JPH0497231A - nonlinear optical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a nonlinear optical element in which an optical waveguide is formed using an organic nonlinear optical material.

[Prior art and problems to be solved by the invention] Many organic nonlinear optical materials exhibit nonlinear optical constants that are 10 times or more larger than those of inorganic crystals such as LiNbO3 and KTP. Crystals such as aniline are well known as second-order nonlinear optical materials. It is also well known that materials that exhibit a large second-order nonlinear optical effect due to a delocalized π-electron system also exhibit a large electro-optic effect.

On the other hand, a characteristic of an optical waveguide type nonlinear optical element is that light is confined in a narrow space, so nonlinear optical effects are likely to appear, and a characteristic of an electro-optical element is that it can operate at low voltage and at high speed. In order to take advantage of these characteristics, research is being conducted on applying materials with large nonlinear optical effects and electro-optic effects to optical waveguide type optical elements.

However, there are only a few organic crystals that have been obtained that are large enough to be put to practical use, and even if the constituent molecules have a large second-order molecular polarizability β, the molecular arrangement in the crystal is inversion symmetric. Even if it is crystallized, it is often impossible to convert the wavelength. Furthermore, in order to apply organic crystals to light-guiding optical elements, it is necessary to process them into fibers or thin films, but there are even fewer examples of success in this process. As described above, it has been difficult to produce an optical element that can withstand practical use using organic molecules in the form of organic crystals and having a large second-order molecular polarizability β.

In addition to crystalline materials, there are also dispersed polymer materials in which organic polymers are doped with nonlinearly optically active organic molecules, and side chain-modified polymers in which nonlinearly optically active structures are introduced into the side chains of organic polymers through chemical bonds. Side chain-modified polymer materials have been devised, in which the molecular aggregates of molecular materials have the arrangement necessary for the expression of nonlinear optical effects. A method of imparting regularity to the state of molecular assembly is to apply an external electric field while heating it to around the glass transition temperature (Tg), align the nonlinear optically active sites along the electric field, cool it to 7 g or less, and then Methods of fixing the array state are known. The second-order nonlinear optical constant d of the oriented polymeric nonlinear optical material is d=N−fω−fω−f2ω−β'<CO3'θ>N:
Number of nonlinear active sites per unit area (pieces/c-J) β: Secondary molecular polarizability of nonlinear optically active sites θ: Angle between electric field direction and polarization β fω, f2ω: Modification factor for wavelength ω, 2ω It is expressed by the formula. In order to increase the nonlinear optical constant, N,
It is necessary to increase β and decrease θ.

Although organic polymer materials have a large degree of freedom in production, they have the problem that the arrangement relaxes at room temperature and the nonlinear optical effect disappears, or when N is increased, the nonlinear optically active sites associate and the transparency deteriorates. Problems such as this may occur.

To solve the former problem, methods such as increasing the Tg temperature and using crosslinking reactions are being considered, but these methods have limited the number of organic polymer materials that can be used in practical nonlinear optical elements. .

Therefore, an object of the present invention is to provide an optical waveguide type nonlinear optical element that has excellent nonlinear optical effects and electric field orientation.

[Means for Solving the Problems] The present invention provides an optical waveguide using a polymeric organic nonlinear optical material containing acetalized polyvinyl alcohol having a structure represented by the following general formula (I) as a constituent component. The above object can be achieved by providing a nonlinear optical element characterized in that 1,000-CH-CH, -CH-CH1
-ToCH.

[However, R3 is a hydrogen atom, any one of a straight chain or branched alkyl group having 1 to 6 carbon atoms, and R2 is a hydrogen atom, a straight chain or branched alkyl group having 1 to 6 carbon atoms, or a straight chain or branched alkyl group having 1 to 6 carbon atoms.
-6 represents any one of a linear or branched alkoxy group, a hydroxy group, a nido tetragroup, or a halogen atom] The acetalized polyvinyl alcohol represented by the general formula (I) in the present invention is represented by the following general formula ( It is synthesized by reacting 4-nitrophenylaminoacetaldehyde acetal represented by II) with polyvinyl alcohol. An example of the synthesis method will be explained below.

B2 However, R3 and R4 in the above general formula (II) represent any one of a hydrogen atom and a straight chain or branched alkyl group having 1 to 6 carbon atoms.

Put polyvinyl alcohol in a suitable container), add 1 to 5 times the mole of raw material acetal, preferably 2 to 3 times the mole, add acid in an amount equal to the acetal, heat and stir, and precipitate the polymer. Acetalized polyvinyl alcohol can be obtained by purifying it by reprecipitation or the like.

