JP2002082414A - Optical recording medium as well as reproducing method and reproducing device for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium which allows a non- destructive reading-out and can make reproduction at a high signal-to-noise ratio even if near field light is used as reproducing light, and a reproducing method and reproducing device for the same. SOLUTION: The method of reproducing information by irradiating the optical recording medium 1 having an information recording layer 4 containing organic dyestuffs reversibly changed in their molecular structure in a font mode and an electrode layer 3 disposed on the information recording layer 4 on the side opposite to its light incident side in order to impress voltage to the information recording layer 4 with the near field light 7a, consists of irradiating the information recording layer 4 with the reproducing light 7a, impressing the voltage thereto and separating holes and electrons from the excited molecules of the organic dyestuffs in the information recording layer 4 generated by the absorption of the reproducing light 7a.

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 having an information recording layer containing an organic dye, and a method and apparatus for reproducing the same.

[0002]

2. Description of the Related Art In recent years, with the spread of computers and the increase in multimedia information such as digital moving images, demand for large-capacity information recording has been increasing. In the technical field of optical disk recording, shorter wavelengths of light such as blue lasers and higher NA of condensing lenses are being studied. Optical recording technology using light has attracted attention.

In optical recording using near-field light, information is recorded and reproduced by irradiating a recording medium with near-field light (evanescent light) leaking from a probe having a minute aperture exceeding the diffraction limit of light. . As this probe, a probe having a sharpened optical fiber or a probe having a minute opening at an emission portion of a surface emitting laser is being studied. In optical recording using near-field light, since the evanescent light leaking from the opening transmits only a very short distance from the opening, it is necessary to keep the opening and the recording layer at a very short distance. Therefore, it is necessary to irradiate the recording layer directly, instead of irradiating the recording layer with light through a thick transparent substrate as in an ordinary optical disk.

As recording media for optical recording using such near-field light, magneto-optical recording media, phase-change recording media,
Photochromic recording media and the like are being studied. However, in a magneto-optical recording medium, when a minute recording mark is formed, the magnetic domain fluctuates thermally and becomes unstable, and it is difficult to obtain a sufficient SN ratio for reproducing information. is there. Also in the phase change recording medium, there is a problem that minute amorphous recording marks become unstable and are easily crystallized.

On the other hand, in a photochromic recording medium, since recording is performed at a molecular level by a photoreaction,
It has high resolution and is suitable for high-density optical recording.
When a stable molecular material such as a diarylethene-based material is used, even a very small recording mark does not become unstable. Therefore, the photochromic recording medium is
It is considered as a recording medium that is optimal for ultra-high-density optical recording using near-field light.

[0006]

A problem in a photochromic recording medium is how to realize so-called non-destructive reproduction. Since photochromic molecules are recorded by a photoreaction, there is a problem that even if a weak light is irradiated during reproduction, the photoreaction progresses little by little, and eventually the recorded information is erased.

On the other hand, in optical recording using near-field light, there is a problem of how to reproduce information at a high SN ratio. When a photochromic molecule is used for a recording layer, reproduction is usually performed by detecting a change in transmittance or a change in reflectance of the medium when the reproduction light is irradiated. However, when trying to achieve ultra-high-density recording using near-field light, the reach of the near-field light from the opening depends on the opening distance and is equal to or less than the opening diameter. For example, 0.
When recording is performed using a probe having an opening of 1 micron or less, a recording layer having a thickness of less than 0.1 micron is formed.
It is necessary to approach the probe opening to a distance sufficiently smaller than 0.1 micron. When the thickness of the recording layer is extremely small, even if the transmittance or the reflectance changes, the change amount is extremely small, and the signal level becomes small. When the thickness of the recording layer is small, the coloring density is relatively low, so that the reflectance level of the recording medium is high, and as a result, the shot noise level depending on the absolute intensity of light is also high. For this reason, there is a problem that a sufficient value cannot be obtained as the SN ratio given by the ratio of the signal level to the noise level, in combination with the low signal level.

A first object of the present invention is to provide an optical recording medium capable of nondestructive reading, a reproducing method and a reproducing apparatus therefor. A second object of the present invention is to provide an optical recording medium capable of reproducing at a high SN ratio even if the recording layer is thin, a reproducing method and a reproducing apparatus therefor.

A third object of the present invention is to provide an optical recording medium capable of detecting and reproducing information recorded on an optical recording medium by a novel method, and a reproducing method and a reproducing apparatus therefor.

[0010]

The optical recording medium according to the first aspect of the present invention is an optical recording medium from which information is reproduced by light irradiation, and uses an organic dye whose molecular structure is reversibly changed in a photon mode. It is characterized by comprising an information recording layer to be contained and an electrode layer for applying a voltage to the information recording layer.

[0011] In a first aspect of the present invention, the electrode layer comprises:
It can be provided on the light incident side or the side opposite to the light incident side with respect to the information recording layer. When the electrode layer is provided on the side opposite to the light incident side with respect to the information recording layer, the application of the voltage to the information recording layer is arranged, for example, on the light incident side of the information recording layer when reproducing the optical recording medium. It can be performed by applying a voltage between an external voltage applying means (for example, a probe electrode) and the above-mentioned electrode layer in the optical recording medium. With this configuration, for example, the position of the probe electrode or the like can be easily matched with the position of the light spot.

A light-transmitting electrode is provided on the optical recording medium on the light incident side of the information recording layer, and a voltage is applied between the light-transmitting electrode and the electrode layer to apply a voltage to the information recording layer. It may be applied.

[0013] In the first aspect of the present invention, the electrode layer may be made of a translucent material, and may be provided on the light incident side with respect to the information recording layer. In this case, the voltage is applied to the information recording layer by, for example, external voltage applying means (for example, a probe) arranged on the side opposite to the light incident side with respect to the information recording layer when reproducing the optical recording medium; This can be performed by applying a voltage between the electrode layer and the recording medium.

An optical recording medium according to a second aspect of the present invention comprises:
An optical recording medium from which information is reproduced by light irradiation, an information recording layer containing an organic dye whose molecular structure changes reversibly in a photon mode, and a light absorption layer which generates electric carriers by absorbing reproduction light. The light absorbing layer is arranged so that electric carriers generated in the light absorbing layer are transmitted through the information recording layer by applying a voltage, and the molecular structure of the organic dye in the information recording layer changes. It is characterized in that the conduction characteristics of electrical carriers passing through the information recording layer change.

