JPH06301071A - Semiconductor superfine particle-dispersed nonlinear optical element - Google Patents

Abstract

PURPOSE:To provide a nonlinear optical element reduced in optical loss and capable of being operated even at room temp. by using a highly light transparent wavelength range on the longer wavelength side than a superfine particle exciton absorption peak as the signal light wavelength anti pump light wavelength for the semiconductor superfine particle dispersing element. CONSTITUTION:The semiconductor superfine particles have an average diameter of 1-100nm, and group IV element such as silicon and germanium, the oxide semiconductor such as TiO2 and ZnO and the compd. semiconductor such as GaAs and InP are used. For example, the hydride such as gaseous hydrogen sulfide and hydrogen selenide, org. chalcogenides, etc., is added to a raw material soln. contg. the compd. of metal such as Cd and Zn and irradiated with light to form a semiconductor particle, and the particle is grown to produce the II-VI compd. semiconductor superfine particle of CdS, CdSe and ZnSe. The semiconductor superfine particles are dispersed in glass or polymer and formed into the thin film, lens, fiber, etc., which are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to generation of a phase conjugate wave used in devices such as ultra-high speed optical switching devices and holographic devices for optical-optical information transmission, optical-optical information processing, optical-optical image processing and the like. Optical bistability, optical Kerr effect, etc. 3
The present invention relates to a nonlinear optical element that utilizes the following nonlinear optical characteristics.

[0002]

[Prior art]

(General Characteristics of Semiconductor Ultrafine Particle Material) It goes without saying that semiconductors are used in a wide variety of fields in the form of thin films and particles such as electronic component materials, optoelectronic materials, medical materials, catalyst materials, and sensor materials. Furthermore, it has been noted that when the semiconductor is made of ultrafine particles having a small particle size of 100 nm or less, a unique property that cannot be seen in the bulk body or the size of conventional particles appears. It is being applied. Above all, the emergence of nonlinear optical properties that apply the electronic singularity due to the small crystal space is expected. The shape of such a small crystal space may be a thin film shape, a rod shape, a disk shape, or the like.
In the case of ultrafine particles, there is an advantage in that the appearance of performance is isotropic as compared with these forms. (Conventional manufacturing method of semiconductor ultrafine particles) As a manufacturing method of semiconductor particles or semiconductor ultrafine particles, generally, a manufacturing method by mechanical pulverization or a vapor phase utilizing evaporation using heat or plasma is used. Known production methods, liquid phase production methods utilizing precipitation, hydrolysis, and the like are known. These manufacturing methods are described in, for example, "Particle Handbook" (edited by Genji Jimbo et al., Asakura Shoten, 1991).

In the production and handling of semiconductor ultrafine particles, control of particle size and particle size distribution and enhancement of storage stability thereof are important issues for exhibiting a unique function of ultrafine particles.

With respect to ultrafine particles, some techniques have been proposed for controlling the particle size of the nanometer order. For example, there is a method of narrowing the particle size distribution using a protective colloid in the production in the liquid phase, and a method of collecting the produced particles from a predetermined position of the evaporation flame in the gas evaporation method in the gas phase. . Further, as described in JP-A-4-189801, a method has been proposed in which an electron transfer agent and a monomer having an unsaturated bond are allowed to coexist in a solution, and semiconductor ultrafine particles are synthesized while being irradiated with light. ing. (Conventional performance and problems of semiconductor ultrafine particle materials) On the other hand, semiconductor ultrafine particle materials as nonlinear optical materials exhibit relatively large non-linearity in colored glass filters, which are dispersion materials of semiconductor ultrafine particles in a glass matrix. Has been reported. In the range of third-order nonlinear optical susceptibility of these color glass filter chi ⁽³⁾ is approximately 10 ^{@ 10} to ^{10 -9} electrostatic units (esu), also 1.3 × the largest of
10 it ^{over 8} an electrostatic unit, for example, Applied Physics 59
Volume 6, pages 738-745 (1990). However, these nonlinear optical susceptibility χ
The value of ⁽³⁾ was small and not sufficient for practical use.

In order to put the nonlinear optical material into practical use, it is desired to develop an element to which a semiconductor laser can be applied as a light source. Therefore, a material having a higher third-order nonlinear optical susceptibility χ ⁽³⁾ operating at a light intensity lower than the semiconductor laser level, for example, 10 ⁻⁷
Materials with more than electrostatic units are desired.

(Description of the Drawings) The prior art and the present invention will be described below with reference to the accompanying drawings as needed. First, the attached drawings will be described.