The polyvinyl alcohol used has a degree of polymerization of 500 to 2400.
The stereoregularity may be random, isotactic, heterotactic, or syndiotactic.

The solvent may be any solvent as long as it dissolves polyvinyl alcohol, but water is preferably used. Examples of the acid to be added include hydrochloric acid, sulfuric acid, acetic acid, I)-toluenesulfonic acid, etc. The amount added is 1 to 5 times the mole of the raw material acecool, preferably 1 to 2 times the mole. is 0-100
'C2 It is preferably carried out by heating and stirring at 50 to 80°C.

The acetal side chain introduction rate X in the acetalized polyvinyl alcohol can be controlled by the molar ratio of the raw materials and the reaction temperature.

Furthermore, if the polymeric organic nonlinear optical material used in the present invention contains an acetalized polyvinyl alcohol having a structure represented by the formula (I) as a constituent component, it is a copolymer of polyvinyl alcohol. It may be,
The composition of the copolymer is not particularly limited as long as it has a structure derived from polyvinyl alcohol, such as a vinyl alcohol structure, vinyl ether structure, vinyl ester structure, or acetal structure, and two or more types of structures are included in the copolymer composition. Also, the morphology of the copolymer may be random,
It can be either eye-tactic, heterotactic, or syndiotactic. In addition, the side chain introduction rate is 10 to 1
Any value between 00% and 00% is acceptable.

The obtained nonlinear optical polymer generates second harmonics (SHG) by orienting it in an electric or magnetic field, but in the case of electric field orientation, it is usually necessary to apply a high voltage of 200 KVZ1 to achieve orientation. .

The polymer organic nonlinear optical material used in the present invention is 30
It is highly useful in that it can be oriented in the direction of an electric field at a relatively low voltage of KV/cm and can be relatively easily aligned.

Furthermore, by utilizing the hydrophilicity of the hydroxyl group residue of polyvinyl alcohol in the polymeric organic nonlinear optical material of the present invention, it can also be oriented by spreading it as a monomolecular film (LB film) on the water surface and scooping it onto a substrate. I can do it.

There are various methods for synthesizing 4-nitrophenylaminoacetaldehyde acetal represented by the above general formula (II), but
- Outline an example. That is, it is obtained by reacting a 4-nitrofluorobenzene derivative and an aminoacetal in the presence of a base. The reaction solvent may be any solvent that dissolves the raw materials, such as benzene, toluene, xylene, DMSO, DMF, NMP, chloroform, methylene chloride, ethyl alcohol, methyl alcohol, ether, THF, hexane, cyclohexane, etc. When the raw materials are liquid, may be solvent-free. Examples of the base used include carbonates such as sodium carbonate, potassium carbonate, lithium carbonate, magnesium carbonate, and calcium carbonate, and hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate. These may be anhydrous or may contain water of crystallization. When using an organic base, pyridine, pyrimidine, piperazine, triazine, lutidine, morpholine, pyrrolidine, etc. can be used. These bases are added to prevent the acetal group from being decomposed into aldehyde by the hydrofluoric acid produced by the reaction. The reaction proceeds at room temperature or by heating, and varies depending on the raw materials used. The aminoacetal is reacted in an amount of 1 to 5 times, preferably 1 to 2 times the equivalent of 4-nitrofluorobenzene.

The guided waveguide type nonlinear optical element of the present invention may have, for example, an optical fiber shape or a thin film coated on a substrate.

An optical fiber-shaped optical waveguide type nonlinear optical element uses, for example, a polymeric organic nonlinear optical material containing the above-mentioned acetalized polyvinyl alcohol in the core (cladding), and the cladding (core) has a bending index lower than that of the core (cladding). It can be formed by using a material with low (high) In this case, the polymer organic nonlinear optical material described above is injected in a molten state into a silica glass capillary, heated to 7 g or more, and an external electric field is applied to unidirectionally polarize the site of the side chain exhibiting a large molecular polarizability β. After being arranged, a nonlinear optical element having a core made of a polymeric organic nonlinear optical material and a cladding made of quartz glass can be obtained by cooling and solidifying the materials.

In addition, after applying a solution or melt of the polymeric organic nonlinear optical material to the outer periphery of a glass fiber having a refractive index higher than that of the polymeric organic nonlinear optical material, the glass is solidified while passing through an electric field. An optical fiber type nonlinear optical element having an organic nonlinear optical material as a cladding can be obtained.

