JPH03211535A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain high optical nonlinearity, UV and visible ray absorption at a shorter wavelength side and high crystallinity by using a methyl-4- hydroxybenzoate crystal. CONSTITUTION:A methyl-4-hydroxybenzoate crystal has superior optical nonlinearity and crystallinity and the UV and visible ray absorption is at a shorter wavelength side than the second harmonic region of semiconductor laser light (lambda=0.83-0.9mum). Since the UV and visible ray absorption is at the shorter wavelength side, when the wavelength of the semiconductor laser light is transformed, the deterioration of the compd. and the lowering of the efficiency of transformation due to the reabsorption of second harmonics are not caused. High optical nonlinearity, high crystallinity and UV and visible ray absorption at a shorter wavelength side can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an organic nonlinear optical material suitably used in optical information processing, optical communication, and the like.

[Prior Art] Many materials exploration studies have been conducted with the aim of realizing nonlinear optical elements as new elements in the field of optoelectronics.In recent years, organic compounds with π-electron conjugated systems have been It is attracting attention because of its fast photoresponsiveness.

In particular, materials with second-order optical nonlinearity have been studied using various compound systems, and there are many general explanations. (1) A CS symposium
ries 233 (1983), 2) D. J. Wil.
liams Angew, CbemInf, Ed.
Engl., 23 p690 (1984), 3)
D, S, Chemlg and J, 2yss,'
Non1inear optical property
iea of organic molecules
and crystals' vol 1, 2
^cademicpress (1987) etc.

) The optical nonlinearity of organic compounds with a π-electron conjugated system is said to be caused by the fluctuation of π-electrons when laser light is incident, and in order to increase this fluctuation, donor and acceptor properties are added to the π-electron conjugated system. The conventional molecular design guideline was to introduce substituents.

However, the compound according to the above molecular design guideline, i.e., π
Compounds in which donor and acceptor substituents are introduced into an electronically conjugated system have strong dipole-dipole interactions between molecules, so in many cases they have a central symmetry structure in which the dipoles of the two molecules cancel each other out. crystal, and does not exhibit second-order optical nonlinearity.

In previous research, attempts have been made to introduce optically active substituents or hydrogen bond-forming substituents into the π-electron conjugated system in order to break the central symmetry of the crystal and develop second-order optical nonlinearity. It's here.

A huge number of organic compounds have been studied, and 2-methyl-
4-Nitroaniline (MNA), N,N dimethyl-2
-acetylamino-4-nitroaniline (I)AN),
N-(4-nitrophenyl)-(L)-prolinol (
It has been found that benzene derivatives such as NPP) exhibit relatively large optical nonlinearity at the Nd:YAG laser wavelength (λ = 1.06 μm).

However, since these benzene derivatives have strong donor groups and strong acceptor groups such as amino groups and nitro groups, their optical nonlinearity at the Nd:YAG laser wavelength is relatively large, but their ultraviolet-visible absorption is There are even long wavelengths. Therefore, the semiconductor laser light (λ 0.83 to 0.9 μm) is transmitted through the material, that is, the fundamental wave (semiconductor laser light) propagates through the material, and the second harmonic also transmits at least a portion of the material. When converting, these compounds themselves reabsorb the second harmonics, resulting in problems such as compound deterioration and reduction in conversion efficiency.

Examples of molecules whose molecules have been designed with short wavelengths of UV-visible absorption in mind include 2-methyl-4-nitropyridine-N-oxide (POM) and N-[2(5-nitropyridyl).
] -(L)-prolinol (PNP), N-[4-nitrophenyl]-2-ethylimidazole (NPEI)
, 4-hydroxy-3-methoxybenzaldehyde (V
AN), etc. However, POM, NPEI,
PNP has a problem that optical nonlinearity is small because the wavelength is insufficiently shortened, and VAN lacks storage stability because it has high sublimation property.

As mentioned above, material searches have been carried out extensively, and Nd:Y
Materials that exhibit relatively large optical nonlinearity have been found when the fundamental wave is an AG laser, but there are promising materials that can be applied even when the fundamental wave is a semiconductor laser (λ 0.83 to 069 μm). has not yet been discovered.

[Problems to be Solved by the Invention] The problems of the present invention are to achieve ■large optical nonlinearity, ■ultraviolet-visible absorption on the short wavelength side, and ■high crystallinity in order to produce a transmission type semiconductor laser wavelength conversion element. An object of the present invention is to provide an organic nonlinear optical material having the following properties.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

"An organic nonlinear optical material characterized by comprising crystals of methyl-4-hydroxybenzoate." That is, the gist of the present invention is that methyl-4-hydroxybenzoate (
The crystal (hereinafter abbreviated as MPHB) is excellent in terms of ■optical nonlinearity and ■crystallinity, and ■ultraviolet-visible absorption is the second harmonic of semiconductor laser light (λ 0.83 to 0.9 μm). The point is that it was discovered that the wavelength is shorter than the wavelength range. Since UV-visible absorption is on the shorter wavelength side than the second harmonic region of semiconductor laser light, when converting the wavelength of semiconductor laser light, problems such as compound deterioration and reduction in conversion efficiency due to reabsorption of the second harmonic do not occur. do not have.

