JPH05313217A - Nonlinear optical element and its production - Google Patents

Abstract

PURPOSE:To obtain the nonlinear optical element which has high wavelength conversion element and has multilayered films of inverted bipoles by widening the selectivity of materials and improving thermal and mechanical stability. CONSTITUTION:This nonlinear optical element has the multilayered structure formed with a first layer 1 and second layer 2 respectively consisting of nonlinear optical materials on a substrate 10 consisting of light transmissive glass, etc. Arrows d1 to d4 (or d11 to d14) respectively show the directions of the bipole moments of the respective layers and the respective layers are so laminated that these directions are counter-paralleled with each other with respect to the film thickness direction. Then, such trouble that the bipole moments of the respective layers adjacent to each other of the multilayered films are reversed during the formation of oriented films is averted and the nonlinear optical element having the inverted multilayered film constitution is stably obtd. The extremely higher conversion efficiency than the conversion efficiency of the nonlinear optical element of the single-layered film constitution is obtd. in the case, for example, a second harmonic wave generating element is obtd. by forming the element into the multilayered film structure in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film optical waveguide type non-linear optical element having a large non-linear optical effect and a high wavelength conversion efficiency, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as an organic nonlinear optical material, an organic compound having a π-electron conjugated system has attracted great attention as a molecule because of its nonlinear optical property. However, in order to fabricate a practical device mainly using this material, especially its second-order nonlinearity, the directions of dipole moments are aligned in crystals obtained from these compounds or in an alloy matrix. It is necessary.

On the other hand, for example, second harmonic generation (SHG)
In addition, when manufacturing a device such as light mixing, it is an important matter to use a film having optical characteristics with phase matching. Various methods have been reported for the phase matching method in the thin film optical waveguide type. In those methods, if the distribution structure in which the sign of the nonlinear optical constant (corresponding to the dipole direction in the case of an organic nonlinear molecule) is inverted in the film direction of the optical waveguide, the conversion efficiency is greatly improved. The calculation results have been reported (for example, Yanagawa, Hayata, and Koshiba “Improved Efficiency of Cherenkov Radiation-Type Wavelength Converter with Domain Inversion Structure”, IEICE Transactions Vol.J74-C.
-1, No. 4,1991, p. 119-125). As a method of forming a film having such an inversion structure, when LiNbO ₃ is used as a substrate, a domain inversion method by ion diffusion is suggested, for example, in the above document, but it has not been realized.

[0004]

Further, the applicant of the present invention has previously proposed, for example, DCANP by the LB (Langmuir-Blodgett) method in Japanese Patent Application No. 3-278615.
(2-docosylamino-5-nitropyridine) It was possible to obtain such an inversion structure film by an accumulation method in which the substrate is inverted using an organic molecule.

The LB method is a method of orienting and accumulating organic molecules, for example, New Experimental Chemistry Course Vol. 18, "Interface and Colloid" p. 439-516 (published by Maruzen Co., Ltd. in 1977), it is a method of accumulating monomolecular layers in a state of standing on the water surface, and generally obtaining a film in which molecules are vertically aligned on a substrate. However, this LB method requires that the structure of the material molecule is elongated and the molecule is designed so that hydrophilic groups and hydrophobic groups are well balanced at both ends in order to produce the target thin film. It Further, in order to form a monomolecular layer or a cumulative film, there are problems that productivity and workability are low due to time-consuming, and the mechanical and thermal stability of the film is poor.

Another method of forming an alignment film is a vacuum vapor deposition method. For example, in Japanese Patent Laid-Open No. 62-180427, a non-linear optical material having a constant non-linear optical material is formed by a vacuum vapor deposition method using a uniaxially oriented polymer film. A method of obtaining an oriented non-linear optical material is shown. However, in this method, the device itself is complicated and expensive, and a considerably complicated process is required to form the inversion structure.

