JPH0588223A - Organic nonlinear optical material and organic nonlinear optical element - Google Patents

Abstract

PURPOSE:To obtain the excellent nonlinear optical characteristics rapid in response by converting 3-methyl-4-aniline (MNA) substituted by a >=19C on the amino group unto built-up molecular films by the Langmuir-Blodgett's method (LB method) to form a waveguide. CONSTITUTION:The organic nonlinear optical material us represented by formula I and the built-up molecular films (LB) films are laminated on a substrate, and it us the MNA alkyl chain derivative made by substituting >=19C long alkyl on the amino group. It is important to increase the carbon number to >=19 to execute the LB method, thus permitting the balance between the hydrophilicness and hydrophobicness of the MNA to be improved and facilitated for building up molecular films as the LB films. If the carbon number is smaller than 19, hydrophobicness becomes insufficient and difficult to laminate such films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic non-linear optical element and an organic non-linear optical material which are important key devices in an optical electronic system such as optical communication, optical disk, optical information processing.

[0002]

2. Description of the Related Art Nonlinear optical materials are expected to be used as element materials for wavelength conversion elements, optical modulators, etc., since light transmitted through the materials is converted into higher harmonics. In such non-linear optical materials, inorganic materials have been widely studied as element materials, but in recent years, organic non-linear optical materials have been aimed at transmitting and processing a large amount of information. It is attracting attention as a key material for optoelectronic devices. That is, while the nonlinear optical phenomenon of inorganic materials is caused by lattice vibration, the nonlinear optical phenomenon of organic materials is caused by conjugation of π electrons.
If an organic nonlinear optical material is used, high response and a large optical constant can be obtained, and it is possible to obtain a high-performance nonlinear optical element. Also, since organic materials have a wide variety of structures, material development is possible. Expectations are being put on. So far, organic non-linear optical materials exhibiting non-linear optical characteristics actually surpassing those of inorganic materials have been obtained.

In order to realize an organic non-linear optical element using an organic non-linear optical material, it is essential to make the organic material into a thin film waveguide. However, the above-described thinning technique for an organic material having high nonlinearity is still under study and has not been established at present.

The Langmuir-Blodgett method (LB method) is an effective method for thinning the organic material. The LB method is a method in which amphipathic molecules are spread on a water surface to form a monomolecular film, and the flat plate is vertically passed through the monomolecular film while pressing the monomolecular film with a constant two-dimensional pressure. This is a method of forming a cumulative film by transferring a fixed number of layers onto the flat plate surface.

In order to obtain a good organic thin film by the LB method, it is necessary that the organic material forming the thin film is an amphipathic molecule (a molecule having both a hydrophilic group and a hydrophobic group in the molecule). For this reason, many attempts have heretofore been made to form a thin film waveguide by using the LB method for an amphipathic molecule having a large non-linearity. Few.

For example, Japanease Jour
nal of Applied Physics (vo
l 26 No10 October, 1987, pp
1622-1624), Nakanishi et al., N-octadecyl-2-methyl, a material obtained by adding an alkyl group having 18 carbon atoms to the amino group of 2-methyl-4-nitroaniline, which is a known organic nonlinear optical material. It reports on the preparation of LB film when -4-nitroaniline (C18-MNA) is used. But here, C18-M
Accumulation of LB film with NA alone has not been successful and C18
A mixture of MNA and another molecule (eg arachidic acid)
Only the results accumulated as B film are mentioned.

[0007]

As described above, some organic materials exhibiting good nonlinearity have been found.
None of them are suitable for use as an LB film, and the fact is that no organic material that can actually be used as a material for the organic nonlinear element has been obtained so far. Therefore, the present invention has been proposed in view of such conventional circumstances, and provides an organic non-linear optical material and an organic non-linear optical element which are excellent in non-linearity and can be formed into a cumulative film by the LB method. With the goal.

[0008]

Means for Solving the Problems MNA alkyl chain derivatives in which an alkyl group is added to an amino group are known to exhibit good non-linear optical characteristics. For example, an MNA alkyl group having 18 carbon atoms in the alkyl group. Chain derivatives have been investigated as materials for nonlinear optical elements. However,
It is difficult for the MNA alkyl chain derivative having the above carbon number to form a cumulative film by the LB method, and at present, it cannot be formed into a thin film waveguide. In order to produce a cumulative film by the LB method, the balance between the hydrophobic group and the hydrophilic group of the material is important. From such a point, as a result of intensive studies by the present inventors, by setting the number of carbon atoms of the alkyl group added to the amino group of MNA to 20 or more, the balance between hydrophobicity and hydrophilicity is improved, and LB It has been found that an organic nonlinear optical material that can be formed into a thin film can be obtained by the method.

