JPH03210539A - Nonlinear optical element - Google Patents

Abstract

PURPOSE:To separate high-intensity second harmonic waves even with weak light and to efficiently develop an electrooptical effect by incorporating a specific oxadiazole compd. into the nonlinear optical element. CONSTITUTION:The oxadiazole compd. expressed by formula I is used. In the formula (I), R1 denotes the substituent selected from an amino group, amide group, hydrogen atom, etc.; R2 denotes an alkyl group or hydrogen atom. The oxadiazole compd. expressed by the formula (I) is has a pi conjugation system in the molecule structure and has the excellent compatibility with a liquid crystalline high polymer, other high-polymer compds. or liquid crystal compd. Namely, this compd. has a large nonlinear optical constant and exhibits a marked quadratic nonlinear optical effect. The high-intensity second harmonic waves are separated even with the weak light in this way and the electrooptical effect is efficiently developed even with a slight change in voltage.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to organic nonlinear optical elements, and in particular to nonlinear optical elements using oxadiazole compounds having excellent second-order nonlinear optical effects. do.

"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 Photobiomaterials R&D)
No. 72, Masao Kato, Misaki Nishihebu (1985)
According to these, as represented by 2-methyl-4-nitroaniline (hereinafter referred to as MNA), π
It is known that compounds with an electron system and an electron-donating group and an electron-withdrawing group in the molecule have a large second-order nonlinear optical constant β (hereinafter simply referred to as "β value"). Even.ru.

However, even if the β value is large, as typified by 4-dimethylamino-4'-nitrostilbene (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 (1977)), and the molecular arrangement in organic molecular crystals is often uniquely determined by individual molecular species in a certain temperature range, making it extremely difficult to control the molecular arrangement in the crystal. . For these reasons, there have been few reports of organic compounds that exhibit higher second-order nonlinear optical effects than MNAs, and therefore, there are few known devices that are more efficient than nonlinear optical devices using MNAs. do not have.

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. However, various studies have been conducted (0.S, C
hewla, J, Zyss, Non1inearOpt
icalProperties of Organi
c Molecules and Crystals, A
academic Press, Inc., New Yo
rk(1G&?)) *One of the methods is to use a liquid crystal compound or a liquid crystal polymer material as a medium. In other words, the molecular orientation of liquid crystal materials can be controlled by electric or magnetic fields in the liquid crystal state. Taking advantage of this property, an organic compound with a large β value is mixed into the liquid crystal material and an electric or magnetic field is applied. This is a method that eliminates the center of symmetry by aligning the organic compound in the alignment direction of the liquid crystal on the other side of the voltage. 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
, p405, Academic Press, Inc.
New York (19B?)) @ Another method is to use a thermoplastic transparent polymer material as a medium. That is, a method using polymethyl methacrylate as a polymeric medium (K, D, Singer, J, ε
, 5ohn, S. J., La1a, Appl.

Phys, Lett, 49, 248 (1986)),
Method using acrylamide (JP-A-62-87139
There are methods 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 point of the polymer medium is Applying an electric field under the above heating condition,
This is a method of orienting organic compounds and eliminating 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)), in this method, even without applying an electric field,
Generation of second harmonics has been observed.

In addition, some of the four compounds with -N-N- bonds that exhibit second-order nonlinear optical effects are known (J, F,
? 1icoud, R, J, Twieg, Non1ine
ar 0pticalProperties of O
rganic Molecules and Crys
tals.

vol 2 p221, Academic Pres
sinc, Nev York (1987)), 4-nitrophenylhydrazine is the 1.
The nonlinear optical effect is not satisfactory, since the second harmonic is generated at six times the intensity.

``Problems to be Solved by the Present Invention'' Although the conventional organic nonlinear optical materials described above have very large nonlinear optical constants, they also have problems such as difficulty in obtaining large crystals, poor stability of the crystals, and phase problems 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 an oxadiazole compound represented by the following general formula (1).

That is, in the formula, R1 is a substituent selected from an amino group, an amide group, an alkyl group, a halogen atom, and a hydrogen atom, and R2
represents an alkyl group or a hydrogen atom.

