JPH06235947A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To provide an organic nonlinear optical material stable thermally, hardly causing orientation relaxation, and having a large secondary nonlinear optical effect by using the material having a specific cyclic unit. CONSTITUTION:An organic nonlinear optical material has a cyclic unit expressed by the formula. This material has many nonlinear optical units in a fixed volume, and it indicates an excellent nonlinear optical effect. The thin film having the thickness of about 1mum of this material applied with poling process has the SHG efficiency about double that of the thin film added with 2-methyl-4- nitroaniline of 2wt.% to polycarbonate, having the same film thickness, and applied with poling process. When this material is heated into imide while being applied with the electric field in the polyamide acid state of its precursor, a nonlinear optical thin film aligned with orientation can be obtained. This thin film rarely causes orientation relaxation, the SHG efficiency is hardly reduced when it is left at 150 deg.C for one month, and it is excellent in thermal stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic nonlinear optical material preferably used in the field of optoelectronics and a nonlinear optical element using the organic nonlinear optical material.

[0002]

2. Description of the Related Art Nonlinear optical materials include those using a second-order nonlinear optical effect and 3
It can be roughly classified into two types using the following effects, and can be broadly divided into two types as materials for frequency conversion of laser light and the like and optical signal processing materials utilizing the change in refractive index. Among these, organic nonlinear optical materials, which are roughly classified into the following five types, have been proposed as materials for optical signal processing using the second-order nonlinear optical effect. B) Organic low-molecular weight materials b) System in which a material having nonlinear optical effect is added to general-purpose polymer for optics c) Pendant type system in which a site having nonlinear optical effect is introduced as side chain of polymer d) Nonlinear optical effect in polyimide A system in which a material having a is added e) A main chain type system in which sites having a non-linear optical effect are connected to each other. Hereinafter, a site or a molecule having a non-linear optical effect is referred to as a “non-linear optical unit”. Although many studies have been conducted on these materials, there are the following drawbacks when they are actually used as optical signal processing elements. Material b) It is difficult to obtain a thin film with uniform orientation. Poor thermal stability. (Example: MNA (2-methyl-4-nitroaniline) has a melting point of about 130 ° C.) Poor chemical stability. Material of b) Orientation relaxation easily occurs. Easy to be thermally deformed. Since the number of nonlinear optical units per fixed volume is small, the magnitude of macroscopic nonlinear optical effect is small. Material of c) Orientation relaxation easily occurs. Easy to be thermally deformed. Since the number of nonlinear optical units per fixed volume is small, the magnitude of macroscopic nonlinear optical effect is small. Material d) The orientation relaxation is unlikely to occur and the thermal stability is good, but the size of the macroscopic nonlinear optical effect is small because the number of nonlinear optical units per fixed volume is small. Material of e) Depending on the structure, some materials are less likely to undergo thermal deformation and less likely to undergo orientation relaxation, but in producing them, the polymerization process such as the LB film method or polymerization by addition of a catalyst is complicated.

Regarding the above-mentioned "orientation relaxation", it is necessary to align the dipole moments of the nonlinear optical unit by the poling process when an optical signal processing device utilizing the second-order nonlinear optical effect is produced. . Generally Tg
In a temperature range slightly lower than the (glass transition temperature), a poling treatment is performed by applying an electric field, and the thin film having a uniform orientation is prepared by returning the temperature to room temperature while applying the electric field. However, in the cases of the above b) and c), since the Tg of the base polymer or the polymer serving as the main chain is low, the direction of the dipole moment is immediately randomized, so-called orientation relaxation occurs, and the optical signal The function as a processing element is lost. For example, when PMMA, which is often used as the base polymer of type (b), is used, the orientation state becomes random at about 100 ° C. In addition, when the main chain of the type c) is a polyethylene type, it does not have 100 ° C. B),
In both types c) and d), since the non-linear optical units are scattered in the base polymer, the number of non-linear optical units in a material of a certain volume has an upper limit, and it is macroscopic. The nonlinear optical effect cannot be increased. In order to increase the nonlinear optical effect per nonlinear optical unit, it is the current mainstream research to develop larger molecules and atomic groups having a conjugated system. This leads to a decrease in the number.

[0004]

In order to solve the above problems, the present inventors have made the subject of keeping a large number of non-linear optical units in a constant volume, and conventionally, in order to improve strength and formability. The polymer backbone, which is irrelevant to the nonlinear optical effects that have been used, is composed of polymers that exhibit nonlinear optical effects. Further, the main chain structure is an aromatic polyimide skeleton for thermal stability and suppression of orientation relaxation.
The present inventors have found that an organic nonlinear optical material having a repeating unit represented by the following general formula (1) exhibits a high second-order nonlinear optical effect, is less likely to cause orientation relaxation, and is thermally stable. The invention was completed.

[0005]

[Chemical 2]

The present substance exhibits excellent nonlinear optical effects due to the large number of nonlinear optical units in a given volume. The thin film having a thickness of about 1 μm of the substance subjected to the poling treatment had the SHG efficiency about twice as high as that of the thin film having the same thickness obtained by adding 2% by weight of MNA to the polycarbonate. In the polyamic acid state which is the precursor of this material, the temperature is raised while applying an electric field,
By performing imidization, a non-linear optical thin film with uniform alignment can be obtained. The poling condition at this time is 100 KV / m or more, preferably 1 MV / m or more, because the magnitude of the electric field must have energy enough to cause the orientation. The imidization temperature is the same as that of general polyimide, and is 250 ° C. or higher, preferably 300 ° C. or higher, and it is desirable to carry out in a non-oxidizing atmosphere such as nitrogen gas.

