JP2866940B1 - Nonlinear optical materials and devices using transition element-doped fine particles - Google Patents

Abstract

An object of the present invention is to provide an optical material having a fast response time and exhibiting large nonlinearity in order to realize high-speed optical information processing. It is another object of the present invention to provide a hole-burning material family in which deep holes are formed in a short time at a temperature close to room temperature, particularly in order to realize high-density optical information recording. A non-linear optical material utilizing a non-linear optical effect exhibited by fine particles having a diameter of 0.5 nm to 10 μm doped with a transition element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonlinear optical material and a nonlinear optical element, and more particularly to a nonlinear optical material suitable for high-speed processing of optical information and high-density optical recording, and an element using the same.

[0002]

2. Description of the Related Art For high-speed processing of optical information, electronic circuit technology is mainly used at present. In other words, in the current optical communication, the backbone signal carried by the optical fiber is once converted into electronic information, then subjected to information processing such as modulation, demodulation, and multiplexing, and then converted into an optical signal again and transmitted. ing.
If all-optical communication and optical information processing in which light is controlled by light can be realized without performing such multi-step processing, a dramatic increase in information processing speed can be realized.

[0003] However, light does not directly interact with other light. Therefore, it would be advantageous if a material capable of causing a change in polarization or electronic state by light irradiation as an intermediate process could be used. Such a material is required to have a fast response speed and exhibit a large nonlinear optical effect. According to one study, a material whose response speed is less than 10 picoseconds and whose nonlinear susceptibility is 10 ^-7 esu or more when expressed by third-order nonlinearity is required. The technology to control light with light has not yet been put to practical use, since no has been found.

[0004] In the high-density optical recording technology, 1-bit information is currently recorded in one place of a recording medium. For this reason, the recording density is defined by the spot diameter of light condensed during information recording and reproduction. Since the diameter of the light spot has already reached the diffraction limit of about 1 μm with the current technology, it is said that the recording density will not be able to greatly exceed the already realized recording density of 100 Mbit / cm ² in the future.

As a method of greatly exceeding the recording density determined by the diffraction limit, Castro et al. Have already proposed a wavelength multiplexing optical recording system using a permanent hole burning phenomenon.
(U.S. Patent No. 4,101,976; July 18, 1978). The permanent hole burning phenomenon refers to a phenomenon in which a sharp decrease (hole) occurs in the light absorptance of a specific wavelength in an absorption spectrum, and this does not disappear even after a lapse of time. By taking advantage of this phenomenon, which is particularly noticeable at cryogenic temperatures, the presence or absence of holes at specific wavelengths can correspond to digital recordings 0 and 1. Therefore, by changing the wavelength of the light applied to one recording spot, a large amount of information can be recorded. This technique is called wavelength multiplexed optical recording. Using this technology, high recording density is unlikely to be achieved with current methods
To achieve (> 10 Gbit / cm ² ), it is necessary to open (record) a deep hole in a short time. Further, practically, it is preferable that recording and reproduction can be performed at a temperature as close to room temperature as possible. Heretofore, it has been reported that holes can be formed at room temperature particularly in crystals and glass materials doped with samarium ions. However, even in such a case, the samarium ion absorbs light very easily (oscillator strength) as compared with an organic dye or the like. Therefore, in order to form a hole, irradiate strong light for a long time. There is a need. For this reason, at present, no suitable material has been found for putting the idea of wavelength-division multiplex optical recording to practical use.

[0006]

SUMMARY OF THE INVENTION The present invention provides an optical material having a fast response time and a large nonlinearity in order to realize the high-speed processing of optical information described in connection with the above-mentioned prior art. The purpose is to:

Another object of the present invention is to provide a hole burning material family in which deep holes are formed in a short time at a temperature close to room temperature in order to realize the high-density optical recording described in relation to the above prior art. Also aim.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor has made various studies and, as a result, has conceived of utilizing a unique optical effect exhibited by fine particles doped with a transition element. For more information, see the Fork Report (Fizigal
Review Letters, Volume 32, 781-783 (1974) and Physical Review Bee, Volume 19, 3365-3398 (1979)
Letters, Vol. 72, pp. 416-419 (1994)), was conceived to utilize the unique optical effect exhibited by the transition element-doped fine particles.

