JPH0242422A - Nonlinear optical element and production thereof - Google Patents

Abstract

PURPOSE:To allow the precise control of the film thickness of the light guide layer of a waveguide type element for which an org. material having a nonlinear optical effect is used by providing a transparent material layer having the refractive index higher than the refractive index of the org. material having the optical nonlinearity as the guide layer. CONSTITUTION:The transparent material layer 2 having the refractive index higher than the refractive index of the org. material 1 is formed as the light guide layer on the planar org. material 1 having the optical nonlinearity. The inorg. compd. having >=80% transmittance of light in a 0.3-12mum wavelength region is used as the transparent material layer and is formed by a vacuum vapor deposition method. The precise control of the film thickness is possible in this way and the nonlinear optical characteristic of the org. material is not degraded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a waveguide type nonlinear optical element suitably used in industrial fields such as optical information processing, optical communication, and optical measurement control, and a method for manufacturing the same. I'll go.

[Prior art] As an element applying a nonlinear optical effect, there is an S I-I G element that converts the wavelength of a laser beam to 172 by second harmonic generation (hereinafter abbreviated as S I-I G), and a S Proposals include wavelength conversion devices such as parametric oscillators that continuously convert the wavelength of laser light, optical switches and optical modulation devices that use electro-optic effects, and optical bistable devices that utilize the fact that the refractive index changes depending on the light intensity. It has been.

The magnitude of the nonlinear optical effect depends not only on the magnitude of the nonlinear optical constant of the nonlinear optical material, but also as the power density of the laser beam increases. Attempts have been made to increase the power density by confining the

Attempts have been made to realize nonlinear optical materials as waveguide elements for a long time using inorganic materials, and various forms have been proposed (for a review, see G. 1. SteCl
Eman et al., Journal of Applied
Physics.

Volume 58, page R57 (1985)). A typical form is one in which a transparent film is deposited on a nonlinear optical crystal (P
.

K, Tien, ^1) I) Iied Physi
cs Letters, vol. 17, p. 447 (197
0), etc.), using lithium niobate as a nonlinear optical crystal and forming a waveguide on its surface by material diffusion, ion exchange, etc., Japanese Patent Application Laid-Open No. 60-57825,
Go-11202, etc.) are known.

On the other hand, regarding organic nonlinear optical materials, a method in which a nonlinear optical material is provided on a substrate and the nonlinear optical material itself functions as a leading wave layer (Ito et al., Journal of the Institute of Electronics and Communication Engineers, '
87/2, Vol. J70-C, p. 224), and as shown in Figure 4 (in Figure 4, 2 is a transparent waveguide layer, 3 is a laser beam, 6 is a prism, and 7 is a nonlinear optical material. waveguide layer,
8 indicates a transparent substrate. ), a waveguide layer made of an organic nonlinear optical material is loaded as a top layer on a normal transparent waveguide layer that does not have a nonlinear optical effect, and the light that has been guided through the normal transparent waveguide layer is once converted into a nonlinear optical waveguide layer. There are two known methods in which the wave moves to the material (loaded layer) and then returns to the normal waveguide layer (% formula % (198G)), in which the nonlinear optical material itself becomes the waveguide layer. ing.

[Problems to be Solved by the Invention] However, techniques such as Japanese Patent Application Laid-Open No. 60-57825 use an inorganic material as a nonlinear material, and therefore have small nonlinearity.

In addition, in such conventional technology using organic materials with optical nonlinearity, the film thickness of the waveguide layer must be precisely controlled to around 1 μm in order to optimize the optical transmission "C" of the waveguide layer. However, since it is difficult to control the organic material having optical nonlinearity, which is the waveguide layer, in this way, there is a problem that the device performance cannot be optimized.

An object of the present invention is to provide a nonlinear optical element that uses an organic material that has a large nonlinear optical effect, and which can precisely control the thickness of the waveguide layer, and a method for manufacturing the same. It is to be.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

(1) On an organic material with plate-like optical nonlinearity,
A waveguide type nonlinear optical element comprising, as a leading wave layer, a layer of a transparent material having a higher refractive index than an organic material having nonlinearity.

(2) The waveguide shape according to claim (1), wherein the transparent material layer is made of a composite material having a transmittance of at least 80% for at least part of light in a wavelength range of 0.3 to 12 μm. Nonlinear optical element.

(3) The waveguide shape according to claim (1), wherein the transparent material layer is made of an inorganic compound having a transmittance of at least 80% for at least part of light in a wavelength range of 0.3 to 12 μm. Nonlinear optical element.