In a second aspect of the present invention, a light absorbing layer is provided in addition to the information recording layer. In the second aspect of the present invention, the light absorbing layer is irradiated with reproduction light, an electric carrier is generated by absorption of the reproduction light, and then a voltage is applied to the light absorption layer, whereby an electric carrier is generated. Move through the information recording layer. Since the conduction characteristics of the electric carrier passing through the information recording layer change depending on the molecular structure of the organic dye in the information recording layer, the conduction characteristics of the electric carrier at this time are taken out as an electric current and detected to obtain information. The molecular structure of the organic dye in the recording layer can be known, and information can be reproduced. By using a material that easily generates electric carriers by absorbing reproduction light as a material forming the light absorbing layer, the generation efficiency of electric carriers can be increased, and a high SN ratio can be obtained.

The wavelength of the reproduction light may be any as long as it is absorbed by the light absorbing layer to generate electric carriers.
Therefore, the wavelength of the reproduction light can be a wavelength that is not substantially absorbed by the organic dye of the information recording layer. Therefore, information can be reproduced without affecting the recording state of the information recording layer, and more complete nondestructive reading can be performed.

In the optical recording medium according to the second aspect of the present invention, an electrode layer can be provided in the optical recording medium to apply the voltage. When the electrode layer is a non-light-transmitting electrode layer, the electrode layer is preferably provided on the side opposite to the light incident side with respect to the light absorbing layer. In this case, the application of the voltage to the light absorbing layer includes, for example, an external voltage applying means such as a probe electrode arranged on the light incident side of the light absorbing layer when reproducing the optical recording medium, and It can be performed by applying a voltage between the electrode layers.

In the optical recording medium, a light transmitting electrode is provided on the light incident side of the light absorbing layer, and a voltage is applied between the light transmitting electrode and the electrode layer to apply a voltage to the light absorbing layer. It may be applied.

The optical recording medium according to the second aspect includes the first recording medium.
The optical recording medium according to the above aspect may be provided with the light absorbing layer. In the first and second aspects of the present invention, examples of the organic dye whose molecular structure is reversibly changed in the photon mode include a photochromic dye such as a diarylethene dye.

The electrode layer can be formed from a material having high conductivity, and for example, can be formed from a thin film such as a metal or an alloy. When irradiating light such as a laser beam as reproduction light, this electrode layer may be used as a reflection layer. Further, the electrode layer may be formed of a light-transmitting material.

The light-transmitting electrode layer only needs to have a light-transmitting property that does not block reproduction light, and can be formed of an ITO film, a tin oxide film, or the like, which is generally known as a transparent conductive film.

The optical recording medium according to the first and second aspects of the present invention can use near-field light as reproduction light, but is not limited to this. It may be a laser beam focused to the diffraction limit using a lens.

The reproducing method according to the first aspect of the present invention reproduces information by irradiating a reproducing light to an optical recording medium having an information recording layer containing an organic dye whose molecular structure reversibly changes in a photon mode. The method is characterized in that the information recording layer is irradiated with reproducing light and a voltage is applied to separate holes and electrons from excited molecules of the organic dye in the information recording layer generated by absorption of the reproducing light.

By separating holes and electrons from the excited molecules of the organic molecules generated by the absorption of the reproduction light, the excited molecules of the organic dye can be returned to the ground state, and the isomerization reaction of the organic dye can be suppressed. Therefore, nondestructive reading can be performed.

Further, information recorded on the optical recording medium can be reproduced by extracting the electric charge generated by applying a voltage to the information recording layer to the outside as a current and detecting the electric current. According to such a reproducing method, even when the thickness of the information recording layer is small and the amount of change in reflectance or transmittance is small, it is possible to reproduce information recorded on the optical recording medium with a high SN ratio. it can. Therefore, even when near-field light is used as reproduction light, reproduction can be performed with a high SN ratio.

However, the reproducing method according to the first aspect of the present invention is not limited to such a method of detecting current, but is a method of reproducing by detecting a change in reflectance or transmittance. In such a reproducing method, non-destructive reading can be performed.

[0027] The reproducing method according to the second aspect of the present invention comprises an information recording layer containing an organic dye whose molecular structure changes reversibly in a photon mode, and a light absorbing layer which generates electric carriers by absorbing reproduction light. This is a method for reproducing information by irradiating the optical recording medium with reproducing light comprising: applying a voltage to the light absorbing layer while irradiating the light absorbing layer with the reproducing light; Carriers are conducted through the information recording layer, and the conduction characteristics of the electric carrier, which change due to the change in the molecular structure of the organic dye in the information recording layer, are extracted to the outside as a current and detected. It is characterized by reproducing information. This reproducing method is a method for reproducing the optical recording medium according to the second aspect described above. Since a material having high carrier generation efficiency can be used as a material used for the light absorbing layer, the reproducing is performed at a high SN ratio. be able to.

By using a wavelength that is not substantially absorbed by the organic dye in the information recording layer as the wavelength of the reproduction light, nondestructive reading can be performed. A reproducing device according to a first aspect of the present invention is a device for reproducing information by irradiating a reproducing light to an optical recording medium having an information recording layer containing an organic dye whose molecular structure is reversibly changed in a photon mode. And a means for irradiating the information recording layer with reproduction light and a means for applying a voltage to the information recording layer irradiated with the reproduction light.

By applying a voltage to the information recording layer irradiated with the reproduction light, holes and electrons are separated from the excited molecules of the organic dye in the information recording layer as described above, and the isomerization reaction of the organic dye is performed. , It is possible to perform non-destructive reading.

[0030] The reproducing apparatus according to the first aspect of the present invention may further include a means for extracting a charge generated by applying a voltage to the information recording layer as an electric current to the outside and detecting the electric charge. By performing reproduction using such a detecting means, it is possible to reproduce with a high SN ratio even on an optical recording medium having a small change in reflectance or transmittance. Therefore, even when near-field light is used as reproduction light, recording can be reproduced with a high SN ratio.

