JPH05142605A - Nonlinear optical material and its production - Google Patents

Abstract

PURPOSE:To provide a nonlinear optical material having high nonlinear susceptibility and to provide its production method. CONSTITUTION:This nonlinear optical material is produced by the following process. First, Au fine particles are deposited on a substrate 6 under conditions of 1.0Pa Ar gas pressure, 400 deg.C substrate 6 temp., 250W applied on a SiO2 target 4, 10W applied on an Au target 5, and 5sec residence time of the substrate 6 on the Au target 5. Then the substrate 6 is kept on the SiO4 target 4 for 5sec to deposit a SiO2 film. This process is repeated for 500 times to obtain a laminar structure in which Au fine particles are dispersed in a laminar state in SiO2 glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear optical material having a laminated structure of fine metal particles and an optically transparent substance, which is the basis of an optical device utilizing the nonlinear optical effect, and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Applied physics is that dispersion of fine metal particles in glass increases the third-order nonlinear susceptibility of the metal and increases optical nonlinearity.
A Vol. 47, p. 347 (Applied Physics A, vol.47,347 (1
988)).

As a method for producing a glass containing dispersed fine metal particles, a silicate glass containing gold prepared by a melting method is heat-treated to disperse the fine gold particles in a glass matrix.

[0004]

The third-order nonlinear susceptibility of the metal fine particle-dispersed glass produced by the conventional method as described above is a value of 10 ^-14 to 10 ^-11 esu, which is very small. This is because the metal fine particles in the glass are very small, less than 0.01% by volume. In the conventional manufacturing method, if the metal content is increased more than this, the melting limit is exceeded and the particles are aggregated and precipitated as bulk particles during melting, so that the metal cannot be dispersed as fine particles in the glass. Further, since the nucleation and growth of the metal fine particles are performed by the heat treatment, it is unavoidable that they are governed by thermodynamic equilibrium and the particle size is distributed. Therefore, the non-linearity varies, and the controllability of the non-linear optical material is poor.

The present invention is intended to solve such a problem, and a non-linear optical material having a large non-linear susceptibility in which fine metal particles having a uniform particle size are dispersed in an optically transparent substance and a particle size in the optically transparent substance. It is an object of the present invention to provide a method for producing a non-linear optical material having a large non-linear susceptibility capable of dispersing a large amount of metal fine particles.

[0006]

In order to achieve the above object, the non-linear optical material of the present invention is a non-linear optical material in which fine metal particles having a uniform particle size are dispersed in a layer in an optically transparent substance.

In the above structure, the metal fine particles are gold,
It is preferably at least one metal selected from silver, copper, platinum, or palladium. The method for producing a nonlinear optical material of the present invention is a method for producing a nonlinear optical material in which fine metal particles are dispersed in an optically transparent substance,
It is characterized in that the metal fine particles and the optically transparent substance are alternately deposited on the surface of the substrate.

In the above manufacturing method, when the metal fine particles and the optically transparent substance are alternately deposited on the substrate surface, it is preferable to heat the substrate surface so that the metal fine particles have a spherical shape. ..

[0009]

In the non-linear optical material of the present invention, since fine metal particles having a uniform particle size are dispersed in a layer in an optically transparent substance, the particles grow in bulk even if a large amount of the metal particles are dispersed. It is possible to provide a highly efficient nonlinear optical material without fear. Further, since the metal fine particles are used, it is possible to utilize the increase in the third-order nonlinear susceptibility associated with the surface plasmon resonance absorption of the metal fine particles. By making the particle diameters uniform, the plasmon resonance absorption becomes sharp and The non-linear susceptibility of can be increased.

In the above structure, the fine metal particles are gold,
By adopting a preferred structure of at least one metal selected from silver, copper, platinum, or palladium, these metals have a small imaginary part of the complex permittivity, and the surface plasmon resonance frequency has an optically transparent region. In addition, since it is highly reducible and can stably exist as metal fine particles,
A non-linear optical material having the following non-linear susceptibility can be provided.

The method for producing a non-linear optical material according to the present invention is a method for producing a non-linear optical material in which fine metal particles are dispersed in an optically transparent substance, wherein the fine metal particles and the optically transparent substance are alternately provided on the substrate surface. Since the particles are deposited, it is possible to prevent the particle size from increasing due to the growth of the metal particles, and therefore it is possible to disperse the metal particles having a uniform particle size in a large amount.

In the above manufacturing method, when the metal fine particles and the optically transparent substance are alternately deposited on the substrate surface, the surface of the substrate is heated so that the metal fine particles have a spherical shape. The surface plasmon resonance absorption peak of the fine particles becomes sharp, and the third-order nonlinear susceptibility can be increased, which is preferable.

