JP2002288840A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium, in which information is recorded as a hologram, in which the time required for recording is short, and in which diffraction efficiency is large. SOLUTION: The hologram recording medium includes a recording layer, which has a charge generating agent generating a charge by irradiation with visible light, a charge transfer agent transferring the charge, a non-linear optical material, and a trap agent holding the charge, and on which information is recorded by forming interference fringes by the irradiation of the visible light. It is characterized that the trap agent holding the charge consists of molecules whose charge transferring characteristic is modulated by absorption of the visible light, and that a mean free path of the charge in the hologram medium is increased by the irritation with the visible light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording medium, and more particularly, to an optical recording medium having a recording layer in which an internal electric field is formed by light irradiation.

[0002]

2. Description of the Related Art An optical recording medium is known as a medium on which large-capacity data such as a high-density image can be recorded. Conventionally, as an optical recording medium, a magneto-optical recording medium, an optical phase change type medium, and the like have been developed, but the demand for a higher density of information recordable on the optical recording medium is increasing.

A holographic memory has been known as a recording medium for realizing a high-density information recorded on such an optical recording medium. In this method, page data in which light intensity and its phase are two-dimensionally distributed interfere with reference light and are recorded in a recording layer in the form of a hologram. In a holographic memory, a large number of holograms are recorded in an overlapping region by making the recording layer thick and slightly changing the incident angle of the reference light and the recording position.

As a recording medium for such a holographic memory, an inorganic substance has been studied so far, but recently, an organic material has been developed for reasons such as the production of crystalline materials and the difficulty of controlling characteristics. The development of photorefractive media using molecular compounds has been active (for example, JP-A-9-22034). Further, for example, JP-A-6-175167, JP-A-6-23
JP-A-5809 and JP-A-6-235949 describe photoreactive polymers.

In these media, information is recorded and reproduced as shown in FIG. That is, the recording layer 2
Is irradiated with a laser beam to record information. At this time, transparent electrodes 1 and 3 may be provided at both ends of the recording layer 2 to perform recording while applying a voltage between the electrodes. The laser light is divided into a signal light 4 and a reference light 5 which contain information in the form of spatial intensity distribution and phase distribution. The two lights interfere with each other in the recording layer, and the information is formed in the form of interference fringes. Be recorded. 2
After blocking the two lights, by irradiating the recording layer 2 with the reference light 5 under the same conditions as when recording, the reproduction light 6 having the same spatial characteristics as the signal light is reproduced. Information can be reproduced by detecting the intensity distribution and the phase distribution of the reproduction light 6.

[0006] The photorefractive material generates electric charges by irradiating light, and separates them spatially.
It is a material whose refractive index changes depending on the internal electric field determined by the resulting charge distribution. When light that can interfere with each other is irradiated into a photorefractive medium in which this material is applied to a recording layer of an optical recording medium, the intensity pattern of the irradiated light is recorded as a change in the refractive index in the recording layer. . That is, the intensity distribution and / or the phase distribution of the signal light 4 are recorded on the recording layer in the form of a hologram.

[0007] The principle of redistributing the charge generated by light irradiation consists of two parts: charge transport and charge retention.
That is, the charge transport agent transports the photo-generated charge by drift due to an external electric field and hopping conduction due to diffusion. Further, the trapping agent captures the charge transported by the charge transporting agent. At this time, the probability of the charge hopping from the trapping agent to the charge transporting agent needs to be smaller than the probability of hopping from the charge transporting agent to the trapping agent. To achieve this, the energy difference between the electron orbits of the charge transporting agent and the trapping agent has generally been used. The electron trajectory to be compared here is, as shown in FIG. 2A, the HOMO (Hi
gest Occluded Molecular
Orbital), and when electrons are transported,
As shown in FIG. 2B, LUMO (Lowest
Unocculed Molecular Orbi
tal).

However, if the amount of dispersion of the trapping agent is reduced so that the charge is easily transported, the charge is not trapped by the trapping agent unless it is transported over a long distance, and it takes much time until the charge is trapped. Cost.
That is, the response time of recording becomes slow. Conversely, when the amount of dispersion of the trapping agent is increased, the charge is immediately captured by the trapping agent, so that the mobility of the charge is reduced and the separation of electrons and holes is not performed quickly. Therefore, there is a problem that carrier generation efficiency is reduced. That is, at this time, the photorefractive effect does not occur.

On the other hand, as an optical recording medium using a photochromic medium exhibiting a change in absorption due to light irradiation, for example, “Chemistry of Organic Photochromism”, Quarterly Chemistry Review No.
28 (1996) is known. Spiropyran has been the photochromic molecule that has been studied for the longest time, but this molecule could not be used as an optical recording medium because of its poor ring-opening thermal stability. In addition to poor thermal stability, many photochromic materials have various problems. Specifically, it is necessary to irradiate short-wavelength light that has no repetition resistance and is hard to oscillate with a semiconductor laser to show a structural change. In order to solve these problems, various molecules have been synthesized, and molecules can be designed so as to exhibit a structural change at an arbitrary wavelength.
However, such a molecule has a problem that the efficiency of showing a structural change is low and it takes time to record.

As a recording medium using such photochromic molecules, there are many such media as a CD or DVD having a photochromic layer of 1 μm or less. The thickness of the recording layer is 1μ
If it is less than m, a plurality of holograms cannot be multiplexly recorded in the overlapping area, so that the capacity as an optical recording medium cannot be increased. As an optical recording medium using other photochromic molecules, for example, US Pat. No. 5,496,670 discloses an optical recording medium in which bacteriorhodopsin having heat stability is dispersed in polyvinyl alcohol. Describes a multiplex recording medium for recording bit data by using two-photon absorption in an arbitrary area in the above. However, in order to use such an optical recording medium as a hologram recording medium,
The hologram cannot be recorded unless the light from the two light sources is incident simultaneously or the laser light intensity is extremely high. In addition, S.I. H. Lin et al. Optics
Letters vol. 25, pp. 451-453
The optical recording medium disclosed in (2000) is a medium on which a hologram is recorded by utilizing the fact that monomer molecules are polymerized by light irradiation. In such a medium, due to the difference in volume between the monomer state and the polymer state, information recording causes unevenness in the optical recording medium, and the unevenness scatters light. For this reason, it has been difficult to increase the number of pixels per hologram and achieve a high capacity.

[0011] Examples of a substance that changes optical characteristics by applying an electric field include “Electrochr.
omism "(PMS Monk et al. e.
d. , VCH Weinheim, (1995)) discloses a polyaniline film. In this film, it has been observed that the absorption spectrum changes according to the applied external electric field. However, this film cannot form an electric field according to the light intensity distribution, and therefore cannot record a hologram.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical recording medium on which information is recorded as a hologram, wherein the recording time is short and the diffraction efficiency is high. .

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a charge generating agent that generates a charge by irradiation with visible light, a charge transporting agent that transfers a charge, a nonlinear optical material, A hologram recording medium comprising a recording layer for recording information by forming interference fringes by irradiating visible light, wherein the trapping agent for retaining the electric charge absorbs the visible light. An optical recording medium comprising molecules whose charge transport characteristics are modulated, and wherein the mean free path of the charges in the hologram medium is increased by the irradiation of the visible light.

The charge retaining trapping agent is preferably a photochromic molecule. Further, the content of the trapping agent is preferably 1% by weight or more and 20% by weight or less based on the recording layer.

It is preferable that the charge retaining trapping agent is a photochromic molecule exhibiting a cis-trans type structural change.

According to the present invention, there is further provided a charge generating agent for generating a charge upon irradiation with visible light, a charge transporting agent for transferring a charge,
A hologram recording medium comprising a nonlinear optical material, a trapping agent that retains electric charge, and a dye, and a recording layer that records information by forming interference fringes by irradiation with visible light, wherein the dye is An optical recording medium comprising a molecule whose dipole moment increases when excited by absorbing visible light, and wherein the mean free path of the electric charge in the hologram medium is increased by irradiation of the visible light. I do.

Preferably, the trapping agent is an electrochromic molecule, and the charge transporting property is increased by an electric field generated by the dipole moment of the excited dye.

It is preferable that the content of the dye is 0.1% by weight or more and 10% by weight or less based on the recording layer.

Hereinafter, the present invention will be described in detail.

