JPH03211533A - Nonlinear optical element - Google Patents

Abstract

PURPOSE:To obtain the nonlinear optical element which has a large quadratic nonlinear optical constant and good compatibility with high-polymer compds. and for which an org. compd. is used by incorporating a specified hydrazone compd. into a medium on which light is made incident. CONSTITUTION:The hydrazone compd. expressed by formula I has a pi conjugation system in the molecule skeleton, consists of the rigid pi electron conjugation part and the hydrazone part having high refractiveness and has the excellent compatibility with liquid crystalline high polymers, other high-polymer compds. or liquid crystal compds. In the formula I, R1 denotes the substituent selected from 0<pi<1.5 in substituent constant pi of Hansche; R2 denotes an alkyl group or hydrogen atom. The content of the above-mentioned compd. is increased in this way at the time of using the compd. as the org. nonlinear compd. of the nonlinear optical element formed by using the mixture composed of the liquid crystalline high polymer, the other high-polymer compd. or the liquid crystal compd.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to an organic nonlinear optical element, and particularly to a nonlinear optical element using a hydrazone compound having an excellent second-order nonlinear optical effect.

"Conventional technology" In the field of optoelectronics, as the wavelength of laser light has become shorter, existing laser light has been doubled in frequency (second
development of nonlinear optical materials that convert harmonics into light;
The development of nonlinear optical materials that exhibit large nonlinear optical effects and respond at high speed is being actively pursued. Traditionally, inorganic materials have been the main focus of development, but organic compounds are expected to have large nonlinear optical constants, fast response speeds, and low optical damage. For these reasons, organic compounds with π-electron conjugated systems have attracted attention (CMC Organic Nonlinear Optical Materials R&D
No. 72, Masao Kato, Hebe Nakanishi (1985)
According to these, as represented by 2-methyl-4-nitroaniline (hereinafter abbreviated as MNA), π
It is known that compounds having an electronic system and having an electron donating group and an electron withdrawing group in the molecule have a large second-order nonlinear optical constant β (hereinafter simply abbreviated as "β value").

However, even with a large β value, as typified by 4-dimethylamino-4'-nitrostilhene (hereinafter abbreviated as DANS), second-order nonlinear optical phenomena occur due to the crystal structure with a center of symmetry. It also has the disadvantage that there is no (J
, L., Oudar, J., Chem., Phys.

87.446 (+977)). Furthermore, the molecular arrangement in organic molecular crystals is often uniquely determined by individual molecular species in a certain temperature range, and it is extremely difficult to control the molecular arrangement in the crystal. For these reasons, until now,
There are few reports of organic compounds that exhibit a second-order nonlinear optical effect higher than that of MNA, and therefore, there are not many known elements that have higher efficiency than nonlinear optical elements using MNA.

On the other hand, due to the above-mentioned problems, there is a method for producing a second-order nonlinear optical effect in an organic compound that does not exhibit a second-order nonlinear optical effect due to its crystal structure, despite exhibiting a large β value. have been variously studied (D, S, Ch
eila, J, Zyss+ Non1inearOp
ticalProperties of 0r3an
tc Molecules and Crystals,
Academic Press, Inc., New Y
ork(+987)).

One of the methods is to use a liquid crystal compound or a liquid crystal polymer material as a medium. That is, the liquid crystal material is
In the liquid crystal state, molecular orientation can be controlled by an electric or magnetic field. Taking advantage of this property, by mixing an organic compound with a large β value into the liquid crystal material and applying an electric or magnetic field, liquid crystal This method eliminates the center of symmetry by orienting the organic compound in the orientation direction of . For example, the generation of second harmonics has been observed in polymer media obtained by mixing DANS in a liquid crystal polymer, applying an electric field in the liquid crystal state, and rapidly cooling it (D, J).

Williams, Non1inear 0pti
cal Properties of Organic
Molecules and Crystals, p4
05, Acade+w+cPress, Inc., Ne
York (1987)) *Another method is to use a thermoplastic transparent polymer material as the medium. That is, a method using polymethyl methacrylate as a polymeric medium (D., Singer, J.E., 5
ohn+S, J, Lalama, Appl.