[0009] These reports indicate that doping of crystalline or amorphous solid fine particles of chalcogenide or fluoride with europium ion, manganese ion or the like makes it easier to absorb and emit light as compared with a bulk material. (More precisely, the oscillator strength) is improved by 5 orders of magnitude or more. The present invention has succeeded in solving the above-mentioned important problems in high-speed optical information processing and high-density optical recording by using this phenomenon.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, transition element-doped fine particles as a nonlinear optical material according to the present invention, an element using the fine particles, high-speed optical information processing and high-density optical recording using the element will be described in detail.

The transition element used as a dopant in the present invention is an element belonging to Group 3A to Group 7A, Group 8 and Group 1B of the Long Periodic Periodic Table (published by Iwanami Shoten Co., Ltd., 4th edition). Say. Of these, lanthanides are the lanthanides from atomic number 57 to lutetium 71.
Refers to an element. Among these transition elements, lanthanides and manganese such as samarium and europium,
Transition metals such as iron, cobalt, nickel, copper, silver, chromium and the like are more preferred. When lanthanide is used as a dopant, the absorption line width of the optical spectrum is narrow,
A material having even more excellent nonlinearity can be obtained. It is also possible to use two or more transition elements in combination as a dopant.

The fine particles doped with such a transition element include semiconductors, chalcogenides and fluorides. More specifically, ZnS, ZnSe, which are II-VI group semiconductors,
CdS, CdSe; III-V group semiconductors such as GaAs, InP, and GaP;
Examples of chalcogenides include EuO, EuS, and EuSe; and fluorides such as CaF ₂ , SrF ₂ , BaF ₂ , and CdF ₂ .

In the combination of the dopant and the fine particles, it is advantageous that the valence and the ionic radius of the dopant element match those of the fine particles.

In particular, when semiconductor fine particles are used as fine particles, they are advantageous because they absorb visible light or ultraviolet light and transmit energy to doped elements.

The particle size of the fine particles is in the range of 0.5 nm to 10 μm, particularly preferably in the range of 1 to 10 nm. That is, the fine particles targeted by the present invention exhibit a unique phenomenon of increasing the oscillator strength when the diameter is 10 μm or less. This phenomenon is particularly remarkable when the diameter of the fine particles is 10 nm or less. In the case of fine particles having a diameter of 10 nm, typically about 5000 molecules are contained. The number of transition elements doped therein is typically about several atoms (or several ions),
The doping amount at this time is on the order of 0.1 atomic%. On the other hand, when the size of the fine particles becomes about 0.5 nm or less in diameter and the number of molecules becomes a cluster, the effect of increasing the oscillator strength can no longer be recognized. In this case, even if one atom (or one ion) is doped in one fine particle, the doping amount is several tens of atomic%. Therefore, the doping amount of the transition element with respect to the fine particles is in the range of 0.1 to several tens atomic%, and more preferably in the range of 0.2 to 5 atomic%.

One specific example in which the effect of increasing the oscillator strength becomes remarkable is ZnS doped with Mn ²⁺ ions (having a diameter of 3 nm).
In this case, the doping amount of Mn ²⁺ ions at this time is on the order of about 1 atomic%.

In the present invention, the size (particle size) of the fine particles is represented by the expression "diameter". However, the fine particles need not be spherical, and even if they have other shapes, the size is within the specified range. To the extent possible, it is naturally included in the present invention. The particle size can be measured by a transmission electron microscope, a line width of an X-ray diffraction spectrum, a shift of a light absorption wavelength from a bulk, and the like.

Fine particles doped with a transition element (hereinafter referred to as "doped fine particles" unless otherwise required) can be produced by a known method. Such a manufacturing method,
For example, (1) Chemistry Letters, pp1665-1666 (19
92), (2) Bulletin of Chemical Society of Japan, vol. 68, pp. 752-758 (1995), and the like.

In general, fine particles have a large surface energy, and therefore are apt to aggregate with each other and are unstable. For this reason,
Also in the present invention, it is preferable to coat the surface of the doped fine particles with a transparent material such as methyl methacrylate which does not hinder the optical properties, in the same manner as the method already reported.