The present inventors have conducted intensive studies on the hologram recording medium, and as a result, have found the following relationship between the ratio of the content of the molecules holding the charges and the content of the molecules transporting the charges and the distance at which the charges are transported. We focused on the existence of such a relationship. That is, when the amount of the charge-retaining molecule is smaller than that of the charge-transporting molecule, the distance over which the charge is transported is much longer than the distance between the interference fringes. On the other hand, when a large number of molecules retaining charges are present relative to molecules transporting charges, no carriers are generated. In order to solve this problem, the inventors of the present invention have focused on the fact that photochromic molecules change their charge transporting properties when photoisomerized, and have made the present invention. In addition, the present invention has been achieved by paying attention to the fact that the charge transporting property of the charge hopping-conducted in the polymer depends on the local electric field.

In a hologram recording medium for recording information in the form of interference fringes, in order to increase the response speed of recording, it is ideal that the charge transport characteristics locally differ in the optical recording medium. This is explained as follows. The carrier generation efficiency of the charge generating agent increases when the generated charges are easily transported. Therefore, if the charge is easy to be transported in the region where the light intensity of the interference fringe is high, and the charge is difficult to be transported in the region where the light intensity is low, the carrier is selectively generated in the region where the light intensity is high. The charges generated in the region where the light intensity is high are easily transported. However, when the charge reaches the region where the light intensity is low, the charge is difficult to be transported, so that the charges are not further transported. In other words, the charge photo-generated in the region of high light intensity is transported to an adjacent region of low light intensity and is retained there. Therefore, the charge is held after being transported substantially by the interval of the interference fringes, so that the distance over which the charge is transported is reduced. For this reason, the response time of recording is shortened.

On the other hand, in such a situation, the diffraction efficiency per charge also increases. This is explained as follows with reference to FIG. 3. FIG. 3 shows the relationship between the position and the density distribution when the charge that can be transported is a hole. The same is true when is an electron.

When the transport properties of holes are uniform in the medium, holes and electrons are separated in a region where the light intensity is high.
At this time, FIG.
It is represented by the curve a2 in (a). Although not shown,
The density distribution of the generated holes is the same as the electron density distribution.
When electrons are not transported and holes are transported, the hole density distribution eventually becomes almost uniform as shown by the curve a1 in FIG. Therefore, the density distribution of the total charge including the contribution of electrons and holes is represented by a curve a in FIG.
As shown in FIG. That is, when the amplitude of the density distribution of holes and electrons generated initially is [rho ₀ is the amplitude [rho _0/2
A spatial distribution of the total charge with

On the other hand, in a situation where the mean free path of the charge is large where the light intensity is strong and the mean free path is small where the light intensity is weak, the charge is transferred from a place where the light intensity of the interference fringes is strong to a place where it is weak. Transported and retained.
At this time, the spatial distribution of the holes is concentrated at a place where the light intensity is weak, as shown by a curve b1 in FIG. Therefore, the density amplitude of holes and electrons generated at the beginning is ρ
If it is 0, a spatial distribution of charges having an amplitude of ρ0 occurs as represented by the curve b3. The curve b2 shows the electron density distribution inverted.

Therefore, the magnitude of the internal electric field generated under the condition of FIG. 3B is twice the magnitude of the internal electric field generated in FIG. For example, with respect to a nonlinear optical molecule having the Pockels effect, when the nonlinear optical molecule is oriented in the direction of an electric field, optical characteristics such as a refractive index and an absorption coefficient change in proportion to the absolute value of the electric field. At this time, the diffraction efficiency due to the interference fringes is proportional to the square of the change in the refractive index and the change in the absorption. Therefore, under the condition of FIG. 3B, a diffraction efficiency four times larger than that of FIG. Will be obtained. If the change in refractive index or change in absorption is proportional to higher terms of the electric field, such as in the Kerr effect, the improvement in diffraction efficiency will be greater.

Further, according to the present invention, an improvement in the recording life is expected. That is, when not irradiating light,
If the mean free path is sufficiently small, there is little probability that the charge held according to the recorded information will be transported far away when de-excitation from the trapping agent occurs. Therefore, the charge distribution generated by light irradiation does not change significantly.

In the optical recording medium according to one embodiment of the present invention, a specific trapping agent is blended so that the mean free path of the charge is large where the light intensity is high and the mean free path of the charge is small where the light intensity is low. did. In particular,
The trapping agent is made of a molecule that absorbs visible light and increases the charge transporting property, and it is particularly preferable to use a structural change of the photochromic molecule. By dispersing photochromic molecules having sensitivity to visible light, which is recording light, in the recording layer, the photochromic molecules selectively change their structure only in a region where the light intensity is high. As a result, the charge transport properties of the photochromic molecule increase. Therefore,
The mean free path of the charge in the recording layer can be modulated by the intensity of the light intensity.

The photochromic molecule used in the present invention has no thermal stability and immediately after stopping light irradiation,
You may return to the structure before light irradiation. Photochromic molecules are required to exhibit structural changes only when irradiated with light. In the present invention, it is not necessary to use a thermally stable molecule as the photochromic molecule, and it is possible to select a molecule that changes the structure efficiently. When a photochromic molecule having thermal stability is added, the state before the light irradiation may be restored by irradiating light having a wavelength different from the wavelength of the recording light.

In the optical recording medium according to another aspect of the present invention, the photoexcited dye has a large mean free path at a high light intensity and a small mean free path at a low light intensity. The dipole moment was used. That is, a dye having sensitivity to visible light as recording light is selectively excited at a place where the light intensity is strong.
As the dye, a dye whose dipole moment increases when excited is used. Literature (Hirao, Nishizawa,
“Physical Review vol. B56,
pp. R2904 to R2907 (1997) ", the transport characteristics of charge hopping conduction in an organic substance are as follows.
It varies greatly depending on the magnitude of the local electric field. Therefore, due to the large dipole moment of the excited dye,
The mean free path of the charge is selectively increased in a region where the light intensity is high. Alternatively, molecules exhibiting electrochromism, such as spiropyran, change their structure depending on the magnitude of an electric field and change their charge transport properties. Therefore,
If molecules exhibiting electrochromism are dispersed in the recording layer as a trapping agent, the mean free path of charges in the recording layer can be more effectively increased.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

The charge transport agent used in the present invention
For example, a machine that transports charge by hopping conduction
Any functional material can be used. example
For example, Si, Ge, S known as an amorphous semiconductor
e, S, Te, B, As, Sb, etc.
Body, SiC, InSb, GaAs, GaSb, Cd_1-x
Ge_xAs_Two, Cd_1-xSi_xP_Two, Cd_1-xSn_xAs_Two, A
s_TwoSe_Three, As_TwoS_Three, Ge-Sb-Se, Si-Ge-
As-Te, Ge-As-Se, As_TwoSe_Three-As_TwoT
e_Three, As-Se-Te, Tl_TwoSe-As_TwoTe_Three, Cu
_1-xAu_xTe_Two, V _TwoO_Five−P_TwoO_Five, MnO-Al_TwoO_Three−
SiO_Two, V_TwoO_Five−P_TwoO_Five-BaO, CoO-Al_TwoO_Three
-SiO_Two, V_TwoO_Five-GeO_Two-BaO, FeO-Al_Two
O_Three-SiO_Two, V_TwoO_Five-PbO_Two-Fe_TwoO_Three, TiO_Two−
B_TwoO_Three-BaO, SiO_x, Al_TwoO_Three, ZrO_Two, Ta_Two
O_Three, Si_ThreeN_FourSemiconductors with irregular composition such as BN and BN
Body. Furthermore, polyacetylene, polypillow
Π conjugation such as toluene, polythiophene, and polyaniline
-Based polymers and oligomers; polysilane and polygerma
Conjugated macromolecules and oligomers such as anthracene;
Polycyclics such as pyrene, phenanthrene, and coronene
Aromatic compounds; indole, carbazole, oxazo
, Isoxazole, thiazole, imidazole,
Lazole, oxadiazole, pyrazoline, thiathiazo
And nitrogen-containing cyclic compounds such as triazole
Or a compound having these in the main chain or side chain
Compounds: hydrazone compounds, triphenylamines, tri
Phenylmethanes, butadienes, stilbenes, TC
Derivatives such as NQ, anthraquinone, diphenoquinone, C
₆₀, C ₇₀Fullerene and its derivatives
Can be

More specifically, for example, chloroanil,
Bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-tetrafluorenone, 2,4,7-trinitro-9-dicyano Methylenefluorenone, 2,4,5,7-tetranitro-xanthone, 2,4,9-trinitrothioxanthone, N,
N-bis (3,5-dimethylphenyl) -3,4,9,
10-perylenetetracarboximide, diphenone,
Examples thereof include low molecular weight compounds such as stilbenzoquinone, and high molecular weight compounds in which these compounds are introduced into the main chain or side chain of the high molecular weight compound.