Phys, Lett, 49.248 (1986))
, a method using acrylamide (Japanese Patent Application Laid-Open No. 62-8713
9), a method using polyethylene glycol (Japanese Unexamined Patent Publication No. 64-522.523), etc. In these methods, as in the case of the liquid crystal material medium, the glass transition of the polymer medium is This is a method in which an electric field is applied under heating above a point to orient the organic compound and eliminate the center of symmetry.

An even newer method is the method developed by Miyata et al. That is, it is a method using polyε-caprolactone as a polymeric medium (Ken Miyazaki, Toshiyuki Watanabe, Seizo Miyata,
Proceedings of the 35th Applied Physics Union Lecture Conference, pl 79
(1989)'), with this method, generation of second harmonics has been observed even without applying an electric field.

In addition, among hydrazone compounds, some compounds with -CH=N-NHCO- groups that exhibit second-order nonlinear optical effects are known (B, L
,Davydov, e/ J/, ,Sov, J, Qua.
ntuo+εIectron, Engl, Trans,
,? (1), 129 (1977)), 5-nitrofurfuryl semicarbazone generates second harmonics with an intensity 30 times that of lithium formate, and its nonlinear optical effect is not satisfactory.

"Problems to be Solved by the Present Invention" Although the conventional organic nonlinear optical materials described above have very large nonlinear optical constants, it is difficult to obtain large crystals, the stability of the crystals is poor, and there are problems with compatibility with polymer materials. It has problems such as poor solubility. Furthermore, the nonlinear optical constants are still not satisfactory.

SUMMARY OF THE INVENTION In order to solve these problems, the present invention provides a nonlinear optical element using an organic compound that has a large second-order nonlinear optical constant and is highly compatible with polymeric materials.

"Means for Solving the Problems" The above problems can be achieved by using a hydrazone compound represented by the following general formula (1).

That is, 2 ``However, in the formula, R1 is Hansch's substituent constant π, and 0〈
R2 represents a substituent selected from π<1.5 and an alkyl group or a hydrogen atom. The present invention relates to a nonlinear optical element characterized by comprising a medium containing at least a compound represented by j.

The present invention has the above configuration, and the hydrazone compound represented by the general formula (I) has a π-conjugated system in its molecular skeleton. In addition, 1. It is composed of a rigid π-electron conjugated system part and a highly flexible hydrazone part, and has excellent compatibility with liquid crystal polymers, other polymer compounds, or liquid crystal compounds. Therefore, in a nonlinear optical element using a mixture of a hydrazone compound represented by the general formula (1), a liquid crystal polymer, another polymer compound, or a liquid crystal compound, the general formula (1) is used as the organic nonlinear compound. ) When using a hydrazone compound represented by (), the content can be increased, so a high nonlinear optical effect can be obtained.

Note that the second-order nonlinear optical constant (β value) of an organic compound is
P P P (Pariser-Parr-Pople
) -MO method is known to be able to perform theoretical calculations, and β values can be calculated using each molecular parameter obtained by the PPP-MO method (J, L, 0u
dar, J. CheIl, Phys., 67.448 (
+977)).

Using the above Oudar method, the β value of the compound represented by the general formula (I), R1: (CH2N- group, R2: hydrogen atom (compound (2) described later), was determined. When calculated, it was 40.4X 10-"esu. Similarly, when the β value was calculated for MNA and DANS, it was 14.9X 10-"esu and 2, respectively.
It was 80×1O-SO. In addition, in the measurement results of the above compound using the powder method, a slightly stronger second harmonic was observed compared to MNA, and it was difficult to estimate the β value of the compound using PPP-MO.
The validity of using the method is shown.

In addition, we investigated parameters that have a correlation with the β value and found that there is a correlation with the electronic parameter π of the Hansis substituent (C.