[0013]

EXAMPLE FIG. 1 shows the cross-sectional structure of a nonlinear optical material according to the present invention. As shown in FIG. 1, the non-linear optical material of the present invention comprises a substrate 1, a metal fine particle 2 and an optically transparent substance 3.
It has a laminated structure in which and are alternately deposited.

In the nonlinear optical material according to the present invention, attention is paid to the fact that the island-shaped growth substance formed in the very initial stage of the metal thin film formation is fine particles, and the island-shaped growth substance is used as the metal fine particles 2 to be optically transparent. It is actively used to contain a large amount in the substance 3.

The reason why a large amount of spherical metal fine particles 2 having a uniform particle size can be contained in the optically transparent substance 3 in the present invention will be described. The metal particles flying from the evaporation source (not shown) onto the substrate 1 lose energy in the direction perpendicular to the substrate 1 in a short time and stay on the substrate 1. However, since it is a transition process between the gas phase and the solid phase, and since thermodynamic equilibrium has not been reached at this point, after moving around on the surface of the substrate 1, it is trapped on the substrate 1 by adsorption points such as defects. Adhere to. If there are no adsorption points, the vapor deposition particles will re-evaporate. By the vapor deposition particles that fly one after another, some adhering particles in the vicinity gather, and they become crystal nuclei. After the crystal nuclei are formed, the island structure grows. If the metal fine particles are prevented from flying at this point, the metal island fine particles are dispersed on the substrate 1. In this case, the island-shaped fine particles are generally in surface contact with the substrate and have a hemispherical or semi-spheroidal shape, not a spherical shape.

Next, a thin film of the optically transparent substance 3 is formed on this to cover the surface of the metal island fine particles. At this time, the vapor-deposited particles of the optically transparent substance 3 coming in release their kinetic energy as heat energy, so that a transition to a new thermal equilibrium state occurs at the interface with the metal island-shaped fine particles. here,
When the metal island-shaped fine particles receive sufficient thermal energy to make the interface energy difference with the optically transparent substance 3 zero, the metal island-shaped fine particles 2 become spherical metal fine particles 2. This energy varies depending on the type of the metal and the optically transparent substance 3, the surface energy and the kinetic energy of the vapor deposition particles, and also depends on the vapor deposition conditions. However, when a sputtering method or a vacuum vapor deposition method is used, Heating to a suitable temperature provides sufficient energy to make the fine particles spherical, which is preferable. The heating temperature of the substrate 1 varies depending on the conditions used and the type of substance used as described above, so it is difficult to specify in a general manner, but generally a range of 100 to 700 ° C. is a standard. Usually, a low temperature is used when an organic substance such as an organic polymer is used as the optically transparent substance 3, and a relatively high temperature is used when an inorganic compound that melts at a high temperature such as quartz glass is used. Temperature can be adopted.

When the optically transparent substance 3 is deposited thicker than the particle size of the metal fine particles 2, the particles of the optically transparent substance 3 are stopped from flying and the metal fine particles are vapor-deposited again. By repeating this operation, it is possible to disperse spherical metal fine particles having a uniform particle size in the optically transparent substance 3 in layers.

The particle size of the metal fine particles 2 can be controlled by changing the deposition amount or the heating temperature of the substrate 1, and the surface density of the fine particles in the layer in which the metal fine particles 2 are present is
It can be controlled by changing the kinetic energy of vapor deposition particles or the heating temperature of the substrate 1. Furthermore, the density of the metal fine particles 2 in the present material can be controlled by changing the vapor deposition amount of the optically transparent substance 3. In this example, the metal fine particles 2 could be contained at a maximum density of 40% by volume, which is 4000 times or more that of the conventional one.

It is necessary that the particle size of the metal fine particles 2 is small enough to exhibit a local electric field effect, and it depends on the kind of the metal used and the like, but a size of, for example, 50 nm or less, preferably 1 to 15 nm is suitable. It was When the size of the fine particles is 100 nm or more, the bulk property becomes remarkable, and the optical nonlinearity becomes small.

The material used for the substrate 1 may be the same as or different from the material used for the optically transparent substance 3. When the nonlinear optical material is formed and then peeled off from the substrate 1, the substrate 1 need not be an optically transparent substance.

The material used as the metal fine particles 2 is gold,
A metal selected from silver, copper, platinum, or palladium is preferable. The material used as the optically transparent substance 3 may be an inorganic crystalline substance, a glass substance, or an organic polymer compound as long as it is optically transparent in the wavelength region required to obtain the nonlinear optical characteristics. May be
Specifically, for example, quartz glass, magnesium fluoride,
Examples thereof include, but are not limited to, LiF, CaF ₂ , Al ₂ O ₃ , MgO, borosilicate glass, aluminate glass, fluoride glass, acrylic acid resin, methacrylic acid resin, polystyrene, and polyethylene.