[0031] In the reproducing apparatus according to the first aspect of the present invention, a probe electrode arranged on the light incident side of the information recording layer or on the opposite side to the light incident side may be included as voltage applying means. Such a probe electrode can also be used as an electrode for extracting a current generated by applying a voltage to the information recording layer to the outside. Therefore, it may be included as a photocurrent detecting means.

The reproducing apparatus according to the second aspect of the present invention comprises an information recording layer containing an organic dye whose molecular structure changes reversibly in a photon mode, and a light absorbing layer which generates electric carriers by absorbing reproduction light. A device for reproducing information by irradiating the optical recording medium with reproduction light, comprising: means for irradiating the light absorption layer with reproduction light; and means for applying a voltage to the light absorption layer irradiated with the reproduction light. And characterized in that:

[0033] The reproducing apparatus according to the second aspect of the present invention is an apparatus capable of reproducing the optical recording medium according to the second aspect. Therefore, reproduction can be performed with a high SN ratio. Further, by using a wavelength that is not substantially absorbed by the organic dye of the information recording layer as the wavelength of the reproduction light, non-destructive reading becomes possible.

In the reproducing apparatus according to the second aspect of the present invention, it is preferable that the reproducing apparatus further includes a means for extracting electric charges generated by applying a voltage to the light absorbing layer to the outside as a current and detecting the electric current.

In the reproducing apparatus according to the second aspect of the present invention, a probe electrode arranged on the light incident side or on the opposite side of the light absorbing layer may be included as the voltage applying means. Such a probe electrode can also be used as an electrode for extracting a current generated by applying a voltage to the light absorbing layer to the outside. Therefore, it may be included as a photocurrent detecting means.

The reproducing apparatus according to the first and second aspects of the present invention can use near-field light as reproducing light, but is not limited to this. The focused laser beam may be used as reproduction light.

The principle by which the first aspect of the present invention enables nondestructive reading will be described below. FIG.
FIG. 4 is a schematic diagram illustrating a process in which a photochromic dye is changed by light absorption when a photochromic dye is used as an organic dye. The photons contained in the irradiated light are absorbed by the dye molecules A, so that the dye molecules are in an excited state and become excited dye molecules A ^* . This excited dye molecule A ^* usually has the following 3 as shown in FIG.
Inactivation occurs through any of the following processes (1) to (3).

(1) The molecule is isomerized by a photochromic reaction. (2) It emits fluorescence and returns to the molecule in the original ground state. (3) Thermally deactivated without radiation, returning to ground state molecules.

However, a voltage (electric field) is applied to the information recording layer.
Is applied, a fourth process different from the above processes (1) to (3) exists. FIG.
FIG. 7 is a schematic diagram for explaining the fourth process. As shown in FIG. 3, molecules are excited from the ground order to the excitation order by absorbing photons. At this time, the excited molecule A ^* is composed of holes (holes) and electrons (electrons).
Are separated. At this time, if a voltage is applied, the electrons are immediately attracted to the positive electrode and the holes are attracted to the cathode, so that the molecule immediately returns to the ground state. Therefore, by applying a voltage to the information recording layer according to the first aspect of the present invention, the dye molecules can be brought into the ground state without going through the above-mentioned steps (1) to (3). For this reason, according to the first aspect of the present invention, the photochromic isomerization reaction can be suppressed, and nondestructive reading can be performed.

On the other hand, electric carriers such as electrons and holes attracted to the electrodes become currents at the electrodes and can be taken out of the recording medium. Since this current value changes depending on the isomerization state of the photochromic molecule,
By detecting this current, information recorded on the recording medium can be read. Normally, information is recorded on an optical recording medium by a change in a coloring state of a dye molecule such as a photochromic molecule. Generally, reproduction is performed by detecting a change in intensity of reflected light or transmitted light. When the thickness of the information recording layer is extremely small, the average value of the reflected light or the transmitted light is high, so that the shot noise level is increased, which results in a problem that the SN ratio is reduced. As described above, if the absorbed light is extracted and detected as an external current, the absorbed light is small, so that the shot noise level is reduced, and as a result, a high SN ratio can be obtained. That is, if the absorbed light is detected as a photocurrent, the noise level is reduced, so that a high SN ratio can be obtained.

Next, the principle of the reproducing method according to the second aspect of the present invention will be described. FIG. 10 and FIG. 11 are schematic diagrams for explaining the principle of the reproducing method according to the second aspect of the present invention. Here, the optical recording medium is configured by laminating an electrode layer 21, a light absorbing layer 22, an information recording layer 23, a hole transport layer 24, and a translucent electrode layer 25. FIG. 10 shows the ionization potential level in each layer of the optical recording medium thus configured. The information recording layer 23 contains a photochromic molecule such as a diarylethene-based molecule as an organic dye whose molecular structure is reversibly changed in a photon mode.

FIG. 10 shows the ionization potential level when the photochromic molecule in the information recording layer 23 is in one state (for example, a ring-closed state in the case of a diarylethene-based molecule). 23a is at a relatively high level. Therefore, the difference from the ionization potential level 22a of the light absorption layer 22 is small, and the height of the potential barrier for holes from the light absorption layer 22 is low.

When the reproduction light is irradiated in this state and the light absorption layer 22 absorbs the reproduction light, the light absorption layer 22
, Electrical carriers (ie, electrons and holes) are generated. As shown in FIG. 10, a DC power supply 8 is connected to the electrode layer 21 and the translucent electrode layer 25, and a voltage is applied between the electrode layer 21 and the translucent electrode layer 25. Therefore, the electrons generated in the light absorption layer 22 are attracted to the electrode layer 21, and the holes are attracted to the translucent electrode layer 25. As described above, since the ionization potential level 23a of the information recording layer 23 is at a relatively high level, holes generated in the light absorption layer 22 easily pass through the information recording layer 23. Ionization potential level 24 of hole transport layer 24
a and the ionization potential level 2 of the translucent electrode layer 25
5a is the ionization potential level 2 of the information recording layer 23.
Since the holes are at a level higher than 3a, the holes further pass through the hole transport layer 24 and reach the translucent electrode layer 25.

Since the ionization potential level 21b for electrons in the electrode layer 21 is lower than the ionization potential level 22b for electrons in the light absorption layer 22, electrons generated in the light absorption layer 22 can be easily formed. It reaches the electrode layer 21.

