JPH06228113A - Molecular crystal and wavelength shift of light using the same molecular crystal - Google Patents

Abstract

PURPOSE:To provide a molecular crystal exhibiting a high blue light transmission, having a secondary nonlinear optical effect because of its molecular arrangement not containing an inversional symmetry, useful for generation of a converted wave especially within a range of blue color and having a specified molecular arrangement. CONSTITUTION:A molecular crystal having a monoclinic system composed of a molecule represented by the formula and a P21 space group. The crystal structure of the compound of the formula is shown in the figure [(a) to (c) are the respective crystal axes] and this compound can be obtained by reacting a corresponding aldehyde with a corresponding ketone in the presence of a base catalyst. This molecular crystal is useful as a nonlinear optical material for shifting the wavelength of light using laser light and a nonlinear optical material. This conversion of light is carried out by utilizing responsibility related to shift of the wavelength of light among nonlinear response properties of this molecular crystal. Further, this molecular crystal can provide a light wavelength changing module exhibiting a high efficiency of wavelength change and capable of readily generating the second higher harmonic waves in the range of blue color.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a molecular crystal useful as a nonlinear optical material. The present invention also relates to a light wavelength conversion method and a light wavelength conversion module using a molecular crystal as a nonlinear optical material.

[0002]

2. Description of the Related Art In recent years, a material having a non-linear optical material-a non-linearity between a polarization and an electric field, which appears when a strong optical electric field such as laser light is applied, has been attracting attention. Such materials are generally known as nonlinear optical materials and are described in detail in, for example, the following. "Nonlinear Optical Properties of Organic and Polymeric Materials"
C.S. Symposium Series 233 Edited by David Jay Williams (American Chemistry Society 1983)
Annual) "" Nonlinear Optical Properties of Organic
and Polymeric Material ”ACS SYMPOSIUM SERIES 23
3 Edited by David J. Williams (American Chemical Societ
y, 1983) "," Organic Nonlinear Optical Materials ", supervised by Masao Kato, Hachiro Nakanishi (CMC, Inc., 1985," Nonlinear Optical Properties of Organic Moleculars and Crystals ") Volumes 1 and 2, edited by DS Schmula and Jay Jiss (Academic Press, 1987)
Annual publication) "" Nonlinear Optical Properties of Organic M
olecules and Crystals "vol 1 and 2 DSChemla
and edited by J. Zyss (Academic Press).

One of the applications of the nonlinear optical material is a second harmonic generation (SHG) based on the second-order nonlinear optical effect and a wavelength conversion device using a sum frequency and a difference frequency. So far, those which have been practically used are inorganic perovskites represented by lithium niobate. However, recently, it has become known that a π-electron conjugated organic compound having an electron-donating group and an electron-withdrawing group has various performances as a nonlinear optical material, which greatly exceeds the above-mentioned inorganic substances. In order to form a higher performance non-linear optical material, it is necessary to arrange compounds having a high non-linear susceptibility in a molecular state so as not to generate inversion symmetry. It is known that a compound having a long π-electron conjugated chain is useful for the expression of a high non-linear susceptibility, which is one of them, and various compounds are described in the above-mentioned documents. Obviously, the maximum absorption wavelength becomes longer, and the transmittance of blue light decreases, for example, which hinders the generation of blue light as the second harmonic. This also occurs in the p-nitroaniline derivative, and the fact that the transmittance of the wavelength has a large influence on the efficiency of the second harmonic generation is due to Alain Azema et al., Proceedings of SPII,
Volume 400, New Optical Materials (Alai
n Azema et al., Proceedings of SPIE, Volume 400, New
Optical Materials), (1983) page 186, FIG.