A nonlinear optical element characterized by comprising a medium containing at least a compound represented by:

The present invention has the above configuration, and the oxadiazole compound represented by the general formula (1) has a π-conjugated system in its molecular skeleton, and also has a liquid crystalline polymer, other polymeric compound, or Excellent compatibility with liquid crystal compounds. Therefore, the general formula (1
) in a nonlinear optical element using a mixture of an oxadiazole compound represented by formula (1), a liquid crystal polymer, another polymer compound, or a liquid crystal compound, as an organic nonlinear compound. When using an oxadiazole-based compound, 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-Purr-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, 0
udar, J. Chem, Phys., 67.446 (
1977)) - A compound represented by the general formula (I), in which R1 is a p-dimethylamino group, using the method of Oudar.

Compound in which R2 is a hydrogen atom (compound (2) below)
When we calculated the β value of 170X 1O-30esu
It became. Similarly, when the β values were calculated for MNA and DANS, they were 14.9X 10-”es
In addition, in the powder method measurement results of the above compound, a considerably stronger second harmonic was observed compared to MNA, and P
The validity of using the P P-MO method is demonstrated.

Therefore, using this method, we estimate the β value of the molecule1,
After predicting the optimal molecular structure from the standpoint of molecular design, actually measuring and evaluating it using methods such as the powder method, and adding various considerations, we found that the oxadiazole compound represented by general formula (1) is effective. The present invention was made based on this knowledge, and in a nonlinear optical element composed of a medium into which light is incident, the medium has the following general formula (
The present invention relates to a nonlinear optical element characterized by containing an oxadiazole compound represented by I).

The oxadiazole compound has the following structure.

r In the formula, R1 represents a substituent selected from an amino group, an amide group, an alkyl group, a halogen atom, and a hydrogen atom;
2 represents an alkyl group or a hydrogen atom.

The substituent represented by R1 is a substituent selected from an amino group, an amide group, an alkyl group, a halogen atom, or a hydrogen atom, and examples thereof include -NH2, -NH
(CI(s) , -N (CHs) 2--NH(
02H5)--N (C2H5)2t-NH(C12H
21), -NHCOCHs--NHCOC, H1, -N
HCOC,2H2,.

-CH3, -02M S--C5H* -C4H9
e-C12H25, -ct, -Br, -H
etc.

R2 is a substituent represented by an alkyl group or a hydrogen atom,
To illustrate these, -CH3゜-C2H6, -C
! 1H7--C4H9-C52H25--H and the like. Furthermore, the substituents are not limited to those exemplified here.

Typical specific examples of the compound represented by the general formula (1) are shown below.

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 (1), or may be a crystal or powder consisting of a single component of the compound represented by the general formula (1), or a thermoplastic transparent A mixed solid of a compound represented by general formula (1) and a thermoplastic transparent polymer, a liquid crystal polymer, or a liquid crystal compound, which may be a solid material consisting of a mixture with a molecule, a liquid crystal polymer, or a liquid crystal compound. By using the molecular orientation of these media, the molecular orientation of the compound represented by the general formula (1) can be controlled, and a larger nonlinear optical effect can be obtained. Furthermore, these media have the advantage that they have high film formability and 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 on the side chain is preferable. These include chain-type polysiloxane-based 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 (I) can be obtained by heating and melting the compound represented by the general formula (1), cooling it, and crystallizing it (Bridgeman method, 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.

In addition, a solid mixture of a compound represented by general formula (1) 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 imm and cooling and solidifying in 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 not particularly limited as long as the compound represented by general formula (1) can take a solid state with molecular orientation.
The compound represented by the general formula (1) has excellent compatibility with these media, so it has a wide range of lI! You can choose from the box below. 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 using the medium. Usually, the content of the compound represented by general formula (1) is 2 to 2. 6
A range of 0% is preferably used.

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 GL 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 increased optical power density and longer interaction length. 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 wI as a second harmonic generation element.
FIG. 1 shows a schematic diagram of a type wavelength conversion element, in which a core (4) made of a medium containing an oxadiazole compound represented by the general formula (1) having a second-order nonlinear optical effect is shown.
However, a medium that does not exhibit a second-order nonlinear optical effect such as glass (
Cladding (5) consisting of (hereinafter abbreviated as isotropic medium)
It has a structure covered with. In the figure, the solid line indicates the fundamental wave of the incident light, and the dotted line indicates the second harmonic. The laser light is focused by a lens (3), and is transmitted from one end of the element to the core (4).
). 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 an oxadiazole 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, the low refractive index layer (9) is composed of an organic thin film such as vinylidene fluoride-trifluoroethylene copolymer or an inorganic thin film such as 5in2. In the figure, the solid line represents the fundamental wave of the incident light,
The dotted line indicates the second harmonic, and the laser light is transmitted through a lens etc. (3
) and enters the waveguide (8) from one end of the element. A second harmonic is generated within the waveguide, and from the other end,
A second harmonic including the fundamental wave is emitted, and can be extracted by separating the light using a spectroscopic means such as a prism or a filter.

