JPH04130423A - Molecular crystal and method and module for converting light wavelength by using the crystal - Google Patents

Abstract

PURPOSE:To provide the molecular crystal having the molecular configuration suitable for a wavelength conversion element which has excellent transmittability of blue light and has no inversion symmetry by constituting this crystal of specific molecules. CONSTITUTION:The above-mentioned crystal is constituted of the molecules expressed by formula I. The compd. of the formula (I) is obtd. by reaction with 3, 5-dimethyl-1H-1, 2, 4-triazole and 2-chloro-5-nitropyridine. Amide, sulfur- contg. compd. and nitrile are preferable as a solvent. A base is preferably used at the time of reaction and the base to be used may be any of org. bases, such as pyridine and trieramine and inorg. bases, such as potassium carbonate, sodium hydrogen carbonate and sodium hydroxide. The molecular crystal having the molecular configuration suitable for the wavelength conversion element which has the excellent transmittability of blue light and has no inversion symmetry is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a molecular crystal useful as a nonlinear optical material. The present invention also relates to an optical wavelength conversion method and an optical wavelength conversion module using a molecular crystal as a nonlinear optical material.

(Prior Art) In recent years, nonlinear optical materials - materials with nonlinearity between polarization and electric field that appear when a strong optical electric field such as a laser beam is applied have attracted attention.

Such materials are generally known as nonlinear optical materials and are described in detail in, for example: 'Non-linear optical properties of organic and polymeric materials'
So Niss Symposium Series 233 David J. Williams & I (American Chemical Society 198
3 years) r”Non1inear 0ptical P
properties of organic and P
o1y＊eric Material"ASC5YFI
PO5TυM 5ERIES233 David J
, William + ms W (American Ch.
``Emical Society, 1983)'', ``
"Organic Nonlinear Optical Materials" supervised by Masao Kato and He Nakanishi (C.
MC Co., Ltd., 1985, “Nonlinear Optical Properties of Organic Molecules and Crystals” Volumes 1 and 2. Published by Press, 1987) “Non1inea”
r 0ptical Properties of O
rganic Molecules and Crystal
sis vol 1 and 2 D,S.

Chemla and J, ZySs [(Acade
Published by mic Press).

One of the applications of nonlinear optical materials is second harmonic generation (SHG) based on second-order nonlinear effects and wavelength conversion devices using sum frequency and difference frequency.

What has been practically used so far is inorganic perovskite a typified by lithium niobate. However, recently, π with electron-donating and electron-withdrawing groups has been developed.
Electronically conjugated organic compounds greatly exceed the aforementioned inorganic materials.
It has become known that it has various properties as a nonlinear optical material.

In order to form nonlinear optical materials with higher performance, it is necessary to arrange compounds with high nonlinear susceptibility in the molecular state so as not to cause inversion symmetry. It is known that compounds with long π-electron conjugated chains are useful for expressing high nonlinear susceptibility, which is one of these, and are variously described in the above-mentioned literature, but in these compounds, As is obvious, the maximum absorption wavelength becomes longer, leading to a decrease in the transmittance of blue light, for example, which impairs the generation of blue light as the second harmonic.

This also occurs in p-nitroaniline derivatives, and the fact that the transmittance of that wavelength has a large effect on the efficiency of second harmonic generation is described in Proceedings of the National Institutes of Science by Aline Azema et al. , Volume 400, Now 0ptial Materials
(1983), p. 186, FIG. 4.

Therefore, the emergence of nonlinear optical materials with high transmittance for blue light is desired. Conventionally, attempts have been made to replace the carbon atoms in the Hensen nucleus of nitroaniline with nitrogen atoms, etc., but satisfactory results have not always been obtained.

In addition, the present applicant has disclosed a better method in Japanese Patent Laid-Open No. 62
-210430 and JP-A-62-210432.

Furthermore, JP-A-62-59934, JP-A-63-231
No. 36, JP 63-26638, JP 63-31
No. 768, JP-A-63-163827, JP-A-63-
No. 146025, JP-A-63-85526, JP-A-6
3-239427, JP 1-100521, JP 64-56425, JP 1-102529, JP 1102530, JP 1-237625, JP 1-207724, etc. Materials are disclosed.