Therefore, the advent of a nonlinear optical material having a high transmittance for blue light is desired. Conventionally, replacement of carbon atoms in the benzene nucleus of nitroaniline with nitrogen atoms has been studied, but satisfactory results have not necessarily been obtained. In addition, the applicant of the better method,
JP-A-62-210430 and JP-A-62-210
It was disclosed in Japanese Patent No. 432. Further, JP-A-62-599
34, JP-A-63-23136, JP-A-63-26
No. 638, Japanese Patent Publication No. 63-31768, and Japanese Patent Laid-Open No. 63-1.
63827, JP-A-63-146025, JP-A-6-
3-85526, JP-A-63-239427, JP-A-1-100521, JP-A-64-56425, JP-A-1-102529, JP-A-1-102530,
Many materials are disclosed in JP-A-1-237625, JP-A-1-207724 and the like. However, as described above, in order to be useful as a second-order nonlinear optical material, the performance in the molecular state alone is insufficient, and it is essential that the molecular arrangement in the aggregated state has no inversion symmetry. is there. However, at present, it is extremely difficult to predict the molecular arrangement, and the existence probability in all organic compounds is not high.

Further, when it is used as an element for wavelength conversion, it is necessary to sufficiently consider the arrangement of molecules in the crystal, but most of the above-mentioned ones are not always sufficiently considered. Furthermore, until now, no wavelength conversion element using an organic nonlinear optical material has appeared in the world as a product. The reason for this is considered as follows, for example. First of all, most compounds rely only on the evaluation of the powder method SHG, and do not consider the relationship between the molecular arrangement in the single crystal and the polarization directions and angles of the incident fundamental wave and the emitted converted wave. Further, when a fiber type optical wavelength conversion element is formed using the above-mentioned nonlinear optical material, the crystal is not oriented in a direction in which the maximum nonlinear optical constant of each material can be used, so that the optical wavelength conversion element The wavelength conversion efficiency will not be so high. Further, the wavelength conversion efficiency of the light wavelength conversion element increases as the element length increases, but it is difficult to obtain a uniform single crystal with the above-mentioned materials, and thus it is unsuitable for making a long light wavelength conversion element. There are also problems.

[0006]

Therefore, a first object of the present invention is to provide a molecular crystal having a molecular arrangement suitable for a wavelength conversion element which is excellent in blue light transmission and has no inversion symmetry. . A second object is to provide a method utilizing the responsivity related to the conversion of the light wavelength among the non-linear responsivities. A third object is to provide an optical wavelength conversion module having high wavelength conversion efficiency and capable of easily obtaining the second harmonic in the blue region.

[0007]

Means for Solving the Problems As a result of intensive studies, the inventors of the present invention obtained a molecular crystal characterized by being composed of a molecule represented by the following formula (1). Found that can be achieved. Formula (1)

[0008]

[Chemical 2]

The synthesis of compounds of formula (1) can generally be accomplished by using the so-called aldol condensation reaction. That is, it can be synthesized by reacting the corresponding aldehyde and ketone in the presence of a base catalyst. Examples of the base catalyst include sodium hydroxide, potassium hydroxide, sodium hydride, sodium methoxide, sodium ethoxide, potassium-t-butoxide, pyridine, triethylamine, 1,8-diazabicyclo [5,5].
4,0] -7-undecene (DBU), sodium carbonate, potassium carbonate, sodium hydrogen carbonate, sodium acetate, potassium acetate. Hydroxides and alkoxides are preferred, of which hydroxides are preferred.

The catalyst used in the reaction can be selected from a range of polar solvents such as N, N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO) to nonpolar solvents such as benzene and hexane. D
Polar solvents such as MF and N, N-dimethylacetamide,
Alcohols such as methanol and ethanol, ethers such as tetrahydrofuran and 1,2-dimethoxyethane are preferable, alcohols are more preferable, and a mixed solvent of the above can be used. The reaction temperature can be selected from the range of -80 ° to 150 ° C. The range from -10 ° to 100 ° C is preferable, and the range from 5 ° C to 85 ° C is more preferable. Specific examples of the synthesis method are described in Japanese Patent Application No. 4-131159.

Next, the powder obtained here is single-crystallized. Examples of the method for single-crystallization include solvent evaporation method, temperature drop method, solution method such as vapor diffusion method, Bridgman method and the like. The melt method and the method by sublimation are mentioned. For single crystallization, "Crystal Engineering Handbook (Kyoritsu Shuppan, 1971), Part VII, edited by the Crystal Engineering Handbook Editorial Committee
This can be done by referring to the description in Chapter 8 of the volume. Wavelength conversion methods include a method using angular phase matching and temperature phase matching using a single crystal of an appropriate size, and a method using Cherenkov radiation using a waveguide. An example of the latter is 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 the formula (1). Is used in a single crystal state, and the crystal orientation of (1) constituting this core is set so that its a-axis extends substantially in the major axis direction of the core, while the light source device is substantially orthogonal to the a-axis. It is characterized in that the fundamental wave linearly polarized in the direction of the b-axis or the c-axis of the crystal is incident on the optical wavelength conversion element.