Further, a method of preparing an alignment film by mixing an organic nonlinear molecule with a thermoplastic polymer, heating the polymer to a glass transition temperature of the polymer under an electric field, and cooling while being aligned has been reported. (Appl.Phys.Lett., 49 (5), 248
(1986)).

Although these methods are suitable for manufacturing a nonlinear optical element having a single-layer alignment film as shown in FIG. 15A or B, for example, a structure in which the dipole moments of adjacent layers in a multilayer film are inverted. When forming a new alignment film, there was a problem that the molecular orientation of the alignment film prepared before was disturbed and the dipole moment was reversed during the formation of the new alignment film.

As described above, in the method shown in the prior art, the dipole-inverted multilayer film, which is actually difficult to manufacture due to the problems that the manufacturing technique is complicated, it takes a long time, the material is limited, etc. The present invention provides a non-linear optical element having the above and a method for manufacturing the same, and in such an element and its manufacturing, the selectivity of the material is expanded, the thermal and mechanical stability are improved, and the element is far superior to the conventional structure. An object is to obtain a non-linear optical element having high wavelength conversion efficiency.

[0010]

A nonlinear optical element of the present invention is a transparent polymer thin film containing an organic nonlinear optical compound, in which the direction of the molecular dipole moment of the organic nonlinear optical compound is determined by an outline of an example. 1 is oriented in the film thickness direction as shown in FIG. 1, or is a schematic enlarged cross-sectional view of another example oriented in the film plane as shown in FIG. It is constructed by stacking layers whose molecular dipole moments are antiparallel to each other.

The method of manufacturing the nonlinear optical element of the present invention is
After molding a mixture of a monomer and / or oligomer that crosslinks by irradiation with ultraviolet rays and / or electron beams with an organic nonlinear optical compound into a film, the mixture is irradiated with ultraviolet rays and / or under an electric field in one direction perpendicular to the film surface. A step of forming a first layer by crosslinking a monomer and / or an oligomer by irradiation of an electron beam, and applying the same material and mixture as the above-mentioned mixture thereon to form an electric field opposite to that for curing the first layer. The step of cross-linking the monomer and / or oligomer by irradiation with ultraviolet rays and / or electron beams to form the second layer while applying is performed while sequentially applying an electric field opposite to that of the molecular dipole moment in the film thickness direction. It is formed by stacking layers whose directions are antiparallel to each other.

Furthermore, the method for producing a non-linear optical element according to the present invention comprises the steps of molding a film of a mixture of an organic non-linear optical compound and a monomer and / or oligomer which are crosslinked by irradiation of ultraviolet rays and / or electron beams, and then forming a film. A step of cross-linking the monomer and / or oligomer by irradiation of ultraviolet rays and / or electron beams to form a first layer under an electric field parallel to the plane and perpendicular to the light propagation direction; A step of forming a second layer by coating and forming a mixture of the same material as the mixture and cross-linking the monomer and / or oligomer by irradiation of ultraviolet rays and / or electron beams while applying an electric field opposite to that at the time of curing the first layer. And are sequentially applied while applying opposite electric fields, and layers are formed by stacking layers whose molecular dipole moments are antiparallel to each other in the film plane direction. That.

[0013]

In view of the above-mentioned current situation, the inventors of the present invention have conducted extensive studies and as a result, have completed the constitution of the present invention and the method of manufacturing the same. That is, the non-linear optical element of the present invention, in a transparent polymer film comprising an organic non-linear optical compound,
There is a layer in which the direction of the molecular dipole moment of the organic nonlinear optical compound is parallel to the thickness direction of the film or the film surface direction and aligned in one direction, and the dipole moments of adjacent layers are antiparallel to each other. It has a multi-layered film structure oriented in the direction of.

