JPH02132423A - Nonlinear optical element - Google Patents

Abstract

PURPOSE:To form a single crystal of the size sufficient to constitute a light guide and to obtain the element exhibiting a high nonlinear optical effect without having absorption of visible light by using the crystal of a specific org. compd. CONSTITUTION:The nonlinear optical element is formed by using the org. compd. expressed by general formula I. In the formula, A denotes <=5C electron- withdrawing group; R1 denotes a hydrogen atom, alkyl group, alkenyl group; R2 denotes a hydroxyl group, acylamino group, ureide group; R3 denotes a hydrogen atom or monovalent substituent. The carbon atoms having the electron withdrawing property are preferably <=3 and the electron-withdrawing groups are preferably a nitro group, cyano group, formyl group, alkylsulfonyl group. R1 is preferably an alkyl group, R2 a hydroxyl group and R3 a hydrogen atom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an organic nonlinear optical element used for generation of harmonics of laser light, parametric amplification, and the like.

[Background of the invention] The nonlinear optical effect that appears prominently when a substance is irradiated with intense light such as a laser beam can be applied to wavelength conversion, intensity modulation, switching, etc., and in recent years, materials with this nonlinear optical effect have been developed. Many exploratory studies have been conducted.

Wavelength conversion, especially second harmonic generation based on second-order nonlinear optical effects.
ration, hereinafter abbreviated as SHG. ), it has been pointed out that organic compounds may have an order of magnitude higher performance than conventionally known inorganic materials such as lithium niobate (LiNbO3) and potassium dihydrogen phosphate (KDP). (
For example, "Organic Nonlinear Optical Materials", supervised by Masao Kato and Hachiro Nakanishi, published by CMC Co., Ltd., 1985) The origin of the nonlinearity of organic compounds is the intramolecular π electrons,
The following nonlinear molecular polarizability β becomes particularly large when the compound has both an electron-donating group and an electron-withdrawing group.

However, as typified by p-nitroaniline, even if the nonlinear polarization at the molecular level is large, there are many that do not exhibit total<SHG in the crystalline state, or even if they do, the SHG is small. This is due to the fact that the molecular arrangement of highly polar organic crystals tends to have inversion symmetry.

In addition, research into optical recording media is being actively conducted in response to demands for larger capacity and higher density information recording media, but since the recording density of these optical recording media depends on the wavelength of the light source (
As the light source wavelength becomes shorter, the recording density limit increases in inverse proportion to the square of the wavelength. ), there are great expectations for wavelength conversion elements to obtain shorter wavelength light sources.

Examples of compounds with SHG effect include 2-methyl-4
-Nitroaniline (MNA), 2-acetamide 4
-Nitro-N,N-dimethylaniline (DAN), 2
-acetamido-4-nitro-1-pyrrolidinobenzene (
PAN), 2'-(αmethylbenzyl)amino-5
-Nitropyridine (MBA-NP) and the like are known.

However, known compounds with high SHG activity, such as 2-methyl-4-nitroaniline, m-nitroaniline, etc., are yellow-colored, so they have low transmittance to short-wave light, and they cannot be used for short-wave light by wavelength conversion. It is disadvantageous for this to occur. In addition, conventionally known compounds with SHG effects are:
It is advantageous to have a single crystal large enough to form the core of an optical waveguide.
<It was extremely difficult to create an optical waveguide for use as a wavelength conversion element.

For example, in order to make a conventional fiber-type optical waveguide device, a nonlinear optical material with a high refractive index is melted and injected into a hollow fiber made of a material with a low refractive index, and then a simple method such as the Bridgman-Stockberger method is used. A method of crystallization is used. (Reference book D.S. Chemla,
J. Zyss: Nonlinear Optic
al Properties of Organic
Molecules and Crystals Vol.
．． 1; ACADEMIC PRESS INc. (
19B? )) However, conventionally known organic nonlinear optical materials exhibiting excellent nonlinear optical effects are generally difficult to form into single crystals by such methods, making it difficult to form the core of an excellent leading waveguide. For example, PANSMBA-NP decomposes when melted, making it impossible to obtain a single crystal.

As a result of research on the nonlinear optical effect, crystallization, and visible light transmittance of the compound, the present inventors found that it has a high nonlinear optical effect, no absorption of visible light, and is sufficient to easily be used as a leading waveguide. We have discovered a compound that forms crystals of a large size.

[Objective of the Invention] An object of the present invention is to provide a nonlinear optical element that can easily form a single crystal large enough to be used as an optical waveguide, does not absorb visible light, and exhibits a high nonlinear optical effect. It's about doing.

[Structure of the Invention] The above object of the present invention was achieved by forming a nonlinear optical element using a crystal of an organic compound represented by the following general formula [1].

General formula [Ico (wherein A is an electron-withdrawing group having 5 or less carbon atoms, R,
represents a hydrogen atom, an alkyl group, or an alkenyl group, R2 represents a hydroxyl group, an acylamino group, or a ureido group, and R represents a hydrogen atom or a monovalent substituent. ) Hereinafter, the present invention will be explained in more detail.