Further, from a practical point of view, dispersing the doped fine particles in a transparent matrix (inorganic glass, polymer material, etc.) in the wavelength range of the light to be irradiated can also prevent the aggregation of the fine particles and improve the stability. It is extremely effective for maintaining. In particular, when the sol-gel method is used, an inorganic glass such as silica glass can be produced at a low temperature from the state of a solution. By mixing dope particles in this solution, glass in which the dope particles are easily dispersed can be produced. it can. The glass thus produced becomes porous by heat treatment at a temperature not exceeding 800 ° C, more preferably at a temperature in the range of 500 to 600 ° C. Can be modified. Examples of such a gas include hydrogen, hydrogen sulfide, naphthalene, metal carbonyl, and iodine. The dangling bond on the surface of the fine particles can be eliminated by contact with hydrogen, or the fine particles can be sulfurized by contact with hydrogen sulfide. Further, when the sol-gel method is used, there is also an advantage that a glass thin film containing dispersed dope particles can be easily formed on a desired substrate by dip coating, spin coating, or the like from a solution in which the doped particles are dispersed. is there. Since the matrix thus formed basically exhibits the properties of glass, it has the advantage of being excellent in various properties such as mechanical, thermal and chemical.

Further, by dispersing doped fine particles obtained by combining a plurality of transition elements (dopants) and a plurality of fine particles in a transparent matrix in the wavelength range of irradiation light,
A material having a plurality of absorption / emission wavelength bands is obtained. In this case, for example, as a wavelength multiplexed optical recording material, the wavelength width to be recorded can be widened, which is advantageous. Further, by changing the applied electric field, the Stark effect can be caused to obtain the same effect as the wavelength sweep.

Further, by dispersing semiconductor fine particles doped with a transition element in a conductive matrix and irradiating light while applying an electric field, a photochemical reaction can be promoted.

The application of the doped fine particles according to the present invention to a high-speed optical information processing technique will be described. First, the reason why the nonlinear optical effect can be increased in the transition element-doped fine particles is as follows.

In general, when light is incident on a substance, the substance is shaken by the electric field E of the light and has a polarization P. If the polarization in the coordinate axis x direction is Px,

[0025]

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## EQU2 ## Here, j, k, and l represent the directions of the spatial coordinate axes (any of x, y, and z) in the laboratory system. According to the teaching of quantum mechanics, the nth-order nonlinear susceptibility (the magnitude of nonlinearity) χ ⁽ⁿ⁾ is proportional to K
χ Approximately, using the frequency ω of the irradiated light, the frequency ω _{mg at} which the substance absorbs light, and the oscillator strength f _mg of the transition.

[0027]

Embedded image

(For example, see Koji Kushida, Asakura Shoten, "Optophysical Physics", Chapter 3). In the fine particle system targeted in the present invention, the oscillator strength f _mg is extremely large. Therefore, by irradiating light having a frequency ω near the frequency ω _mg at which the substance is absorbed, the numerator is large in the equation (2) and the denominator becomes a value close to 0, so that a very large χ ^{( n)} is obtained.

Next, the reason why the response speed of the nonlinear optical effect can be increased in the transition element-doped fine particles is as follows.

The time t required for a transition between two levels is:
Energy difference between levels ω _mg , energy of irradiated light ω
And using the proportionality constant K _t

[0031]

Embedded image

(Eg, by Rodney Loudon, Oxfo
rd University Press, "The QuantumTheory of Light",
Second Edition, see Chapter 2). In general, in the 4f-4f transition of a lanthanide ion, the 4f orbital is shielded by outer electrons and is hardly affected by surroundings, so that the line width of the absorption spectrum is extremely narrow. Therefore, if lanthanide ions are selected as the element to be doped, even if the energy ω of the irradiated light is close to the energy difference ω _mg between the levels, since the light is transparent, the light sufficiently enters the substance, which is convenient. . At this time, ω _mg -ω can be set to a value that makes the response time t shown in (3) less than 1 picosecond and also makes χ ⁽ⁿ⁾ shown in equation (2) sufficiently large.