The amount of the fine metal particles 2 dispersed in the optically transparent substance 3 is usually 0.01 to 50% by volume, preferably 1.
It is about 40% by volume, and the third-order nonlinear susceptibility increases in proportion to the volume occupancy of the metal fine particles. In the present invention, the metal fine particles 2 having a uniform particle size are dispersed in the optically transparent substance 3, but the particle size distribution is smaller than that of the metal fine particles of the nonlinear optical material obtained by the conventional method. When the standard deviations are small and dispersed (however, if the average particle size is the same, compare)
Can be said to have a uniform particle size.

In the method of manufacturing the nonlinear optical material of the present invention, a sputtering method which is a thin film manufacturing method, a vacuum vapor deposition method, or the like can be used. In the case of the sputtering method, argon gas is usually used as the sputtering gas and the sputtering is performed under a pressure of about 10 ^-2 to 10 Pa.
The vacuum deposition method is performed under a reduced pressure of about 10 ⁻³ Pa to 10 ⁻⁴ Pa. It is preferable to select which method is to be selected and the conditions thereof in consideration of the melting point, vapor pressure, oxidizing property, etc. of the metal and the optically transparent substance used.

In order to make the shape of the metal fine particles spherical, it is preferable to heat the substrate and maintain it at an appropriate temperature, for example, a temperature of about 100 to 700 ° C. as described above. Hereinafter, the present invention will be described in more detail with reference to specific examples.

Example 1 Using the sputtering apparatus shown in FIG. 2, the nonlinear optical material of the present invention was manufactured by the sputtering method. The sputtering source was composed of a quartz (SiO ₂ ) glass target 4 and a gold (Au) target 5. The substrate 6 is fixed to a substrate holder 8 equipped with a heater 7, and by a rotary shaft directly connected to this,
By rotating the SiO ₂ target 4 or A
It can be brought above any of the u targets 5. The position of the substrate 6 and the staying time above the target are controlled by a computer. In order to prevent contamination during vapor deposition, each target is provided with a shield plate 9 that covers the periphery of the target and its extension. Quartz glass was used for the substrate 6. Argon is used as the sputtering gas, the gas is introduced from the gas inlet 10, the gas outlet 11 is connected to a vacuum pump (not shown), the gas pressure is 1.0 Pa, the substrate temperature is 400 ° C., and Si is
The power applied to the O ₂ target 4 was 250 W, and the power applied to the Au target 5 was 10 W.

First, the substrate 6 is placed on the Au target 5 by 5
After being left for a second, Au particles were deposited. Next, the substrate 6 was rotated and allowed to stay on the SiO ₂ target 4 for 5 seconds to deposit a SiO ₂ film. The above operation of alternately depositing Au and SiO ₂ on the substrate 6 was repeated 500 times to form a nonlinear optical material having a laminated structure in which Au particles were dispersed in a layered form in SiO ₂ glass.

The thickness of the produced nonlinear optical material was 2 μm, the average particle size of the spherical Au particles was 2 nm, the standard deviation of the particle size distribution was 0.4 nm, and the distance between the layers in which the Au particles were dispersed was 4 nm. , The content of Au fine particles was 40% by volume.

In the case of a non-linear optical material produced by changing the staying time on the Au target 5, the A
It was possible to obtain an u particle having an average particle size of 4 nm, a standard deviation of particle size distribution of 0.7 nm, an average particle size of 7 nm and a standard deviation of 1 nm in 10 seconds.

The Au target 5 is replaced with silver (Ag),
Copper (Cu), platinum (Pt), or palladium (P
Even if the target is manufactured in place of the target d), the particle size is 1 to 10 n.
A similar nonlinear optical material was obtained in which the metal fine particles of m were dispersed in layers.

Example 2 Instead of the sputtering target shown in FIG. 2, a non-linear optical material of the present invention was manufactured by using a vacuum evaporation method in which an evaporation source was placed on a tungsten boat and evaporation was performed by resistance heating. The structure of the substrate portion is the same as that in FIG. 2, and the point that the shield plate 9 is provided for each evaporation source is also the same. Magnesium fluoride (MgF ₂ ) was used as the optically transparent substance, and Au was used as the metal. Quartz glass was used for the substrate 6. Vacuum degree is 10 ⁻⁴ Pa, substrate temperature is 200 ° C., MgF
_The power applied to the boat on which ₂ was on was 120 W, and the power on the boat on which Au was on was 200 W.