In the above general formula [I], the number of carbon atoms represented by A is 5
The following electron-withdrawing groups have a Hammett elongation p value of 0 or more, and examples of these electron-withdrawing groups include nitro groups, cyano groups, formyl groups, halogen atoms (bromine atoms, chlorine atoms, etc.), Alkylsulfonyl group (e.g. methylsulfonyl group), alkoxycarbonyl group (e.g. methoxycarbonyl group, butoxycarbonyl group), trifluoromethyl group, dicyanovinyl group, succinimide group,
Examples include heterocyclic groups (eg, imidazolyl group, thiazolyl group, furyl group).

The number of carbon atoms in the electron-withdrawing group is preferably 3 or less.

More preferred electron-withdrawing groups are a nitro group, a cyano group, a formyl group, and an alkylsulfonyl group.

Examples of the alkyl group represented by R include methyl group,
Examples of the alkenyl group include ethyl group, probyl group, and isoprobyl group, and examples of the alkenyl group include ethenyl group, propenyl group, and butenyl group.

These alkyl groups and alkenyl groups may have a substituent, and examples of the substituent include a halogen atom (bromine atom, chlorine atom, fluorine atom, etc.), an alkoxy group (methoxy group,
(ethoxy group, etc.), hydroxyl group, cyano group, etc. are preferable.

Preferred as R1 is an alkyl group, and more preferred is a substituted or unsubstituted methyl group.

Examples of the acylamino group represented by R2 include an acetamide group and a penzamide group, and examples of the ureido group include a methylureido group and a phenylureido group.

Preferred as R2 is a hydroxyl group.

The monovalent substituent represented by R is preferably, for example, a chlorine atom, a bromine atom, a nitro group, a cyano group, an acetamido group, or a methyl group.

Preferred R is a hydrogen atom.

Specific examples of compounds preferably used in the present invention are shown below, but the invention is not limited thereto.

The following margins are below: The compounds of the present invention can be easily synthesized by conventional general synthesis methods, and parts can be purchased as reagents.

The nonlinear optical element according to the present invention has a fiber shape, a flat plate shape, a shape in which a single crystal is surrounded by a cladding material, etc. as shown in the above-mentioned documents, Japanese Patent Application Laid-Open No. 63-77035, etc., for example. It is a wave path.

Of these, fiber-shaped ones are particularly preferred.

The single crystal growth method used in the present invention is described in the above-mentioned documents. Preferred single crystal growth methods are the Bridgman method and the reverse Stockberger method, in which crystals are grown from a melt.

The nonlinear optical element of the present invention can be used for wavelength conversion (generation of harmonics, etc.), intensity modulation, switching, etc. of laser light, particularly near-infrared semiconductor laser light.

[Examples] Examples are shown below, but the embodiments of the present invention are not limited thereto.

Example 1 A compound of the present invention was heated to a temperature 10°C higher than its melting point,
The outer diameter of the melt is 1.0++++n, the inner diameter is 7Bm, and the length is 50.
It was injected into a hollow glass fiber made of mm borosilicate glass using capillary action.

Thereafter, using the Bridgman-Stockberger method, the hollow glass fiber injected with the compound was pulled at a pulling rate of 1 mm per hour from a heating furnace maintained at a temperature 5°C higher than the melting point of the compound, and then kept at room temperature. It was cooled and crystallized.

The length of the single crystal portion was measured using a polarizing microscope.

These results are shown in the following table.

Margin table below*; A: Length of the obtained single crystal 1 D mm or more B: Length of the obtained single crystal 1 mm or more and less than 10n+n+ C: Length of the obtained single crystal 0.2 w++ or more L less than L w D = Example 2 where the material decomposes during melting and a single crystal cannot be obtained The single crystal fibers of Samples 1, 2, and 3 obtained in Example 1 were cut to a length of approximately 3 mm, and repeatedly 1Opps was used as the incident fundamental wave. , pulse width 10 ns, pulse energy 320 mJ Q-switched Nd: A YAG laser (YGfiBOA, wavelength 1064 nm, manufactured by Quantel International in the United States) was used, and when it was attenuated and focused, the light was guided from the end face of a single crystal fiber, and it appeared on the screen. A ring-shaped second harmonic (green light) was observed.

[Effects of the Invention] According to the present invention, there is provided a nonlinear optical element that can easily obtain a single crystal large enough to be used as an optical waveguide, does not absorb visible light, and exhibits a high nonlinear optical effect. Can be done.

Applicant Co., Ltd.

Claims (1)

[Claims] A nonlinear optical element using a crystal of an organic compound represented by the following general formula [I]. General formula [I] ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, A represents an electron-withdrawing group with 5 or less carbon atoms, R_
1 is a hydrogen atom, an alkyl group, an alkenyl group, R_2 is a hydroxyl group, an acylamino group, a ureido group, R_
3 represents a hydrogen atom or a monovalent substituent. )