Hanseh, r/ J/,, J, Med, Chew.
,,IS, +207(+973),NoAt'd
, , 20,304 (197?)). Therefore, using this method, we estimated the β value of the molecule, predicted the optimal molecular structure from the standpoint of molecular design, measured them using methods such as the powder method, and conducted various studies. Formula (1)
It has become clear that the hydrazone compound represented by is effective. The present invention has been made based on this knowledge, and is characterized in that, in a nonlinear optical element constituted by a medium into which light is incident, the object contains a hydrazone compound represented by the following general formula (1). It relates to nonlinear optical elements.

The hydrazone compound has the following structure.

2 ``However, in the formula, R1 is Hansch's substituent constant π, and 0〈
R2 represents a substituent selected from π<1.6 and an alkyl group or a hydrogen atom. Typical substituents for R1 include a nitro group, an alkoxy group, a dialkylamino group, a monoalkylamino group, a halogen atom, and a halogenated alkyl group.

R2 is represented by an alkyl group or a hydrogen atom.

Further, the compound represented by the general formula (1) can be easily produced by a dehydration condensation reaction between a corresponding aromatic benzaldehyde derivative and formylhydrazine.

(:)' Hereinafter, typical examples of the compound represented by the general formula (1) will be shown, but the invention is not limited to these compounds.

502 30 / / The nonlinear optical element of the present invention may be a crystal or powder consisting of a single component of the compound represented by the general formula (rE), or may be formed by combining the compound represented by the general formula (1) with heat. A compound represented by general formula (I) and a thermoplastic transparent polymer, a liquid crystal polymer, or a liquid crystal compound may be a solid material consisting of a mixture with a plastic transparent polymer, a liquid crystal polymer, or a liquid crystal compound. By using a mixed solid, the molecular orientation of the compound represented by the general formula (1) can be controlled using the molecular orientation of these media, and a larger nonlinear optical effect can be obtained. Since these media have high film formability, they also have the advantage that they can be easily formed into devices such as thin films.

The transparent polymer used in the present invention is not particularly limited, but examples include polymethyl methacrylate, polyacrylamide, polyethylene glycol, polyoxyalkylene oxide, polyvinylidene fluoride, polyε-caprolactone, etc. be.

Although there are no particular limitations on the liquid crystal polymer used in the present invention, for example, a side chain type liquid crystal polymer having a mesogen group in the side chain is preferred. Examples include side chain type polyacrylate liquid crystal polymers and side chain type polysiloxane liquid crystal polymers.

The liquid crystal compound used in the present invention is not particularly limited, but for example, a compound having a liquid crystal transition point higher than room temperature is preferably used.

Crystals consisting of a single component of the compound represented by the general formula Ralski method, etc.), by dissolving in an appropriate solvent (for example, methanol, ethanol, tetrahydrofuran, benzene, toluene, etc.) at an appropriate temperature, and then lowering the temperature or gradually removing the solvent, etc. It can be obtained by a crystallization method, a vacuum evaporation method, a vapor phase growth method such as molecular beam epitaxy, or the like.

Further, a solid mixture of a compound represented by general formula (I) and a thermoplastic transparent polymer, a liquid crystal polymer, or a liquid crystal compound is a solid mixture of a compound represented by general formula (1), a thermoplastic transparent polymer, or a liquid crystal compound. After melting a polymer or a mixture with a liquid crystal compound, in the case of a thermoplastic transparent polymer, it is in that state, and in the case of a liquid crystal polymer or a liquid crystal compound, it is gradually cooled in the liquid crystal state obtained by applying an electric field. Alternatively, it can be obtained by applying a magnetic field and solidifying in the cold under that state. By applying an electric field or a magnetic field, the compound represented by the general formula (1) is solidified while maintaining the molecular orientation without a center of symmetry according to the orientation of the polymer or liquid crystal material. The mixing ratio of each component is
The compound represented by the general formula (1) is not particularly limited as long as it can take a solid state with molecular orientation.The compound represented by the general formula (I>) is compatible with these media. Since the content is excellent, it can be selected from a wide range.If the content is too low, a sufficient nonlinear optical effect cannot be obtained, and if it is too high, it becomes difficult to control the molecular orientation by the medium. The content of the compound used is preferably in the range of 2 to 60%.