When the M P HB of the present invention is deuterated, there is a near-infrared absorption shift effect, but it has the same ultraviolet-visible absorption and nonlinear optical effect as a non-deuterated compound. Therefore, in the nonlinear optical compound, some or all of the hydrogens may be replaced with deuterium.

The method of crystallizing the compound of the present invention is not particularly limited, and it is possible to easily obtain a high-quality MP (B) single crystal using conventionally known methods such as a solution method, a melt method, and a gas phase method. can.

As mentioned above, MPHB crystal is an extremely useful material for producing wavelength conversion elements. Since it has excellent crystallinity and processability, it is useful for producing wavelength conversion elements having various forms such as planar waveguide type and fiber type.

[Example code] Example I Optical nonlinearity, UV-visible absorption, and crystallinity of MPHB.

First, commercially available (Tokyo Kasei, special grade) M P HB was recrystallized twice with benzene/chloroform (volume ratio 1/1).
Melting point 127-128°C).

The white crystals obtained here are further crystallized by slow evaporation in a nitrogen atmosphere, resulting in a large square crystal with good transparency (5 mm x 7 mm) from a methyl ethyl ketone solution.
mm x 3 mm) was obtained. Even when ethyl acetate or ethanol was used as the crystallization solvent, large angular products with good transparency were similarly obtained, and it was found that the M P HB of the present invention has extremely excellent crystallinity.

Next, in order to investigate the optical nonlinearity of the compound, SHG (second harmonic generation) was performed using a powder method (S, K, Kurlx,
T, T.

Pet+y, J, Appl, Phys 393798
(1966)). The laser light source used here was a dye laser (wavelength: 0°83f1m) with second harmonic excitation of an Nd:YAG laser, and the sample was a square crystal obtained from a methyl ethyl ketone solution that was crushed to 10 μm or less in a mortar. used.

The measurement of the ultraviolet-visible absorption spectrum was performed by the diffuse reflection method. A sample for measurement was prepared by mixing potassium bromide/MPHB at a weight ratio of 10/1 and molding the mixture into a disk.

Table 1 shows the measurement results of S T-I G and the absorption edge of ultraviolet-visible absorption.

M P ) (B according to the present invention) has an optical nonlinearity three times that of urea, which is a standard nonlinear optical compound, and has an absorption edge on the shorter wavelength side than the second harmonic wavelength of a semiconductor laser. It was found that this material is suitable as a material for a transmission type wavelength conversion element of a laser.

Comparative Example 1 3-Methyl-4-nitropyridine-N-oxide (PO
M) Optical nonlinearity and UV-visible absorption.

When a commercial product (Lancaster) was recrystallized with acetone/benzene (volume ratio 1/1), pale yellow angular crystals were obtained.

Next, the optical nonlinearity and ultraviolet-visible absorption spectrum of the compound were measured in the same manner as in Example 1.

Table 1 shows the measurement results of the absorption edges of SHG and UV-visible absorption.
Shown below.

P OM is one of the standard nonlinear optical compounds, urea.
．． It showed only 1x optical nonlinearity. In addition, the absorption edge measurement results revealed that POM is not preferable as a material for a transmission type wavelength conversion element of a semiconductor laser because it has ultraviolet-visible absorption in the second harmonic region.

Comparative Example 2 Optical nonlinearity, ultraviolet-visible absorption, and crystallinity of N-[2-(5-nitropyridyl)co(I,)prolinol (PNP).

1) NP is as described in the literature (R1, Twieg et al.
al., J. Chem, Phys., 85(6
), 3537 (1986)).
child.

The obtained crude crystals were recrystallized twice from benzene.

PNPs were prepared using chloroform/cyclohexane (volume ratio 1
: When recrystallized with a mixed solvent of 1), pale yellow angular crystals (5 mm x 4 mm x 4 mm) with relatively good transparency are obtained.
It became. However, this crystal devitrified when left at room temperature for several days.

Next, the optical nonlinearity and ultraviolet-visible absorption spectrum of the compound were measured by the method of Example 1.

Table 1 shows the measurement results of STI G and the absorption edge of ultraviolet-visible absorption.

PNP is a standard nonlinear optical compound, 0.0.
It showed only twice as much optical nonlinearity. Furthermore, the absorption edge measurement results revealed that PNP is not preferable as a material for a transmission type wavelength conversion element of a semiconductor laser because it has ultraviolet-visible absorption in the second harmonic region.

Table 1. Organic nonlinear optical compounds SHG and UV cuiof
f (λ: 0.83 μm) [Effects of the invention] High-performance organic nonlinearity that has large optical nonlinearity, high crystallinity, and ultraviolet-visible absorption on the short wavelength side, and enables wavelength conversion of semiconductor lasers in a transmission type. We can provide optical materials.

Claims (1)

[Claims] (1) An organic nonlinear optical material comprising crystals of methyl-4-hydroxybenzoate.