The charge transporting agent is preferably used at a ratio of about 1% by weight to 70% by weight based on the entire recording layer. It is desired that the photo-generated charges hop between the charge transporting agents and eventually be trapped by the trapping agent to form an internal electric field. When the amount of the charge transporting agent is less than 1% by weight, the charge is not injected into the charge transporting agent but is deactivated in the charge generating agent, making it difficult to generate an internal electric field. On the other hand, 70% by weight
If the ratio is more than 3, the charge transporting agents may aggregate and crystallize, and it may not be possible to form an element in which different molecules are dispersed.

When two types of charges having different polarities are generated in the optical recording medium, a charge transporting agent for transporting two types of charges having different polarities can be used.
At this time, one of the charge transport agents functions as an erase charge transport agent.

As the nonlinear optical material, for example, 1) F
a substance whose absorption coefficient or reflectance changes by the ranz-Keldysh effect, 2) a substance whose absorption coefficient, refractive index or luminous efficiency changes by the exciton effect, 3) a substance whose refractive index changes by the Pockels effect, 4) excitation Examples include substances whose optical characteristics change and the life of the excited state is extended by an electric field.

Specifically, the following compounds can be used. For example, spirobenzofuran-based molecules, fulgide molecules, cyclophen molecules, diarylethene-based molecules, azobenzene-based molecules, polyacrylates or polysiloxanes having a cyanobiphenyl group containing a photochromic molecule in a polymer liquid crystal, polysiloxanes containing a spirobenzofuran group, etc. And p-azoxy ethyl benzoate, ammonium oleate, and materials exhibiting liquid crystal such as p-azoxy anneal.

Further, fine particles of the following materials can be used. For example, semiconductors having irregular structures such as Si, Ge, Se, S, Te, B, As, and Sb known as amorphous semiconductors, SiC, InSb, GaAs, and Ga
_{Sb, Cd 1-x Ge x} As 2, Cd 1-x Si x P 2, Cd 1-x
Sn _x As ₂ , As ₂ Se ₃ , As ₂ S ₃ , Ge-Sb-S
e, Si-Ge-As-Te, Ge-As-Se, As
₂ Se ₃ -As ₂ Te ₃ , As-Se-Te, Tl ₂ Se-
_{As 2 Te 3, Cu 1-} x Au x Te 2, V 2 O 5 -P 2 O 5, M
_{nO-Al 2 O 3 -SiO 2} , V 2 O 5 -P 2 O 5 -BaO,
_{CoO-Al 2 O 3 -SiO 2} , V 2 O 5 -GeO 2 -Ba
_{O, FeO-Al 2 O 3} -SiO 2, V 2 O 5 -PbO-F
_{e 2 O 3, TiO 2 -B} 2 O 3 -BaO, SiO x, Al
Semiconductors whose composition is irregular, such as ₂ O ₃ , ZrO ₂ , Ta ₂ O ₃ , Si ₃ N ₄ , and BN, are mentioned. Urea and its derivatives; thiourea and its derivatives; nitrobenzenes; carbonylbenzenes; π-conjugated benzene derivatives such as benzenesulfonates;
Oxides; pyridine derivatives such as nitropyridines;
Π-conjugated polymers and oligomers such as polyacetylene, polypyrrole, polythiophene, and polyaniline; σ-conjugated polymers and oligomers such as polysilane and polygermane; anthracene, pyrene, phenanthrene,
And polycyclic aromatic compounds such as coronene; indole,
A compound having a nitrogen-containing cyclic compound such as carbazole, oxazole, isoxazole, thiazole, imidazole, pyrazole, oxadiazole, pyrazoline, thithiazole, and triazole, or a compound having these in a main chain or a side chain; a hydrazone compound,
Derivatives such as triphenylamines, triphenylmethanes, benzeneamines, butadienes, stilbenes, orphans, imines, piperonal, TCNQ, anthraquinone, diphenoquinone; fullerenes such as C ₆₀ and C _{70 and} derivatives thereof; No.

Further, selenium and selenium alloys, Cd
Inorganic photoconductors such as S, CdSe, AsSe, ZnO and amorphous silicon; phthalocyanine dyes and pigments such as metal phthalocyanine and non-metal phthalocyanine; azo dyes such as monoazo dyes, cisazo dyes, trisazo dyes and tetrakisazo dyes, perylene dyes And pigments, indico dyes and pigments, quinacridone dyes and pigments, polycyclic quinone pigments such as anthraquinone and anthantrone, cyanine pigments such as TT
Examples thereof include a charge transfer complex composed of an electron-capturing substance and an electron-donating substance, a eutectic complex composed of a pyrylium dye and a polycarbonate resin, and an azulenium salt as known in F-TCNQ.

These materials can be used alone or in combination of two or more. It is desirable that the compounding amount is about 0.1 to 80% by weight based on the entire recording layer. If less than 0.1% by weight,
It is difficult to obtain a sufficient change in optical characteristics. on the other hand,
If the content exceeds 80% by weight, aggregation and crystallization may occur, making it impossible to form an element in which different molecules are dispersed.

In one optical recording medium of the present invention (hereinafter, referred to as a first optical recording medium), a trapping agent is blended in addition to the charge transporting agent and the nonlinear optical material.

The trapping agent used in the first optical recording medium is a molecule which absorbs visible light as recording light and whose charge transporting property is modulated by the absorption. Since such molecules are contained as a trapping agent, the mean free path of the charge in the first optical recording medium is increased by irradiating visible light. The mean free path of the charge refers to an average distance that the charge is transported on the charge transporting agent without being trapped by the trapping agent, and is preferably increased at least about twice. Such an increase in the mean free path can be measured using a method described later. In the first optical recording medium, the visible light irradiated to modulate the charge transport characteristics of the trapping agent is non-polarized,
Preferably, the light is uniform. In the case of polarized light,
If the absorption of the charge transport agent is highly dependent on the polarization direction of the light, when irradiated with polarized light, the charge transport agent will be oriented in a less light absorbing direction, thereby modulating the mean free path of the charge There is a risk. In addition, when light whose spatial intensity is largely changed is irradiated, more electric charges are generated in a region where the intensity is large, and thus the generated electric charges may generate an internal electric field. When the mean free path of charge is modulated by such an internal electric field, a structural change is caused by light irradiation, which makes it difficult to separate from the case where the mean free path of charge is modulated (that is, in the case of the present invention). become.

Examples of the trapping agent include a molecule having a -C = C- bond such as stilbene or a derivative thereof and exhibiting a cis-trans type isomerization or photocyclization reaction; -N = N- such as azobenzene or a derivative thereof. A molecule containing a bond and exhibiting cis-trans isomerization;-such as salicylideneaniline;
A molecule containing a C = N-bond and showing a hydrogen transfer reaction; a molecule showing an ion pair formation reaction such as spiropyran; a molecule showing an electrocyclic reaction such as spirooxazines, fulgides, diarylethenes, spirooxazines, and cancon derivatives; Cyclophanes such as anthracene-containing cyclophane and metacyclophane; cyclophanes such as carbazophanes in which groups having charge transport ability are cross-linked to each other, such as molecules that exhibit stereoisomerization between a syn-form and an anti-form. No.

In particular, when using a cyclophane in which groups having charge transporting ability are cross-linked, it is preferable to use a group having charge transporting ability of the charge transporting agent and a group which can easily transfer charges. Therefore, it is desired to crosslink groups having a charge transporting ability of molecules contained as a charge transporting agent.

The trapping agent is desirably contained in an amount of 1% by weight or more and 20% by weight or less based on the entire recording layer. If the amount is less than 1% by weight, the amount of dispersion is too small, so that it takes time for the photo-generated charges to be captured by the trapping agent, and it takes a long time for recording. On the other hand, if it exceeds 20% by weight, the amount of dispersion is too large, so that the modulation of the charge transport characteristics due to the irradiation of the recording light is not sufficient, and the recording takes time. In addition, more preferably, the content of the trapping agent is:
The content is 5% by weight or more and 10% by weight or less based on the entire recording layer.

Further, in another optical recording medium of the present invention (hereinafter, referred to as a second optical recording medium), a dye and a trapping agent are blended in addition to the charge transporting agent and the nonlinear optical material.