Furthermore, the nonlinear optical element of the present invention can take various forms, such as crystals or powder consisting of a single component of the compound represented by the general formula (1), or a crystal or powder represented by the general formula (I). A solid material (hereinafter referred to as
(hereinafter collectively referred to as a nonlinear medium) can be used as a nonlinear optical element, and furthermore, the nonlinear medium can be used as a waveguide-type nonlinear optical element that uses the nonlinear medium as an optical waveguide. In the latter case, since light can be confined within the waveguide, high efficiency can be achieved, such as increasing the optical power density and lengthening the interoperating period. Furthermore, phase matching becomes easier.

"Examples" The present invention will be explained in more detail using Examples below.
The present invention is not limited by these embodiments. Figures 1 and 2 are examples of the nonlinear optical element of the present invention, and the optical waveguide type wavelength waveguide as a second harmonic generation element. FIG. 1, which shows a schematic diagram of a conversion element, shows a core (4) made of a medium containing a hydrazone compound represented by the general formula (I) having a second-order nonlinear optical effect, and a core (4) made of a medium such as glass. It has a structure covered with a cladding (5) made of a medium (hereinafter abbreviated as an isotropic medium) that does not exhibit the following nonlinear optical effect. In the figure, the solid line indicates the fundamental wave of the incident light, and the dotted line indicates the second harmonic.
3), and enters the core (4) from one end of the cord. A second harmonic is generated within the core, and the second harmonic including the fundamental wave is emitted from the other end.The second harmonic can be extracted by dispersing it with a spectroscopic means such as a prism or filter. can.

FIG. 2 shows a cross-sectional view of the device, in which a waveguide (8) containing a hydrazone compound represented by the general formula (1) having a second-order nonlinear optical effect is connected to a low refractive index layer (9). It has a structure in which it is sandwiched between electrodes (6) and (7). These layers are formed on a substrate (10) consisting of an isotropic medium. In the figure, low refractive index layer (9)
is composed of an organic 7i film such as vinylidene fluoride-trifluoroethylene copolymer or an inorganic thin film such as 5i02. In the figure, the solid line represents the fundamental wave of the incident light, and the dotted line represents the fundamental wave of the incident light.
The second harmonic is shown. The laser light is focused by a lens or the like (3), and enters the waveguide (8) from one end of the element.

A second iE harmonic is generated within the waveguide, and the second harmonic including the fundamental wave is emitted from the other end, and the second harmonic is extracted by dispersing it with a spectroscopic means such as a prism or filter. I can do it.

Furthermore, it can also be used as a conventionally known optical modulation element. FIG. 3 is an example of a light modulation device, and shows a schematic diagram of an optical waveguide type light modulation device, in which a hydrazone system represented by the general formula <X> is contained in a substrate (13) made of an isotropic medium. Waveguide gil (12) consisting of a medium containing a compound
is provided, and two further electrodes (11) are connected to the waveguide (12).
) are provided at opposing positions along the length direction, and an electric field is created by applying a voltage between the electrodes (11) using an external electric field (14). In the above element, the laser beam incident from one end of the waveguide is directed to the waveguide (12).
When the light passes through the nonlinear medium and is emitted from the other end, the refractive index of the nonlinear medium changes due to the electric field, and therefore the phase of the emitted light also changes, allowing phase modulation.

In the figure, (1) indicates a laser light source, (2> indicates an optical modulation device such as an optical switching element or an optical polarizer, and (
3) represents a condensing lens.

In the nonlinear optical elements shown in FIGS. 1, 2, and 3 above, the core (4) or the waveguide (8), (
12) are formed on substrates (10) and (13) made of a capillary or an isotropic medium such as glass or plastic according to the crystal growth method described above. Furthermore,
If necessary, after treating the contact interface with the nonlinear medium with an alignment treatment material, the nonlinear medium may be precipitated to form the nonlinear optical element. 21st! In I and Figure 3,
As an electrode, indium tin oxide (ITO),
Conductors such as tin oxide, indium oxide, gold, silver, copper, and aluminum can be used.