Based on such knowledge, the organic nonlinear optical material of the present invention is represented by the following chemical formula 2, and the organic nonlinear optical element of the present invention is a Langmuir made of the organic nonlinear material shown in the chemical formula 2. -Blodgett films are laminated.

[0010]

[Chemical 2]

The organic nonlinear optical material of the present invention is a MNA alkyl chain derivative in which an alkyl group is added to the amino group of MNA. Here, in order to enable thinning by the LB method, it is important that the alkyl group has 19 or more carbon atoms. By setting the carbon number n to 19 or more, M
The balance of hydrophilicity and hydrophobicity of NA is improved, and the LB film has a structure that easily accumulates. When the carbon number n is less than 19, the hydrophobicity becomes insufficient and it becomes difficult to stack the carbon substrate on the substrate.

The nonlinear optical material having the above structure is MN
It can be synthesized by reacting A with a halogenated hydrocarbon having a predetermined carbon number in the presence of a suitable catalyst.

Here, it is preferable to use an ether solvent as the solvent used when the MNA and the halogenated hydrocarbon are reacted. Examples of ether solvents include linear ethers and cyclic ethers such as dioxane,
Any ether type solvent that is usually used may be used.

As the reaction catalyst, an alkali compound is usually used. At this time, if a solid state alkali compound is used, high reactivity can be obtained and the target product can be obtained in a high yield. When a solid state alkali compound is used, the contact between liquid MNA and halogenated hydrocarbons and the solid alkali compound should be good, and solid-liquid phase should be used in order to enhance the reactivity. Add an interphase transfer catalyst. As the solid-liquid phase-to-phase transfer catalyst, quaternary ammonium salts such as tetra-n-butylammonium bromide and crown ethers can be used.

The non-linear optical material functions as a non-linear optical element by forming a thin film waveguide by laminating it on the substrate by the LB method. To form a thin film made of the above nonlinear optical material by the LB method, first,
The non-linear optical material is floated on the water surface (sub-face) and an appropriate pressure is applied from the lateral direction. Then, this molecule forms a monomolecular film in which water molecules are regularly arranged with the hydrophobic groups on the water surface and the hydrophilic groups on the water surface. When the molecules are held in such a state and the solid substrate (for example, a glass substrate) is vertically moved up and down with respect to the monomolecular film, the monomolecular film on the water surface is transferred and accumulated on this substrate, It will be a thin film waveguide.

Here, in forming the LB film, various conditions such as the surface pressure of the monomolecular film and the water temperature have a great influence, and therefore it is necessary to set them appropriately.
That is, in order to form an LB film having good characteristics,
It is required that the collapse surface pressure of the monomolecular film (the surface pressure at which the monomolecular film is broken) at the cumulative temperature is large, and that the area change of the monomolecular film when kept under the cumulative condition is small.

In consideration of these points, the water temperature and the surface pressure during the production of the LB film are usually 5 ° C. and 20 mN / m, respectively. When accumulating the monomolecular film, slowing down the substrate moving speed allows the monomolecular film on the water surface to be stably transferred onto the substrate, which is advantageous in obtaining an LB film having good characteristics.

[0018]

In the organic material, one of the reasons why the LB film cannot be accumulated is that the collapse surface pressure is too low to stably exist as a monomolecular film. In the organic nonlinear optical material of the present invention, the carbon number n of the alkyl group in the MNA alkyl chain derivative is set to be 19 or more. Increasing the length of the alkyl group increases the hydrophobicity in the molecule and increases the collapse surface pressure. Therefore, it becomes very stable when it is formed into a monomolecular film, and it is easily formed as a thin film by the LB method and made into a thin film waveguide.

Further, the organic nonlinear optical material has a quicker response than the inorganic nonlinear optical material and exhibits excellent optical characteristics.
Therefore, the non-linear optical element obtained by converting the above organic material into a thin film waveguide exhibits an excellent function as an optical functional device.

[0020]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

Thinning of Organic Non-Linear Optical Material (1) Synthesis of Organic Non-Linear Optical Material First, 3-methyl-4-nitroaniline (MNA) is reacted with docosyl bromide in the following manner to show Chemical Formula 3. An MNA alkyl chain derivative (C22-MNA) was synthesized.