However, as mentioned earlier, in order to be useful as a second-order nonlinear optical material, performance in the molecular state alone is insufficient, and it is essential that the molecular arrangement in the aggregate state has no inversion symmetry. be. However, currently it is extremely difficult to predict the molecular arrangement, and the probability of its existence among all organic compounds is not high.

Furthermore, when used as an element for wavelength conversion, it is necessary to take into account the arrangement of molecules in the crystal;
In many of the above, this point has not necessarily been sufficiently considered. Furthermore, to date, no wavelength conversion element using an organic nonlinear optical material has appeared on the market as a commercial product.

Possible reasons for this include, for example, the following.

When forming a fiber-type optical wavelength conversion element using nonlinear optical materials such as those mentioned above, the crystals are not oriented in a direction that makes use of the maximum nonlinear optical constant of each material, so the wavelength of the optical wavelength conversion element ends up being The conversion efficiency will not be very high.

In addition, the wavelength conversion efficiency of an optical wavelength conversion element increases as the element is longer, but it is difficult to obtain a uniform single crystal with the materials mentioned above, and therefore it is not suitable for creating long optical wavelength conversion elements. There are also problems.

(Problems to be Solved by the Invention) Therefore, the first object of the present invention is to provide a molecular crystal that has excellent blue light transparency and has a molecular arrangement suitable for a wavelength conversion element without inversion symmetry. . The second objective is to provide a method that utilizes the response related to optical wavelength conversion among nonlinear responses. The third object is to provide an optical wavelength conversion module that has high wavelength conversion efficiency and can easily overcome the second harmonic in the blue region.

(Means for Solving the Problem) As a result of extensive research, the present inventors have discovered Shimonami's formula (1
) It has been found that the object of the present invention can be achieved by a molecular crystal characterized by being composed of molecules represented by:

Hs The compound of formula (1) can generally be synthesized by the following method. That is, 3,5-dimethyl IH-1,2,4
-) can be obtained by reaction of lyazole and 2-chloro5-nitropyridine. As a solvent, hydrocarbons such as n-hexane, tetrahydrofuran, 1,2-
ethers such as dimethoxyethane, amides such as N,N-dimethylformamide, N-methylpyrrolidone,
Sulfur-containing compounds such as dimethyl sulfoxide and sulfolane, nitriles such as acetonitrile, and esters such as ethyl acetate are used.

Among these, amides, sulfur-containing compounds, and nitriles are preferred. It is preferable to use a base during the reaction, and examples of the base include organic bases such as pyridine, triethylamine, 1-day-diazabicyclo[5,4,0)-7-undecene, potassium carbonate, sodium hydrogen carbonate, and sodium hydroxide. Any inorganic base such as The reaction temperature is preferably 10°C to 150°C, preferably 20°C to 100°C.

An example is shown below.

Synthesis example Synthesis of compound of formula (1) 3.5-dimethyl-IH-1,2,4-) lyazole 4
8.5 g (0.5 mol), 2-chloro5-nitropyridine 79. 3 g (0', 5 mol), potassium carbonate 69.0 (0,5 mol) were weighed into a 500 d three-turn flask equipped with a stirrer and a thermometer, and an additional 250 I
1 liter of dimethyl sulfoxide (DMSO) was added. 5
After continuing to stir at 0°C for 5 hours, it was allowed to cool to room temperature and heated to 500°C.
Pour it into iced water. The precipitated crystals were collected by filtration and washed with water.

The crystals were recrystallized twice from acetone while being decolorized using activated carbon to obtain a compound of formula (1). Yield 48g (yield 43.8%) Melting point = 147°C 1(-nmr(δ pp+w): 2,433(3Hs)
, 2.914 (3Hs) 8.069 (IHd) 8
617 (IHdd), 9.316 (IHd) Next, the powder obtained here is single crystallized, and methods for single crystallization include the solvent explosion method, temperature drop method, vapor diffusion method, etc. Examples include the solution method, the melt method such as the Brifugeman method, and the sublimation method.

Regarding single crystallization, please refer to "Crystal Engineering Handbook (Imori Publishing, 1971)" by the Crystal Engineering Handbook Editorial Committee.
This can be done by referring to the descriptions in Part 4, Chapter 8.

Methods of wavelength conversion include methods using a single crystal of an appropriate size, methods using angular phase matching or temperature phase matching, and methods using Cerenkov radiation using a waveguide.