For the first time, the oscillator strength is high and the light of such ω is used as the irradiation wavelength.
Expressed by the following nonlinear susceptibility, 10 ^-7 esu or more, response speed is 10
A fine particle-dispersed nonlinear optical material having a picosecond or less can be obtained, and application to high-speed optical information processing technology is possible. The nonlinear susceptibility and the response speed can be measured simultaneously by, for example, a degenerate four-wave mixing test as reported in Sakaguchi et al., Chemistry Letters, pp 281-284 (1992).

The material according to the present invention having such high nonlinearity and response speed can be used for a circuit exhibiting optical bistability for high-speed optical information processing. Further, it can be used for an optical multistable element in which a large number of optical bistable circuits are connected. Further, it is also possible to manufacture an optical operation element or a storage element using such an optical bistable circuit.

Next, application of the doped fine particles according to the present invention to a high-density optical recording technique will be described.

In order to realize a high recording density, as described in the paper by Murase et al. (Journal of Optical Society of America, Vol. 9, pp. 998-1005 (1992), It is necessary to make holes in a short time, so that information can be read out with a sufficient S / N ratio in a realistic time (less than 10 nanoseconds / bit). Lanthanide (eg, samarium ion) -doped glass is known as a material in which permanent hole-burning is observed even at room temperature. According to the present invention, it is necessary to dope samarium ions into microparticles for a very long time (for example, about several minutes). Doko strength can be improved by several orders of magnitude, it is possible to hole formation in a short time.

Further, when an electric field is applied to such doped fine particles, the energy level can be shifted by the Stark effect. As a result, for example, in the case of high-density recording, the same effect as when the wavelength is swept is obtained. Practically, it is useful to change the applied electric field rather than sweep the wavelength in many cases. Further, when an electric field is applied in a state where the transition element-doped semiconductor fine particles are dispersed in a conductive matrix, it is also possible to promote the photochemical reaction by causing the movement of electrons at the time of light irradiation. . Use of a semiconductor as the fine particles provides such advantages.

The nonlinear optical effect referred to in the present invention is:
This utilizes the polarization by the photoelectric field shown in the equation (1). Therefore, a laser utilizing the fine particles targeted in the present invention is not included in the present invention.

According to the present invention, a nonlinear optical phenomenon that can be applied to high-speed optical information processing and high-density optical recording by applying a unique optical phenomenon of an abnormal increase in oscillator strength caused by doping fine particles with a transition element. An optical material and an element using the same can be manufactured.

[0040]

When the doped fine particles according to the present invention are used in the field of high-speed optical information processing, a large nonlinear optical effect is exhibited, so that light can interact with another light without passing through an electronic circuit. Will be possible. Moreover, since the response time is as fast as 10 picoseconds or less, it can satisfy the demands of the real world.

When the doped fine particles according to the present invention are used in the field of high-density optical recording, the oscillator strength of dopant ions can be increased by several orders of magnitude, so that a hole burning phenomenon can be observed with less light irradiation. Become like
As a result, a deep hole can be formed (recorded) in a short time even at a high temperature particularly near room temperature, which satisfies the demand for a realistic memory. Also,
By changing the wavelength of light applied to one recording spot, wavelength multiplexing optical recording can be performed, and the recording density can be dramatically increased.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings.

Example 1 A system (ZnS: Sm) in which zinc sulfide (ZnS), a kind of semiconductor, was doped with samarium (Sm), a kind of lanthanide, was divided into material (fine particle) production and hole burning experiments. Will be explained.

1. Preparation of material (fine particles) The preparation of fine particles was reported by Yanagida et al. (Chemistry Letters, pp1665-1666 (1992) and Bulletin of Chemical Society of Japan, Vol. 68, pp752-75)
8 (1995)).

First, 0.1 mol of zinc acetate and samarium acetate
0.001 mol was dissolved in methanol containing acetonitrile under stirring. Meanwhile, 0.1 mol of sodium sulfide was dissolved in methanol containing water with stirring. The obtained solution of sodium sulfide was added dropwise to a solution containing zinc acetate and samarium acetate while stirring. At this stage, ZnS fine particles doped with Sm were generated, and the solution became colloidal and became cloudy.

