JPH02201747A - Optical memory element - Google Patents

Abstract

PURPOSE:To enable recording, reproducing and erasing based on PHB phenomenon which occurs significantly even at high temp. by forming a specific optical memory layer in a polymer matrix and constituting the polymer matrix of three-dimensional crosslinking polymers. CONSTITUTION:Informations are recorded, reproduced and erased by irradiating a recording medium, namely, an optical memory layer with light. The recording medium is constituted by dispersing in a matrix of three-dimensional crosslinked org. compd. which is photochromic or causes rearrangement of hydrogen atoms by laser light. By this method, thermal dynamics of matrix molecules 4 around a guest molecule 3 are limited and the local structure around the guest molecule 3 remains even at high temp., so that the stability of the PHB hole in the absorption spectrum caused by laser light is more stabilized against temp. Thus, recording, reproducing and erasing based on the PHB phenomenon can be performed at high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an optical memory element. For more details,
The present invention relates to an optical memory element that uses a photochemical hole burning phenomenon (PI-IB phenomenon) to record, reproduce, and erase information using light such as a laser beam.

(B) Prior Art In recent years, the need for optical memory devices that record, reproduce, and erase information using light has been increasing year by year as high-density, large-capacity memory devices. Optical memory devices are classified into three types depending on their normal use: read-only memory, additionally recordable memory, and rewritable memory.

Among these, optical memory elements used as rewritable memories include those that utilize the magneto-optical effect and those that utilize the phase change of a recording medium. The former, which utilizes the magneto-optical effect, irradiates a recording medium containing a magnetic film that is magnetized in a direction perpendicular to the surface of the recording medium with light such as a laser beam, raising the temperature of the irradiated area to a temperature higher than the Curie temperature. By applying a magnetic field from the outside in the raised state, the direction of magnetization in that part is reversed from the direction of magnetization in the part not irradiated with light, thereby recording information.

On the other hand, in the latter type of phase change, the recording medium is irradiated with light such as a laser beam, and the irradiated portion of the recording medium undergoes a phase change from an amorphous state to a crystalline state, or from a crystalline state to an amorphous state. This is how information is recorded. Note that the above recording methods for optical memory elements all utilize light such as laser light as a heat source and can therefore be summarized as heat mode recording.

Incidentally, recently, research and development of optical memory elements using a photon mode recording method has been actively conducted, in addition to the dual heat mode recording method. As this photon mode recording, photochemical hole panning (P I-I B
') is known (US Pat. No. 4,101,976). The principle of optical memory using this PHB phenomenon will be briefly described.

Generally, the light absorption spectrum of a sample in which organic compounds (guest molecules) such as dye molecules are dispersed in a matrix composed of polymers is that the absorption spectra of the individual molecules themselves are the same and cannot be distinguished. However, as a result of individual differences in the local structure around the guest molecules, differences in transition energy occur, resulting in an overall width Δ as shown in Figure 6(a).
This results in an absorption curve 5 with a wide width of Wi. In such an absorption band, there is a strong laser beam with a narrow wavelength width, for example, a wavelength of λ1.
When irradiated with a laser beam, only a group of guest molecules with an excitation energy equal to that energy are excited. If the guest molecule undergoes a photochemical reaction such as phototautomerization or rearrangement of hydrogen atoms from an excited state, the electronic state of the guest molecule changes and becomes the same state as if it had been effectively removed.

Since such guest molecules no longer contribute to absorption,
When observing the above-mentioned absorption spectrum, a hole 6 is observed in the irradiated laser wavelength portion (λl) as shown in FIG. 6(b). Free base phthalocyanine, polyfin, chlorin, and their derivatives are known as organic compounds that exhibit phototautomerism as described above, and compounds that cause hydrogen bond rearrangement by light include ginizarin,
Trihydrogenthraquinones and their derivatives are known. In addition, general-purpose thermoplastic resins such as polymethyl methacrylate and polyvinyl alcohol are used as the polymer matrix that disperses and supports these organic compounds.