In the non-linear optical element having such a multilayer film structure, as described above, irradiation of ultraviolet rays and / or electron beams, that is, ultraviolet rays and electron beams are performed in a predetermined order or simultaneously, or ultraviolet rays or electron beams are used. A monomer and / or oligomer that is crosslinked by irradiating either one of them, that is, a monomer and an oligomer, or a mixture of one of the monomer and the oligomer and an organic non-linear optical compound, is formed into a film, and then a film is formed. Under an electric field in a direction perpendicular to the surface or in a direction parallel to the film surface and perpendicular to the light propagation direction, the monomer and / or oligomer is cross-linked by irradiation of ultraviolet rays and / or electron beams to form the first layer. To form this first layer as an alignment film in a predetermined direction, and further to form the above-mentioned mixed film on it. And mixtures of the same material is formed by coating, and the time of first layer UV cured and while applying a reverse electric field /
Alternatively, the monomer and / or oligomer is cross-linked by irradiation with an electron beam to form a second layer, and the second layer is similarly configured as an alignment film in a predetermined direction, so that the molecular dipole can be easily and relatively short-timed. It is possible to stack layers in which the directions of moments are antiparallel to each other, and by sequentially stacking such layers while applying opposite electric fields, it is possible to obtain a nonlinear optical element having a multilayer film structure.

With such a multi-layered film structure, a very large conversion efficiency can be obtained when, for example, a second harmonic generation element is obtained, as compared with a nonlinear optical element having a single-layered film structure.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The non-linear optical element of the present invention will be described in detail below with reference to the drawings together with its manufacturing method, but the present invention is not limited to these. In this example, the case where the present invention is applied to an SHG conversion element is shown.

The organic nonlinear optical compound used in the present invention is an organic compound having a π-electron conjugated skeleton in the molecule and having a large degree of charge transfer. Such organic compounds are already well known, for example, in “Organic nonlinear optical material” (edited by Masao Kato and Hachiro Nakanishi, CMC). Specifically, a urea derivative shown in the following chemical formula 1, a nitroaniline derivative shown in the chemical formula 2, an enone derivative shown in the chemical formula 3, a stilbene derivative and a merocyanine derivative shown in the chemical formula 4, a nitroazene derivative, and a heterocyclic derivative shown in the other chemical formula 5 Can be raised.

[0018]

[Chemical 1]

[0019]

[Chemical 2]

[0020]

[Chemical 3]

[0021]

[Chemical 4]

[0022]

[Chemical 5]

There is no particular limitation on the type of material which is mixed with an organic nonlinear optical compound and is cured by light or heat, as long as it can be formed into a film, but a material having a transmittance of 80% or more for natural light is used. desirable. As an example of such a material, a monomer / or oligomer that crosslinks upon irradiation with ultraviolet rays and / or electron beams can be used. For example, polyester acrylate type, polyepoxy acrylate type, polyester acrylate type compound polyol acrylate type, etc. can be used.
You may use it in mixture of 2 or more types. As a specific example, an example of a polyester acrylate compound is shown in Chemical Formula 6 below.

[0024]

[Chemical 6]

Further, at the time of crosslinking, a photoinitiator may be used if necessary. Examples of the photoinitiator include acetophenones, benzophenones, Michler's ketones, benzyls, benzoins, benzoin ethers, benzylmethyl ketals, and thithioxanthones.

Specifically, acetophenone, benzophenone, Michler's ketone, benzyl, benzoin, benzoin isobutyl ether, benzyl methyl ketal, 1
-Hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-dimethyl-1-phenylpropan-1-one, azobisisobutylnitrile, benzoyl peroxide and the like.

As the cross-linking conditions, the conditions which are usually used can be used without any problem, but an oxygen-free atmosphere is preferable because the curing property is better. A method for producing a non-linear optical film using such a curable resin is disclosed, for example, in JP-A-2-281240-281242.

In the present invention, the molecular dipole moments of the organic non-linear compound are arranged parallel to the film thickness direction and arranged in one direction, and adjacent to the layer arranged in parallel to the film thickness direction and opposite one direction. As a method for producing each layer with an appropriate thickness, for example, the following method can be used.