Next, a solution of pentafluorothiophenol in acetonitrile was added dropwise to the colloid solution with vigorous stirring. By this operation, the surface of the doped fine particles is covered with the phenyl group, and the fine particles do not polymerize with each other, and are stabilized. The solution was centrifuged to remove the supernatant, and the solution was evaporated to remove fine particles. At this stage, if necessary, it may be washed with water and then with methanol. All of the synthesis of the fine particles was performed under a nitrogen atmosphere, and the solvent was blown with nitrogen before use to expel other dissolved gases.

From the results of X-ray diffraction and transmission electron microscope observation, it was confirmed that the obtained fine particles had an average diameter of about 5 nm.

2. Hole Burning Experiment As shown in FIG. 1, the powdery fine particle sample prepared above was placed in a small quartz cell and fixed in a cryostat. The cryostat can keep the sample at any temperature from 2 Kelvin to room temperature as needed. Next, the dye (rhodamine 6G) was excited by an argon laser to oscillate laser light having a wavelength of about 560 to 620 nm.

In this embodiment, since the material is a powder,
The absorption spectrum cannot be easily measured. For this reason, the excitation spectrum was measured. That is, the wavelength was continuously swept by rotating the optical element shown in FIG. 1 by a stepping motor. After adjusting the intensity of the excitation light to about 10 mW using an intensity stabilizer, the excitation light was focused on the sample surface through an ND filter. The light emitted from the sample was collected by a lens, input to a spectroscope, and the split light was guided to a photomultiplier tube.
In order to cause permanent hole burning, the sample was directly irradiated with light from a dye laser having a fixed wavelength without passing through an ND filter.

FIG. 2 shows an excitation spectrum when hole burning is performed at room temperature with an irradiation light wavelength λ _b of 592.9 nm. It can be seen that the hole is free to the wavelength λ _b. In this case, changing the samarium ion from divalent to trivalent is considered to be the mechanism of the photochemical reaction. This hole exists stably even at room temperature, indicating that permanent hole panning has occurred. In this example, holes were able to be formed in a shorter time than in the prior art because the oscillator strength of the doped fine particles was increased.

Embodiment 2 An example of wavelength multiplexed optical recording will be described.

The doped fine particles produced in Example 1 were
It was dispersed in glass using the gel method. That is, 5.5 g of ethanol was added to 3 g of the aqueous solution containing the doped fine particles, and chloroform was added as needed to further improve dispersibility. Next, tetramethoxy orthosilicate
An ethanol solution containing 7 g of (Si (OCH ₃ ) ₄ ) was added and stirred for 30 minutes. The obtained sol solution was dip-coated on a clean quartz substrate, heat-treated, hydrolyzed, and polymerized to prepare a fine particle-dispersed glass thin film.

Since the produced glass thin film is optically transparent, its absorption spectrum can be easily measured. Using an apparatus similar to that shown in FIG. 1, the absorption spectrum of a thin film sample usable as the recording medium was measured. By changing the irradiation wavelength sequentially by setting the sample at a very low temperature, permanent hole burning was caused at many wavelengths, and a lot of information could be recorded in one place of the recording medium. FIG. 3 shows an example in which five holes are opened. At the top of FIG. 3, digital records 1 and 0 are written corresponding to the presence or absence of a hole.
In the case of this embodiment, 11-bit information is recorded in the same location on the recording medium.

From the results shown in this example, it is clear that wavelength multiplex optical recording is possible when the optical material of the present invention is used.

Example 3 Using the fact that a titanium oxide (TiO ₂ ) thin film formed by a sol-gel method exhibits conductivity, hole burning using a photochemical reaction caused by photoexcitation and application of an electric field will be described.

The fine particles ZnS: Sm prepared in Example 1 were mixed with a mixed solution of Ti (OC ₃ H ₇ ) ₄ in water and ethanol, and the mixture was placed on a glass substrate coated with an electrically conductive nesa film (ITO film). By dip coating and heat treatment, a TiO ₂ thin film (n-type semiconductor) was formed. A film with a thickness of about 1 μm can be formed by one dip coating, so by repeatedly coating,
The film thickness could be increased.