FIG. 1 shows the absorption of a conventional semiconductor ultrafine particle dispersion.
Light coefficient α, third-order nonlinear susceptibility χ ⁽³⁾, Χ⁽³⁾/ Α and light
It is explanatory drawing which shows the relationship of wavelength, and a horizontal axis is a light wavelength.

In FIG. 1, 1 is a solid line showing the relationship between the absorption coefficient of the ultrafine semiconductor particle dispersion and the light wavelength, 2 is a broken line showing the relationship between the third-order nonlinear susceptibility χ ⁽³⁾ and the light wavelength, 3 is a two-dot chain line showing the relationship between χ ⁽³⁾ / α and the light wavelength, 4 is a one-dot chain line showing an exciton absorption peak, and 5 is an arrow showing an example of the operating wavelength.

FIG. 2 is an explanatory diagram of the relationship between the absorption coefficient α of the semiconductor ultrafine particle dispersion of the present invention, the third-order nonlinear susceptibility χ ⁽³⁾ , χ ⁽³⁾ / α, and the light wavelength. The axis is the wavelength of light.

In FIG. 2, 1 is a solid line showing the relationship between the absorption coefficient of the semiconductor ultrafine particle dispersion and the light wavelength, 2 is a broken line showing the relationship between the third-order nonlinear susceptibility χ ⁽³⁾ and the light wavelength, 3 is a two-dot chain line showing the relationship between χ ⁽³⁾ / α and the light wavelength, 4 is a one-dot chain line showing an exciton absorption peak, and 5 is an arrow showing an example of the operating wavelength.

FIG. 3 is an explanatory view of a wavelength region having a wavelength longer than the exciton absorption peak, and the horizontal axis is the light wavelength.

In FIG. 3, 1 is a solid line showing the relationship between the light absorption wavelength and the absorption coefficient of the semiconductor ultrafine particle dispersion, and 2 is χ ⁽³⁾ /
A broken line showing the relationship between α and the light wavelength, 3'denotes a one-dot chain line showing an exciton absorption peak, and 4'denotes a two-dot chain line showing an example of the operating wavelength (light pulse).

FIG. 4 shows χ ⁽³⁾ / α at each wavelength of the cadmium sulfide ultrafine particle dispersion film obtained in Example 1.
2 is a graph of the extinction coefficient α and χ ⁽³⁾ .

In FIG. 4, 1 is a solid line showing the spectrum of the absorption coefficient α of the cadmium sulfide ultrafine particle dispersion obtained in Example 1 with respect to wavelength, and 2 is the third-order nonlinear susceptibility χ ^{(3) at} each wavelength. The measurement results are shown by ●, 3 is the result of χ ⁽³⁾ / α at each wavelength, and Δ is the one-dot chain line showing the exciton absorption peak.

FIG. 5 shows χ ⁽³⁾ / α at each wavelength of the cadmium sulfide ultrafine particle dispersion film obtained in Comparative Example 1.
2 is a graph of the extinction coefficient α and χ ⁽³⁾ .

In FIG. 5, 1 is a solid line showing the spectrum of the absorption coefficient α of the cadmium sulfide ultrafine particle dispersion obtained in Example 1 with respect to wavelength, and 2 is the third-order nonlinear susceptibility χ ^{(3) at} each wavelength. The measurement results are shown by ●, 3 is the result of χ ⁽³⁾ / α at each wavelength, and Δ is the one-dot chain line showing the exciton absorption peak. (Issues of semiconductor ultrafine particle dispersion element) In the semiconductor ultrafine particle dispersion material and an element using the same, conventionally, a photoexcitation process exhibiting relatively large nonlinearity, and a nonlinearity manifestation phenomenon mainly in the resonance region using exciton absorption, The wavelength of the non-linearity which has been investigated and used as a non-linear optical element was overlapped with the light absorption of the semiconductor ultrafine particle material. In this case, the absorption coefficient α representing the light absorption and the third-order nonlinearity χ
Relationship between ⁽³⁾ and χ ⁽³⁾ / α and optical wavelength, wavelength examples used λ
The relationship is shown in FIG.