FIG. 11 shows the ionization potential level when the photochromic molecules in the information recording layer 23 are in the other state (for example, in the case of a diarylethene-based molecule, a ring-opened state). At this time, the ionization potential level 23a of the information recording layer 23 is at a low level as shown in FIG. Therefore, the potential barrier against holes generated in the light absorption layer 22 is extremely high. Therefore, even if the light absorbing layer 22 is irradiated with the reproduction light and the absorption of the reproduction light generates holes and electrons as electric carriers, the large potential barrier by the information recording layer 23 prevents the conduction of holes. .

Therefore, the current flowing between the electrode layer 21 and the translucent electrode layer 25 is taken out as an external current, and by detecting this, the state of the photochromic molecules in the information recording layer 23 can be known. Information recorded on the recording layer can be reproduced.

In the second aspect of the present invention, since the light absorbing layer which generates electric carriers by absorbing the reproduction light is provided, the organic dye contained in the information recording layer is made of a material which does not easily generate electric carriers. There may be. By using a material having a high electric carrier generation efficiency as a material forming the light absorption layer, reproduction with a high SN ratio can be performed.

The wavelength of the reproduction light may be any wavelength as long as it is absorbed by the light absorbing layer 22, and may be a wavelength that is not substantially absorbed by the information recording layer 23. Therefore, by using light having a wavelength that is not substantially absorbed by the information recording layer 23 as reproduction light, photoisomerization of photochromic molecules in the information recording layer 23 can be prevented, and complete nondestructive Reading can be realized.

In FIGS. 10 and 11, an optical recording medium having a hole transport layer is described as an example, but the optical recording medium of the present invention has such a hole transport layer as an essential component. is not.

[0050]

FIG. 4 is a schematic sectional view showing an optical recording medium according to an embodiment according to the first aspect of the present invention. The optical recording medium 1 is formed by laminating a translucent electrode layer 10, an information recording layer 4, and an electrode layer 3 on a substrate 2. In this embodiment, a glass substrate is used as the substrate 2. The translucent electrode layer 10 is formed of a transparent conductive film made of ITO. The information recording layer 4 is made of a diarylethene-based photochromic material having a structure shown in FIG.
It is formed by deposition so as to be 00 °. The electrode layer 3 is formed on the information recording layer 4 by depositing metallic magnesium by a vacuum evaporation method. In this embodiment, the thickness of the electrode layer 3 is set to 1000 °. In the optical recording medium 1 of this embodiment, the electrode layer 3 also functions as a reflection layer.

In the present embodiment, the molecular structure of the diarylethene-based material used as the organic dye of the information recording layer changes between the ring-opened state and the ring-closed state by the photochromic photoisomerization reaction, and the molecular The size of the π-conjugated chain changes. At this time, the electrical carrier mobility and the height of the hole injection barrier change greatly, so that the material is suitable as a dye material for the information recording layer of the optical recording medium of the present invention.

FIG. 5 also shows the absorbance of the diarylethene dye used in this example. The solid line is the absorbance in the open ring state and the dotted line is the absorbance in the closed ring state.
As is clear from FIG. 5, this molecule has an absorption only in the ultraviolet light region in the ring-open state, but also absorbs in the visible light region in the ring-closed state. Therefore, when the visible light laser is applied to the recording layer in the closed state, electric carriers are generated in the film. However, when the visible light laser is applied to the open recording layer, no carrier is generated because there is no absorption itself. .

First, the effect of improving the SN ratio will be described below. The optical recording medium 1 shown in FIG. 4 was sufficiently irradiated with visible light as light 7 from the translucent electrode layer 10 side, so that all of the dye molecules were opened. The reflectance at this time is 10
The relative reflectance was 99% when ultraviolet light was sufficiently irradiated as the light 7 to bring the dye molecule into a closed state. Therefore, in this optical recording medium 1, a change in reflectance of about 1% occurs due to recording.

Next, as shown in FIG. 4, a DC power supply 8 and an ammeter 9 were connected between the electrode layer 3 of the optical recording medium 1 and the translucent electrode layer 10. The positive electrode of the power supply 8 was connected to the electrode layer 3, and the negative electrode of the power supply 8 was connected to the translucent electrode layer 10, and a voltage of 10 V was applied. In this state, no current flows unless light 7 is incident. Next, He 7 is applied to the information recording layer 4 in the closed state as light 7.
When red laser light from a Ne laser was condensed on a spot of about 1 micron and irradiated with an intensity of 1 μW, a photocurrent due to carrier generation was detected at about 51 pA.

Next, after irradiating the entire surface of the information recording layer 4 with visible light to bring the molecules in the information recording layer into a ring-open state, a HeNe laser was irradiated in the same manner as described above, and photocurrent detection was attempted. No current was detected.

From the above, a photocurrent is detected when light absorption by a dye molecule occurs in a closed state of a molecule, but a photocurrent is detected when light absorption does not occur in a molecule in an open state. It turns out that it is not done. Shot noise current I _sn for the signal current I _s can be calculated using the following equation.

[0057]

(Equation 1)

[0058] (where, e is the elementary charge, W is 1MHz to that assumed in the bandwidth) from the above equation, the shot noise current I _sn for the signal current _{I S = 51 (pA) 2} . 8 (pA). Therefore, the shot noise limit SN ratio is about 25 dB.

On the other hand, when the same optical recording medium is reproduced by detecting a change in reflectance, the efficiency of detecting reflected light on the optical recording medium is 0.3, and the light-current conversion efficiency of the detector is 0.
Assuming 4 A / W, the signal current is 1.2 nA and the shot noise current is 140 pA. Therefore, the SN ratio is 19 dB.

As is clear from the above results, according to the method of detecting and reproducing the photocurrent, a higher SN ratio can be obtained than in the case of detecting and reproducing the change in reflectance which is usually performed. FIG. 6 is a diagram showing the relationship between the SN ratio in the photocurrent detection system and the SN ratio in the reflected light detection system and the reflectance change amount. As is clear from FIG. 6, the reflectance change amount is 4
% Or less, the photocurrent detection method shows a higher SN ratio.