In addition, when the above-mentioned polymeric organic nonlinear optical material is used in the form of a thin film, a solution of the polymeric organic nonlinear optical material is uniformly applied onto a substrate having a refractive index lower than that of the polymer by a spin code method, a dipping method, etc. Then, by heating and removing the solvent, a leading waveguide can be obtained. A thin plate-shaped nonlinear optical element can be obtained by heating this to near the Tg of the polymeric organic nonlinear optical material and applying an external electric field to align the nonlinear optically active sites of the side chains in one direction. In this case, it goes without saying that the desolvation treatment and the orientation treatment can be performed at the same time.

Further, the temperature of this alignment treatment is preferably 7 g or more of the polymeric organic nonlinear optical material which is a side chain modified polymer, more preferably about Tg + 40°C, even more preferably about Tg + 20°C. . The strength of the electric field to be applied may be any strength that can impart sufficient orientation to the side chains.
It is preferable to go as high as possible.

The polymeric organic nonlinear optical material used in the present invention may use acetalized polyvinyl alcohol having the structure represented by general formula (I) as a component alone as a polymeric material, or may use it together with other polymer matrix. It may also be used in a composite system.

The polymer matrix used is preferably a polymer with low optical damage, such as:
For example, esters such as poly-ε-caprolactone, polybutylene sebacate, polyhexamethyleneazibe-1, polyethylene oxide, polymethacrylate,
Examples include nylon, cellulose, epoxy resin, phenol novolac, and cresol novolac.

In addition, the polymeric organic nonlinear optical material used in the present invention can be used in the present invention, which utilizes the nonlinear optical effect produced by applying an electric field alignment treatment or a treatment that exhibits an equivalent effect of aligning the nonlinear optically active sites in one direction. In addition to optical waveguide type nonlinear optical elements, the present invention can also be applied to various elements that utilize birefringence, electro-optic effects, and thermal effects.

[Effect]

According to the present invention, nonlinear optical effects, electro-optic effects, etc. can be exerted on light in an optical waveguide.

〔Example〕

The present invention will be described below with reference to Examples, but the present invention is not limited thereto.

Example 1 Polyvinyl alcohol acetalized with 4-nitrophenylmethylaminoacetaldehyde (p-NAn-
PVA) (side chain introduction rate x in general formula (I) = 0.8
8) was dissolved in dimethylformamide to make a 6.6% solution. This solution was placed on a Pyrex substrate at an ambient temperature of 85°C.
After spin-coding at °C1 rotation speed 70 ° rpm, 11
Heat and dry at 0°C for 130 minutes and then at 160°C for 160 minutes. FIG. 1 shows the spectral transmittance when the same substrate was used as a reference object, and FIG. 2 shows the refractive index wavelength dispersion.

As a result, it was found that it could be used as an optical waveguide in this state. When a semiconductor laser beam with a wavelength of 0.789 μm was guided using the prism coupling method, the propagation loss was 10 db/an.
It was found that the following.

Example 2 SiNx with grading for input/output coupling
A P-NAn-PVA waveguide was fabricated on an Ox/Si substrate in the same manner as in Example 1, and a P-NAn-PVA waveguide with a circumference of M20 was formed on it.
A glass substrate with a μm Cr comb-shaped electrode was bonded via a PMMA optical fiber layer and heated to 140°C for 5 minutes.
A voltage of 400 .mu. was applied between the i-Cr electrodes for 15 minutes to carry out an alignment treatment to produce an electro-optical device. When a semiconductor laser beam with a wavelength of 0.825 μm was guided in this electro-optical element in TM mode and a voltage was applied between the 5i-Cr electrodes, the diffracted light intensity changed at the position of the diffracted light with a period of 20 μm corresponding to the applied voltage. was observed (see Figure 3), confirming the electro-optic effect in this optical waveguide, and it was found that there was no change in this characteristic even after several days had passed.

〔Effect of the invention〕

The optical waveguide type nonlinear optical element of the present invention has excellent nonlinear optical effects and electric field orientation.

[Brief explanation of drawings]

Figure 1 is a graph showing spectral transmittance when the same substrate is used as a reference object, Figure 2 is a graph showing refractive index wavelength dispersion, and Figure 3 is a graph showing the relationship between diffraction efficiency of TM mode guided light and applied voltage. This is a graph showing.

Claims (1)

[Claims] An optical waveguide is formed using a polymeric organic nonlinear optical material containing acetalized polyvinyl alcohol having a structure represented by the following general formula (I) as a constituent component. Optical waveguide type nonlinear optical element. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) [However, R_1 is a hydrogen atom or any one of a linear or branched alkyl group having 1 to 6 carbon atoms, and R_2 is a hydrogen atom or a straight chain or branched alkyl group having 1 to 6 carbon atoms. Represents any one of a straight chain or branched alkyl group, a straight chain or branched alkoxy group having 1 to 6 carbon atoms, a hydroxy group, a nitro group, or a halogen atom]