The dye incorporated in the second optical recording medium is a molecule that absorbs visible light as recording light, has a small dipole moment in a ground state, and has a large dipole moment in an excited state. In order to increase the dipole moment in the excited state, by absorbing visible light,
It is preferable to form an intramolecular or intermolecular charge transfer complex. When forming an intermolecular charge transfer complex,
In particular, it is preferable to form a charge transfer complex with the trapping agent because the mean free path of the charge can be efficiently increased. Further, the life of the excited dye is desirably about the same as the time required to record information on the optical recording medium. this is,
After stopping the irradiation of the visible light as the recording light, it is not necessary to secure an increase in the mean free path of the charge, and it is preferable that the state of the mean free path is small to hold the photo-generated charge. It is. The visible light irradiated to excite the dye in the second optical recording medium to increase the dipole moment is preferably non-polarized and uniform light. In the case of polarized light, if the absorption of the charge transport agent is highly dependent on the polarization direction of the light, when the polarized light is irradiated, the charge transport agent is oriented in a direction that absorbs less light, thereby causing the charge to be absorbed. The mean free path may be modulated. In addition, when light whose spatial intensity is largely changed is irradiated, more electric charges are generated in a region where the intensity is large, and thus the generated electric charges may generate an internal electric field. When the mean free path of charge is modulated by such an internal electric field, a structural change is caused by light irradiation, which makes it difficult to separate from the case where the mean free path of charge is modulated (that is, in the case of the present invention). become.

Examples of the dye satisfying these conditions include azo dyes, quinone dyes, diaryl and triazole dyes, cyanine dyes, phthalocyanines, naphthalocyanines, indigo dyes, and condensed ring dyes. .

The dye is 0.1% by weight based on the entire recording layer.
Preferably, it is contained in an amount of at least 10% by weight. More preferably, the content is 1% by weight or more and 5% by weight or less based on the entire recording layer. If the amount is less than 0.1% by weight, the amount of dispersion is too small, and the effect of changing the charge transport characteristics is small. For this reason, the mean free path is not sufficiently large, and it takes time for recording. On the other hand, if it exceeds 10% by weight, the amount of dispersion is too large, so that the absorption of the recording layer becomes large, and there is a possibility that diffracted light may not be observed.

Further, as the trapping agent used in the second optical recording medium, an appropriate molecule can be selected and dispersed from the above-mentioned charge transporting molecules. Unlike the case of the first optical recording medium, the trapping agent in the second optical recording medium absorbs visible light as recording light, and it is not required that the charge transport property is modulated by the absorption. Second, as the trapping agent in the optical recording medium, a molecule exhibiting electrochromism is particularly preferable. As a trapping agent showing electrochromism,
Nitrogen-containing compounds such as aniline, o-toluidine, o-ethylaniline and oligomers and polymers thereof; aromatic amines and oligomers and polymers thereof; nitrogen-containing cyclic compounds such as pyrrol and oligomers and polymers thereof;
Sulfur-containing cyclic compounds such as thiophene, 3-methylthiophene and 3,4-dimethylthiophene, and oligomers and polymers thereof; compounds such as bis (2-thiethyl) benzene, and oligomers and polymers thereof;

The trapping agent is used in an amount of 0.0
It is preferable that the content is 5% by weight or more and 20% by weight or less. More preferably, 0.5% by weight based on the entire recording layer.
Not less than 10% by weight. If the amount is less than 0.05% by weight, the amount of dispersion is too small, so that it takes a long time for the photo-generated charges to be captured by the trapping agent, and it takes a long time for recording. On the other hand, if it exceeds 20% by weight, the amount of dispersion is too large to cause a sufficient change due to the dipole moment of the excited dye, and the modulation of the mean free path is small, so that a sufficient internal electric field is not formed.

However, in any of the first and second optical recording media, as shown in FIG. 2, the following relationship is satisfied between the energy level of the trapping agent and the energy level of the charge transporting agent. It is desirable to be. That is, when holes are transported, the charge transport agent HOMO
Level Orbital Energy (Hc) and HOMO of Trap Agent
Attention is paid to the relationship between the level and the orbital energy (Ht). Hc <Ht is satisfied when the recording light is not irradiated, and Hc to Ht or Hc> when the recording light is irradiated.
It is preferable to satisfy Ht. On the other hand, when electrons are transported, attention is paid to the relationship between the orbital energy (Lc) of the LUMO level of the charge transport agent and the orbital energy (Lt) of the LUMO level of the trapping agent. It is preferable that Lc> Lt is satisfied when the recording light is not irradiated, and Lc to Lt or Lc <Lt is satisfied when the recording light is not irradiated.

The optical recording medium of the present invention may further contain a charge generating agent in the recording layer in addition to the components described above. Alternatively, a charge generation layer 8 as shown in FIG. 4 may be provided adjacent to the recording layer 2. The molecules used as the charge generating agent or the molecules constituting the charge generating layer generate carriers when irradiated with light. Examples of the charge generating agent include selenium and selenium alloys, CdS,
Inorganic photoconductors such as CdSe, CsSSe, AsSe, ZnO, ZnS, and amorphous silicon; various crystal forms such as titanyl phthalocyanine and vanadyl phthalocyanine (α, β, γ, δ, ε, ζ, η, θ, ι, κ) ,
λ, μ, ν, ξ, ο, π, ρ, σ, τ, υ, φ, χ,
フ タ, ω, A, B, C, X and Y type) metal phthalocyanine pigments and various liquid crystal type metal-free phthalocyanine pigments; monoazo dyes, bisazo dyes, trisazo dyes,
And azo dyes and pigments such as tetrakisazo dyes;
Perylene dyes and pigments such as perylene anhydride and perylene imide; perinone pigments; indigo dyes and pigments; quinacridone pigments; polycyclic quinone pigments such as anthraquinone, anthantrone and dibromoanthrone; cyanine dyes; A charge transfer complex comprising an electron-capturing substance such as an electron-donating substance;
A eutectic complex comprising a pyrylium dye or a thiapyrylium dye and a polycarbonate resin; an azulenium salt;
Examples include fullerenes such as C ₆₀ and C ₇₀ and derivatives thereof; terephthalic acid derivatives having a carbonyl group such as dimethyl terephthalate and diethyl terephthalate; xanthene dyes and pigments; azurenium dyes and squarylium dyes.

These charge generating agents may be used alone or in combination of two or more. As described above, two types of charge generating agents having different polarities of generated charges can be dispersed. At this time, one of the charge generating agents is used for erasing. Charge transfer complexes are also effective charge generators.

When the charge generating agent is dispersed in the recording layer,
The content is preferably about 0.001 to 40% by weight based on the entire recording layer. When the content is less than 0.001% by weight, the charge per unit volume generated by light irradiation is small, and it is difficult to generate a sufficient internal electric field. Meanwhile, 4
If the content exceeds 0% by weight, light absorption by the charge generating agent becomes large, and light cannot pass through the recording layer, so that it is difficult to produce an optical recording medium having a large film thickness. On the other hand, FIG.
When the charge generating layer is formed as shown in (1), the charge generating agent may be used alone, or the charge generating agent may be dispersed in a polymer described later and used. It is desired that the thickness of the charge generation layer is about 1 μm or less so that the charge generation light can be sufficiently absorbed and the recording light can be transmitted.

The components described above can be used in appropriate combinations so that the internal electric field can be modulated by light irradiation. In addition, a molecule having two or more functions per molecule can be used, and in such a case, it can be blended without being limited to the above-mentioned weight%.

When the component such as the charge transporting agent is not a polymer in the present invention, a polymer can be mixed with the above-mentioned component. As a polymer that can be used, a polymer that is optically inert and has a small variation in molecular weight is preferable, but is not particularly limited. For example, polyethylene resin, nylon resin, polyester resin, polycarbonate resin, polyarylate resin, butyral resin, polystyrene resin, styrene-butadiene copolymer resin, polyvinyl acetal resin, diallyl phthalate resin, silicone resin, polysulfone resin, acrylic resin, acetic acid Vinyl, polyolefin oxide resin, alkyd resin, styrene-maleic anhydride copolymer resin, phenol resin, vinyl chloride-vinyl acetate copolymer, polyester carbonate, polyvinyl chloride, polyvinyl acetal, polyarylate, and paraffin wax. Can be These can be used alone or in combination of two or more.

In order to adjust the glass transition point of the recording layer, molecules having a small molecular weight called a plasticizer may be dispersed.

Further, compounds generally known as a polymer antioxidant and an ultraviolet absorber can be used in addition to the above-mentioned components. Examples of such compounds include hindered phenols, aromatic amines, organic sulfur compounds, phosphites, chelating agents, benzophenones, benzotriazoles, and nickel complexes. The amount of these components is preferably, for example, 0.0001 to 5% by weight based on the entire recording layer.