Next, a method of utilizing this PHB phenomenon as an optical memory will be explained using FIGS. 7 and 8. FIG. 7 is a schematic diagram illustrating a typical PHB optical memory device. A laser beam 26 whose wavelength has been controlled and signal-processed by a wavelength control section 18 and an information signal processing section 20 passes from a laser light source 19 through a beam shift control section 21 and is formed into a spot 25 with a beam diameter of several microns on a PI (B optical memory element 22). The transmitted light is detected by the light detection section 23, and the light intensity signal is converted into an electrical signal and processed by the information signal processing section 24.For example, a set of "0" and "l" Let us consider the case of recording binary information "old 010", which is expressed as a combination.First, we irradiated the optical memory element 22 with a weak laser beam without signal processing, and measured the wavelength dispersion of the transmitted light intensity. Assume that a wide absorption band as shown by the broken line in a) is obtained.This absorption spectrum is processed by the signal processing unit 2.
4 (Figure 7). Next, the wavelength control section 18
(Figure 7) controlled wavelength λ2. If the absorption spectrum is observed again after irradiating the optical memory element 22 (Fig. 7) with a laser beam of λ4, it is possible to detect the dye contained in the spot 25 (Fig. 7) in the optical memory element according to the principle described in 2. λ2 in the molecule. Only a group of dyes sensitive to the wavelength λ4 undergoes a photochemical reaction, and hole 6 formation is observed at the positions of these wavelengths (FIG. 8(a)).

By comparing this absorption spectrum with the previously stored one, a signal corresponding to the hole as shown in FIG. 8(b) is obtained, indicating that information has been stored and reproduced.

In this way, in PTI B optical memory, guest molecules change into molecules with different electronic states by laser light irradiation, but this change is reversible;
Guest molecules that have changed due to laser irradiation can be returned to their original electronic state using light of a different wavelength. This indicates that the memory device using the PI-IB phenomenon is of an erasable type. P I-r B
In the case of a memory element that utilizes this phenomenon, the ratio of the absorption spectrum width ΔW+ and the formed hole width Δwh shown in FIG. 6(b) is approximately 103 when the temperature is around 4, so the recording density is
Assuming that the laser beam diameter is approximately 1 micron, approximately 10
A large value of 1' bit cm-' is expected.

(c) Problems to be Solved by the Invention As described in Section 2, information recording in optical memory devices using the PHB phenomenon takes advantage of the difference in transition energy that occurs as a result of individual differences in the microscopic local structure around guest molecules. It is something to do. Therefore, in order for this element to actually function as a recording element, it is necessary to stabilize this local structure, and in particular, to suppress the thermodynamic movement of the dispersed polymer matrix molecules themselves as much as possible. is necessary for stabilization. This is because the thermal motion of the polymer matrix molecules, in particular, causes rapid relaxation of the excited state of guest molecules and changes in the local structure, making the formed holes broader and shallower.

Therefore, the above-mentioned conventional optical memory element is used at an extremely low temperature (approximately 4 to 5 degrees T) using liquid helium, and recording, reproducing, and erasing at such a low temperature has only been confirmed.

In addition, there has recently been a report that hole formation was achieved at liquid nitrogen temperature, but the formed poles were wide-ranging.
Because it is shallow, it cannot be used as a memory device.

The present invention was made under such circumstances, and particularly aims to provide an optical memory element that is capable of recording, reproducing, and erasing based on the clear PHB phenomenon even at higher temperatures than in the past. .

(d) Means for Solving the Problems According to the present invention, in the polymer matrix,
There is provided an optical memory element comprising an optical memory layer comprising a dispersed support of an organic compound exhibiting phototautomerism or photo-induced hydrogen bond reorganization, and a polymer matrix comprising a three-dimensionally crosslinked polymer.

In this invention, the organic compound to be dispersed and supported in the polymer matrix is one that exhibits tautomerism or hydrogen bond reorganization property when the laser beam is irradiated onto the memory element. Examples of the latter include phthalocyanine, polyfin, chlorin, and derivatives thereof, and examples of the latter include quinizarin, trihydroxyandraquinone, and derivatives thereof.

In this invention, a three-dimensional crosslinked polymer is used as the polymer matrix that disperses and supports the organic compound described in 1. As this three-dimensional crosslinked polymer, various light-transmitting thermosetting resins, ultraviolet curable resins, electron beam curable resins, etc. can be used. A type photoresist or a photopolymer used in the so-called 2P method when manufacturing an optical disk can be used. Specific examples of such three-dimensional crosslinked polymers include polyester acrylate resins, epoxy acrylate resins, polyurethane acrylate resins, polyvinyl cinnamate resins, phenol resins, polyether acrylate resins, alkyd acrylate resins, etc. Among these, it is preferable to use those having a hydrogen-bonding group such as 01-I group (for example, epoxy acrylate resin, etc.) from the viewpoint of stabilizing the guest molecule. Among these, it is practically preferable to use a cured product of an ultraviolet curable resin.