(4) The method for manufacturing a waveguide-type nonlinear optical element according to claim (3), wherein the transparent material layer is formed by a vacuum evaporation method. Materials include urea, metanitroaniline, 2-methyl-
4-Nitroaniline, N-(4-nitrophenyl)-(
L)-prolinol, 2(N,N-dimethylamino)-
Examples include, but are not limited to, 5-nitroacetanilide, polydiacetylene derivatives, etc.
Any organic material can be applied as long as it has a large second-order nonlinear optical constant and/or third-order nonlinear optical constant.

Furthermore, in order to effectively exhibit the nonlinear optical effect, it is desirable that these organic materials having optical nonlinearity be crystallized, and those processed into a plate shape are used. Further, when utilizing a third-order nonlinear optical effect, transparent plastics such as polymethyl methacrylate, polystyrene, and polyvinyl alcohol, or glass doped with the material can also be used.

The nonlinear optical element of the present invention is formed by providing a transparent material as a waveguide layer on the upper layer of these organic materials having optical nonlinearity, as shown in FIG. 1 (in FIG. 1,
1 is an organic material having optical nonlinearity, 2 is a waveguide layer made of a transparent material layer, 3 is a laser beam, and 4 is SHG light. ). In addition, when it is difficult to grow bulk crystals of an organic material, as shown in Figure 2 (in Figure 2, 1 is an organic material having optical nonlinearity, 2 is a transparent material layer, 3 is a transparent material layer, 5 indicates a laser beam, 5 indicates a flat substrate, and 6 indicates a prism.) After separately forming a thin film crystal of an organic material having optical nonlinearity on the flat substrate 5, a transparent material layer is provided as a leading wave layer. It is also possible to use In order to process bulk crystal bodies, plastic molded bodies, glass molded bodies, etc. into plate shapes, well-known mechanical cutting and polishing techniques can be applied.

In the present invention, any transparent material layer may be used as long as it is made of a transparent material having a refractive index higher than that of an organic material having optical nonlinearity, but a preferable example is a wavelength of 0.
Transmittance of at least part of light in the range of 3 to 12 μm is 8
Examples include those containing 0% or more of inorganic compounds, polymers, and the like.

A preferred inorganic compound is HCl because it has a high degree of freedom in selecting the refractive index, has high transparency, and has high film strength.
0. ThO>, 5n03 LaO2, SiO, In2
03, T! Metal oxides such as 02, 2r02, ZnS,
CdS, Zn5e.

Metal chalcogenide compounds such as znre, Si, Ge
.

Examples include semiconductors such as GaP, GaAs, and InP.

Further, as the transparent polymer, a copolymer of a crosslinked polymerizable monomer having a high refractive index is desirable. As such a monomer,
Tribromophenyl (meth)acrylate, pentabromophenyl (meth)acrylate, tribromophenoxy-2-hydroxypropyl (meth)acrylate, pentabromophenoxy 2-hydroxy (meth)acrylate, monochlorophenoxyethyl (meth)acrylate, dichlorophenoxy ethyl (meth)acrylate,
Trichlorophenoxyethyl (meth)acrylate, monobromophenoxyethyl (meth)acrylate, dibromophenoxyethyl (meth)acrylate, tribromophenoxyethyl (meth)acrylate, pentabromophenoxyethyl (meth)acrylate, α-naphthyl (meth)acrylate , 2,3-dibromopropyl acrylate, and the like. Since these polymers have excellent adhesion to organic materials having nonlinear optical effects, they can form a high-quality waveguide layer.

In the present invention, as a means for forming an optical waveguide layer on an organic material having optical nonlinearity, first, when the transparent material is an inorganic compound, a method that allows precise control of the film thickness is preferred, and vacuum evaporation most preferred. but,
Normally, when these materials are vacuum-deposited, high-temperature heating is required due to the high melting point of the deposited material, and as a result, the sample to be deposited is often exposed to high temperatures of 300'C or higher.

Generally, the melting point of organic materials with optical nonlinearity is 90~
Since the temperature is 250°C, if it is exposed to such high temperatures, it will melt or change in quality due to thermal deterioration, making it impossible to exhibit nonlinear optical effects. Therefore, it is necessary to provide a waveguide layer without causing such deterioration by keeping the organic material having optical nonlinearity, which is the material to be deposited, at a low temperature below its melting point. That is, it is particularly preferable to suppress the temperature of the organic material having optical nonlinearity to 80'C or less. As a method for keeping the temperature below 80'C, (1) Heat only the vapor deposition material and roughly suppress the radiant heat from the vapor deposition source.

■ Increase the distance between the deposited substance and the organic material with optical nonlinearity.

■An organic material with optical nonlinearity is attached to a metal plate through which cooling water is passed, and the material is forcibly cooled. This is an effective method. In particular, the best quality @ deposited film can be obtained when electron beam heating evaporation is performed using the method (2).