First, the substrate was left on the Au evaporation source for 2 seconds to deposit Au particles. Next, the substrate is rotated and allowed to stay on the MgF ₂ evaporation source for 5 seconds, and then the MgF ₂
The film was deposited. The above operation of alternately depositing Au and MgF ₂ on the substrate was repeated 400 times to obtain A in MgF _2.
A non-linear optical material having a laminated structure in which u particles were dispersed in a layer was formed.

The thickness of the produced nonlinear optical material is 2.4 μm.
m, the average particle size of the spherical Au particles is 3 nm, the standard deviation of the particle size distribution is 0.5 nm, the spacing between the layers in which the Au particles are dispersed is 6 nm, and the content of the Au particles is 40% by volume.
Met.

Besides Au, Ag, Cu, Pt,
Alternatively, a similar non-linear optical material in which metal fine particles having a particle size of 1 to 10 nm are dispersed in a layer form was obtained even if it was produced in place of Pd.

Example 3 The third-order nonlinear susceptibility χ ⁽³⁾ of the nonlinear optical material prepared in Example 1 in which Au fine particles having a particle size of 2 nm were dispersed in a layer was measured, and it was 4.8 × 10 at a wavelength of 515 nm. ^-7
It was esu. A Fabry-Perot resonator was constructed by sandwiching this with two external mirrors, and was used as an optical bistable element. When a laser beam with a wavelength of 515 nm was made incident on this element with a spot diameter of 5 μm and the relationship between the intensity of the incident light and the intensity of the emitted light was measured at room temperature (25 ° C.), it showed an optical bistable characteristic.
Very fast switching speeds of less than 5 picoseconds were obtained.

Similarly, χ ⁽³⁾ of the nonlinear optical material prepared in Example 1 containing 25% by volume of Ag fine particles having an average particle size of 5 nm and a standard deviation of particle size distribution of 0.7 nm is 400 nm. , 9.2 × 10 ⁻⁸ esu.
This material forms a Fabry-Perot resonator with a wavelength of 40
When a laser beam of 0 nm was made incident with a spot diameter of 5 μm and the relationship between the intensity of the incident light and the intensity of the emitted light was measured at room temperature (25 ° C), it showed optical bistable characteristics and was extremely fast at 5 picoseconds or less. Got the switching speed of.

From the above results, the nonlinear optical material of the present invention can be applied as a high-speed optical switch and can be applied as an element to which other nonlinear optical characteristics are applied.

[0037]

INDUSTRIAL APPLICABILITY The nonlinear optical material of the present invention can provide an efficient nonlinear optical material having excellent third-order nonlinear susceptibility.

Further, by adopting a preferable structure in which the metal fine particles are at least one kind of metal selected from gold, silver, copper, platinum, or palladium, the metal fine particles can stably exist and have a large third-order nonlinearity. A nonlinear optical material having a susceptibility can be provided.

According to the method for producing a non-linear optical material of the present invention, it is possible to prevent an increase in particle size due to the growth of metal particles, and therefore it is possible to disperse a large amount of metal particles having a uniform particle size.

Further, when the metal fine particles and the optically transparent substance are alternately deposited on the surface of the substrate, the surface of the substrate is heated to make the shape of the metal fine particles spherical, whereby the surface plasmon resonance of the metal fine particles is formed. It is possible to provide a method for manufacturing a nonlinear optical material having a sharp absorption peak and a large third-order nonlinear susceptibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a nonlinear optical material of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of a linear optical material manufacturing apparatus used in an example of the present invention.

[Explanation of symbols]

1 Substrate 2 Metal Fine Particles 3 Optically Transparent Material 4 SiO ₂ Target 5 Au Target 6 Substrate 7 Heater 8 Substrate Holder 9 Shield Plate 10 Gas Inlet 11 Gas Outlet

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshio Manabe 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Tsuneo Sanritsu 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co. Within

Claims (4)

[Claims] 1. A non-linear optical material in which fine metal particles having a uniform particle size are dispersed in layers in an optically transparent substance. 2. The nonlinear optical material according to claim 1, wherein the fine metal particles are at least one metal selected from gold, silver, copper, platinum, and palladium. 3. A method for producing a non-linear optical material in which fine metal particles are dispersed in an optically transparent substance, wherein the fine metal particles and the optically transparent substance are alternately deposited on the substrate surface. Material manufacturing method. 4. The non-linear optical material according to claim 3, wherein when the metal fine particles and the optically transparent substance are alternately deposited on the substrate surface, the shape of the metal fine particles becomes spherical by heating the substrate surface. Production method.