The optical memory layer in the optical memory element of the present invention is formed by forming an uncured (=8) optically transparent glass substrate or synthetic resin substrate onto which an organic compound exhibiting phototautomerism and hydrogen bond reorganization is added. It can be formed by applying an uncrosslinked resin raw material and curing (crosslinking) this coated layer by heat curing, ultraviolet irradiation curing, electron irradiation curing, or the like. In addition, it is also possible to form the three-dimensional polymer layer by first forming the three-dimensional polymer layer on the substrate and then doping the organic compound described in item 1 from the outside. However, in the latter method, the guest molecules (organic compounds) enter the fixed pores in the polymer matrix, and the size of these pores makes it difficult for the guest molecules to be uniformly dispersed in the matrix. Usually, because there are cases where it is not possible to obtain
It is preferable to form by the former method. The amount of the organic compound dispersed and supported is determined by taking into account the solubility of the compound in the polymer matrix and the intermolecular interaction of the organic compound, but it is approximately 1.0-" in the optical memory layer.
moQ/Q level is suitable.

In addition, if the organic compound used in this invention exhibiting phototautomerism or hydrogen bond recoordination property is used in combination with a three-dimensionally crosslinked polymer that is bonded by a hydrogen bond or a covalent bond, the polymer matrix molecule It is possible to suppress not only the thermal movement of the dispersion-supported organic compound itself but also the thermal movement of the dispersed organic compound itself, which is more preferable in terms of reliability of the memory element. For example, dispersion support by hydrogen bonding can be carried out using TSPI' as an organic compound (guest molecule).
(Tetrasodium 5.10,15.20-tetra(
Using a polymer matrix that has a group capable of intermolecular hydrogen bonding, such as water-soluble porphins such as 4-sulfonate (phenyl)porphine), for example, epoxy acrylate-1. This can be easily carried out by using a combination of resins having a group capable of forming an intermolecular hydrogen bond, such as an OI-1 group, in the molecule. On the other hand, dispersion support based on covalent bonds to matrix polymers allows organic compounds (guest molecules) to
For example, this can be easily carried out by using a functional group that causes a crosslinking reaction when exposed to ultraviolet rays, such as an acryloyl group, a methacryloyl group, or an epoxy group. In particular, dispersion and support by covalent bonds is the most preferred embodiment because the local structure around the guest molecule is the most stable.

(e) Effect: According to the optical memory device of the present invention, an organic compound exhibiting phototautomerism or the ability to reorganize hydrogen bonds due to light is dispersed in a polymer matrix that is three-dimensionally cross-linked and whose thermal motion is significantly suppressed. As a result, the local structure around these organic compound molecules is significantly stabilized and stable PHB holes can be formed.As a result, recording, reproducing, and erasing of optical information that can withstand practical use can be performed at high temperatures. It can also be done in

(F) Embodiment (A) shown in FIG. 1 is a partial sectional view showing an embodiment of the optical memory element of the present invention. As shown in the figure, the optical memory element (A) is formed by forming an optical memory layer 2 on a transparent substrate 1 made of glass or plastic deck. The optical memory layer 2 is composed of a polymer matrix made of three-dimensional crosslinked polymers and an organic compound (guest molecule) that exhibits phototautomerism or photo-induced reorganization of f hydrogen bonds dispersed therein. It will be configured.

Here, the dispersion and support state when tetraphenylporphine (TPP) shown below is used as an organic compound and a cured product of an epoxy acrylate ultraviolet curable compound is used as a polymer matrix is schematically shown in the second column. Indicated.

In the figure, 3 indicates a guest molecule (TPP), and 4 indicates a three-dimensional polymer matrix molecule.

In this way, the matrix molecules around the TPP molecule are 3
Since it is dimensionally cross-linked, thermal movement is suppressed and P I-I B holes with good temperature stability can be formed on the absorption spectrum curve.

In addition, as an organic compound, tetrasodium 5,10,15.20- (tetra(4-
A schematic diagram in the case of using zulfonate phenyl)porphine (TSPP) is shown in FIG. In this way, TSPP
If you use something with an intermolecular hydrogen bonding group like
The matrix molecule 4 has OI (P, which has good temperature stability because the thermal movement around the guest molecule is further suppressed by the hydrogen bond 5 with the group) (B hole is formed).