That is, a mixture of a monomer and / or oligomer and an organic nonlinear optical compound, which are crosslinked by irradiation of ultraviolet rays and / or electron beams and / or heating, is applied on a thin film by a spin coating method or the like on a transparent substrate having a flat surface. To form.
At that time, a solvent or the like may be used in combination if necessary, but it is necessary to evaporate the solvent well after the film formation.

Thereafter, for example, by a corona discharge method, or by applying a high voltage to a counter electrode formed on a substrate in advance and applying an electric field in the direction perpendicular to the film surface or in the film surface direction, ultraviolet rays and / or electrons are emitted. Irradiation with radiation and / or heating crosslinks the monomers and / or oligomers in the film,
Cure the film. As a result, the non-linear optical compound in the film is also fixed with its dipole moment oriented in one direction perpendicular to the film surface or one direction parallel to the film surface.

Next, a second layer is formed on the first layer. Up to the coating step, it is the same as in the first layer production. However, the non-linear optical compound and the monomer and / or oligomer that are crosslinked by irradiation with ultraviolet rays and / or electron beams and / or heating are not necessarily the same as those in the first layer. The film thickness may also be different from the first layer, which can be determined based on the design as a nonlinear optical thin film.

In particular, when curing the second layer film, it is necessary to create an environment in which the electric field is opposite to that of the first layer. For this purpose, the polarity of the corona discharge electrode or the electrode formed on the substrate may be reversed from that in the case of the first layer.
In this state, the monomer and / or oligomer that crosslink is crosslinked by irradiation with ultraviolet rays and / or electron beams and / or heating to cure the film.

Further, a third layer or more may be formed, if necessary, based on the design as a non-linear optical thin film. At this time, when the odd-numbered layer and the even-numbered layer are cured and formed, it is important to reverse the polarities of the electrodes such as corona discharge and reverse the direction of the applied electric field. Here, as the material of the last layer formed, that is, the uppermost layer, a usual thermoplastic resin may be used instead of the curable resin.

The purpose of forming a multilayer film structure in which adjacent layers have polarizability moments antiparallel to each other is to enhance the efficiency of wavelength conversion such as SHG. Therefore, it is necessary to design the thickness, refractive index, nonlinear optical constant, etc. of each layer in accordance with the design. As a calculation method that serves as a guideline for this design, for example, when considering conversion of a fundamental wave of a guided mode of a thin film into a SHG of a guided mode, for example, A.Yar
iv by “Coupled-mode theory for guided-wave opti
cs ”(IEEE Journal of Quantum Electronics, vol.QE-9,
919 (1973)), when considering the conversion of the fundamental wave of the guided mode of the thin film to the SHG of the radiation mode,
For example, “Coupled-mode analysis of se” by H. Tamada
cond harmonic generation in the form of Cerenkov r
adiation from a planar optical waveguide ”(IEEE Jo
urnal of Quantum Electronics, vol.27,502 (1991)).

In these methods, the mode of the electric field in the nonlinear waveguide of the fundamental wave and the second harmonic is calculated by the mode coupling theory, and their superposition integral, more precisely, the square of the electric field of the fundamental wave is calculated. This is a method of calculating the SHG conversion efficiency from the superposition integration with the electric field of the second harmonic. Therefore, at the position in the thickness direction where the sign of the electric field of the second harmonic changes in the nonlinear waveguide,
A large wavelength conversion efficiency can be obtained by reversing the orientation direction of the polarizability moment of the nonlinear optical compound. This has already been described in the above-mentioned Japanese Patent Application No. 3-278615, for example.

The layer structure of each example of the nonlinear optical element according to the present invention is shown in FIGS. 1 and 2, and the layer structure of an example of the conventional nonlinear optical element is shown in FIG. As shown in FIGS. 1 and 2, in the nonlinear optical element of the present invention, a multilayer structure in which a first layer 1 and a second layer 2 each made of a nonlinear optical material are formed on a substrate 10 made of light transmissive glass or the like. In the conventional structure, as shown in FIG. 15, a single-layer nonlinear material layer 20 is formed on the substrate 10. 1 and 2, arrows d _{1 to} d ₄ (or d _{11 to} d)
₁₄ ) indicates the direction of dipole moment of each layer,
The layers are laminated so as to be antiparallel to each other in the film thickness direction. In FIGS. 15A and 15B, d ₃₁ and d ₃₂ , or d ₃₃ and d ₃₄ indicate the directions of dipole moments in the material layer 20, respectively.

