavelength of 670 nm (recording / reproducing conditions were linear velocity CLV 3 m / s, rotation speed 1000 rpm, recording power 5 mW, recording frequency 0.8 to 3).
It was confirmed that good reproduction was possible at MHz and reproduction power of about 1.5 mW), the signal amplitude ratio was large, and the masking effect was working.

Comparative Example Similar to the above-mentioned example except that indolenincyanine, which is one of the organic dyes, was formed as a recording layer on the same substrate as in the above-mentioned Example 1 by a spin coating method to a thickness of about 70 nm. I made an optical disc. The transmission spectral characteristic of this thin film was as shown in FIG. Recording was carried out by a recording device equipped with a laser having a wavelength of 670 nm on this recording layer (recording conditions were linear velocity CLV 3 m / s, rotation speed 1000 rpm, recording power 5 mW, recording frequency 0.8 to 3).
MHz). Then, as a result of performing the reproduction in the same manner as in the above example, it seems that the recording could be performed, but the mask effect did not work well during the reproduction, the reproduced waveform was disturbed, and the signal amplitude was small. It is considered that this is because the mask layer also has a large absorption of the reproducing light similarly to the indolenine cyanine of the recording layer, and the mask layer is damaged during recording.

[0024]

As described above, according to the optical recording medium of the present invention, the light absorption wavelength range of the recording layer is set to a shorter wavelength side than the light absorption wavelength range of the mask layer, and the recording is performed. Since the light absorption wavelength range of the mask layer is set so that the mask layer is substantially transparent to the laser light for forming the recording mark on the layer, damage to the mask layer by the recording laser light can be reduced. . Further, by providing the light transmissive substrate, the recording layer, and the mask layer in this order, there is an effect that damage to the mask layer can be further reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical disc according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a main part of the optical disc recording / reproducing apparatus in FIG.

FIG. 3 is a diagram showing transmission spectral characteristics of a recording layer (rhodamine B, indolenine cyanine) and a mask layer.

FIG. 4 is a diagram showing light transmittance characteristics of a mask layer.

FIG. 5 is a diagram showing a mask effect of a mask layer.

FIG. 6 is a diagram comparing the light intensity distributions of the irradiation spot diameter and the effective spot diameter of the mask layer.

[Explanation of symbols]

 1, 11 Optical disc (optical recording medium) 2 Substrate (light transmissive substrate) 3 Mask layer 4 Recording layer

Claims (2)

[Claims] 1. A recording layer on a light-transmissive substrate, on which a recording mark that is optically readable by absorbing light in a specific wavelength range is formed, and by absorbing light in a specific wavelength range. It has at least a mask layer in which the light transmittance returns to its original state by changing the light transmittance and stopping the irradiation of light, and the effective reproduction laser light for reading the recording mark is used by using this mask layer. In an optical recording medium that reduces the spot diameter, in order to form a recording mark on the recording layer while setting the light absorption wavelength range of the recording layer to a shorter wavelength side than the light absorption wavelength range of the mask layer The optical recording medium, wherein the light absorption wavelength range of the mask layer is set so that the mask layer becomes substantially transparent to the laser light. 2. The optical recording medium according to claim 1, wherein the light transmissive substrate, the recording layer, and the mask layer are provided in this order.