As the laser light source used as the fundamental wave, for example, those shown in Table 1 can be mentioned. The wavelength of the fundamental wave is not limited except for the influence of the absorption of the above-mentioned material. This is clear from Laser & Optronics, page 59 (published in November 1987).

[0013]

[Table 1]

[0014]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto. Example 1 A single crystal of the compound of formula (1) was prepared. Japanese Patent Application 4-13
Benzene was added to the powder of the compound of formula (1) obtained by synthesis based on the description of No. 1159, and dissolved at about 45 ° C. This was left overnight at room temperature. At this time, evaporation of the solvent was enabled without attaching a stopper. The precipitated needle crystals were collected by filtration.

Example 2 An X-ray crystal structure analysis of the compound of formula (1) was performed. The smaller crystals obtained in Example 1 were used. The obtained crystallographic data are shown. Crystal system Monoclinic system Space group P2 ₁ point group 2 Lattice constant a = 6.270Å b = 4.661Å c = 24.037Å β = 96.522 ° Z 2 The crystal structure is shown in FIG. From the above crystallographic data, it can be seen that this crystal does not have inversion symmetry.

Example 3 A good quality portion of the large crystal obtained in Example 1 was cut out and second harmonic generation was performed. The apparatus of FIG. 2 was used for the experiment. When the polarization direction of the YAG laser (1064 nm) was set parallel to the crystal axis and the crystal was rotated about the b axis, green light (532 nm) could be observed in a beam form. This indicates that the present crystal is capable of phase matching at 1064 nm, and thus the crystal of the present invention is promising as a nonlinear optical material for optical wavelength conversion.

Reference Example 1 When actually forming a fiber type optical wavelength conversion element,
It was unclear how to set the crystal orientation and what direction the polarization direction of the fundamental wave incident on the crystal orientation should be set to obtain high wavelength conversion efficiency. A method of setting the crystal orientation of the nonlinear optical material and the linear polarization direction of the fundamental wave suitable for obtaining high wavelength conversion efficiency will be described below. The crystal of (1) has a monoclinic system and the point group is 2. Therefore, the tensor of the nonlinear optical constant is
It is represented by. Formula (1)

[0018]

[Equation 1]

Here, d ₂₁ is light linearly polarized in the X direction (hereinafter referred to as X polarized light) when the optical axes X, Y and Z are considered.
The same applies to Y and Z. ) As a fundamental wave and Y
Nonlinear optical constant for extracting the second harmonic of polarized light. Similarly, d ₂₂ is a nonlinear optical constant for extracting the second harmonic of Y polarized light by allowing the fundamental wave of Y polarized light to enter, and d ₂₃ is Z.
Non-linear optical constant when a fundamental wave of polarized light is input to extract the second harmonic of Y-polarized light, d ₂₅ is a non-linear optical constant when a fundamental wave of X and Z polarized light is incident to extract the second harmonic of Y-polarized light The constant d ₃₄ is a non-linear optical constant when the fundamental waves of Y and Z polarization are made incident and the second harmonic of Z polarization is extracted. The magnitude of each nonlinear optical constant will be described below.

Since the refractive index of (1) has not been clarified yet, the nonlinear optical constant d _IJK can be derived by the following equation: d _IJK = _{Nf I} (2ω) f _J (ω) f _K (ω) b _IJK b Indicates _IJK value. In addition, N is the number of molecules per unit volume, f (ω), f (2
ω) are local electric field correction factors for the fundamental wave and the second harmonic, respectively. b ₂₁ = 0 b ₂₂ = 4.0 b ₂₃ = 23.7 b ₁₄ = b ₂₅ = b ₃₆ = 0 b ₁₆ = 0 b ₃₄ = 23.7 Note that these b _IJK values were determined by X-ray crystal structure analysis. And PP
It is a value based on β calculated using the P-CIMO method and the Ward's formula, and the unit is [× 10 ^-30 esu].