In this embodiment, an optical waveguide having such an inversion-accumulation structure was designed, and based on this, the second harmonic generation elements were manufactured by changing the directions of their dipole moments. In each of the following examples, the material M shown in Chemical formula 7 below
A material in which NA (3-methyl-4-nitroaniline) was added to an ultraviolet curable oligomer SD-17 (manufactured by Dainippon Ink and Chemicals, Inc., product name), and a glass substrate FC5 (manufactured by HOYA Glass, product name) Was manufactured using.

[0038]

[Chemical 7]

Table 1 below shows the additive materials and the glass substrate,
The refractive index corresponding to a fundamental wave and a 2nd harmonic is shown.

[0040]

[Table 1]

In Table 1, the refractive index of SD-17 containing 5% MNA after curing was n _d (measured by Abbe refractometer 2T (trade name, manufactured by ATAGO Co., Ltd.) with respect to a film having a thickness of 1 mm cured in an unoriented state. Fraunhofer d-line) and ν _d
(Abbe number with respect to Fraunhofer d-line) and was obtained from the result. The oriented polymer is
A slight difference (birefringence) occurs in the refractive index between the direction in which the electric field is applied and the direction perpendicular thereto. This depends on the degree of orientation and the addition amount of the non-linear molecule. This time, assuming that the addition is only 5% and the degree of orientation is considerably low, the design was performed by ignoring the birefringence.

The result of calculating the conversion efficiency according to the above-mentioned document by H. Tamada is shown by a line a in FIG. In this case, since the absolute value of the non-linear optical constant cannot be estimated, the scale on the vertical axis shows the relative SHG conversion efficiency.

FIG. 4 shows the distribution of the electric field when the film thickness is 1.09 μm. In FIG. 4, the solid line R shows the square of the fundamental wave guided mode electric field, and the solid line S shows the square of the SHG radiation mode electric field. As can be seen from this, the electric field of the SHG radiation mode is inverted in the waveguide, so that the conversion efficiency is 2
The value of the overlap integral, which is affected by the power, is greatly reduced.

On the other hand, the electric field reversal position P in FIG.
The conversion efficiency when the non-linearity is inverted by is shown by the line b in FIG. In this case, it can be seen that the conversion efficiency is greatly improved as compared with the line a. Line c shows the film thickness dependence of the Cherenkov radiation angle.

The SHG electric field reversal position at the film thickness of 1090 nm at which the conversion efficiency is maximum is 400 nm from the substrate, and therefore, an alignment film of 400 nm is first formed and 690 is formed thereon.
It can be seen that a non-linear optical element having a high conversion efficiency can be obtained as shown by the line b in FIG. 3 by producing an antiparallel alignment film having a thickness of nm.

A non-linear optical element was manufactured based on this design. A glass substrate whose surface is optically polished, eg, thickness 1
mm, the length and width of 30 mm, FC5 (manufactured by HOYA Glass Co., Ltd.) on the substrate, the above MNA5
A solution containing a non-linear optical compound consisting of% added SD-17 or the like is applied by spin coating. The film thickness is SD-1
Acetone was added to 7 oligomers to adjust the concentration, and the rotation speed of the spinner was 1500 rpm to 7000 r.
It can be controlled by changing to about pm.