[0022]

[Chemical 3]

1 g of 3-methyl-4-nitroaniline
(0.065 mol) and 2.5 g of docosyl bromide (0.
(064 mol) was dissolved in 10 ml of dioxane and heated under reflux. 1 g of sodium hydroxide (solid) in this solution,
Tetra-n-butylammonium bromide (0.1 g) was added and the reaction was carried out for 2 hours. After 2 hours, water was added to the reaction solution to stop the reaction, the solvent was evaporated and removed, and washed with water to remove sodium hydroxide and tetra-n-butylammonium. Then, 2.7 g of the target product [N-docosyl-3-methyl-4-nitroaniline (C22-MNA)] was obtained by recrystallization using acetone.
(90% with respect to 3-methyl-4-nitroaniline) was obtained.

FIG. 1 shows the proton NMR spectrum of the compound. Each peak of the NMR spectrum is 0.8 pp
m: methyl group (3H), 1.2 to 1.8 ppm: methylene group (40H), 2.2 ppm: methyl group (3H) bonded to benzene ring, 3.2 ppm: methylene group bonded to amino group (2H ), 4.2 ppm: amino group, 6.5
ppm, 8 ppm: Assigned to each hydrogen of the benzene ring.

The compound had a melting point of 93 to 95 ° C. and an elemental analysis value of C ₂₉ H ₅₂ N ₂ O _{2 and} was measured (calculation%) C7.
5.47 (75.60), H11.28 (11.3
7) and N6.14 (6.08).

(2) Examination of LB film forming conditions In order to form a good LB film, the characteristics and stability of the monomolecular film to be laminated are important. Therefore, C obtained by synthesis
22-MNA monolayer was formed, and the surface pressure-area curve (isotherm) of the monolayer was examined at various temperatures.
The characteristics and stability of the monomolecular film were examined using the collapse surface pressure and the collapse area (surface pressure and area at which the monomolecular film is broken) obtained from the above curves as indexes.

For the monomolecular film, C22-MNA was dissolved in a chloroform solution to prepare a developing solution having a concentration of 0.6 mg / ml, and 200 μl of the developing solution was dropped on the water surface using pure water as a subphase. Formed by.

As a result, in the formed monomolecular film,
Corrosion surface pressure increased with decreasing water temperature, which was a valid result for the properties of the monolayer. The collapse area was 0.32 nm ^2, which was a substantially constant value.

Here, the collapse area is one index for estimating the existence state of molecules in the monomolecular film.
The above-mentioned collapse area has a larger value than the collapse area of a fatty acid in which alkyl chains are arranged perpendicularly to the water surface, which is 0.22 nm ² . From this, C22-
It is presumed that the alkyl chain of MNA is tilted (kinked) with respect to the water surface, and a simple estimation determined that the kink angle is tilted by about 40 degrees from the water surface direction.

When the monomolecular film is accumulated to form the LB film, the cumulative temperature and the surface pressure have a great influence on the cumulative property.
That is, in order to obtain an LB film having good characteristics, the collapse surface pressure of the monomolecular film at the set cumulative temperature is large, and the change in the area of the monomolecular film when kept under the cumulative condition is a change with time. There is a need for less. As a result of examining this point, it was found that a cumulative condition of a water temperature of 5 ° C. and a surface pressure of 20 mN / m can be adopted as one of the conditions satisfying these requirements.

That is, FIG. 2 shows the surface pressure-area curve of the monomolecular film at a temperature of 5 ° C. As can be seen from the curve, the collapse surface pressure at a temperature of 5 ° C. is 36 mN / m in the monomolecular film. It is high and can be sufficiently accumulated when the accumulated surface pressure is 20 mN / m.

Further, in FIG. 3, the temperature is 5 ° C. and the surface pressure is 20 mN /
The relationship between the monolayer retention time at m and the surface area is shown below.
The surface area of the monomolecular film when kept under the above conditions tends to gradually decrease with the passage of time, but the decrease amount of the surface area is as small as about 7% per hour. Therefore, the monomolecular film is sufficiently stable at a temperature of 5 ° C. and a surface pressure of 20 mN / m, which indicates that this condition is suitable as the cumulative condition for the LB film.

(3) LB Film Accumulation Experiment Next, the monomolecular film was actually accumulated under the above conditions to form an LB film, and the accumulation property was examined.

First, a glass substrate was prepared as a substrate for forming the LB film, and the surface of the glass substrate was hydrophobized with a silane coupling agent. And C22-
Using MNA, a monomolecular film is formed on the water surface in the same manner as described above, and the glass substrate is vertically moved with respect to the monomolecular film to accumulate the monomolecular film on the glass substrate. , LB film was formed.