Furthermore, if an organic compound having a crosslinkable group such as an acryloyl group is used, the guest molecules will be covalently bonded and dispersedly supported on the polymer matrix. This state is schematically shown in FIG. According to this dispersion support using covalent bonds, the stability around the guest molecule can be further enhanced compared to dispersion support using hydrogen bonds.

FIG. 5 schematically shows an optical memory device system for forming and measuring PHB holes. A wavelength tunable continuous wave dye laser 8 excited by an Ar'' laser 7 is used for P I-I B hole formation and measurement.The oscillation wavelength of the laser is changed by a scan controller. It is divided into two parts by a beam splitter 10, one of which enters a photodetector 15 as a reference light, and the other is reflected by a mirror 11, passes through an ND filter 12 if necessary, and enters a sample 14 cooled by a cryostat 13. In this device, since the change in absorbance due to hole formation is measured, the laser beam is incident on the photodetector 15 after passing through sample 11.14.The light incident on the photodetector 15 is converted into an electrical signal. , an A/D converter 16, and then sent to a computer 17 for processing.

Here, the dye T S P P I O-3m0Q/(l
Disperse it in ultraviolet curing resin (epoxy acrylate resin) and form a film on micro glass (thickness 0.1-1ax)
L, sample 14 of optical memory element cured by ultraviolet rays
was cooled to a temperature near liquid nitrogen using a continuous flow type cryostat 13, and irradiated with light at a wavelength of 64011 m using a wavelength tunable continuous wave dye laser 8 excited by an Ar'' laser 7 to form a PHB hole.

Thereafter, when the holes were measured using the same laser beam by reducing the light intensity by about 10-3.10-' times using the ND filter 12 and scanning the laser's oscillation wavelength, a narrow PHB hole was observed.

In this example, the sample used was one in which dye molecules were simply dispersed in an ultraviolet curing resin and cured by ultraviolet irradiation, but when actually used as an optical memory element, a substrate as shown in Fig. 1 was used. The optical memory layer 2 may be simply formed on the surface of the substrate 1, or a geometric pattern such as groups or pits may be formed on the surface of the substrate 1, or the optical memory layer 2 may be formed on the surface of the substrate l.
the high temperature.

In order to protect it from high humidity, the optical memory layer 2 may be sandwiched between upper and lower optically transparent protective films.

(g) Effects of the Invention As described above, the optical memory device according to the present invention is an optical memory device that records, reproduces, and erases information on a recording medium (optical memory layer) by irradiating light. It is constructed by dispersing and supporting an organic compound that has mutability or causes hydrogen atoms to be rearranged by light such as a laser beam in a three-dimensionally crosslinked matrix.

As a result, the thermal movement of the matrix molecules around the guest molecules is suppressed, so the local structure around the guest molecules is fixed even at high temperatures, and as a result, the temperature of the PHB hole formed by light such as laser light in the absorption spectrum This has the effect of improving stability against Therefore, it becomes possible to perform recording, reproduction, and erasing using the P I-I B phenomenon at higher temperatures than in the past.

[Brief explanation of the drawing]

FIG. 1 is a partial longitudinal sectional view showing an optical memory device according to an embodiment of the present invention, FIGS. 2 to 4 are schematic diagrams showing the structure of the optical memory layer of the optical memory device according to the present invention, and FIG. 5 is an embodiment of the present invention. FIG. 6 is an explanatory diagram of the P I-I B phenomenon, FIG. 7 is a configuration explanatory diagram illustrating a conventional optical memory device, and FIG. FIG. 1 is an explanatory diagram showing the principle of applying the PI-IB phenomenon to optical memory operation. ■... Substrate, 2... Optical memory layer, 3... Guest molecule, 4... Polymer matrix molecule, 5...
・Absorption curve, 6...Hall, 7...
...Ar" laser, 8...Dye laser, 9.
... Scan controller, 10 ... Beam splitter 11 ... Mirror 12 ... ND filter 13 ... Cryostat, 14 ... - Sample, 15...Photodetector 16...A/D converter, 17...Computer, 18...Wavelength control unit, 19... ...Laser light source, 20.24... Information signal processing section, 21
...Beam shift control section, 22... Optical memory element, 23... Photo detection section, 25...
...beam spot, 26...laser light, ...optical memory element. Director Gi Negara Chen

Claims (1)

[Claims] 1. Equipped with an optical memory layer in which an organic compound exhibiting phototautomerism or photo-induced hydrogen bond reorganization is dispersed in a polymer matrix, and the polymer matrix is composed of a three-dimensionally cross-linked polymer. An optical memory device.