However, in order to construct a nonlinear optical element as an optical-optical switching element, it is necessary to avoid attenuation of the optical signal to be propagated. Therefore, in the semiconductor ultrafine particle dispersion type non-linear optical element, the value χ ⁽³⁾ / α obtained by dividing the third-order non-linear optical susceptibility χ ⁽³⁾ by the extinction coefficient α is used as one of the indices representing the performance, The emergence of materials with larger values, such as materials with 10 ⁻⁹ electrostatic units · cm or more, is desired. On the other hand, in the prior art, as shown in FIG. 1, since the optical absorption of the semiconductor ultrafine particle dispersion and the wavelength of the third-order nonlinear optical characteristic expression overlap, such χ ⁽³⁾ / α Large dispersions and devices using them have not been obtained, and only small χ ⁽³⁾ / α dispersions and devices have been obtained. On the other hand, non-resonance in a non-resonant region where light absorption is not observed even in a dispersion of semiconductor ultrafine particles has been studied. For example, the Applied Physics No. 59 cited above.
Volume 6, pages 738-745 (1990), contains Cd.
The third-order non-resonant linear susceptibility χ ^{(3) of} S ultrafine particles is described. However, the value is 10 ^{@ 14} about electrostatic units in a medium, because it is 10 ^-10 electrostatic units in CdS nanoparticles converted value was quite insufficient size for practical use.

Further, from the study of the quantum well structure of semiconductors,
The optical Stark effect in which exciton energy is changed by light has been studied. This uses non-resonant optical virtual excitation of excitons confined in a quantum well structure. For example, parity appendix, vol.
It is described on page 9 (1991). According to this description,
In a GaAs / Al / GaAs quantum well structure element, when an optical pulse is input at a wavelength that is sufficiently longer than the optical absorption of excitons and has no optical absorption at the temperature below the liquid nitrogen temperature, it follows the optical pulse passage. We are observing the phenomenon that the light absorption spectrum changes. That is, it is shown that ultrafast optical switching can be performed by using light having a wavelength with no attenuation of the optical signal.

In such a phenomenon, the change in the refractive index spectrum with respect to the resonance state has a large value even for the photon of the incident light having the energy away from it, and when the input light energy becomes large, It is explained that the excitons and the light field are no longer considered to be independent motions, and the excitons move in the state of wearing the electromagnetic field of light.

However, the experimental and theoretical examination of the optical Stark effect is not sufficient, and the light intensity for causing the optical switch is about 10.
It is said that a megawatt / cm ² or more is required, and further, an operating temperature needs to be 150 K or less, which poses a serious problem in practical use. There is also a problem in that the wavelength of the light used by the optical switch and the wavelength of the pump light that causes the non-linear operation are not necessarily in the same wavelength region.

[0021]

DISCLOSURE OF THE INVENTION An object of the present invention is to obtain a light having a small extinction coefficient α and a high transparency in a wavelength region of light.
An object is to provide an excellent nonlinear optical element having a large third-order nonlinearity χ ⁽³⁾ and an optical information transmission method using the element.

[0022]

The inventors of the present invention have been eagerly developing a non-linear optical material using a dispersion material of semiconductor particles, and, surprisingly, a non-linear optical material in which semiconductor ultrafine particles are dispersed. In the element, not only in the region where there is light absorption, but also in the region on the longer wavelength side than the exciton absorption peak on the longest wavelength side of the light absorption,
Or, it has been discovered that a practical third-order nonlinearity appears even at room temperature even though it is scarce. This completed the present invention.

That is, the present invention relates to a semiconductor ultrafine particle dispersion type non-linear optical element comprising a semiconductor ultrafine particle dispersion, which is operated at a light wavelength longer than the semiconductor ultrafine particle exciton absorption peak. In addition, the semiconductor ultrafine particle dispersion having a third-order nonlinear optical susceptibility peak per absorption coefficient on the longer wavelength side than the semiconductor ultrafine-particle exciton absorption peak, and the third-order nonlinear optical per absorption coefficient A semiconductor ultrafine particle dispersion type non-linear optical element characterized by being operated at a light wavelength near the peak of susceptibility, and using these elements, a wavelength longer than the semiconductor ultrafine particle exciton absorption peak. An optical information transmission method characterized by utilizing a non-linear optical effect in which a wavelength region having high optical transparency can be used as a signal light wavelength and a pump light wavelength.

In summary, the most characteristic feature of the present invention is that a semiconductor ultrafine particle dispersion type non-linear optical element using a light wavelength on the long wavelength side of the semiconductor ultrafine particle exciton absorption peak composed of the semiconductor ultrafine particle dispersion and the element. It is in the optical information transmission method using.

More specifically, the relationship is conventionally shown in FIG.
As revealed, light absorption, mainly overlapping with exciton absorption
However, a large third-order nonlinearity χ⁽³⁾Didn't get
On the other hand, in the present invention, as shown in FIG.
Longer wavelength side than the resonance region with light absorption, more specifically
Large χ even in the region longer than the exciton absorption peak
⁽³⁾As a result, a large χ⁽³⁾/ Α, for example 10^-9
Χ with a value of electrostatic unit cm or more⁽³⁾/ Α peak is obtained
Semiconductor ultrafine particle dispersion type non-linear optical element and the element
The nonlinear optical effect in the wavelength range with high optical transparency used
The optical information transmission method used is provided.