By simultaneously irradiating the obtained thin film (thickness of about 10 μm) with light near 300 nm which is the absorption wavelength of ZnS and light near 600 nm which is the absorption wavelength of samarium while applying an electric field, Permanent hole burning was able to occur in the absorption region of samarium with about 1.5 times efficiency. This is probably because the holes formed in ZnS were moved by the electric field and efficiently combined with the samarium ions.

Embodiment 4 A method of applying an electric field instead of the wavelength sweep will be described.

The same fine particle dispersion sol as in Example 3 was dip-coated on a quartz substrate on which a transparent conductive film was attached to prepare a thin-film glass, and then narrowed by the quartz substrate on which a similar transparent conductive film was attached. By keeping the wavelength of hole burning constant and applying a voltage of 1000 V, it was possible to form holes at different positions on the wavelength, as shown in FIG.

Example 5 For a system (ZnS: Mn) in which zinc sulfide (ZnS), a kind of semiconductor, was doped with manganese (Mn), a kind of transition element, material (fine particles) preparation and optical bistable element Will be described separately.

1. Preparation of material (fine particles) The sample preparation was reported by Sukhral et al. (Journal of Physical Chemistry, vol. 100, pp4551-4555 (199
6 years).

A 20 mM (mmol / liter) aqueous solution of zinc nitrate, manganese nitrate and sodium sulfide was prepared. Distilled water was used after degassing with argon. A new solution was prepared for each experiment. The preparation of the fine particles was all performed in an argon atmosphere.

A solution of zinc nitrate and manganese nitrate was mixed to a volume of 50 ml so that the ratio of Mn to Zn was 2%.
10M (mol / liter) sodium hydroxide was added dropwise with stirring to adjust the pH to about 10. While stirring this solution at a constant speed, 50 ml of an aqueous solution of sodium sulfide was dropped at a constant speed to prepare fine particles of ZnS: Mn2%. Stirring was continued for 10 minutes to ensure the progress of the reaction. After leaving the generated aqueous solution for a while, the supernatant was discarded, and the remaining portion was used for the experiment.

The fine particles were found to be zinc sulfide having an average diameter of about 4 nm from the X-ray diffraction peak position and the half width of the peak. Also, transmission electron microscope observation confirmed that the average particle size was about 4 nm.

The fine particles were converted to polyvinyl alcohol (PVA)
The inside was doped by the following procedure.

4 g of PVA was dissolved in 50 ml of distilled water, and about 2 ml of an aqueous solution containing Mn-doped zinc sulfide fine particles was added dropwise with vigorous stirring, followed by stirring for about 10 minutes and mixing. This solution was dip-coated on a quartz substrate whose reflectivity was appropriately controlled to prepare a thin film having a suitable thickness. The emission of manganese ions is around 590 nm, and in this wavelength range, the PVA used as the matrix in this example is transparent.

2. Production of Optical Bistable Element A Fabry-Perot interferometer was produced by covering the thin film on the substrate produced above with another quartz substrate whose reflectance was controlled. The usual method shown in FIG.
4, light emitted from a dye (rhodamine 6G) laser was incident on the interferometer, and the transmitted light intensity was measured by the method described in Optical Bistability, by Eiichi Hanamura.

FIG. 6 shows the incident light intensity dependence of the transmitted light intensity. When the incident light intensity was gradually increased starting from FIG. 6, the transmitted light intensity change indicated by the curve was obtained. Next, when the intensity of the incident light was reduced, the transmitted light intensity change indicated by the curve was returned. As a result, it is understood that optical bistability appears as a whole. Since the nonlinearity is large, the light intensity can be reduced and the response speed can be increased.

Since this optical bistable characteristic corresponds to a flip-flop in the case of an electronic circuit, the nonlinear optical material of the present invention can be used for an arithmetic element using light, a storage element utilizing hysteresis, and the like.

Example 6 In addition to ZnS, the type of semiconductor to be dispersed was zinc selenide.
In the case of using (ZnSe), cadmium sulfide (CdS) and cadmium selenide (CdSe), the optical material of the present invention can be manufactured in the same manner as in Example 1 or Example 5.

As shown in FIG. 7, it is possible to continuously set the wavelength to be absorbed by using a plurality of semiconductors. As a result, it was possible to irradiate a specific light within a wide range of 300 to 500 nm to cause the semiconductor to absorb the light once and then cause energy transfer to the doped ions.