Furthermore, when a transparent polymer is used as the transparent material, any conventionally known coating method for a polymer film can be applied as a means for providing a polymer on an organic material having optical nonlinearity. It is possible to apply the polymer itself, but it is also possible to apply it in a wet state and then polymerize it by heat radiation or light. The refractive index of a polymer film can be adjusted and controlled not only by the refractive index of the polymer itself, but also by adding high refractive index molecules.
This has the effect of increasing the degree of freedom in controlling the refractive index difference between the waveguide layer and the substrate, which is essential for producing a waveguide element. Examples of such additive components include compounds containing benzene nuclei, bromine, chlorine, iodine, etc. that contribute as high refractive index components in the molecule. Particularly preferred are molecules whose radicals are generated by light irradiation or heat and are trapped in the polymer chain of the polymer during the photopolymerization process or thermal polymerization process, since these molecules stably exist in the polymer film. Such an example is
Benzoin, benzoin ether, deoxybenzoin, α-deoxybenzoin, deoxybenzoin derivatives such as 2-7enyl-1-indanone, benzoin derivatives such as benzoin methyl ether, penzoin edyl ether, benzoin isopropyl ether, or chlorine, bromine , halogenated alkylphenyl ketones containing iodine, etc. are well known. A well-known example of a specific method is to mix benzyl dimethyl ketal with a monomer as a photopolymerization initiator, apply it, and then trap it in the polymer chain during the photopolymerization process to increase the refractive index. (R,5ChreiVer et al., P.

ymer, 2 (3 volumes, 1423 pages, (1985))
. In order to precisely control the film thickness to around 1 μm and form a coating film with a uniform thickness, it is most preferable to apply with a spinner. Furthermore, even if the polymer coating solution is diluted with an organic solvent, the evaporation rate of the solvent increases when it is applied using a spinner, making it possible to apply it without roughening the surface of an organic material with optical nonlinearity. It also has the advantage of being possible.

The waveguide-shaped element obtained by the present invention can be used as a nonlinear optical element such as an SHG element, a wavelength conversion element such as a parametric excavator, an optical switch using an electro-optic effect, an optical modulation element, or an optical bistable element. is possible.

[Examples] Next, the present invention will be briefly described in detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 As an organic material having optical nonlinearity, 5q of metanitroaniline powder was dissolved under heat in 500ml of acetone,
After cooling, the acetone was slowly evaporated while maintaining the temperature at 25°C.

When the mixture was left to stand for one month, all the acetone evaporated, and metanitroaniline crystals with a maximum size of 4 x 5 x 10 mm were obtained. Next, this crystal was cleaved to expose a smooth surface and roughly cut to obtain a flat plate of 2 x 3 x 5 mm.

Next, a 1r02 thin film having a thickness of 0.5 μm was formed on this flat plate by electron beam heating vapor deposition. Actual measurements using a thermoelectric stack confirmed that the temperature near the surface of the metanitroaniline crystal plate during vapor deposition was 65° C. at maximum.

Finally, the four surfaces surrounding the vapor deposition surface were polished to form a waveguide element.

Pulsed YAG with a peak output of 500W is used in this waveguide element.
When laser light is focused to a beam diameter of approximately 200 μm and incident from the end face of the waveguide, and a part of the laser light is combined and guided, a 2 mW SHG generated by Cerenkov phase matching is generated as shown in Figure 1. Observed light. In FIG. 1, 1 is an organic material having optical nonlinearity, 2 is a transparent material layer, 3 is a laser beam, and 4 is SHG light.

Example 2 2-methyl-4- as an organic material with optical nonlinearity
Nitroaniline powder was melted and sandwiched between glass slides, and then crystallized according to the Bridgman method. After crystallization, one glass plate was peeled off to expose one side of the 2-methyl-4-nitroaniline crystal film. The crystal film thickness was approximately 35 μm. Furthermore, observation under crossed Nicols confirmed that the single crystal portion was about 5 x 15 mm. Next, a film with a thickness of 0.0 mm is deposited on this crystal film.
A 7 μm TiO2 thin film was formed by electron beam heating evaporation to create a waveguide element with the structure shown in Figure 2). In FIG. 2, 1 is an organic material having optical nonlinearity, 2 is a transparent material layer, 3 is a laser beam, 5 is a flat substrate (slide glass), and 6 is a prism.

Argon laser light is coupled and guided through a prism as shown in Figure 2 on the single crystal part of the waveguide shaped element thus made 1q, and the guided light is extracted by the other prism. The intensity of the emitted light was measured. At this time, when the intensity of the incident light was continuously changed up and down between 50 mW and 800 mW and the relationship with the output light intensity was measured, the third
As shown in the figure, the input-output relationship due to changes in the refractive index depending on the light intensity was observed.