It should be noted that the nonlinear optical element of the present invention is not limited to the above-mentioned embodiments, and can take various forms, and may be composed of crystals, powders, etc. Furthermore, in the optical modulation element shown in FIG. 3, the direction of applying the electric field for performing phase modulation varies depending on the symmetry of the nonlinear medium, the direction of the crystal axis, etc., and the configuration of the electrodes is changed as appropriate based on these factors. There is a need.

Hereinafter, the present invention will be described in detail based on Examples,
The present invention is not limited to the following measurement examples.

Example 1 1064 of a hydrazone compound represented by general formula (1)
Theoretical calculation of the β value for a nm laser beam was performed using the PPPMO method. The results are sent to MNA, DANS
A comparison is shown in Table 1.

/ Table Example 2 Crystals of a hydrazone compound represented by general formula (1) were crushed and filled into a 0.1 mm thick glass cell. When this cell was irradiated with focused Nd:YAG laser light (wavelength: 10B4 nm), the second harmonic (532 nm) was observed.

Table 2 shows the intensity of the second harmonic, which is classified into three levels: the same level, slightly stronger, and considerably stronger, compared to MNA.

/ Table 2 / / 9''''/' Example 3 0.4 g of the compound represented by (2) or ClO) and 2 g of polyoxyethylene with a molecular weight of 5 million were mixed with 5 m of benzene.
The resulting solution was spin-coded onto a glass substrate on which aluminum had been vacuum-deposited, and evaporated to dryness while maintaining the temperature at 80° C. to obtain a uniform film. Furthermore, aluminum was vacuum-deposited thereon to obtain a waveguide type nonlinear optical element. This girl was maintained at 80°C and cooled to room temperature while applying a 1000V electric field to the upper and lower aluminum electrodes. For this nonlinear optical girl, Nd:YAC;
When laser light (1064 nm) was focused and irradiated, a strong second harmonic (532 nm) was observed.

"Effects of the Invention j As described above, the nonlinear optical element of the present invention has the following properties:
The hydrazone compound represented by the general formula (1) has a large nonlinear optical constant (β value) and exhibits a remarkable second-order nonlinear optical effect. Therefore, the nonlinear optical element of the present invention is characterized in that it can separate high-intensity second harmonics even with weak light, and can also efficiently produce electro-optic effects even with small voltage changes. In general, hydrazone compounds represented by the general formula (2) have excellent compatibility with thermoplastic transparent polymers, liquid crystal polymers, or liquid crystal compounds, so they are expressed by the general formula (1) created in this way. A nonlinear optical device containing a hydrazone-based compound is a wavelength conversion element, a second-order ?f&
Nonlinear optical elements such as wave display parametric oscillators and optical switches, and optical communication systems using them;
It is useful for constructing optical information processing.

[Brief explanation of drawings]

1 and 2 are schematic diagrams of a wavelength conversion element as an embodiment of the nonlinear optical element of the present invention, and FIG. 3 is a schematic diagram of a light modulation element. (1) Laser light source (2) Modulator (3) Lens (4) Core (5) Clad (6) Upper electrode (7) Lower electrode (8) Nonlinear optical waveguide (9) Low refractive index layer (10) Substrate (I I) Electrode (12) Nonlinear optical waveguide (13) Substrate (14) External electric field

Claims (3)

[Claims] (1) A nonlinear optical element comprising a medium into which light is incident, wherein the medium contains a hydrazone compound represented by the following general formula (I). ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) ``However, in the formula, R1 is Hansch's substituent constant π, and 0<
R2 represents a substituent selected from π<1.5 and an alkyl group or a hydrogen atom. ” (2) The nonlinear optical element according to claim 1, wherein the medium is a powder or crystal of the hydrazone compound. (3) The nonlinear optical element according to claim 1, wherein the medium is a transparent polymer or a liquid crystal compound containing the hydrazone compound.