An example of the latter is one composed of a fiber-type optical wavelength conversion element and a light source device, and in the case of the present invention, the core of the optical wavelength conversion element is a nonlinear optical material represented by formula (1). is used in a single crystal state, and the crystal orientation direction of (1) constituting this core is set so that its a-axis extends approximately in the long axis direction of the core, while the light source device is arranged in a direction perpendicular to the above-mentioned axis. The device is characterized in that it is configured such that a fundamental wave linearly polarized in the direction of the crystal axis or C-axis is made incident on the optical wavelength conversion element.

Examples of the laser light source used as the fundamental wave include those in Table 1. Note that the wavelength of the fundamental wave is not limited in any way except for the effect of material absorption mentioned above.
This is true for laser and obtronics (Lasers and Obtronics).
This is clear from page 59 of ER & Optronics (published in November 1987).

(Example) Next, the present invention will be explained in more detail based on an example.
The present invention is not limited to this.

Example 1 The compound of formula (1) obtained by the above method was dissolved in tetrahydrofuran, and almost colorless and transparent columnar crystals were obtained by solvent evaporation. The largest size is 3 x 1 mm
It was X0.5m.

At the same time, the smaller crystals obtained were shaped and subjected to X-ray crystal structure analysis (Fig. 1). The results are shown below.

Crystallographic data Orthorhombic system, space group Pna 2+ Lattice constant a = 8.054 (1) b = 18.7
90 (1) people c = 6.5573 (1) people v = 99
2.3 (11 people 3 Number of molecules per unit cell Z = 4 The crystal structure diagrams are shown in Figure 2 a), b), and C).

From the space group of the crystallographic data above, it can be seen that this crystal does not have inversion symmetry.

Similar crystals could be obtained by using acetone instead of tetrahydrofuran as the solvent.

Furthermore, when crystals were prepared by the temperature drop method using N,N-dimethylformamide, crystals measuring 10 ml, 10 ml, and 5 circles (Fig. 3) were obtained.

The crystal obtained here was found to be a single crystal by checking the extinction value using a polarizing microscope.

Further, it is preferable that the single crystal has a maximum side length of at least 1 square inch or more.

Example 2 Second harmonic generation was performed using the single crystal shown in FIG. Actually, the apparatus shown in FIG. 4 was used.

532n- green light could be observed in the form of a beam. This indicates the possibility of phase matching, and therefore it can be seen that the crystal of the present invention is useful as a nonlinear optical material for optical wavelength conversion.

Reference Example 1 In order to confirm blue light transmittance, an absorption spectrum was measured. The results are shown in Table 2.

table Ru.

Therefore, it is clear that the compound of the present invention has extremely excellent blue light transmittance.

NA PRO MDT OM Reference Example 2 In actually forming a fiber type optical wavelength conversion element,
It was unclear how to set the crystal ration and how to set the polarization direction of the fundamental wave incident thereon to obtain high wavelength conversion efficiency.

Below, a method for setting the crystal orientation of a nonlinear optical material and the linear polarization direction of the fundamental wave suitable for obtaining high wavelength conversion efficiency will be explained.

The crystal of (1) has an orthorhombic system, and the fish school is -+i2. Therefore, the tensor of nonlinear optical constants becomes. Here, dffl is the crystal axis a, b, c as shown in Figure 1.
Considering the optical axes X, Y, and Z that are determined by It is a nonlinear optical constant when extracting harmonics, and similarly d
52 is a nonlinear optical constant when the fundamental wave of Y polarization is input and the second harmonic of X polarization is extracted, and 63t is the nonlinear optical constant when the fundamental wave of X polarization is input and the second harmonic of X polarization is extracted. The constant, dza is the nonlinear optical constant when the fundamental wave of Y and X polarization is input and the second harmonic of Y polarization is extracted, and dls is the second harmonic of X polarization when the fundamental wave of X and X polarization is input. This is the nonlinear optical constant when extracting . The magnitude of each nonlinear optical constant will be described below.

Since the refractive index of (I) is not yet clear, the blJXO value from which the nonlinear optical constants d and JK can be derived is shown using the following formula. Note that N is the number of molecules per unit volume, f(ω), f
(2ω) are local electric field modification factors for the fundamental wave and the second harmonic, respectively.

Note that these values are based on X-ray crystal structure analysis and β shown in Table 3, and the unit is (XIO-co'esu).