On the other hand, an electric field was applied in the direction perpendicular to the film surface by the corona discharge method to orient the dipole moment in the direction perpendicular to the film surface. The corona discharge method is an effective method for orienting a nonlinear optical compound in a matrix such as a polymer in a direction perpendicular to the film surface. An example of the corona discharge device is shown in FIG. In FIG. 5, 11 is a base, 12 is an element sample, 13 is a discharge grid, 14 is a high-voltage power supply, 15 is a switch for polarity reversal, 16 is a UV light (ultraviolet light) fiber, and 17 is a UV lamp. The voltage was set to +5 kV, and ultraviolet rays were irradiated for curing about 5 minutes after the start of discharge.

The film thickness after curing was measured by a stylus type film thickness meter such as α step, and a film having a thickness of 400 nm ± 20 nm was selected. Further, when the film thickness unevenness was measured, it was possible to form the film with a thickness of approximately 5%.

When the first layer is formed on the next formed first layer
Spin coat in the same way as. Then corona discharge device
Underneath and discharge with a polarity opposite to that used when forming the first layer.
As with the first layer, the discharge voltage was set to about 5 kV and the discharge started.
About 5 minutes after the start, ultraviolet rays were irradiated to cure the composition. So
After the film thickness is measured, the total thickness becomes 1090 nm.
This is referred to as Example 1. That is, in this case, as shown in FIG.
And the dipole moment of the first layer 1 is the arrow d₁As shown in
Upward, the dipole moment of the second layer 2 is indicated by the arrow d. ₂Indicated by
And the thickness t of each layer 1 and 2 is₁Over
And t₂Of about 400 nm and about 690 nm, respectively.
I made it.

As a comparative example, one layer and two layers were spin-coated, respectively, and cured in a state in which the directions of the dipole moment of the nonlinear optical compound were randomly oriented without applying an electric field, and the comparative example shown in FIG. A comparative example 2 shown in FIG. 7 was produced in which curing was performed while applying an electric field in the same direction when forming 1, 1 layer, and 2 layers. In FIG. 7, arrows d ₅ and d ₆ indicate the orientation direction of each layer. Comparative Example 1
1 and 2 layer thicknesses t ₁₃ and t ₁₄ , t ₅ and t ₆
Was selected similarly to the thicknesses t ₁ and t ₂ of each layer in Example 1.

A YAG laser was incident on the nonlinear optical elements according to Example 1 and Comparative Examples 1 and 2, and Cherenkov radiated SHG light was observed. At that time, in order to efficiently enter the laser from the end face of the film, the glass substrate was cut together and the laser was narrowed down from the end face with the objective lens of the microscope and made incident. The optical system is shown in FIG. In FIG. 8, 31 is Y
With the AG laser, the laser light is vertically polarized by a polarizing lens or the like as shown by an arrow E ₁ , and the YAG laser 3
The laser light from No. 1 is incident on the sample 34 via the cylindrical lens 32 and the objective lens 33, and the output light from this sample 34, that is, the SHG light is input to the photodetector 36 via the IR cut filter 35.

In such a structure, the laser power is about 1 kW at the focal position, the beam size is 200 μm in the direction parallel to the film, about 10 μm in the direction perpendicular to the film, the laser irradiation time is 60 ns, and the repetition is 6 kHz. S
The HG light was observed. The result is shown in FIG. In FIG. 9, solid lines A to C represent Example 1 and Comparative Examples 1 and 2, respectively.
The SHG intensity | strength in.

As a result, SHG having a Cherenkov angle of 4 ° was recognized from Example 1 and Comparative Example 1 described above. It was confirmed by the photodetector 36 including a Si power meter that the brightness of Example 1 was about 20 times higher than that of Comparative Example 1. From Comparative Example 2, SHG light was not recognized.