Next, the effect of non-destructive reading according to the first aspect of the present invention will be described. As an optical recording medium,
The same thing as the above was used. The optical recording medium is sufficiently irradiated with ultraviolet light from the translucent electrode layer side in advance to bring the optical recording medium into a closed state, and the voltage of 633 nm from the HeNe laser is applied without applying a voltage to the information recording layer. Pulse irradiation (10 ^-4 J / cm ² per pulse) was performed at 100 msec and irradiation area of about 1 cm ² at 10 mW, and the change in reflectance was examined.
As a result, about 10,000 pulse irradiations (total irradiation energy 1
J / cm ² ), the relative reflectance is 99% to 99.5%.
And changed about 0.5%. This is because photochromic isomerization accompanying the photoreaction proceeded and the ring-closed molecule changed to the ring-opened state. Therefore, it is understood that the recording state is partially destroyed.

Next, as shown in FIG.
The same experiment as above was performed while connecting a negative electrode to the electrode layer and connecting a positive electrode to the electrode layer 3 and applying a voltage of 10 V.
The reflectance did not change even after 1 million pulse irradiations. Therefore, it can be seen that the recording state is not destroyed and non-destructive reading is possible.

Next, light having a wavelength of 633 nm was condensed to a diameter of about 1 μm at a power intensity of 1 μW and a voltage was applied in the same manner as described above at the time of the first pulse irradiation to detect a photocurrent. However, it was about 50 pA. Next, pulse irradiation was performed 10,000 times without applying a voltage, and the photocurrent was detected with the voltage applied again. As a result, the current value was 10 pA. Therefore, the current value was reduced to about 1/5.

Next, after the pulse irradiation (total irradiation energy 10 ⁴ J / cm ² ) was performed 10,000 times in the same manner as described above except that a voltage of 10 V was applied, the photocurrent was detected.
The current value obtained by the photocurrent detection hardly changed.

From the above, it can be seen that the non-destructive readout is possible according to the photocurrent detection / reproduction method, similarly to the reproduction method in which the above-mentioned voltage is applied and the reflectance is detected.
FIG. 1 is a schematic diagram showing an example of an optical recording medium reproducing device according to the first aspect of the present invention. In FIG. 1, an optical recording medium 1 is configured by laminating an electrode layer 3 and an information recording layer 4 on a substrate 2. The electrode layer 3 is made of, for example, Ag
Can be formed by vacuum evaporation. The information recording layer 4 can be formed by vacuum-depositing a photochromic material.

The probe 5 is provided with a minute aperture 5a having a size smaller than the diffraction limit of light. Light 7 is introduced into the probe 5 from the outside, and the information recording layer 4 of the optical recording medium 1 is irradiated with evanescent light 7a leaking from the minute opening 5a. Light for recording is used for information recording, light for reproduction is used for reproduction, and light for erasure is used for erasure. Reproduction will be described here.

A probe electrode 6 is provided on the outer peripheral surface of the tip of the probe 5. The probe electrode 6 is, for example, Al
It can be formed by layers. A DC power supply 8 is connected to the probe electrode 6 and the electrode layer 3 of the optical recording medium 1, a cathode is connected to the probe electrode 6, and a positive electrode is connected to the electrode layer 3. An ammeter 9 is connected to detect the value of the current flowing between them.

Normally, the distance between the tip of the probe 5 and the information recording layer 4 is maintained at a distance of several tens to several hundreds of degrees, but may be in a contact state. The irradiation of the evanescent light 7a excites the dye molecules in the information recording layer 4 and separates them into holes and electrons. Since a voltage is applied between the probe electrode 6 and the electrode layer 3, the electrons thus generated are absorbed by the electrode layer 3 connected to the positive electrode, while the holes are formed on the surface of the information recording layer 4. Stored. The holes are eliminated by electrons flowing from the probe electrode 6 as a tunnel current. As a result, the photocurrent generated in the information recording layer 4 is
It is taken out as an external current and a reproduced signal can be obtained.

The above-described reproducing apparatus is merely an embodiment of the present invention, and various modifications are possible. For example, a metal other than aluminum can be used as a material for the probe electrode. In addition, the probe 5 is not limited to a type that introduces light from the outside, and may be, for example, a type in which a minute opening is provided in a surface emitting laser. In this case, the probe electrode is formed around the minute opening.

Further, a light-transmitting and conductive thin film may be provided on the surface of the optical recording medium. Such a translucent conductive thin film is formed to have a thickness sufficiently smaller than the distance between the probe and the optical recording medium.

FIG. 7 is a schematic diagram showing another example of the reproducing apparatus according to the first aspect of the present invention. The optical recording medium 1 is configured in the same manner as described above. In the embodiment shown in FIG.
Near-field light (evanescent light) is used as the reproduction light. In the reproduction apparatus of this embodiment, the laser beam 12 condensed to the diffraction limit using the condensing lens 13 is used as in the ordinary optical disk system. ing. In the laser beam 12, a metal probe electrode 11 having a very sharp tip is provided. A DC power supply 8 is connected to the probe electrode 11 and the electrode layer 3 of the optical recording medium 1. A negative electrode is connected to the probe electrode 11, and a positive electrode is connected to the electrode layer 3.

As shown in FIG. 8, a strong electric field is applied between the tip of the probe electrode 11 and the electrode layer 3, whereby an electric field is applied to the information recording layer 4. The carriers generated from the excited molecules due to the light absorption are taken out of the optical recording medium 1 and detected as a reproduced signal according to the same principle as in the above embodiment.

In this embodiment, the area to be reproduced is limited by the tip of the probe electrode 11. In the embodiment shown in FIG. 1, the area to be reproduced by the evanescent light from the minute opening is limited.
It has a diameter of about 00 nm. Therefore, it is not possible to reproduce the data in a limited area of 100 nm or less. In the present embodiment, the area to be reproduced is limited by the tip of the probe electrode 11, so that it is possible to read a recording mark of about 10 nm or less. In addition, since evanescent light is not used, irradiation can be performed with a high light intensity, and a higher SN ratio can be expected.

In this embodiment, since the carriers are not separated in the area other than the tip of the probe electrode 11, a photoreaction occurs in the light-irradiated area other than the tip of the probe electrode 11. Records may be destroyed.
To avoid this, for example, a photochromic material having a photoreaction having a thermal threshold may be used as the organic dye contained in the information recording layer.