From this table, d sz,, d 3! s d za, di
It can be seen that s takes on a large value. Therefore, as shown in FIG. 5, when forming a fiber-type optical wavelength conversion element 10 in which a core 11 made of (1) is filled in a cladding 12, the crystal of (1) is X
The optical wavelength conversion element 10 is oriented so that the crystal's C-axis (optical axis is Z-axis) or b-axis (this can be achieved by the method described below). If a linearly polarized fundamental wave is incident in the direction (Y axis in the optical axis), the large nonlinear optical constants dt4, aZZ
, dls can be used.

Embodiment 3 FIG. 6 shows an optical wavelength conversion module according to a third embodiment of the present invention. This optical wavelength conversion module includes a fiber type optical wavelength conversion element 10, and this optical wavelength conversion element 1.
It is composed of a light source device 20 that manually generates a fundamental wave.

Here, a method for manufacturing the optical wavelength conversion element 10 will be explained.

First, an airborne glass fiber that will serve as the cladding is prepared. This glass fiber is, for example, a 5FS3 glass fiber with an outer diameter of approximately 100 μm and a hollow portion diameter of 6 μm.

On the other hand, 120g of (1) was dissolved in acetone solvent In, and (
A saturated solution (at a temperature of 35°C) of I) is prepared. this(
The saturated solution of I) is maintained at a constant temperature of 35° C. in a constant temperature bath, and one end of the glass fiber is inserted into this solution as shown in FIG. Then, the solution (1) enters the glass fiber due to capillary action. If stored in this state, the solvent acetone will evaporate, resulting in a supersaturated state. A crystal nucleus is then generated inside the glass hollow tube, and a single crystal grows. As a result, a single crystal state in which the crystal orientation is uniformly aligned over a long range of 20+w+ or more can be obtained.

When (I) is filled in the glass fiber 12 in a single crystal state as described above, the crystal orientation state is such that the a-axis (the optical axis is the X-axis) extends in the direction of the core axis, as shown in FIG. state.

After the core 11 was filled in the manner described above, both ends of the glass fiber 12 were cut with a fiber cutter to form an optical wavelength conversion element IO having a length of 10 aa. As shown in FIG. 6, an optical wavelength conversion module is constructed by combining this optical wavelength conversion element 10 with a light source device 20. In this embodiment, a semiconductor laser 21 is used as a light source that generates a fundamental wave, and a laser beam (fundamental wave) 15 with a wavelength of 820n- is emitted from the semiconductor laser 21, which is converted into a parallel beam by a collimating lens 22, and then converted into an anamorphic beam. The light passes through a pair of Fick prisms 23 and a λ/2 plate 25, is condensed into a small beam beam by a condenser lens 26, and is then irradiated onto the incident end face 10a of the optical wavelength conversion element 10. Thereby, this fundamental wave 15 enters into the optical wavelength conversion element 10. As described above, (1) constituting the core 11 has a crystal orientation state in which the X axis extends in the core axis direction, while in this example, the λ/2 plate 25 of the light source device 20
By rotating , the fundamental wave 15 in the Z polarization state is input to the optical wavelength conversion element 10 .

The fundamental wave 15 that has entered the optical wavelength conversion element IO is the core 1
1, the wavelength is 1/2 (=410n
i) is converted to the second harmonic of 15°.

This second harmonic wave 15' repeats total reflection between the outer surfaces of the crand 12 and propagates inside the element 10, and the waveguide mode of the fundamental wave 15 in the core part and the waveguide mode of the second harmonic wave 15' in the cladding part are formed. (so-called Cherenkov radiation).

From the output end face 10b of the optical wavelength conversion element 10, the second
A beam 15°, which is a mixture of a harmonic wave of 15° and a fundamental wave of 15°, is emitted. After this emitted beam 15' is passed through the condensing lens 27 and condensed, the second harmonic of 410n11 is well transmitted, while the fundamental wave of 820nm is 15'.
5 is passed through an absorbing node pass filter 28, and only the second harmonic 15 is extracted. Using a polarizing plate or the like, it was confirmed that the second harmonic 15'' was Z-polarized light. In other words, in this example, the nonlinear optical constant d33 in (1) mentioned above was used. The wavelength conversion efficiency was determined by measuring the light intensity of the 15th harmonic with an optical power meter 29, and found to be about 1% in terms of IW.