Next, as shown in FIG. 2, a non-linear optical element having a dipole moment in the in-plane direction of each layer was produced. In this example, first, as shown in FIG. 10, electrodes 21 made of Al or the like are patterned and formed with a distance W of, for example, 100 μm held, on a substrate 10 made of the same material as in the first embodiment. To cover, for example, thickness 10
An insulating layer 22 made of SiO ₂ or the like having a thickness of 0 nm is deposited, and thereafter, a material such as SD-17 with MNA added at 5% is applied by a spin coating method or the like as in the above-mentioned embodiment. Then, as shown in FIG. 11, the counter electrode 21 formed on the substrate 10
A voltage of 5 kV was applied to the film to orient the dipole moment of the nonlinear optical molecule parallel to the film surface, and at the same time, ultraviolet rays were irradiated to cure the film. Also in this case, the film thickness was measured by a stylus type film thickness system such as α step, and the first layer 1 having a thickness t ₃ of 400 nm ± 20 nm was selected. Then, a second layer 2 is similarly applied thereon by a spin coating method or the like, and then a voltage of about 5 kV is applied with a polarity opposite to that used for curing the first layer 1 to form the second layer 2 with a thickness t ₄ . Almost 690n
A non-linear optical element was produced by curing and forming m. Also in this case, the total film thickness was selected to be 1090 nm, and the optical characteristics were measured using this as Example 2.

Also in this case, as in the example described with reference to FIG. 6, Comparative Example 3 was cured in a state in which the dipole moment directions were randomly oriented, and further shown by arrows d ₇ and d ₈ in FIG. As described above, Comparative Example 4 was prepared in which the first layer 1 and the second layer 2 were both cured while being applied with an electric field in the same direction parallel to the film surface. In these Comparative Examples 3 and 4, the thickness t of each layer 1 and 2 is t.
₁₃ and t ₁₄ , t ₇ and t ₈ were selected in the same manner as the thicknesses t ₃ and t ₄ in Example 2 described above.

In these Examples 2 and Comparative Examples 3 and 4, the same optical system as described in FIG. 8 was used, and in this case, the laser light from the YAG laser 31 was polarized in the horizontal direction as shown by arrow E _2. The laser power was set to about 1 kW at the focal position, the beam size was set to 200 μm in the direction parallel to the film, and set to about 10 μm in the direction perpendicular to the film, the laser irradiation time was set to 60 ns, and the measurement was repeated at 6 kHz. The result is shown in FIG. In FIG. 13, the solid line D shows the results of Example 2, the solid line E shows the results of Comparative Example 3, and the solid line F shows the results of Comparative Example 4. Also in this case, SHG can be recognized from Example 2 and Comparative Example 3, and it was confirmed with the Si power meter that the SHG light in Example 2 was about 20 times brighter than that in Comparative Example 3. In addition, SHG light was not observed in Comparative Example 4.

Further, as shown in FIG. 14, a channel waveguide type non-linear optical element can be manufactured. That is, it can be obtained by laminating the channel type optical waveguides 44 and 45 made of an organic nonlinear optical compound on the substrate 43 and depositing and forming the cladding layer 46 so as to cover them. In this case, each channel type optical waveguide can be formed by squeezing and irradiating a UV laser as a UV light source for irradiation for curing with an objective lens.

Such a channel type optical waveguide has a higher performance than a slab waveguide type non-linear optical element as a non-linear optical element. For example, in the case of a wavelength conversion element, its conversion efficiency is significantly increased. It is also possible to form another polymer or the like in the waveguide layer as the clad layer, and in addition to the advantage of protecting the waveguide layer, selecting a material with an optimum refractive index for this clad layer further improves conversion efficiency. Can be improved.

The non-linear optical element of the present invention is not limited to the above-mentioned embodiments, but can be modified in various other materials, the configuration of the dipole moment direction, and the like. It goes without saying that the manufacturing method can also adopt various aspects.

[0060]

As described above, according to the nonlinear optical element of the present invention and the manufacturing method thereof, it is possible to obtain a nonlinear optical element having a multilayer film in which dipoles are inverted, which has been difficult to manufacture in the past. That is, it is possible to avoid the inconvenience that the dipole moments of adjacent layers in the multilayer film are reversed during the preparation of the alignment film, and it is possible to stably obtain the nonlinear optical element having the inverted multilayer film structure. In such an element and its production, it is possible to obtain a nonlinear optical element having a much higher wavelength conversion efficiency than that of the conventional structure by expanding the material selectivity and improving the thermal and mechanical stability.