FIG. 16 is a schematic diagram showing still another example of the reproducing apparatus according to the first aspect of the present invention. In this embodiment, the electrode layer 3 is provided on the light incident side with respect to the information recording layer 4. The electrode layer 3 is formed of a translucent material such as ITO. The probe 11 is provided on the information recording layer 4 on the side opposite to the light incident side. Even in such a configuration, a reproduced signal can be detected based on the same principle as that of the reproducing apparatus shown in FIG.

FIG. 9 is a schematic diagram showing still another example of the reproducing apparatus according to the first aspect of the present invention. In this embodiment,
A plurality of probe electrodes 11 are provided. A DC power supply 8 and an ammeter 9 are connected between each probe electrode 11 and the electrode layer 3, and a voltage is separately applied at the tip of each probe electrode 11. By providing a plurality of probe electrodes 11 in parallel in such a manner, a plurality of areas can be reproduced simultaneously, and a low transfer speed, which is a problem in probe-type optical recording, can be improved.

FIG. 12 is a schematic sectional view showing an optical recording medium of one embodiment according to the second aspect of the present invention. The optical recording medium 20 is formed by stacking a light-transmitting electrode layer 25, a hole transport layer 24, an information recording layer 23, a light absorbing layer 22, and an electrode layer 21 on a substrate 26. In this embodiment, a glass substrate is used as the substrate 26. The translucent electrode layer 25 is formed of a transparent conductive film made of ITO. The hole transport layer 24 has an α-NP expressed by the following equation:
B, that is, N, N'-di (naphthalen-1-yl)-
It is formed by depositing N, N′-diphenyl-benzidine to a thickness of 200 ° by a vacuum evaporation method.

[0078]

Embedded image The information recording layer 23 is made of a diarylethene-based organic dye having a structure represented by the following formula, and has a film thickness of 10 by a vacuum evaporation method.
It is formed so as to be 0 °.

[0079]

Embedded image

FIG. 13 shows the absorption spectrum of the diarylethene organic dye. As shown in FIG. 13, the ring-opened molecule 1A has absorption in the infrared region, and the ring-closed molecule 1B has absorption also in the red wavelength region. Therefore, for example, in recording information, after the entire surface of the optical recording medium is closed, light of 635 nm wavelength is irradiated to form an open region in the information recording layer of the optical recording medium by photoisomerization reaction. Can be performed.

The light absorbing layer 22 is formed by depositing a phthalocyanine dye to a thickness of 200 ° by a vacuum evaporation method. The electrode layer 21 is formed by depositing metallic magnesium on the light absorbing layer 22 by a vacuum evaporation method to a thickness of 1000 Å.
It is formed by depositing such that

The ionization potential of the ring-opened molecule 1A of the diarylethene-based organic dye used in the information recording layer in the optical recording medium of this embodiment is 6.2 eV or more, and the ionization potential of the ring-closed molecule 1B is not less than 6.2 eV. 5.82 eV. Therefore, the organic dye is a dye in which the molecular structure changes between a ring-opened state and a ring-closed state by a photochromic photoisomerization reaction, and the level of the ionization potential of the molecule changes greatly. The phthalocyanine dye used for the light absorption layer 22 has an absorption of 800 nm for both the ring-opened molecule 1A and the ring-closed molecule 1B.
It has substantially no absorption in the near infrared wavelength region. Therefore, almost complete nondestructive reading can be realized by using infrared light as reproduction light.

With respect to the optical recording medium, detection of photocurrent by irradiation of reproduction light was confirmed as follows. First, as shown in FIG. 12, a DC power supply 8 and an ammeter 9 were connected between the electrode layer 21 and the translucent electrode layer 25 of the optical recording medium 20. The positive electrode of the power supply 8 was connected to the electrode layer 21 and the negative electrode of the power supply 8 was connected to the translucent electrode layer 25, and a voltage of 10 V was applied. The information recording layer 23 was irradiated with ultraviolet light in advance to bring the entire surface of the optical recording medium into a closed state. Next, as shown in FIG. 12, an infrared laser beam 7 (wavelength 780 nm) from a semiconductor laser is focused on a spot of about 1 μm, and the intensity is 1.5 μW.
Irradiation, the photocurrent due to carrier generation is about 0.
5 μA was detected.

Next, after irradiating the entire surface of the optical recording medium with visible light to bring the photochromic molecules in the information recording layer 23 into the ring-opened state, the infrared laser light 7 from the semiconductor laser is similarly irradiated and irradiated with light. When current detection was attempted, no current was detected.

As described above, according to the second aspect of the present invention, the light absorbing layer is provided, and the electric carrier generated in the light absorbing layer by irradiating the reproduction light is detected. It is possible to know the state of the molecular structure of the organic dye in the information recording layer provided in the passage, and to detect the information recorded in the information recording layer. Further, according to the second aspect of the present invention, a dye layer having high carrier generation efficiency can be used as a light absorbing layer separately from the information recording layer, so that a large photocurrent can be obtained and a high SN ratio can be obtained. Can be obtained.

Further, by using light having a wavelength at which the organic dye in the information recording layer does not absorb light as reproduction light, reproduction can be performed without causing photoisomerization of the organic dye in the information recording layer. Therefore, complete non-destructive reading is possible.

In the optical recording medium shown in FIG. 12, the hole transport layer 24 is provided, but as described above, the hole transport layer is not an essential component in the present invention. Further, although the translucent electrode layer 25 is provided, a probe electrode or the like may be used instead of such an electrode as in the first aspect of the present invention.

Further, it has been confirmed that even when a diarylethene dye having the structure shown in FIG. 5 is used as the organic dye in the information recording layer, the reproduction can be performed by the reproducing method according to the second aspect of the present invention. The structural formula of the diarylethene dye shown in FIG. 5 is shown below again.

[0089]

Embedded image

This diarylethene compound has an ionization potential of 5.8 eV in the ring-closed state and 6.2 eV or more in the ring-opened state. Therefore, the level of the ionization potential changes greatly between the ring-opening state and the ring-closing state. As the diarylethene-based compound in which the level of the ionization potential changes greatly between the ring-opened state and the ring-closed state, a compound represented by the following formula is also exemplified.