The recording layer in the optical recording medium of the present invention can be formed by dissolving a composition containing the above-described components in a solvent and forming a film. As the solvent, various organic solvents can be used, for example, alcohols, ketones, amides, sulfoxides, ethers, esters, aromatic halogenated hydrocarbons, and aromatic hydrocarbons. No.

The recording layer is formed, for example, by various coating methods such as spin coating, dip coating, roller coating, spray coating, wire bar coating, blade coating, roller coating, casting, and vacuum deposition. And can be formed by a sputtering method or the like. Further, it may be formed by, for example, a plasma CVD method using glow discharge. When the casting method is adopted, the recording layer can be formed not only by casting the solution but also by evaporating the solvent from the solution and then heating and melting the powdered mixed material.

The thickness of the recording layer thus formed is usually about 0.05 to 10 mm, and preferably 0.5 to 1 mm. Depending on the composition and the characteristics required for the optical recording medium, It can be selected as appropriate.

In the present invention, a recording layer is formed by applying a solution containing a composition containing the above-mentioned components on a suitable support. As the support, any material having an appropriate thickness and hardness and having sufficient strength for handling can be used.

This support is used not only for film formation but also for film formation.
The optical recording medium of the present invention can also be used as a substrate. That is, the optical recording medium of the present invention may be configured to have a substrate and a recording layer formed on the substrate.
In this case, the substrate is desired to be transparent to some extent in the wavelength range of the light used. In the case of a semiconductor laser, the wavelength of light is, for example, 780 nm, 650 nm,
405 nm. Normal resin has a visible range of 400
Transparent to light of wavelengths in the range of ~ 600 nm,
In many cases, transparency is maintained up to around 800 nm, which is a long wavelength region. Therefore, polyvinyl chloride, polyvinylidene chloride, polyethylene, polycarbonate, polyester, polyamide, acrylic resin, polyimide and the like are preferable.

These substrate materials can be used as a flat plate or, if necessary, as a cylindrical sheet. When used as a cylindrical sheet, the substrate is required to have appropriate flexibility.

On the recording layer side of the above-mentioned substrate, a layer serving as an electrode may be formed as necessary. The material for forming the electrode layer is desired to be transparent to some extent in the wavelength range of the light to be used, like the substrate. For this reason, indium tin oxide and aluminum are preferably used. Further, it is desired that the sheet resistance of the electrode is 50 Ωcm ⁻² or less.

In the present invention, a protective layer can be formed on the recording layer if necessary. Any material can be used as a material for forming the protective layer. For example, a thermosetting resin such as an acrylic resin, a fluororesin, a silicone resin, a melamine resin, a photocurable resin, E
B-curable resin, X-ray curable resin, UV-curable resin and the like.

In such a protective layer, additives such as an antioxidant, an ultraviolet absorber and an antioxidant may be added in a small amount. Examples of additives that can be used include hindered phenols, aromatic amines, organic sulfur compounds, phosphites, chelating agents, benzophenones, benzotriazoles, and nickel complexes.

The optical recording medium of the present invention may be subjected to a polling process in advance. In this case, the recording layer is heated to a temperature around its glass transition point, and an external electric field is applied. This allows molecules with large permanent dipole moments, especially nonlinear optical materials, to be oriented in the direction of the external electric field.

Next, a method of using the optical recording medium of the present invention as a hologram memory, that is, a method of recording information on the medium and reproducing the recorded information will be described.

FIG. 5 shows an example of a recording apparatus for recording information on the optical recording medium of the present invention in which a charge generating agent is dispersed in a recording layer.

As shown in FIG. 5, a rectangular parallelepiped optical recording medium 7 is prepared. The image display element 15 is disposed on one side of the optical recording medium 7, and the reading device 19 is disposed on the opposite side of the optical recording medium 7. It is preferable that the reading device 19 is disposed so as to be perpendicular to the optical axis of light emitted from the image display element 15 to the optical recording medium 7. Examples of the image display element 15 include a liquid crystal element, a digital mirror array, and a Pockets Readou.
t Optical Modulator, Multi
-Channel Spatial Modulat
Or, a Si-PLZT element, a deformed surface type element, an AO or EO modulation element, a magneto-optical effect element, and the like can be used. Further, as the reading device 19, any photoelectric conversion element can be used. For example, CC
D, photodiode, Photoreceptor,
And a photomultiplier tube.

In FIG. 5, it is assumed that light passes through the image display element 15, but the image display element 15 may be of a type that reflects light.

Recording of information on the optical recording medium can be performed, for example, in the following procedure. The light source used for recording needs to be coherent light represented by a laser, that is, coherent light. Here, a case where a laser is used will be described. The wavelength of the laser can be selected according to the components of the optical recording medium used. Specifically, in the first optical recording medium, the second optical recording medium is used in accordance with the electric field generating agent and the trapping agent. In the medium, it is selected according to the charge generating agent and the dye. As the laser 10, existing gas lasers, liquid lasers,
Any solid-state laser or semiconductor laser can be used. The output from the laser 10 is split into two using, for example, a beam splitter 12. One is used as the reference light 5, and the other is used as the signal light 4 transmitted through the image display element 15.

In recording information with such a configuration, the signal light 4 and the reference light 5 are incident on the optical recording medium 7 so as to intersect in the recording layer. This is specifically performed by the following method. After the light from the laser 10 is spread into parallel light by, for example, a beam expander 11, the light is split into two by a beam splitter 12, for example. Information to be recorded is digitized in advance, and an image pattern corresponding thereto is input to the image display device 15. One of the two light beams split by the beam splitter 12 is applied to the image display element 15 via the mirror 13, and is spatially modulated according to, for example, data for recording the light intensity distribution to form the signal light 4. . Further, the signal light 4 is condensed by the lens 16 and irradiated on the optical recording medium 7. It is desirable that the distance between the lens 16 and the image display element 15 is equal to the focal length of the lens 16. At this time, the optical recording medium 7 is irradiated with the reference light 5 so that the reference light 5 intersects in the recording layer at the same time. The reference light 5 is expanded into a parallel light, and is condensed by a mirror 14 and a lens 17 for irradiation.

An internal electric field is generated by interference fringes generated by the superposition of the signal light 4 and the reference light 5, and the modulation of optical characteristics occurs to form a diffraction grating. At this time, it is possible to form a plurality of interference fringes in the overlapping region by changing the incident angle of the reference light, the incident angle of the signal light, or both. Alternatively, the incident angles of the reference light and the signal light can be changed by rotating the optical recording medium 7 with respect to the direction of the incident light. Further, a plurality of interference fringes can be similarly recorded in the overlapping area by shifting the irradiation position of the laser light by about 1/2 to 1/1000 with respect to the overlapping area of the signal light and the reference light. it can.

In reading the recorded information,
First, the signal light 4 is blocked, and only the reference light 5 is applied to the optical recording medium 7.
Irradiation. That is, the reference light 5 can be used as a reading light. At this time, the reproduced light having the same spatial intensity distribution as the signal light 4 is reproduced by the recorded interference fringes.
Read at 9. The recorded information can be reproduced by the intensity distribution of the read light. The distance from the lens 18 to the reading device 19 is preferably equal to the focal length of the lens 18. It is desirable that the distance from the lens 16 to the lens 18 is equal to the sum of the focal lengths of the lens 16 and the lens 18.

Here, a light source having the same wavelength is used for recording and reading, but when the thickness of the recording layer is about 0.5 mm or less, a light source having a wavelength slightly different from that for recording is used. Can also be read. In such a case, the reference light may be incident at an angle slightly different from that at the time of recording so that the intensity of the diffracted light becomes large at the time of reproduction.

In this case, the reference light 5 is also condensed by using the lens 17, but the reference light is not necessarily condensed. The lens 17 can be omitted by disposing the beam expander 11 at any position between the laser 10 and the image display element 15.

When reading recorded information, phase conjugate reproduction is also possible. This will be described with reference to FIG. In FIG. 6, coherent light having the same wavelength as that used for recording is irradiated in a direction opposite to that for recording.

That is, when the light from the laser 20 oscillating light having the same wavelength as the light used for recording is irradiated with reference light using the lens 22 after the light diameter is expanded by, for example, the beam expander 21. Irradiate the optical recording medium 7 in the completely opposite direction. Due to the diffraction grating recorded on the optical recording medium 7, a virtual image is reproduced in a direction completely opposite to the direction in which the signal light 4 has advanced. After the virtual image passes through the lens 16, for example, it is reflected by the beam splitter 23 and read by the reading device 19. As in the case of recording, also in this case, the distance from the lens 16 to the reading device 19 is preferably equal to the focal length of the lens 16. In phase conjugate reproduction,
Coherent light having a wavelength slightly different from that at the time of recording can be used as read light. At this time, it is preferable to slightly adjust the incident angle of the readout light so that the optical axis of the virtual image completely matches the optical axis of the signal light 4.