The cumulative conditions are a temperature of 5 ° C. and a surface pressure of 20.
mN / m, substrate moving speed during accumulation 3 to 5 mm / m
set to in. Further, the accumulation of the monomolecular film started from the substrate descent because the substrate surface was made hydrophobic. In addition, for the accumulation of the monomolecular film, a joy robuter rough (manufactured by Joys Roble Co., Ltd.) is used, and the vertical movement of the substrate is started,
Everything was done under computer control.

With respect to the LB film thus formed, the accumulative property was examined by the trace at the time of accumulation (relationship between the position of the substrate and the surface area accumulated and decreased). It was confirmed that the Y-type LB film was excellent.

Investigation of Nonlinear Optical Characteristics of LB Film The nonlinear optical characteristics of the LB film were examined.

Under the same accumulation condition as above, C22-MN
Ten monolayers of A were accumulated to form an LB film, and its nonlinear optical characteristics were evaluated by the maker fringe method.

In the maker fringe method, the thin film laminated on the substrate is irradiated with laser light to measure the intensity of the generated second harmonic wave (SHG) and third harmonic wave (THG). , Rotate the sample to change the effective thickness (optical path length of the light that passes through the thin film), and change the SHG light or TH
The interference pattern of the fringe caused by the G light is also observed. This maker fringe method has a feature that it can be applied even when phase matching cannot be achieved.

FIG. 4 schematically shows the maker fringe measuring device used. That is, this device is an optical system composed of a light source section composed of a YAG laser 14 and a He-Ne laser 15, an IR transmission filter 16, an ND filter 17, a Fresnel Rom prism 18, a polarizer 19 and a lens 20, and is vertically rotatable. Sample stage 21, IR
An optical system 26 including an absorption filter 22, a lens 23, a lens 24, a detector 25 including an analyzer 25, a detector for reference, an information processing device 27, and a calculator 28.
It consists of the analysis part.

In order to perform the measurement with this maker fringe measuring device, the sample 29 is placed on the sample stage 21 which rotates in the vertical direction, and the sample 29 is put on the sample stage 21 by the YAG laser 14.
Irradiate the laser through the R transmission filter 16, the ND filter 17, the Fresnel Rom prism 18, the polarizer 19, and the lens 20 to obtain the IR absorption filter 22 and the lens 2.
3, the lens 24 and the analyzer 25 measure the second harmonic and the third harmonic. Then, this and the laser that has passed through the optical system 38 including a detector or the like for reference are analyzed by the information processing device 27 and the arithmetic unit 28 to determine the maker fringe pattern. For example, if a nonlinear material can be processed into a parallel plate, by rotating the sample and changing the incident angle of the laser, the optical path of the laser (effective thickness of the sample) through the nonlinear medium is continuously changed. On the other hand, we observe a pattern (fringe pattern) in which the harmonic generation efficiency changes periodically due to the phase shift caused by the refractive index dispersion of the fundamental wave and the harmonic wave.

Here, regarding the fringe pattern, SH
Explaining only the G light, the intensity S of the SHG light S
_2w is expressed as in _Equation 1, where L is the thickness of the medium,
By changing the thickness L (position of the sample) of this medium, the fringe pattern is drawn and changed. Therefore, when such a fringe pattern is observed in the thin film to be the sample, it can be determined that the thin film has a non-linear characteristic.

[0043]

[Equation 1]

In the present embodiment, in such a maker fringe method, the fundamental wave (1.06 μm) of the YAG laser is horizontally deflected and incident on the substrate, and the second harmonic wave is generated in the same polarization direction. SHG was detected by detecting the light intensity of 514 nm.

As can be seen from FIG. 5, a clear fringe pattern based on the second-order nonlinear optical property is observed in the LB film made of C22-MNA. In addition, as a comparison, the non-linear optical characteristics of the glass substrate on which the LB film was not formed were also examined in the same manner, but no fringe pattern was observed. So from this,
It has been found that the LB film made of C22-MNA has good non-linear optical properties.

Further, from the different direction of the σ constant obtained by the Maker Fringe method, it was shown that the dipole moment lies in the horizontal plane with respect to the substrate and is oriented in the same direction as the accumulation direction of the LB film.

Fabrication and Evaluation of Organic Nonlinear Optical Element Here, a wavelength conversion element, which is one of the nonlinear optical elements, was actually fabricated using C22-MNA, and the function as an element was evaluated.