From this table, d ₂₂ , d ₂₃ , d _{34 and} especially d ₂₃
It can be seen that and d ₃₄ can take large values. Therefore, as shown in FIG. 3, in forming the fiber type optical wavelength conversion element 101 in which the core 111 made of (1) is filled in the clad 121, the a-axis of the crystal of (1) is oriented in the core axis direction. This optical wavelength conversion element 1 is oriented so as to extend (this can be realized by the method described below).
If the fundamental wave linearly polarized in the direction of the c-axis or the b-axis of the crystal is made incident on 01, the above large nonlinear optical constants d ₂₂ and d ₂₃ can be utilized.

Embodiment 4 FIG. 4 shows an optical wavelength conversion module according to a fourth embodiment of the present invention. This optical wavelength conversion module includes a fiber type optical wavelength conversion element 101 and this optical wavelength conversion element 1
01 and a light source device 20 for inputting a fundamental wave. Here, a method for producing the light wavelength conversion element 101 will be described. First, a hollow glass fiber to be a clad is prepared. As an example, this glass fiber is made of SF15 glass fiber and has an outer diameter of 100 μ.
The diameter of the hollow portion is about 2 m and is about m. on the other hand,
120 g of (1) is added to 1 liter of a solvent of benzene to prepare a saturated solution of (1) (at a temperature of 35 ° C.). This saturated solution (1) is kept at a constant temperature of 35 ° C. in a constant temperature bath, and one end of the glass fiber is introduced into this solution as shown in FIG. Then, the solution of (1) enters into the glass fiber due to the capillary phenomenon. When stored in this state, the solvent benzene evaporates and becomes supersaturated. Then, crystal nuclei are generated inside the glass hollow tube, and a single crystal grows. As a result, a single crystal state in which the crystal orientation is uniform over a long range of 20 mm or more can be obtained.

When (1) is filled in the glass fiber 129 in the single crystal state as described above, the crystal orientation state is such that the a-axis extends in the core axis direction as shown in FIG. After the core 111 has been filled as described above, both ends of the glass fiber 129 are cut by a fiber cutter, and the optical wavelength conversion element 1 having a length of 10 mm is cut.
01 was formed. As shown in FIG. 4, the light wavelength conversion element 101 is combined with the light source device 20 to form a light wavelength conversion module. In this embodiment, a semiconductor laser 21 is used as a light source for generating a fundamental wave, and laser light (fundamental wave) 15 having a wavelength of 870 nm emitted from the semiconductor laser 21 is collimated by a collimator lens 22 and then anamorphic. Prism pair 2
3 and the λ / 2 plate 25, the light beam is converted into a small beam spot by the condenser lens 26, and then the optical wavelength conversion element 10
It is irradiated to the incident end surface 10a of No. As a result, the fundamental wave 15 enters the light wavelength conversion element 101. As described above, (1) configuring the core 111 is in a crystal orientation state in which the a-axis extends in the core axis direction, while in the present example, by rotating the λ / 2 plate 25 of the light source device 20, The fundamental wave 15 in the polarization state in the b-axis direction is input to the light wavelength conversion element 101.

The fundamental wave 15 entering the optical wavelength conversion element 101 has a wavelength of 1 due to (1) which constitutes the core 111.
It is converted into the second harmonic wave 16 of / 2 (= 435 nm).
The second harmonic 16 repeats total reflection between the outer surfaces of the clad 121 and travels inside the element 101, and the guided mode in the core part of the fundamental wave 15 and the clad part of the second harmonic 16 propagates. Phase matching is performed with the radiation mode (so-called Cherenkov radiation).

A beam 16 ', which is a mixture of the second harmonic wave 16 and the fundamental wave 15, exits from the exit end face 10b of the light wavelength conversion element 101. This outgoing beam 16 ′ is passed through a condenser lens 27 and is focused, and then the second harmonic wave 16 of 435 nm is satisfactorily transmitted, while the fundamental wave 15 of 870 nm is passed through a bandpass filter 28 which absorbs the fundamental wave 15. , The second harmonic 16 is extracted. It was confirmed that the second harmonic 16 was polarized in the b-axis direction by using a polarizing plate or the like. That is, in this example, the above-mentioned nonlinear optical constant d ₂₃ of (1) is used. This second harmonic 1
The light intensity of No. 6 was measured with the optical power meter 29, and the wavelength conversion efficiency was determined to be about 1% in terms of 1 W.