If the reference beam 5 is not condensed during recording, the beam splitter 2 can be used even during phase conjugate reproduction.
1 and the lens 22 can be omitted.

The information recorded on the optical recording medium can be erased in some cases. For example, the recording is erased by irradiating light having a uniform intensity distribution over an area wider than the recording area, or by heating the optical recording medium to a temperature lower than the glass transition point.

The method for recording information on the optical recording medium and the method for reproducing information according to the present invention are not limited to the examples described above, and various modifications are possible. For example, the signal light 4 and the reference light 5 may enter the optical recording medium 7 from different surfaces.

When information is recorded as digital data, a plurality of pixels of the image display element 15 may represent one data.

In the case where information is given by the intensity distribution of the signal light, the light intensity of the bright part and the dark part may not be uniform over the entire beam diameter. That is, the light transmittance of the image display element can be reduced at the center portion and increased at the portion away from the center. This makes it possible to correct in advance that the reproduction light is weakened in a portion farther from the center than the center of the reproduction signal. Alternatively, the same applies when a light intensity modulation element having a large absorption coefficient near the center and a small absorption coefficient away from the center is arranged in front of the reading device 19.

Further, the charge generation layer 8 as shown in FIG.
It is also possible to record information on an optical recording medium provided with. This case will be described with reference to FIG.

As shown in FIG. 7, a light source 30 for generating electric charges is provided.
The information can be recorded by the same method as in the case of FIG. 5 except that the light emitted from the optical recording medium 7 is irradiated on the optical recording medium 7. At this time, if the charge generation light 31 is irradiated from the surface of the recording layer, the charge generation light having a substantially uniform intensity distribution may be absorbed by the recording layer and hinder hologram formation. In order to avoid this, it is preferable to irradiate the charge generation light from the charge generation layer 8 side. However, the optical recording medium provided with the charge generation layer may be used by any of the methods described above. For example, when the charge generation layer hardly absorbs the recording light 4 and the reference light 5, even if the recording light and the reference light are irradiated from the surface on which the charge generation layer is provided, information can be recorded in a short time. it can. In addition, information can be recorded by irradiating the recording light and the reference light from different surfaces of the optical recording medium 7. Alternatively, when a sufficient amount of charges can be generated by the recording light, recording can be performed without using a separate light source for generating charges.

The fact that the mean free path of charge is increased by light irradiation in an optical recording medium in which a charge generating agent is dispersed in a recording layer can be measured as follows. First, a sample for measuring the mean free path is prepared. In preparing a sample, a solution is prepared by dissolving a recording layer of an optical recording medium in a solvent in which all of the recording layer is dissolved. On the other hand, ITO (Indium T
in Oxide) film and an aluminum electrode are formed, and the above solution is applied on the electrode and dried to form a film having a thickness of 10 μm.
An about m thin film is formed. 1 cm ² to 1
A gold electrode having an area of about 0 cm ^{2 is} formed by vapor deposition.

The mean free path of the thus prepared sample was calculated as Physical Review Letters.
vol. 75 pp. 1787-1790 (1995)
(Hirao, Nishizawa, Sugiuchi) using the measurement system described. Specifically, the electric field actually applied to the film is 5
A positive voltage is applied to the aluminum electrode side of the sample so that the voltage is about 00 V / μm, and the gold-side electrode is grounded via a resistance sufficiently smaller than the film to be measured. Irradiate a nitrogen laser having a pulse width of about 1 ns from the aluminum electrode side,
The time change of the displacement current flowing at this time is measured. In general, the penetration depth of light into the organic film is sufficiently small at the wavelength of the nitrogen laser, and it can be considered that carriers are generated in the form of a sheet at the aluminum electrode interface by this light.

If the film to be measured does not show a large absorption by the nitrogen laser, carriers are generated using a combination of a wavelength lamp showing a large absorption and a color glass filter, and a short time is generated using a shutter or the like. The same measurement can be performed by irradiation. In order to measure the difference in the mean free path due to light irradiation, non-polarized light that has the same wavelength and the same surface intensity as the recording light and can be regarded as almost uniform in the area where the electrodes are provided is irradiated, and the current Investigate changes over time. Further, even when such light is not irradiated, the time change of the current is examined, and the difference between the time changes of the two currents is compared. However, the intensity of the nitrogen laser is adjusted so that the photo-generated charges do not become larger than the charges stored in the current by applying an external electric field.

An example of adjusting from the region where the nitrogen laser intensity is weak will be described below with reference to the graph of FIG. When the nitrogen laser is not irradiated, carriers are generated by the uniform light reaching the inside of the recording layer, and the carriers are transported to the counter electrode. If the magnitude of the external resistance is set to an appropriate magnitude, the time change of the current obtained at this time is as shown in FIG.
As shown in (a), it can be distinguished from the dark current flowing when light is not irradiated.

Next, when the intensity of the nitrogen laser is increased without changing the value of the external resistance, electric charges generated near the substrate by the nitrogen laser are also transported. In this case, as shown in FIG. 8B, a current larger than the current flowing in FIG. 8A flows. Further, FIG.
As shown in (1), there is a time region where the current shows a substantially constant value.

When the nitrogen laser intensity is further increased,
As shown in FIG. 8C, the flowing current becomes larger, but the current changes over time with a slight delay and rises. This indicates that the charge generated by the nitrogen laser cannot be ignored with respect to the charge stored in the electrode. In other words, the intensity of the nitrogen laser
It is necessary to carry out the experiment by setting the region.

Further, when the same measurement is performed without irradiating uniform light and keeping the resistance and the intensity of the nitrogen laser at the values shown in FIG. 8B, a waveform as shown in FIG. 8D is obtained. Can be
When the mean free path is smaller than the film thickness, the obtained waveform is represented as shown in FIG. 8D or no current flows at all.

Therefore, when such a difference in waveform is observed, it means that the mean free path of the charge in the optical recording medium has been increased by light irradiation. In addition, even when the uniform light is not irradiated, when the waveform as shown in FIG. 8B is obtained, as shown in FIG. Kink) to compare.
The kink substantially coincides with the time required for the center of gravity of the electric charge excited on the surface of the aluminum electrode to be transported by drift and reach the counter electrode. (For example, Physical Review
Letters vol. 75, pp, 1787-1
790 (1995) (Hirao, Nishizawa, Sugiuchi)). In other words, a slower time to show a kink indicates that the drift mobility of the charge is smaller. When the mixing ratio of the charge transporting agent is constant, the drift mobility does not significantly change unless the mean free path changes due to trapping of the charge by the trapping agent. Therefore, if the time required to show a kink differs by at least one digit due to uniform light irradiation, this also indicates that the mean free path is increased by uniform light irradiation. When the displacement current as shown in FIG. 8B is not observed even when the uniform light is irradiated, the same measurement is performed by setting the thickness of the film to be measured to a value of 3 μm to 10 μm. The difference in displacement current due to uniform light irradiation is measured at a film thickness at which a waveform like 8 (b) is observed.

In the optical recording medium provided with the charge generation layer 8 as shown in FIG. 4, the fact that the mean free path of the charge in the recording layer 2 is increased by light irradiation is measured by the following method. can do. First, a solution is prepared by dissolving the charge generation layer and the recording layer, respectively. On the other hand, ITO (Indium Tin Ox) is formed on a quartz substrate.
ide) A film and an aluminum electrode are formed, and a solution of the charge generation layer is applied and dried on the aluminum electrode to form a thin film. The thickness of the charge generation layer depends on the absorption of the charge generation light by the charge generation layer, but is generally preferably about 1 μm. Further, a solution of the recording layer is applied and dried to form a thin film. The thickness of the recording layer is preferably about 10 μm. A gold electrode having an area of about 1 cm ² to 10 cm ² is deposited on the recording layer film.

The mean free path of the thus obtained film is measured by the same method as described above. However, when the charge generation layer absorbs uniform light strongly, an aluminum electrode is deposited on the recording layer film instead of the gold electrode, and measurement is performed by irradiating uniform light from the deposited aluminum electrode side. I do.

Since the optical recording medium of the present invention contains a specific trapping agent or dye, irradiating visible light as recording light increases the mean free path of charges in the optical recording medium. . Therefore, in the interference fringes irradiated with visible light, the mean free path is large in a region where the light intensity is high, and the mean free path is small in a region where the light intensity is low. As a result, an electric charge was transported from a region having a high light intensity to a region having a low light intensity, and was retained in that region, whereby an optical recording medium having a short recording time and a high diffraction efficiency was obtained.