[0091]

Embedded image

This diarylethene compound has an ionization potential of 5.7 eV in a ring-closed state and 6.2 eV or more in a ring-opened state. Since this compound has a hole transporting triphenylamino group bonded to an aryl group, it is a suitable compound when utilizing the carrier transporting property of a molecule as in the present invention. Further, as compared with the two kinds of diarylethene-based compounds shown in the above (Chemical Formula 2) and (Chemical Formula 3), the ring-opening reaction proceeds with high sensitivity, and is therefore a desirable material for achieving a higher transfer rate. The absorbance of this compound is shown in FIG.

Each of the playback devices shown in FIGS. 1, 7, 9 and 16 has been described as a playback device according to the first aspect of the present invention. It can also be used as a playback device according to an aspect. In this case, the optical recording medium shown in these drawings has a structure in which a light absorbing layer is provided between the electrode layer 3 and the information recording layer 4. In order to prevent the information recording layer from being exposed to the outside in the optical recording medium, a protective layer may be provided thereon. The hole transport layer described above may be provided as such a protective layer.

FIG. 14 is a perspective view showing an example of a reproducing head that can be used in the first and second aspects of the present invention. The slider 31 that scans on the optical recording medium,
The semiconductor laser chip 32 is mounted on the side surface 31 a of the slider 31, which is supported by the gimbal 30. Side surface 31a around semiconductor laser chip 32
The wiring 33 is formed thereon.

FIG. 15 is a side view showing a state where the reproducing head shown in FIG. 14 scans on the optical recording medium. As shown in FIG. 15, from the semiconductor laser chip 32,
The laser light 35 is directly applied to the optical recording medium 34 without passing through an optical system such as a lens. Semiconductor laser chip 3
A plurality of wirings 33 are formed around the area 2, and in the irradiation area of the laser light 35, these wirings 33 extend toward the optical recording medium 34, and a probe electrode 33 a having a sharp tip is formed. Have been. The wiring 33 can be formed by, for example, a photolithography method. The wiring 33 is connected to a DC power supply, and a voltage is applied to the probe electrode 33a. Since a plurality of probe electrodes 33a are provided, a plurality of recording areas can be reproduced simultaneously, similarly to the reproducing apparatus shown in FIG.
For this reason, the transfer speed can be improved. In addition,
The probe electrode 33a may be single.

The laser beam 35 emitted from the semiconductor laser chip 32 is not spread so much because the distance to the optical recording medium 34 is short, and reaches the optical recording medium 34 with a spot within about several microns. High light density is obtained. Therefore, the absolute value of the photocurrent is also increased, and a higher SN ratio can be obtained.

Since the reproducing head shown in FIGS. 14 and 15 scans while sliding on the optical recording medium, the distance between the probe electrode and the optical recording medium is automatically maintained. It should be noted that the same slider may be equipped with an information recording function and an information erasing function at the same time, and may be used as a recording and reproducing head.

[0098]

According to the first aspect of the present invention, non-destructive reading can be performed. Even when near-field light (evanescent light) is used as the reproduction light, reproduction can be performed with a high SN ratio. Further, information recorded on the optical recording medium can be detected and reproduced by a novel method.

According to the second aspect of the present invention, a light absorbing layer which generates electric carriers by absorbing reproduction light is provided, and information is reproduced by detecting electric carriers from the light absorbing layer. . Therefore, a material having high carrier generation efficiency can be used for the light absorbing layer, and reproduction can be performed at a high SN ratio. Further, by using a wavelength that is not substantially absorbed by the organic dye of the information recording layer as a wavelength of the reproduction light, more complete nondestructive reading can be performed. Further, the information recorded on the optical recording medium can be detected and reproduced by a novel method different from the first aspect of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a reproducing apparatus according to the present invention.

FIG. 2 is a diagram for explaining a process until a photochromic dye molecule A is excited by light absorption and deactivated.

FIG. 3 is a view for explaining the principle of nondestructive readout according to the first aspect of the present invention.

FIG. 4 is a schematic sectional view showing an optical recording medium according to one embodiment according to the first aspect of the present invention.

FIG. 5 is a diagram showing the structure of a photochromic material used in an example of the present invention and its absorbance.

FIG. 6 is a diagram showing the relationship between the SN ratio and the amount of change in reflectance by the photocurrent detection method according to the present invention.

FIG. 7 is a schematic diagram showing another example of the playback device according to the present invention.

FIG. 8 is a schematic diagram for explaining a playback principle in the playback device shown in FIG. 7;

FIG. 9 is a schematic diagram showing still another example of the playback device according to the present invention.

FIG. 10 is a schematic diagram for explaining the principle of the reproducing method according to the second aspect of the present invention.

FIG. 11 is a schematic diagram for explaining the principle of the reproducing method according to the second aspect of the present invention.

FIG. 12 is a schematic sectional view showing an optical recording medium according to an example according to a second aspect of the present invention.

FIG. 13 is a graph showing the absorbance of a photochromic material used in an example of the present invention.

FIG. 14 is a perspective view showing an example of a reproducing head according to the present invention.

FIG. 15 is a side view showing the arrangement of the reproducing head and the optical recording medium shown in FIG. 14;

FIG. 16 is a schematic diagram showing still another example of the playback device according to the present invention.

FIG. 17 is a diagram showing the absorbance of a photochromic material that can be used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical recording medium 2 ... Substrate 3 ... Electrode layer 4 ... Information recording layer 5 ... Probe 5a ... Micro opening of probe 6 ... Probe electrode 7 ... Light 7a ... Evanescent light 8 ... DC power supply 9 ... Ammeter 10 ... Light transmission Transparent electrode layer 11 Metal probe electrode 12 Laser beam 13 Condensing lens 20 Optical recording medium 21 Electrode layer 22 Light absorbing layer 23 Information recording layer 24 Hole transport layer 25 Translucent electrode layer 26 ... Substrate 30 ... Gimbal 31 ... Slider 32 ... Semiconductor laser chip 33 ... Wiring 33a ... Probe electrode 34 ... Optical recording medium 35 ... Laser light