The contents of the present invention will be described in detail below. (Ultrafine Particles and Measuring Method Thereof) The ultrafine particles referred to herein are particles having an average diameter of 1 to 100 nanometers, and more preferably 1 to 20 nanometers.

Means for measuring the particle size and composition of ultrafine particles, which are very small particles, are generally known methods, for example, observation and analysis by a transmission electron microscope, powder X-ray diffraction, optical absorption spectrum. Measurement or the like can be used.

In particular, by measuring the light absorption spectrum of ultrafine particles, it is possible to easily obtain information on the particle size distribution. That is, as the particles get smaller,
Since electrons and holes are confined in the semiconductor space, and a quantum box-like phenomenon occurs, the smaller the particle size, the more the light absorption end moves to the short wavelength side and the splitting between electron levels becomes larger, resulting in light absorption. From the appearance of the absorption peak, the particle size and particle size distribution can be estimated. (Range of Particle Size Distribution Range of Ultrafine Semiconductor Particles) The particle size distribution range of the ultrafine semiconductor particles in the present invention is preferably narrow. Preferably, the particle size distribution is within ± 20% of the average particle size and 90% or more of all particles. As a method for measuring the particle size distribution, as described above, a generally known method, for example, observation by a transmission electron microscope or measurement of a light absorption spectrum, and an analysis method by light scattering in a solution, etc. Can be given. (Semiconductor) The semiconductor in the present invention means a group IV element such as silicon or germanium, or an oxide semiconductor such as TiO ₂ or ZnO, or GaAs, InP, InSb or the like.
III-V group compound semiconductor, or CdS, CdSe, Z
It refers to II-VI group compound semiconductors such as nSe and CdTe, and further I-VII group compound semiconductors such as CuCl and CuBr. (Manufacturing Method of Ultrafine Semiconductor Particles) Such semiconductor particles are manufactured by a publicly known manufacturing method in a gas phase or a liquid phase, or in a solid containing a gas phase or a liquid phase. To be done.

For example, in the vapor phase, an evaporation condensation method such as a vapor deposition method in a gas or a laser evaporation method, a plasma CVD method,
Ultrafine semiconductor particles can be produced by using a CVD method such as a laser CVD method, a coprecipitation method in a liquid phase, a metal alkoxide method, a protective colloid method, or the like.

From the viewpoint of easy control of reaction and mass productivity, production methods in liquid phase such as coprecipitation method, metal alkoxide method, protective colloid method and organosol method can be mentioned as preferable examples. (More preferable method for producing semiconductor ultrafine particles) As a more preferable method for producing semiconductor ultrafine particles, from the viewpoint that the particle size and particle size distribution can be more controlled, the inventors have proposed irradiation with light in the presence of a monomer. However, a method for producing semiconductor ultrafine particles, and particularly a method for producing semiconductor ultrafine particles while irradiating laser light can be mentioned. (Monomer) The monomer here is not particularly limited as long as it causes a polymerization reaction, and examples thereof include compounds having an unsaturated bond such as styrene, methyl methacrylate, acrylonitrile, vinylpyrrolidone, or a mixture thereof. Can be preferably used.

Or a heterocyclic compound such as thiophene, selenophene, tellurophene or thiophene vinylene,
It may be an azulene, indole, pyrene, carbazole, or an aromatic compound such as benzene, benzene sulfide, anthracene or aniline. (Light source) The term "light source" as used herein refers to a commonly used light source such as a mercury lamp, a xenon lamp, a halogen lamp, a laser beam, and a combination thereof. Further, these lights can be used through a cut filter, a bandpass filter, or the like. (Laser light source) The laser light referred to here is laser oscillation from gas lasers such as nitrogen laser, argon ion laser, excimer laser, solid-state lasers such as YAG laser, semiconductor lasers, dye lasers, chemical lasers. Light or light that is a combination of these.

As the wavelength of the laser light to be irradiated, a wavelength that can excite the semiconductor superparticles being synthesized is selected. The wavelength of the laser light to be irradiated can be arbitrarily set depending on the combination of the optical absorption spectrum of the target semiconductor and the possible laser oscillation line. However, it should be appreciated that the wavelength of light selected must be shorter than the absorption wavelength of the bulk of the semiconductor. Irradiation with light having a short wavelength within 200 nm from the absorption end of the bulk of the semiconductor is preferable.