In the wavelength conversion element manufactured in this example, among the SHG elements that convert the fundamental wave of YAG laser light of 1.06 μm into 0.53 μm by the second harmonic generation (SHG), the phase matching is Cerenkov. It is a Cerenkov type SHG element which is performed by using the method. The phase matching by the Cherenkov method will be briefly described below.

When the fundamental wave mode propagates through the waveguiding layer with an effective refractive index, the nonlinear polarization wave that generates the SHG wave also propagates with the same phase velocity. If the refractive index of the SHG wave of the substrate is lower than the refractive index of the fundamental wave of the waveguiding layer, the SHG wave phase-matched to the substrate side at a certain angle is radiated. This nonlinear polarization wave (SHG wave) is automatically generated in a phase-matched direction and has a faster phase velocity than the fundamental wave, and is therefore called the Cherenkov phase matching method.

The specific structure of the Cherenkov type SHG element manufactured in this example is as shown in FIGS. 6 and 7. The SHG element shown in FIG.
A two-dimensional slab waveguide type SHG element in which an LB film 62 made of NA12 is laminated. The SHG element shown in FIG. 7 has a photoresist 73 formed on a part of a substrate 71, and further on the substrate 71 and the photo resist. C on the resist 73
This is a three-dimensional ridge waveguide type SHG element in which an LB film 72 made of 22-MNA is laminated.

Here, in the case of the SHG element adopting the Cherenkov phase matching method, the refractive index of the substrate is important as described above. From this point, the two-dimensional slab waveguide SH is used.
In the G element, the glass substrate PC2 (refractive index 1.51) was used as a substrate, and in the three-dimensional ridge waveguide type SHG element, a photoresist having a refractive index of 1.51 was formed on the glass substrate.

A two-dimensional slab waveguide type SHG element,
In any of the three-dimensional ridge waveguide type SHG elements,
The LB film made of C22-MNA was formed under the same accumulation condition as described above, and the film thickness was set to 0.65 μm based on the mode coupling theory.

Element evaluation was performed on the SHG element having such a structure. For the element evaluation, a YAG laser beam is introduced into the optical waveguide using a prism and the SHG emitted from the waveguide is used.
This was done by detecting light with a photomul.

As a result, in all the devices, 0.
SHG light of 53 μm could be observed. Therefore, from this, it was found that the nonlinear optical element using C22-MNA sufficiently functions as a wavelength conversion element. In this example, the case where C22-MNA was used as the organic nonlinear optical material was shown, but any MNA alkyl chain derivative in which the alkyl group has a predetermined number of carbons is similarly used. It goes without saying that a non-linear optical element exhibiting excellent characteristics can be obtained.

[0055]

Since the organic nonlinear optical material of the present invention is an MNA alkyl chain derivative having an alkyl group having 20 or more carbon atoms, it exists as a stable monomolecular film on the water surface, and the conventional LB film accumulation method is used. By using, good Y type L
It can be an organic nonlinear optical waveguide of B film.

Since this organic nonlinear optical waveguide has a quick response and shows good optical characteristics as compared with an optical waveguide made of an inorganic material, by using such an organic nonlinear optical material, high performance wavelength conversion is achieved. Non-linear optical elements such as elements and optical modulators can be obtained, and large-capacity optical disk systems and optical communication systems can be realized.

[Brief description of drawings]

FIG. 1 is a ¹ H-NMR spectrum of synthesized C22-MNA.

FIG. 2 is a characteristic diagram showing a surface pressure-area curve of a C22-MNA monomolecular film at a temperature of 5 ° C.

FIG. 3 is a characteristic diagram showing the relationship between the holding time and the area of a C22-MNA monomolecular film under the conditions of a temperature of 5 ° C. and a surface pressure of 20 mN / m.

FIG. 4 is a schematic diagram showing the measurement principle of the maker fringe method.

FIG. 5 is a characteristic diagram showing a maker-fringe pattern of an LB film made of C22-MNA.

FIG. 6 is a schematic cross-sectional view of a main part showing the configuration of a two-dimensional slab waveguide type SHG element.

FIG. 7 is a schematic cross-sectional view of an essential part showing the configuration of a three-dimensional ridge waveguide type SHG element.

Front Page Continuation (72) Inventor Bourne Haworth 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Ichiro Fujiwara 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation Shares In the company

Claims (2)

[Claims] 1. An organic nonlinear optical material represented by the following chemical formula 1. [Chemical 1] 2. An organic nonlinear optical element having a Langmuir-Blodgett film made of the organic nonlinear material according to claim 1 laminated on a substrate.