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/24 522 G11B 7/24 522A 538 538A F-term (Reference) 2H123 AA00 AA08 5D029 HA01 JA04 JC09 MA04 5D090 AA01 BB20 CC04 EE11 5D119 AA09 BA01 BB06 DA05 MA06 MA30

Claims (26)

[Claims] 1. An optical recording medium from which information is reproduced by light irradiation, comprising: an information recording layer containing an organic dye whose molecular structure changes reversibly in a photon mode; and applying a voltage to the information recording layer. Recording medium provided with an electrode layer for the optical recording medium. 2. The optical recording medium according to claim 1, wherein the electrode layer is provided on a side opposite to a light incident side with respect to the information recording layer. 3. The optical recording medium according to claim 1, wherein the electrode layer is provided on a light incident side with respect to the information recording layer, and is made of a translucent material. 4. A light absorbing layer which generates electric carriers by absorbing reproduction light, wherein the electric carriers generated in the light absorbing layer are transmitted through the information recording layer by applying the voltage. The light absorbing layer is disposed as described above, and a change in a molecular structure of the organic dye in the information recording layer changes a conduction characteristic of the electric carrier passing through the information recording layer.
The optical recording medium according to any one of claims 1 to 3, wherein 5. An optical recording medium from which information is reproduced by light irradiation, comprising: an information recording layer containing an organic dye whose molecular structure is reversibly changed in a photon mode; Wherein the light absorbing layer is arranged such that the electric carriers generated in the light absorbing layer are conducted through the information recording layer by applying a voltage, and the information recording is performed. An optical recording medium in which the conductivity of the electric carrier passing through the information recording layer changes due to a change in the molecular structure of the organic dye in the layer. 6. The optical recording medium according to claim 4, wherein the wavelength of the reproduction light is a wavelength that is not substantially absorbed by the organic dye of the information recording layer. 7. The optical recording medium according to claim 5, further comprising an electrode layer for applying the voltage to the light absorbing layer. 8. The device according to claim 7, wherein the electrode layer is provided on a side opposite to a light incident side with respect to the light absorbing layer.
An optical recording medium according to claim 1. 9. When reproducing the optical recording medium, an external voltage applying means is arranged on a light incident side or a side opposite to the light incident side of the information recording layer or the light absorbing layer. 9. The optical recording medium according to claim 1, wherein the voltage is applied to an electrode layer. 10. The optical recording medium further comprises a light-transmitting electrode layer provided on a light incident side of the information recording layer or the light absorbing layer, wherein a light-transmitting electrode layer is provided between the light-transmitting electrode layer and the electrode layer. 3. The method according to claim 1, wherein the voltage is applied.
9. The optical recording medium according to 3, 4, 7, or 8. 11. The optical recording medium according to claim 1, wherein light irradiated during reproduction is near-field light. 12. A method of reproducing information by irradiating reproduction light to an optical recording medium having an information recording layer containing an organic dye whose molecular structure reversibly changes in a photon mode. And applying a voltage to separate holes and electrons from excited molecules of the organic dye in the information recording layer generated by absorption of the reproduction light. 13. The information recorded on the optical recording medium is reproduced by detecting a charge generated by applying a voltage to the information recording layer to the outside as a current and detecting the electric current. 13. The method for reproducing an optical recording medium according to item 12. 14. The optical recording medium according to claim 1,2,3,
The method for reproducing an optical recording medium according to claim 12, wherein the method is an optical recording medium according to claim 9. 15. Reproduction light is applied to an optical recording medium including an information recording layer containing an organic dye whose molecular structure is reversibly changed in a photon mode, and a light absorption layer that generates electric carriers by absorbing the reproduction light. In the method of reproducing information by irradiating, irradiating the light absorbing layer with reproducing light and applying a voltage, the electric carriers generated in the light absorbing layer by the absorption of the reproducing light are conducted through the information recording layer. The information recorded on the optical recording medium is reproduced by extracting the conduction characteristic of the electric carrier, which changes due to a change in the molecular structure of the organic dye in the information recording layer, to the outside as a current and detecting it. A method for reproducing an optical recording medium, comprising: 16. The reproducing method for an optical recording medium according to claim 15, wherein the wavelength of the reproduction light is a wavelength that is not substantially absorbed by the organic dye of the information recording layer. 17. The reproducing method for an optical recording medium according to claim 15, wherein the optical recording medium is the optical recording medium according to any one of claims 4 to 10. 18. The reproducing method for an optical recording medium according to claim 12, wherein the reproducing light is near-field light. 19. An apparatus for reproducing information by irradiating reproduction light to an optical recording medium having an information recording layer containing an organic dye whose molecular structure is reversibly changed in a photon mode, wherein the information recording is performed. An apparatus for reproducing an optical recording medium, comprising: means for irradiating a layer with reproduction light; and means for applying a voltage to the information recording layer irradiated with the reproduction light. 20. Reproducing light to an optical recording medium comprising an information recording layer containing an organic dye whose molecular structure is reversibly changed in a photon mode and a light absorbing layer which generates electric carriers by absorbing the reproducing light. An apparatus for irradiating and reproducing information, comprising: means for irradiating the light absorption layer with reproduction light; and means for applying a voltage to the light absorption layer irradiated with the reproduction light. Playback device. 21. The apparatus according to claim 19, further comprising means for extracting a charge generated by applying a voltage to the information recording layer or the light absorbing layer to the outside as a current and detecting the current. An apparatus for reproducing an optical recording medium. 22. The optical recording medium reproducing apparatus according to claim 19, wherein said reproducing light irradiating means is means for irradiating near-field light. 23. The apparatus according to claim 19, wherein said voltage applying means and / or said detecting means includes a probe electrode disposed on a light incident side of said information recording layer or said light absorbing layer. The reproducing apparatus for an optical recording medium according to claim 1. 24. The probe electrode according to claim 2, wherein the probe electrode is a wiring formed on a mounting side surface of a slider on which a semiconductor laser chip as a reproducing light irradiation unit is mounted.
4. The reproducing apparatus for an optical recording medium according to 3. 25. The optical recording medium according to claim 1,
The optical recording medium according to claim 19, wherein the optical recording medium is the optical recording medium according to claim 9. 26. The optical recording medium according to claim 20, wherein the optical recording medium is the optical recording medium according to any one of claims 4 to 10. Playback device.