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 an oxazine compound represented by the general formula (1) is contained in a substrate (13) made of an isotropic medium. Waveguide consisting of a medium containing an azole compound g! (1
2) is provided, and two further electrodes (11) are provided on the waveguide (
An electric field is formed by applying a voltage to the electrodes (11) using an external electric field (14). In the above element,
Laser light incident from one end of the waveguide is transmitted through the waveguide (1
2) 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, making it possible to perform 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 element shown in FIGS. 1, 2, and 3 above, the core (4) or the waveguide gl (8),
(12) is formed on a capillary or a substrate (IO) and (13) made of an isotropic medium such as glass or plastic according to the crystal growth method described above. Furthermore, if necessary, the nonlinear optical element may be formed by precipitating the nonlinear medium after treating the R surface in contact with the nonlinear medium with an alignment treatment material, as shown in FIGS. 2 and 3. Indium tin oxide (ITO) is used as an electrode.
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 embodiments, and can take various forms, and may be composed of crystals, powders, etc. In this case, the direction of applying an electric field for performing phase modulation varies depending on the symmetry of the nonlinear medium, the direction of the crystal axis, etc., and it is necessary to appropriately change the configuration of the electrodes based on these factors.

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 Oxadiazole compound represented by general formula (1)
β value for 1064 nm laser beam is PP
Theoretical calculations were performed using the PMO method.

The results are shown in Table 1 in comparison with MNA and DANS.

Table 1 Example 2 Crystals of the oxadiazole compound represented by the general formula (1) were crushed and filled into a 0.1 mm thick glass cell.

This cell is exposed to Nd:YAG laser light (wavelength 10106
When 4n was focused and irradiated, the second harmonic (532n
m) was observed.

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

Table 2 Example 3 0.4 g of the compound represented by (2) or (14) and 2 g of polyoxyethylene with a molecular weight of 5 million were mixed in 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 form a waveguide Ill type nonlinear optical element. This device was cooled to room temperature while maintaining the temperature at 80° C. and applying a 1000 V electric field to the upper and lower aluminum electrodes. In this nonlinear optical element, Nd:YAG
When laser light (1064 nm) was focused and irradiated, a fairly strong second harmonic (532 nm) was observed.

"Effects of the Invention" As described above, the nonlinear optical element of the present invention has the general formula (1
) The oxadiazole compound represented by the general formula (1) has a large nonlinear optical constant (β value) and a remarkable second-order Since it exhibits a nonlinear optical effect, the nonlinear optical element of the present invention can separate high-intensity second harmonics even with weak light.
Furthermore, the oxadiazole compound represented by the general formula (1), which has the characteristic of efficiently expressing an electro-optic effect even with a small voltage change, can be used as a thermoplastic transparent polymer, liquid crystal polymer, or liquid crystal compound. The nonlinear optical element containing the oxadiazole compound represented by the general formula (1) created in this way has excellent compatibility with wavelength conversion elements, second harmonic displays, parametric oscillators, It is useful for constructing nonlinear optical elements such as optical switches, optical communication systems using them, and 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. (]) Laser light source (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (l 3) (14) Modulator lens core cladding Upper electrode Lower electrode Nonlinear optical waveguide Low refractive index layer Substrate electrode Nonlinear optical waveguide substrate External electric field

Claims (3)

[Claims] (1) A nonlinear optical element comprising a medium into which light is incident, wherein the medium contains an oxadiazole compound represented by the following general formula (I). ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) However, in the formula, R1 is an amino group, an amide group, an alkyl group,
A substituent selected from a halogen atom and a hydrogen atom, and R2 represents 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 oxadiazole compound. (3) The nonlinear optical element according to claim 1, wherein the medium is a transparent polymer or a liquid crystal compound containing the oxadiazole compound.