By making the semiconductor to be dispersed into fine particles, there is also an advantage that the oscillator strength of the semiconductor itself is increased due to the size effect, and energy is easily transferred to the doped ions. By using a plurality of types of fine particles as described above, the wavelength range in which multiplex recording can be performed by, for example, wavelength multiplex optical recording can be expanded. Also, by changing the type of the transition element to be doped, it was possible to extend the operating wavelength range of the optical bistable element.

To further adjust the absorption peak wavelength,
It was also possible to control the particle size and to make a mixed crystal such as Zn _x Cd _(1-x) S _y Se _(1-y) .

[Brief description of the drawings]

FIG. 1 shows a samarium ion source obtained in an example of the present invention.
FIG. 2 is a schematic view of an apparatus for performing hole burning using zinc sulfide fine particles.

FIG. 2 is a graph showing the results of hole burning at room temperature of samarium ion-doped zinc sulfide fine particles obtained in Examples of the present invention.

FIG. 3 is a graph showing a result (11-bit information recording) of performing wavelength multiplex optical recording at an extremely low temperature using samarium ion-doped zinc sulfide fine particles obtained in an example of the present invention.

FIG. 4 uses the samarium ion-doped zinc sulfide fine particles obtained in the example of the present invention, instead of sweeping the wavelength,
4 is a graph showing a result of performing hole burning while applying a voltage of 1000V.

FIG. 5 is a schematic diagram showing a state of interference of light transmitted through a Fabry-Perot resonator made of a nonlinear optical material made of manganese ion-doped zinc sulfide obtained in an example of the present invention.

FIG. 6 is a graph showing the dependence of transmitted light intensity on incident light intensity for a nonlinear optical material comprising manganese ion-doped zinc sulfide obtained in an example of the present invention.

FIG. 7 is a graph showing light emission from manganese in a system in which four types of semiconductor fine particles doped with manganese are mixed.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Atsushi Kurita, Inventor 1-1, Machikaneyama, Toyonaka City, Osaka Prefecture Osaka University Graduate School of Science (72) Inventor, Yasuo Kanematsu 1-1, Machikaneyama, Toyonaka City, Osaka Prefecture Osaka University Graduate School of Science (72) Inventor Masahito Watanabe 1-1, Machikaneyama, Toyonaka City, Osaka Prefecture Osaka University Graduate School of Science (72) Kuniko Hirata 1-1, Machikaneyama, Toyonaka City, Osaka Prefecture Graduate School of Science, Osaka University Within the Graduate School (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/35 503 G02F 1/35 505 JICST file (JOIS) CA (STN)

Claims (11)

(57) [Claims] 1. A nonlinear optical material utilizing a nonlinear optical effect exhibited by fine particles having a diameter of 0.5 nm to 10 μm doped with a transition element. 2. A nonlinear optical material utilizing a third-order nonlinear optical effect exhibited by fine particles having a diameter of 0.5 nm to 10 μm doped with a transition element. 3. A nonlinear optical material utilizing a hole burning phenomenon in an optical spectrum of fine particles having a diameter of 0.5 nm to 10 μm doped with a transition element. 4. A nonlinear optical material utilizing a nonlinear optical effect exhibited by fine particles having a diameter of 0.5 nm to 10 μm doped with one or more kinds of lanthanides. 5. The nonlinear optical material according to claim 1, wherein one or more kinds of semiconductors are used as the fine particles. 6. The nonlinear optical material according to claim 1, wherein a third-order nonlinear susceptibility is 10 ⁻⁷ esu or more and a response time is 10 picoseconds or less. 7. The method according to claim 1, wherein the fine particles doped with a transition element are dispersed in a transparent matrix in a wavelength range of light for irradiation.
7. The nonlinear optical material according to any one of items 1 to 6, 8. An optical bistable element or an optical multi-stable element using the nonlinear optical material according to claim 1. 9. An optical operation element or an optical storage element using the nonlinear optical material according to claim 1. 10. A wavelength-division multiplexed optical recording material using the nonlinear optical material according to claim 1. 11. The material or device according to claim 1, wherein an electric field is applied.