The intensity of the light to be irradiated is preferably higher, but if the light intensity is too high, it may cause photodegradation and the like, so 0.002 W / cm ² to 1 is preferable.
It is preferably 0 kW / cm ² . (Example of Typical Embodiment of Manufacturing Method) A method for manufacturing semiconductor ultrafine particles that can be used in the present invention in a typical liquid phase will be described below. Needless to say, the present invention is not limited to this method.

First, the semiconductor raw material and the monomer are dissolved in a solvent.

The solvent used is water or a non-aqueous solvent,
A non-aqueous solvent having a relatively large polarity, specifically,
For example, acetone, acetonitrile, benzonitrile,
Dimethylformamide, dimethylsulfoxide, chloroform, methanol, ethanol, dioxane, tetrahydrofuran, methyl ethyl ketone, or the like, or a mixed solvent containing these is used.

As the semiconductor raw material, a metal compound soluble in the solvent used in the synthesis of semiconductor particles in such a liquid phase is used. These metal compounds are preferably 1
It is desirable to prepare a solution having a concentration of not more than mol / liter, more preferably 10 ⁻⁶ to 10 ⁻¹ mol / liter.

As the metal compound, for example, organic acid salts such as acetate, metal nitrates, perchlorates, alkoxides, acetylaceronates, halides and the like are used. Preferably, metal halides, metal nitrates, metal perchlorates, and metal acetates are used. These may contain water of crystallization.

As the metal species, a group III element such as Al, Ga and In which produces a group III-V compound semiconductor, a group II element such as Zn, Cd and Hg which produces a group II-VI compound semiconductor, and I- Cu for producing VI, VI-VII group compound semiconductors
Group I element such as P, which produces a IV-VI group compound semiconductor
Examples include group IV elements such as b, Ti, and Sn.

The monomer concentration in the reaction solution is preferably 0.1 to 100 times the molar concentration of the metal compound used, and more preferably 1 to 50 times the molar concentration.

Next, laser light is applied to the solution in which the semiconductor raw material and the monomer are dissolved. The irradiation light is desirably applied to the entire reaction solution.

If the reaction proceeds and the concentration of the generated semiconductor ultrafine particles is too high, the laser light may be almost absorbed in the optical path, and the solution may not be uniformly irradiated with the laser light. Optical density is 3 in absorbance
As described below, if the raw material concentration is adjusted or the optical distance of the reactor is adjusted in advance, the reaction can be suitably carried out.

When a metal compound is used for the semiconductor in the state of being irradiated with light, for example, CdS, CdSe,
Taking as an example the case of producing II-VI group compound semiconductor ultrafine particles such as ZnSe and CdTe, suitable chalcogenization of hydrides such as hydrogen sulfide gas and hydrogen selenide gas and organic chalcogenides such as bistrimethylsilylsulfur. By adding the agent to the raw material solution that is irradiated with light,
The target semiconductor ultrafine particles can be obtained by generating and growing semiconductor particles. These reagents are preferably diluted with an inert gas such as helium or nitrogen or a solvent to control the reaction for producing semiconductor particles. The reaction gas concentration is preferably 10% or less by volume, more preferably 1% or less by volume. The flow rate of the diluted reaction gas may be an amount sufficient to allow the reaction to proceed steadily. When the reaction solution is 100 ml or less, usually 1 ml /
It can be preferably used at a flow rate of 5 to 500 ml / min. The progress of this reaction can be observed by a method such as observation of a light absorption spectrum. The reaction is terminated when the formation reaction of the semiconductor ultrafine particles is saturated by these observations. The produced solution may be purified by a method such as centrifugation or column chromatography.

The obtained semiconductor ultrafine particle dispersion liquid is
The polymer component may be dissolved as it is to form a desired dispersion material, or the solvent may be removed by a method such as evaporation or vacuum distillation and taken out as a powder. (Reason for more preferable production method) The reason why such a method for producing semiconductor ultrafine particles while irradiating with light is not completely clarified as preferable according to the present invention. It is considered that this is because the control effect is practically large and a semiconductor ultrafine particle dispersion having a narrower particle size distribution width can be produced. Further, effects such as modification of the surface state of the semiconductor ultrafine particles by light irradiation can be considered. (Ultrafine semiconductor particle dispersion) The ultrafine semiconductor particle dispersion referred to in the present invention means a dispersion of ultrafine semiconductor particles in a medium.

Even if the manufactured semiconductor ultrafine particles are dispersed in a vacuum or in a gas phase or remain dispersed in a liquid phase, the light passing through the dispersion space of the semiconductor ultrafine particles is characteristic of the present invention. A non-linear optical element that exhibits a third-order non-linear optical effect using a light wavelength on the longer wavelength side of the exciton absorption peak can be configured, but it is preferable to disperse it in a solid medium from the viewpoint of practicality. .