[0026]

The compound of the present invention is disclosed in Japanese Patent Application No. 23750/1993.
As described in the specification, the blue crystal has high transparency, and the molecular crystal composed of the molecule represented by the formula (1) has no inversion symmetry in the molecular arrangement, so that the second-order nonlinear optical effect is generated. Have. Therefore, it is a useful material for wavelength conversion using the second-order nonlinear optical effect. It is particularly useful for generating converted waves in the blue region. Further, as described in detail, according to the optical wavelength conversion module of the present invention, the high nonlinear optical constant of (1) can be actually used in the fiber type nonlinear optical material, and the optical wavelength conversion element can be sufficiently long. Since it can be formed, extremely high wavelength conversion efficiency can be realized. Moreover, since (1) has an absorption edge at 400 nm or less, according to this optical wavelength conversion module,
It is also possible to efficiently extract the second harmonic in the blue region by using the laser light of about 0 nm as the fundamental wave.

Although the method using the Cherenkov radiation method has been described above, the present invention is not limited to these methods, and waveguide-guided phase matching is also possible. The wavelength converted wave is not limited to the second harmonic, but is also used for the third harmonic, sum and difference frequency generation. Further, it is possible to make the above compound into a single crystal, cut out a bulk single crystal therefrom, and input a YAG laser beam to generate a second harmonic thereof.
Angle phase matching is used as the phase matching method at this time. These bulk single crystals can be used not only outside the cavity of the laser but also inside the cavity of a solid-state laser such as an LD-excited solid-state laser to improve the wavelength conversion efficiency. Further, the wavelength conversion efficiency can be improved also by disposing it in the resonator of the external resonator type LD. The Bridgman method, the solvent evaporation method, or the like is used for the above single crystallization.

[Brief description of drawings]

FIG. 1 is a stereo diagram showing the crystal structure of a compound of formula (1). a, b, and c are crystal axes, a, b, and c, respectively.

FIG. 2 is an apparatus for generating a second harmonic using a single crystal.

FIG. 3 shows a crystal orientation of a core in a fiber type optical wavelength conversion element.

FIG. 4 is an explanatory view of a method for producing a fiber type optical wavelength conversion element. Reference numeral 10a denotes an incident end surface and 10b denotes an emission end surface.

FIG. 5 shows a single crystal growth apparatus for a fiber having a single crystal of the compound of formula (1) as a core by a solvent evaporation method.

[Explanation of symbols]

 10 Single crystal composed of compound of formula (1) 11 Nd: YAG laser 13 Fundamental wave cut filter 15 Fundamental wave 16 Second harmonic wave 16 'Second harmonic wave mixed with fundamental wave 20 Light source device 21 Semiconductor laser 22 Collimating lens 23 Anamorphic prism pair 25 λ / 2 plate 26, 27 Condensing lens 28 Bandpass filter 29 Optical power meter 128 Saturated solution of compound of formula (1) 129 Clad (glass fiber) 101 Optical wavelength conversion element 111 Core 121 Cladding

Claims (3)

[Claims] 1. A monoclinic system comprising a molecule represented by the following formula (1): P2 ₁
Molecular crystal having a space group of formula (1) 2. A method of converting a light wavelength using a single crystal composed of the molecular crystal according to claim 1 as a nonlinear optical material when converting a light wavelength using a laser beam and a nonlinear optical material. 3. A single-crystal nonlinear optical material characterized by being constituted by a molecule represented by the formula (1) is filled in the clad as a core, and the a-axis of the crystal of the optical material is substantially the core axis. A light wavelength conversion element oriented so as to extend in a direction, and a light source device for making a linearly polarized fundamental wave incident on the light wavelength conversion element in the direction of the b-axis or the c-axis of the crystal substantially orthogonal to the a-axis. Optical wavelength conversion module consisting of. (However, the crystallographic axis is determined by setting the 2-fold axis as the b-axis, and the other crystallographic axes follow the right-handed system.)