[0099]

The present invention will be described below in further detail with reference to examples.

(Example 1) First, an optical recording medium was manufactured as follows.

0.5% by weight of fullerene (C ₇₀ ), poly N
39.5% by weight of vinyl carbazole (PVK), 15% by weight of N-ethylcarbazole (EtCz), 35 of a compound (piperonal compound) represented by the following chemical formula (1)
% By weight and a compound 1 represented by the following chemical formula (2)
0% by weight was dissolved in toluene to prepare a toluene solution. Among the components used here, PVK is a charge transporting agent, a compound represented by the following chemical formula (1) (a piperonal compound) is a nonlinear optical material, and a compound represented by the chemical formula (1) is a trapping agent.

[0102]

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[0103]

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An ITO (Indium) film was formed on the surface of a glass substrate.
Forming a Tin Oxide) film and an aluminum film,
A substrate was prepared. A recording layer was prepared by applying the above-mentioned toluene solution on the substrate by a casting method,
An optical recording medium was obtained. The thickness of the recording layer was adjusted to 50 μm using a Teflon (registered trademark) spacer.

A hologram was recorded / reproduced on this optical recording medium using a recording apparatus having the configuration shown in FIG. In the illustrated device, light emitted from an argon laser (wavelength 457 nm, output 4 mW) 10 is first split into two by a beam splitter 12. Beam splitter 1
The light reflected by 2 is transmitted through a liquid crystal filter 15 as an image display element after the light diameter is expanded using the beam expander 11. The transmittance of the liquid crystal filter 15 was modulated in accordance with the information to be recorded in advance to obtain the signal light 4. The transmitted light is passed through a lens 16 (focal length 150 mm).
Light is collected using. The distance between the lens 16 and the optical recording medium 7 was 135 mm.

On the other hand, the light transmitted through the beam splitter 12 was applied to the optical recording medium 7 as the reference light 5 as it was. At this time, the optical path of the reference light 5 is adjusted so that the reference light covers an area where the signal light 4 is converged on the optical recording medium.
When the angles at which the signal light 4 and the reference light 5 were incident on the optical recording medium 7 were measured, the angles measured outside the optical recording medium 7 were 40 ° and 50 °, respectively.

Since the substrate of the optical recording medium 7 is connected to an external power supply (not shown) of 2 kV, an external electric field of 40 V / μm is applied. By irradiating light for one second in this manner, a hologram could be recorded on the optical recording medium 7.

Subsequently, the recorded information was reproduced. During reproduction, the optical path of the signal light 4 is blocked by a shutter,
When the light transmitted through the beam splitter 12 was irradiated on the optical recording medium 7 as read light, diffracted light was observed. A lens 18 similar to the lens 16 (focal length 150 m
m), diffracted light is transmitted through C as a reader.
By being incident on the CD 19, reproduction light having an intensity distribution similar to that of the signal light 4 was detected. The lens 18 was arranged perpendicular to the optical axis at a position 300 nm from the lens 16 so that the optical axis passed through the center of the lens 18.
The CCD 19 was also arranged perpendicular to the optical axis. The distance from the lens 18 to the CCD 19 was equal to the focal length of the lens 18.

The observed diffracted light intensity was about 0.1% with respect to the incident light.

Thereafter, the mean free path of the charge in the recording layer was measured by the following method. First, the recording layer was dissolved in toluene, and the obtained solution was formed into a spinner to form a thin film having a thickness of 10 μm. A 20 nm gold electrode was deposited on the obtained thin film, a voltage of 3 × 10 ⁵ V / cm was applied, and a resistance of 100 kΩ was connected. When the mean free path was measured while irradiating with argon laser light, a kink time of 20 ms was obtained.

(Comparative Example 1) The laser 10 was made of He-Ne
A hologram was recorded on the same optical recording medium by the same method using the same apparatus as in the first embodiment except that the laser (wavelength: 633 nm, output: 4 mW) was used. Since the molecule represented by the chemical formula (1) blended as a trapping agent hardly absorbs light of 633 nm, it does not change its state even when irradiated with such recording light. Therefore, when light having a wavelength of 633 nm is used as the recording light, the mean free path of the charge does not increase depending on the intensity of the light intensity. For this reason, recording required one minute. The observed diffraction light intensity was about 0.1% with respect to the incident light.

The mean free path of the charge in the thin film for measuring the mean free path prepared in Example 1 was measured by the same method as described above, except that the He—Ne laser was used instead of the argon laser. As a result, a waveform as shown in FIG. 8D was obtained.

Example 2 Using the same optical recording medium as in Example 1, a hologram was recorded. Here, before recording information, both electrodes were previously set to 1 kV at 100 ° C.
Was connected to the power supply and subjected to polling processing. afterwards,
When information was recorded using the same light source as in Example 1 under the same conditions, recording was sufficiently performed with a recording time of 0.1 second. The observed diffraction light intensity was about 1% with respect to the incident light.

Thereafter, the mean free path of the electric charge in the recording layer was measured by the following method. First, the recording layer was dissolved in toluene, and the obtained solution was formed into a spinner to form a thin film having a thickness of 10 μm. A 20 nm gold electrode was deposited on the obtained thin film.
V was connected to a power supply, and a polling process was performed. Next, when the mean free path was measured by the same method as in Example 1, a kink time of 15 ms was obtained.

(Comparative Example 2) As in Example 2, Example 1
After the optical recording medium manufactured in the above was subjected to a poling treatment in advance, the same He-Ne laser (wavelength of 633 nm,
Using an output of 4 mW) as a light source, information was recorded under the same conditions. As a result, it took 10 seconds to record. The observed diffraction light intensity was about 0.3% with respect to the incident light.

The mean free path of the charge in the thin film for measuring the mean free path prepared in Example 2 was measured in the same manner as described above, except that the He—Ne laser was used instead of the argon laser. As a result, a waveform as shown in FIG. 8D was obtained.

(Example 3) First, an optical recording medium was manufactured as follows.

0.5% by weight of fullerene (C ₇₀ ), 34.5% by weight of polystyrene, 30% by weight of 4- (dimethylamino) benzaldehyde-diphenylhydrazone (DEH), 2- (N, N-dimethylamino) -5 -25% by weight of nitroacetanilide (DAN), 5% by weight of a compound (T405) represented by the following chemical formula (3), and 5% by weight of a compound represented by the following chemical formula (4) are dissolved in toluene to prepare a toluene solution. did. Among the components used here, DEH is a charge transport agent, and 2- (N, N-dimethylamino) -5-nitroacetanilide (DAN) is a nonlinear optical material. The compound (T405) represented by the chemical formula (3) is a trapping agent, and the compound represented by the chemical formula (4) is a dye.

[0119]

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[0120]

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An ITO (Indium) film was formed on the surface of a glass substrate.
Forming a Tin Oxide) film and an aluminum film,
A substrate was prepared. A recording layer was prepared by applying the above-mentioned toluene solution on the substrate by a casting method,
An optical recording medium was obtained. The thickness of the recording layer was adjusted to 50 μm using a Teflon spacer.

The dye represented by the chemical formula (4) absorbs light from an argon laser (wavelength: 457 nm) and has a very large dipole moment in its excited state.
DEH molecules are charge-transporting agents whose mobility varies very greatly with the magnitude of the external electric field.

As in Example 2, before recording information, both electrodes were connected to a power supply of 1 kV at 80 ° C. to perform a polling process, thereby producing an optical recording medium. When information was recorded in the same manner as in Example 1, recording was completed in 10 seconds. The observed diffracted light intensity was about 0.8% with respect to the incident light.

Subsequently, the mean free path of the charge in the recording layer was measured by the following method. First, the recording layer was dissolved in toluene, and the obtained solution was formed into a spinner to form a thin film having a thickness of 10 μm. A gold electrode was deposited to a thickness of 20 nm on the obtained thin film, and both electrodes were set to 1 kV at 80 ° C.
Was connected to the power supply for polling. Then 3
A voltage of × 10 ⁵ V / cm was applied, and a resistance of 10 kΩ was connected. When the mean free path was measured while irradiating with argon laser light, a kink time of 20 ms was obtained.

Comparative Example 3 Information was recorded on the optical recording medium manufactured in Example 3 in the same manner as in Comparative Example 1. The dye represented by the chemical formula (4) does not absorb the light of the He—Ne laser (wavelength: 633 nm). Therefore, even if such a recording light is irradiated, the dipole moment of the dye in the ground state affects the charge transport characteristics. Do not give. Therefore, information cannot be recorded by this method.