As a medium for dispersing the semiconductor ultrafine particles in a solid, it is desirable that the light wavelength used does not absorb light, and an inorganic medium such as glass or an organic medium material such as a polymer can be preferably used.

Nonlinear light composed of a dispersion of semiconductor ultrafine particles
The elements are thin films, multilayer films, blocks, lenses,
It is used in the form of fibers and waveguides. (Method for producing ultrafine semiconductor particle dispersion)
As a method of forming a dispersion, for example, glass or the like
The inorganic medium is Si in the production of semiconductor ultrafine particles in the gas phase.
SiO by evaporation of O in oxygen ₂Formed and manufactured media half
Impregnation of porous glass with conductor ultrafine particle dispersion, sol-gel
Method such as forming a glass medium by the
Wear.

As a method of forming an organic medium such as a polymer, a method of mixing semiconductor ultrafine particles taken out as a powder with a polymer component or a method of adding a polymer component to a semiconductor ultrafine particle dispersion prepared in a liquid phase A method of forming a solid medium by curing by a polymerization reaction or the like or removal of a solvent can be used. These dispersion materials can be further compressed, melted, or formed into a desired form by a method such as screen printing, dip coating, spin coating, or a forming method such as injection molding in a solution state. Further, the formed dispersed thin film of semiconductor ultrafine particles can be further processed by a generally known method such as dry etching to obtain an element having a desired shape.

When a polymer is used as the medium of the dispersion material, the polymer may be selected according to the application of the device and is not particularly limited, but specific preferred examples include polymethylmethacrylate, polyethylmethacrylate and poly ( 2-hydroxyethyl) methacrylate, polycarbonate, polystyrene, polyester, polyethylene terephthalate, polyvinyl chloride, polyether sulfone, polyacrylonitrile, copolymer of vinyl chloride and vinyl acetate, copolymer of styrene and acrylonitrile, or a mixture thereof. Is mentioned. Further, a photocurable resin or a thermosetting resin can also be used. As another component, a surfactant or the like may be mixed. (Semiconductor ultrafine particle resonance region, exciton absorption peak and observation method) The semiconductor ultrafine particle resonance region in the present invention means a light wavelength region in which the semiconductor ultrafine particles dispersed in the dispersion have optical absorption. The exciton peak of the semiconductor ultrafine particles in the present invention is an absorption peak that usually appears on the long wavelength side of the resonance region and refers to an absorption peak due to exciton generation. Regarding exciton absorption in semiconductors, see, for example, Kittel Solid State Physics, Okano et al. (1958), 430.
~ Page 445. This exciton absorption appears as an absorption shoulder or an independent peak on the long wavelength side of light absorption of the semiconductor, and in the case of semiconductor ultrafine particles, wavelength shift or discretization occurs due to the confinement effect by the minute space. The light wavelength may be expressed in energy units, but is usually used in the same meaning.

The semiconductor resonance region and exciton absorption peak of the semiconductor ultrafine particle dispersion can be easily measured by a usual spectroscopic method. For example, an ultraviolet-visible spectrophotometer or a fiber-type optical spectrometer can be used. When the exciton peak appears as a shoulder, the peak value can be obtained by taking the second derivative curve of the spectrum. The absorption coefficient α is obtained by dividing the absorbance thus measured by the optical path length in the dispersion measured by a film thickness meter such as a micrometer. (Wavelength region longer than the exciton absorption peak) Normally, in photoexcitation of a semiconductor, it has the lowest transition energy called a bandgap, so it has light absorption in a region above a specific photon energy depending on the structure and composition of the semiconductor. In other words, it has light absorption from a specific wavelength to the short wavelength side. Exciton absorption usually has an absorption peak near the long wavelength end of this absorption. Therefore, the wavelength region on the longer wavelength side than the exciton absorption peak of the semiconductor ultrafine particles referred to in the present invention is, as shown in FIG. 3, from the exciton peak 3 ′ of the semiconductor ultrafine particles on the longest wavelength side. Also the wavelength range on the long wavelength side,
That is, it refers to a wavelength region with high transparency on the low energy side of exciton absorption having the smallest transition energy. This relationship is shown in FIG. (Signal light, pump light) The signal light in the present invention refers to light input to the element or output light modulated by the element in order to undergo modulation by the nonlinear optical effect, and phase conjugate wave or frequency mixed It refers to light, etc.