Example 3 After dissolving 5 g of urea powder as an organic material with optical nonlinearity in 400 ml of methanol/water (1/1 weight ratio), the solvent was slowly evaporated while maintaining the temperature at 25°C. When this was allowed to stand for two weeks, all the solvent evaporated and a large number of urea single crystals were obtained. These single crystals were polished to obtain urea single crystal plates with a maximum size of about 3 x 4 x 5 mm.

Next, pentabromophenyl methacrylate, which had been heated in a 50° C. hot bath to lower its viscosity, was applied onto this flat plate using a spinner. Roughly heat this sample to 80'C.
After heating in an oven for 24 hours to thermally polymerize the pentabromophenyl methacrylate in the coating film, the coating was left in a vacuum dryer heated to 50'C for 8 hours to remove residual pentabromophenyl methacrylate monomer. The four surfaces surrounding the pentabromophenyl methacrylate polymer film thus prepared was polished to obtain a waveguide element.

This waveguide element has a peak output of 500 as in Example 1.
When W pulsed YAG laser light was focused to a beam diameter of approximately 200 μm and a part of the incident laser light was combined and guided from the end face of the waveguide, 150 μW of SHG light was generated by Cerenkov phase matching. Observed.

Example 4 5-nitrouracil was used as an organic material having optical nonlinearity using a known method (J, G., Bergman et al., p.
plied Physics Letters, Vol. 20, p. 21, (1972)) in an aqueous solution.
℃ to 45℃ by slow cooling at a rate of about 1℃ per day,
A large number of single crystals were obtained. Furthermore, these crystals were polished to obtain plate-shaped single crystals with a maximum size of about 1O10X8X2.

Next, pentabromophenyl methacrylate monomer/benzyl dimethyl ketal-9515 was added as a photopolymerization initiator to the pentabromophenyl methacrylate monomer heated in a hot bath at 50°C.
The mixture was added at a ratio of 0 to the heaviest portion, stirred for 3 hours to mix thoroughly, and then left to stand in a bath at the same temperature for defoaming to prepare a coating liquid. Then, this mixed solution was applied onto the above-mentioned 5-nitrouracil crystal plate using a spinner, and then exposed to ultraviolet rays with an irradiation energy of 2500 mJ/7 under vacuum using an ultra-high pressure mercury lamp to obtain a photopolymerized film. Roughly, the remaining monomers of pentabromophenyl methacrylate and benzyl dimethyl ketal were removed by leaving it in a vacuum dryer heated to 50°C for 8 hours. The four surfaces surrounding the polymer film thus obtained were polished to obtain a waveguide element.

This waveguide element has a peak output of 500 W as in Example 1.
When the pulsed YAG laser beam was focused to a beam diameter of about 200 μm and a part of the incident laser beam was combined and guided from the end face of the waveguide, a 1.2 mW SHG was generated due to Cerenkov phase matching. Observed light.

[Effects of the present invention] According to the present invention, in a waveguide element using an organic material having optical nonlinearity, by providing a waveguide layer made of a transparent material whose film thickness can be precisely controlled, It was possible to provide a waveguide type nonlinear optical element that effectively exhibits a nonlinear optical effect without reducing the nonlinear optical properties of the organic material, and a method for manufacturing the same.

[Brief explanation of the drawing]

FIG. 1 shows the waveguide shape and SHG of Example 1 of the present invention.
Show light. FIG. 2 shows a waveguide shape according to Example 2 of the present invention. FIG. 3 shows the input/output relationship of laser light in the case of using the waveguide shape element of Example 2 of the present invention. FIG. 4 shows the configuration of an example of a conventional waveguide-shaped element using an organic material having optical nonlinearity. 1: Organic material with optical nonlinearity 2: Transparent material layer 3
: Laser light 4: SHG light 5: Flat substrate 6: Prism 7: Waveguide layer made of nonlinear optical material 8: Transparent substrate

Claims (4)

[Claims] (1) A waveguide comprising a plate-shaped organic material having optical nonlinearity and, as an optical waveguide layer, a transparent material layer having a higher refractive index than the organic material having optical nonlinearity. shaped nonlinear optical element. (2) The waveguide shape according to claim (1), wherein the transparent material layer is made of a polymer having a transmittance of at least 80% for at least part of light in the wavelength range of 0.3 to 12 μm. Nonlinear optical element. (3) The waveguide according to claim (1), wherein the transparent material layer is made of an inorganic compound having a transmittance of 80% or more for at least part of light in the wavelength range of 0.3 to 12 μm. shaped nonlinear optical element. (4) The method for manufacturing a waveguide-type nonlinear optical element according to claim (3), wherein the transparent material layer is formed by a vacuum evaporation method.