In particular, a waveguide type SHG adopting an inversion multilayer film structure.
When applied to a device, its SHG conversion efficiency can be increased to about 20 times or more as compared with the conventional one. It can also be applied to the case of producing a photo-sum frequency oscillating element or a photo-difference frequency oscillating element.

[Brief description of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of an example of a nonlinear optical element of the present invention.

FIG. 2 is a schematic linear enlarged cross-sectional view of another example of the nonlinear optical element of the present invention.

FIG. 3 is a diagram showing film thickness dependence of conversion efficiency of a nonlinear optical element.

FIG. 4 is a diagram showing electric field distributions of a fundamental wave and a second harmonic in a nonlinear optical element.

FIG. 5 is a schematic view of a corona discharge UV curing device.

FIG. 6 is a schematic enlarged cross-sectional view of Comparative Example 1 of a nonlinear optical element.

FIG. 7 is a schematic enlarged cross-sectional view of Comparative Example 2 of a nonlinear optical element.

FIG. 8 is a configuration diagram of a Cherenkov radiation type SHG experimental optical system.

FIG. 9 is a diagram showing the SHG intensity of each example of the nonlinear optical element.

FIG. 10 is a schematic linear enlarged cross-sectional view of a main part of another example of a nonlinear optical element.

FIG. 11 is a schematic view of a UV curing device.

FIG. 12 is a schematic enlarged cross-sectional view of Comparative Example 3 of a nonlinear optical element.

FIG. 13 is a diagram showing the SHG intensity of each example of the nonlinear optical element.

FIG. 14 is a schematic linear enlarged configuration diagram of another example of the nonlinear optical element of the present invention.

FIG. 15 is an enlarged schematic cross-sectional view of each example of a conventional nonlinear optical element.

[Explanation of symbols]

 1 1st layer 2 2nd layer 10 Substrate

Claims (3)

[Claims] 1. A transparent polymer thin film containing an organic nonlinear optical compound, wherein the direction of the molecular dipole moment of the organic nonlinear optical compound is oriented in the film thickness direction or in the film plane direction. A non-linear optical element, characterized in that a layer in which the directions of the molecular dipole moments are antiparallel to each other is laminated. 2. A mixture of a monomer and / or an oligomer that is crosslinked by irradiation with ultraviolet rays and / or electron beams and an organic nonlinear optical compound is formed into a film, and then, under an electric field in one direction perpendicular to the film surface. A step of cross-linking the monomer and / or oligomer by irradiation with ultraviolet rays and / or electron beams to form the first layer,
A mixture similar to the above mixture is formed thereon by coating, and the monomer and / or oligomer is cross-linked by irradiation with ultraviolet rays and / or electron beams while applying an electric field opposite to that used for curing the first layer to form the second layer. The non-linear optical element is characterized in that it is formed by stacking layers in which the directions of the molecular dipole moments are antiparallel to each other in the film thickness direction, by sequentially applying the opposite electric field to the step of forming Of manufacturing. 3. A mixture of a monomer and / or an oligomer which is cross-linked by irradiation with ultraviolet rays and / or electron beams and an organic nonlinear optical compound is formed into a film, and then, the mixture is parallel to the film surface and in the light propagation direction. Under the electric field in the vertical direction, the monomer and / or oligomer is cross-linked by irradiation with ultraviolet rays and / or electron beams,
A step of forming a layer and coating and forming a mixture substantially the same as the above mixture thereon, and irradiating with an ultraviolet ray and / or an electron beam while applying an electric field opposite to that for curing the first layer, and The step of cross-linking the oligomer to form the second layer is performed by sequentially applying opposite electric fields to form layers in which the directions of molecular dipole moments are antiparallel to each other in the film plane direction. A method for manufacturing a non-linear optical element, which is characterized by the above.