The pump light referred to in the present invention means light introduced mainly into the spatial region of the element into which the signal light is input in order to cause the nonlinear optical effect. (Measurement method of chi ^(3)), but as a method of obtaining a third-order nonlinear optical susceptibility chi ⁽³⁾ has several methods known, for example, the excitation of the phase conjugate reflected wave by degenerate four wave mixing method It can be measured from the light intensity dependency. This method is described, for example, in Applied Physics Vol. 59, No. 6, page 785 (1990).
It is described in. The unit is usually an electrostatic unit (esu). The obtained χ ⁽³⁾ can be divided by α to obtain the third-order nonlinear optical susceptibility χ ⁽³⁾ / α per extinction coefficient. (Reason for increasing χ ⁽³⁾ / α) The semiconductor ultrafine particle dispersion has a large χ ⁽³⁾ at room temperature even at a light wavelength longer than the semiconductor ultrafine particle exciton absorption peak.
Alternatively, operation with χ ⁽³⁾ / α has been achieved by the present invention. Although the detailed mechanism of how this phenomenon occurs is not fully understood,
Currently, we estimate as follows.

That is, in the present invention, since the particle size distribution of the semiconductor ultrafine particles becomes extremely narrow, the effect that the conventional wide particle size distribution is extremely small and cannot be observed substantially is first revealed. It has a feature in the points found. The present invention has been achieved by discovering such a novel phenomenon and applying it. It is considered that when the semiconductor ultrafine particles have a uniform size, the characteristics of the particles having a distribution disappear, and the particles start to behave as one kind of macromolecule. At this time, in the particles having a distribution, a large number of excitation levels involved in nonlinear expression and excitation levels not involved in nonlinear expression are mixed, whereas the excitation levels involved in nonlinear expression increase. Or it will be visible.

As a result, by suppressing the thermal disturbance at low temperature, the interaction between the exciton and the photoelectric field, which has been observed only to a slight extent that could not be observed in the past, has been clearly revealed even at room temperature. I presume. Is the present invention, for example, a mechanism involving a hidden shallow level, a two-exciton mechanism, a theory such as a cooperative phenomenon due to ultrafine particle interaction, and a mechanism common to the conventionally known optical Stark effect and the like? Although it is unknown, it must be said that it is a very epoch-making thing that an ultrahigh-speed operation speed of picoseconds or less can be expected because an optical wavelength region out of resonance is used.

At a light wavelength deviated from the resonance region, a large third-order nonlinear optical susceptibility χ ⁽³⁾ appears, which is considered to be due to the narrow particle size distribution width. Phenomena that will occur and epoch-making semiconductor ultrafine particle dispersion type nonlinear optical elements that apply these phenomena are expected. (Χreal) For example, when the particle size distribution becomes narrow, it is expected that the real part components of the third-order nonlinear optical susceptibility due to the respective particle sizes will appear on the long wavelength side without being offset.
Such a real part component appears in the dispersion of light, and a large χ ⁽³⁾ / α can be realized in the wavelength region where the light absorption is substantially close to zero. (2nd harmonic) Further, for example, the nonlinearity in the vicinity of the light absorption edge, which appears remarkably when the light absorption becomes steep due to the narrowing of the particle size distribution, is a wavelength half or one-third the wavelength of the light absorption edge. It is expected that it will be remarkably shown and strengthened in the area.

An example of the embodiment of the present invention will be described below with reference to examples.

[0055]

【Example】

Example 1 cadmium perchlorate hexahydrate _{(Cd (ClO 4) 2 ·} 6H
₂ O) and styrene (C ₆ H ₅ CHCH ₂ ) 2.0 each
45 ml of an acetonitrile solution dissolved at a concentration of × 10 ⁻³ mol / l, 4.0 × 10 ⁻² mol / l was placed in a Pyrex glass square cell equipped with a gas introduction tube, and while stirring, 457. Irradiation with a 9 nm oscillation line. The amount of light applied to this solution was measured with a power meter and adjusted to 0.02 W / cm ² .

In this way, while irradiating laser light, a mixed gas prepared by diluting hydrogen sulfide gas with helium gas to 0.02% by volume was introduced into a solution stirred at a flow rate of 100 ml / min in terms of air. And allowed to react for about 30 minutes.

Next, the obtained dispersion was concentrated under reduced pressure to about 3 ml, and then a solution of an acrylonitrile-styrene copolymer in dimethylformamide (3 g) was added.
/ 15 ml) was added to the petri dish after stirring. This was dried again under reduced pressure to remove the solvent and form a film.

In order to measure the non-linear optical characteristics of the cadmium sulfide ultrafine particle dispersion element thus obtained,
The phase conjugate reflection wave by degenerate four-wave mixing is measured at each wavelength at room temperature, and the third-order nonlinear optical coefficient χ is measured.
⁽³⁾ was measured, and at the same time, from the extinction coefficient α of this material, χ ⁽³⁾
/ Α was calculated. The spectra of χ ⁽³⁾ / α and α, χ ⁽³⁾ are shown in FIG.