(Effects of the Invention) As described above, the molecular crystal composed of molecules represented by the formula (I) of the present invention has high blue light transmittance and has no inversion symmetry in its molecular arrangement, so it exhibits second-order nonlinearity. Has an optical effect. Therefore, it is a useful material for wavelength conversion using second-order nonlinear optical effects. It is particularly useful for generating converted waves in the blue region. Furthermore, as explained in detail, according to the optical wavelength conversion module of the present invention, the high nonlinear optical constant of (1) can actually be used in a fiber-type nonlinear optical material, and the optical wavelength conversion element can be made long enough. Since it can be formed, extremely high wavelength conversion efficiency can be achieved. Also(
I) has an absorption edge near 400 nm, so with this optical wavelength changing module, it is also possible to efficiently extract the second harmonic in the blue region by using a laser beam of about 800 ns as the fundamental wave. It becomes.

Although the method using the Cerenkov radiation method has been described above, the present invention is not limited to this, and waveguide-waveguide phase matching is also possible. Wavelength converted waves are not only limited to second harmonics, but can also be used for third harmonic, sum and difference frequency generation.

It is also possible to single-crystallize the above compound, cut out a bulk single crystal, and input YAG laser light to generate its second optical harmonic. Angular phase matching is used as the phase matching method at this time. These bulk single crystals can be used not only outside the laser cavity, but also within the cavity of a solid-state laser such as an LD-pumped solid-state laser to improve wavelength conversion efficiency. Furthermore, the wavelength conversion efficiency can also be increased by placing it within the resonator of an external resonator type LD.

For the above single crystallization, the Bridgman method, the solvent nuclear method, etc. are used.

The wavelength converted wave is not only limited to the second harmonic, but also the third harmonic.
It is also used to generate harmonics and sum-difference frequencies.

[Brief explanation of the drawing]

Figure 1 shows the shape and surface index of a single crystal prepared by the solvent nuclear method using a tetrahydrofuran solution. The size of the crystal is almost colorless and transparent, and it has the property of elongating in the C-axis direction. Figure 2 shows a crystal structure diagram. a) is a stereo projection view in the a-axis direction, b) is a stereo photographic view in the b-axis direction, and C) is a stereo projection view in the c-axis direction. FIG. 3 shows a single crystal obtained by the temperature drop method of an N,N-dimethylformamide solution. FIG. 4 is a schematic diagram of a second harmonic generation experimental apparatus using the crystal shown in FIG. 3. The numbers in the figure indicate the following. 1: Na: YAG laser 2: Fundamental wave (λ-1, 064 μm) 2': 2nd harmonic (λ = 0.532 μm) 3: 2 (
Single crystal of compound 1) 4: Fundamental wave cut filter FIG. 5 is a schematic diagram showing the crystal orientation of the core in the optical wavelength conversion element according to the present invention. FIG. 6 is an explanatory diagram illustrating a method for producing an optical wavelength conversion element according to the present invention. 10: Optical wavelength conversion element 11: Core 12: Cranode 15: Fundamental wave 5': Second harmonic 20: Light source device 21: Semiconductor laser
22: Collimating lens 23: Anamorphic ink prism pair 25: λ/2 plate 22.27: Condensing lens Figure 7 shows single crystal growth by solvent evaporation of a fiber with a single crystal of the compound of formula (1) as its core. Show the device. ■ Saturated solution of the compound of formula (f) ■ Clad (glass fiber) Patent applicant Fuji Photo Film Co., Ltd. Engraving of the drawing in Figure 2

Claims (3)

[Claims] (1) It is an orthorhombic system characterized by being composed of molecules represented by the following formula (I), and Pna2_1
A molecular crystal with a space group of Formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (2) A method of converting the wavelength of light using a single crystal made of the molecular crystal according to claim (1) as the nonlinear optical material when converting the wavelength of light using a laser beam and a nonlinear optical material. (3) A single-crystal nonlinear optical material characterized by being composed of molecules represented by formula (I) is filled in the cladding as a core, and the crystal of the optical material has its a-axis aligned approximately in the direction of the core axis. A light source device that includes an optical wavelength conversion element oriented to extend, and a light source device that causes a fundamental wave linearly polarized in the direction of the axis or c axis of a crystal perpendicular to the a axis to be incident on the optical wavelength conversion element. Wavelength conversion module. (However, the crystal axis is determined using the 2-fold axis as the C axis, and the other crystal axes follow the right-handed system.)