When the charge mean free path of the thin film for measuring mean free path prepared in Example 3 was measured in the same manner as in Comparative Example 1, no displacement current was observed.

(Example 4) First, an optical recording medium was manufactured as follows.

0.5% by weight of fullerene (C ₇₀ ), 34.5% by weight of polystyrene, 30% by weight of 4- (dimethylamino) benzaldehyde-diphenylhydrazone (DEH), 2- (N, N-dimethylamino) -5 -Nitroacetanilide (DAN) 25% by weight, aniline 5% by weight,
5% by weight of the compound represented by the chemical formula (4) was dissolved in toluene to prepare a toluene solution. Of the components used here, DEH is a charge transport agent, and 2- (N, N
-Dimethylamino) -5-nitroacetanilide (DA
N) is a nonlinear optical material. In addition, aniline is a trapping agent, and the compound represented by the chemical formula (4) is a dye.

An ITO (Indium) film was formed on the surface of a glass substrate.
Forming a Tin Oxide) film and an aluminum film,
A substrate was prepared. A recording layer was prepared by applying the above-mentioned toluene solution on the substrate by a casting method,
An optical recording medium was obtained. The thickness of the recording layer was adjusted to 50 μm using a Teflon spacer.

As in Example 2, before recording information, both electrodes were connected to a power supply of 1 kV at 80 ° C., and a polling process was performed to prepare an optical recording medium. When information was recorded in the same manner as in Example 1, the information could be recorded in 5 seconds. The observed diffracted light intensity was about 0.2% with respect to the incident light.

A film was formed in the same manner as in Example 1, and the displacement current was measured. No displacement current was observed. Therefore, the mean free path of the charge in the recording layer was measured by the following method. First, the recording layer was dissolved in toluene, and the obtained solution was formed into a spinner film to form a thin film having a thickness of 5 μm. A gold electrode is placed on the obtained thin film at 20 nm.
At 80 ° C., both electrodes were connected to a power supply of 1 kV and subjected to a poling treatment. Then, 1.5 × 10 ⁵ V
/ Cm and a resistance of 100 kΩ was connected.
When the mean free path was measured while irradiating with an argon laser beam, a kink time of 30 ms was obtained.

(Comparative Example 4) When information was recorded on the optical recording medium manufactured in Example 4 in the same manner as in Comparative Example 1,
The recording took three minutes. The observed diffracted light intensity was about 0.01% with respect to the incident light.

When the mean free path of the thin film for measuring the mean free path prepared in Example 4 was measured in the same manner as in Comparative Example 1, a waveform as shown in FIG. 8D was obtained.

Example 5 0.5% by weight of fullerene (C ₇₀ ), 34.5% by weight of polystyrene, 30% by weight of DEH, 25% by weight of DAN, and 10% by weight of T405
Was dissolved in toluene to prepare a toluene solution. Of the components used here, DEH is a charge transport agent, and
Is a nonlinear optical material. T405 is a trapping agent, and T405 is an argon laser (wavelength 457n).
m) absorbs the light and modulates its charge transport properties.

An ITO (Indium) film was formed on the surface of a glass substrate.
Forming a Tin Oxide) film and an aluminum film,
A substrate was prepared. A recording layer was prepared by applying the above-mentioned toluene solution on the substrate by a casting method,
An optical recording medium was obtained. The thickness of the recording layer was adjusted to 50 μm using a Teflon spacer.

As in Example 2, before recording information, both electrodes were connected to a power supply of 1 kV at 80 ° C., and a polling process was performed to prepare an optical recording medium. When the information was recorded in the same manner as in Example 1, the information could be recorded in 2 seconds. The observed diffracted light intensity was 1% with respect to the incident light.

Subsequently, the mean free path of the charge in the recording layer was measured by the following method. First, the recording layer was dissolved in toluene, and the obtained solution was formed into a spinner to form a thin film having a thickness of 10 μm. A gold electrode was deposited to a thickness of 20 nm on the obtained thin film, and both electrodes were set to 1 kV at 80 ° C.
Was connected to the power supply for polling. Then 3
A voltage of × 10 ⁵ V / cm was applied, and a resistance of 100 kΩ was connected. When the mean free path was measured while irradiating with argon laser light, a kink time of 5 ms was obtained.

Comparative Example 5 Information was recorded on the optical recording medium manufactured in Example 5 in the same manner as in Comparative Example 1. T40
Since No. 5 does not absorb the light of the He-Ne laser (wavelength 633 nm), the charge transport characteristics do not change even if such recording light is irradiated. Therefore, information cannot be recorded by this method.

When the mean free path of the charge in the thin film for measuring the mean free path prepared in Example 5 was measured in the same manner as in Comparative Example 2, no displacement current was observed.

[0140]

As described above in detail, according to the present invention, there is provided an optical recording medium on which information is recorded as a hologram,
An optical recording medium with a short recording time and high diffraction efficiency is provided. The optical recording medium of the present invention is effective for realizing high-density recording, and its industrial value is enormous.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating recording of information on a photoreactive medium.

FIG. 2 is a diagram illustrating energy levels of a charge transporting agent and a trapping agent.

FIG. 3 is a graph illustrating a charge density distribution in a medium.

FIG. 4 is a sectional view illustrating a configuration of an example of an optical recording medium according to the present invention.

FIG. 5 is a schematic diagram showing a configuration of an example of an apparatus for recording and reproducing a hologram on an optical recording medium according to the present invention.

FIG. 6 is a schematic diagram showing a configuration of an example of an apparatus for reproducing a hologram recorded on an optical recording medium according to the present invention.

FIG. 7 is a schematic diagram showing the configuration of another example of an apparatus for recording and reproducing a hologram on an optical recording medium according to the present invention.

FIG. 8 is a graph showing a measurement result for measuring a difference in mean free path of electric charge.

FIG. 9 is a schematic diagram showing the configuration of another example of an apparatus for recording a hologram on an optical recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Recording layer 3 ... Electrode 4 ... Signal light 5 ... Reference light 6 ... Reproduction light 7 ... Optical recording medium 8 ... Charge generation layer 10 ... Laser 11 ... Beam expander 12 ... Beam splitter 13, 14 ... Mirror 15 ... Image display element 16, 17, 18 Lens 19 Reading device 20 Laser 21 Beam expander 22 Lens 23 Beam splitter 30 Light source for charge generation 31 Charge generation light

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akiko Hirao 1st, Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Inventor Kazuki Matsumoto Komukai Toshiba, Saiwai-ku, Kawasaki City, Kanagawa Prefecture No. 1 town Toshiba R & D Center F term (reference) 2H111 EA03 EA21 EA33 FB41 5D029 JA04 JC05 JC20 VA03 VA08 5D090 AA01 BB17 BB20 CC14 DD01

Claims (6)

[Claims] 1. A charge generating agent that generates charges by irradiation with visible light, a charge transporting agent that transfers charges, a nonlinear optical material, and a trapping agent that retains charges, and interferes with irradiation of visible light. A hologram recording medium having a recording layer that records information by forming stripes, wherein the trapping agent that retains the charge is made of a molecule that absorbs the visible light and modulates charge transport characteristics, The optical recording medium according to claim 1, wherein the mean free path of the electric charges in the recording medium is increased by the irradiation of the visible light. 2. The method according to claim 1, wherein the trapping agent for retaining the electric charge is a photochromic molecule, and the content of the trapping agent is 1% by weight or more and 20% by weight or less based on the recording layer. The optical recording medium according to the above. 3. The optical recording medium according to claim 1, wherein the charge-holding trapping agent is a photochromic molecule exhibiting a cis-trans type structural change. 4. A charge generating agent that generates a charge by irradiation with visible light, a charge transporting agent that transports a charge, a nonlinear optical material, a trapping agent that retains a charge, and a dye,
A hologram recording medium having a recording layer that records information by forming interference fringes by irradiating visible light, wherein the dye is made of a molecule whose dipole moment increases when excited by absorbing the visible light, The optical recording medium according to claim 1, wherein a mean free path of the charge in the hologram medium is increased by irradiation of the visible light. 5. The optical recording medium according to claim 4, wherein the trapping agent is an electrochromic molecule, and the charge transport property is increased by an electric field generated by the excited dipole moment of the dye. 6. The optical recording medium according to claim 4, wherein the content of the dye is 0.1% by weight or more and 10% by weight or less based on the recording layer.