As is clear from FIG. 4, the maximum value of χ ⁽³⁾ / α value of 3 was 1.4 × 10 ⁻⁹ electrostatic unit · cm. Further, it can be seen that the peak is in a region shifted to the longer wavelength side than the exciton peak 4. Comparative Example 1 A cadmium sulfide ultrafine particle dispersed film was obtained by performing the same operations as in Example 1 except that light irradiation such as an argon ion laser was not performed.

In order to measure the non-linear optical characteristics of the cadmium sulfide ultrafine particle dispersion element thus obtained,
The phase conjugate reflection wave by degenerate four-wave mixing was measured at each wavelength as in Example 1, and the third-order nonlinear optical coefficient χ ⁽³⁾
And at the same time, from the extinction coefficient α of this material, χ ⁽³⁾ /
α was obtained. Figure 5 shows the spectra of χ ⁽³⁾ / α and α, χ ⁽³⁾
Shown inside. As shown in FIG. 5, the light absorption spectrum 1 represented by α is shifted to the longer wavelength side as compared with Example 1, and it can be seen that ultrafine particles having a large particle size are formed. Therefore, it can be seen that the particle size distribution is not controlled as compared with Example 1.

As shown in FIG. 5, the value of χ ⁽³⁾ / α is 3
Was 4 × 10 ⁻¹⁰ electrostatic unit · cm even in the maximum value, which was smaller than that in Example 1. Further, it can be seen that there is no peak of χ ⁽³⁾ / α on the longer wavelength side than the exciton peak 4, and the peak overlaps with the light absorption spectrum 1 represented by α.

That is, the dispersion of semiconductor ultrafine particles of Example 1 not only has a remarkably large non-linear optical characteristic as compared with the dispersion of semiconductor ultrafine particles of Comparative Example 1 produced without irradiation with light. , Χ on the longer wavelength side than the exciton peak
^It can be seen that a peak of ⁽³⁾ / α appears and a large χ ⁽³⁾ / α is obtained.

Therefore, it can be seen that in the nonlinear optical element using the ultrafine particle dispersion in which the particle size distribution is controlled, a good nonlinear optical element can be provided by using a light wavelength longer than the exciton absorption peak.

[0064]

As described above, the present invention provides a non-linear optical element which has a small non-optical loss and can sufficiently operate even at room temperature and has good non-linear optical characteristics, and an optical information transmission method using the non-linear optical element.

[Brief description of drawings]

FIG. 1 shows the extinction coefficient α and 3 of a conventional semiconductor ultrafine particle dispersion.
Illustration of the relationship between the following nonlinear susceptibility χ ⁽³⁾ , χ ^{( 3)} / α and optical wavelength

FIG. 2 is an explanatory diagram of the relationship between the light absorption wavelength and the extinction coefficient α and the third-order nonlinear susceptibility χ ⁽³⁾ , χ ⁽³⁾ / α of the semiconductor ultrafine particle dispersion of the present invention.

FIG. 3 is an explanatory diagram of a wavelength region having a wavelength longer than an exciton absorption peak.

FIG. 4 is a graph of χ ⁽³⁾ / α and extinction coefficients α and χ ⁽³⁾ of the cadmium sulfide ultrafine particle dispersion film obtained in Example 1 at each wavelength.

FIG. 5 is a graph of χ ⁽³⁾ / α and extinction coefficients α and χ ⁽³⁾ at each wavelength of the cadmium sulfide ultrafine particle dispersion film obtained in Comparative Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyoji Hayashi Mitsui Toatsu Chemical Co., Ltd. 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa

Claims (3)

[Claims] 1. A semiconductor ultrafine particle dispersion type non-linear optical element comprising a semiconductor ultrafine particle dispersion and operated at a light wavelength longer than a semiconductor ultrafine particle exciton absorption peak. 2. A semiconductor ultrafine particle dispersion having a third-order nonlinear optical susceptibility peak per absorption coefficient on the longer wavelength side of the semiconductor ultrafine particle exciton absorption peak, and the third-order nonlinear per absorption coefficient thereof. A semiconductor ultrafine particle dispersion type non-linear optical element which is operated at a light wavelength near the peak of optical susceptibility. 3. The device according to claim 1 or 2, wherein the wavelength region having high optical transparency on the long wavelength side of the semiconductor ultrafine particle exciton absorption peak is used as the signal light wavelength and the pump light wavelength. An optical information transmission method characterized by utilizing the obtained nonlinear optical effect.