The thus-obtained thin film is very unlikely to undergo orientation relaxation, and the SHG efficiency was hardly reduced even if it was left at 150 ° C. for 1 month. Further, the material of the present invention is characterized by excellent thermal stability because it has an aromatic polyimide skeleton having high heat resistance as a main chain. There is no risk of deformation even in a temperature atmosphere of about 300 ° C. Therefore, when it is made into a device in the future,
Even if soldering work is performed on a board or the like, the quality is not affected for a short time. As a method for producing a thin film of this substance, it is possible to use a vapor deposition polymerization method (see: Japanese Patent Publication No. 2-50984), in addition to the method of producing an amic acid solution as described above. In this case, after the solid polyamic acid is produced by vapor deposition polymerization, imidization may be performed while poling, or by applying an electric field to the substrate surface portion at a substrate temperature of 250 ° C. or higher, vapor deposition is performed. It is also possible to obtain a thin film of this substance with uniform alignment at once by performing poling treatment and imidization at the same time during polymerization.

[0008]

The material of the present invention has good thermal stability, is less likely to undergo orientation relaxation, is easy to form a thin film, and is easy to be made into a device. Since this material has a second-order nonlinear optical effect, it can be used as an optical signal processing element such as an optical switch based on the electro-optical effect.

[0009]

【Example】

Example 1 0.01 mol of PMDA (pyromellitic dianhydride), 2-
0.01 mol of nitro-1,4-phenylenediamine was dissolved in 40 mL of dimethyl sulfoxide to prepare both solutions. The PMDA solution was cooled in a water bath and the 2-nitro-1,4-phenylenediamine solution was added dropwise thereto while stirring. After all the dropping is finished, cover the film with a stirrer to prevent it from absorbing moisture and
The desired polyamic acid solution was obtained by continuing stirring for a time. A polyamic acid thin film was prepared on a slide glass by spin coating. The slide glass was subjected to a poling treatment using a poling treatment kit as shown in FIG. That is, the slide glass (4) was set on the aluminum plate (2) placed on the heater (3), and the flat plate electrode (1) was set at a distance of about 1 mm from the film surface. A poling treatment was performed by applying an electric field of 3 MV / m between the flat plate electrode and the aluminum plate. While applying an electric field, the temperature of the heater was raised to 100 ° C. for 1 hour and then to 300 ° C. and kept for 1 hour. After completion of imidization,
When the temperature was lowered and the temperature was returned to room temperature, the applied voltage was set to 0V. This poling work was performed in a nitrogen gas atmosphere in a simple dry box to prevent the influence of oxygen.

When the finished film was measured by FT-IR, peaks characteristic of imide bonds such as 1780 and 1720 cm ^-1 were observed, and PMD of the monomer was observed.
1850cm ^-1 , which is characteristic of A, and 2-nitro-1,4-
Characteristic of the amino group of phenylenediamine 3400 cm
The peak near ^-1 had disappeared. The SHG efficiency of this thin film having a thickness of 1 μm was measured by the maker fringe method using an Nd: YAG laser. The results are shown in Table 1. The thin film whose SHG efficiency was measured was set in a constant temperature bath, and heat-treated by leaving it in an atmosphere of 150 ° C. for one month. This thin film was taken out one month later, and the SHG efficiency was measured by the maker fringe method. The results are shown in Table 1.

Comparative Example 1 0.02 g of MNA and 1 g of optical grade polycarbonate were completely dissolved in 20 mL of chloroform,
Both solutions were mixed and stirred well. A thin film was formed by a spin coating method using this solution. This thin film was mounted on the poling treatment kit of FIG. 1, and an electric field of 3 MV / m was first applied. Then, raise the temperature of the heater to 14
Hold at 0 ° C. for 30 minutes. Thereafter, the temperature was lowered, and when the temperature returned to room temperature, the applied voltage was set to 0V. The SHG efficiency of this thin film having a thickness of about 1 μm was measured by the maker fringe method using an Nd: YAG laser. The results are shown in Table 1. Further, as in Example 1, the thin film for which the SHG efficiency was measured was set in a constant temperature bath, and heat-treated by leaving it in an atmosphere of 150 ° C. for one month. This thin film 1
Removed after a month, SHG by the maker fringe method
The efficiency was measured. The results are shown in Table 1.

[0012]

[Table 1]

[0013]

As described above, according to the present invention, it is possible to provide an organic nonlinear optical material which is thermally stable, hardly causes orientation relaxation, and has a large second-order nonlinear optical effect.
In addition, since it can be prepared by simply mixing two kinds of monomers at a ratio of 1: 1 and can be carried out by both a solution method and a gas phase method, it has an industrially important meaning in manufacturing an optical signal processing element. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a polling processing kit.

[Explanation of symbols]

 1 Flat plate electrode 2 Aluminum plate 3 Heater 4 Slide glass with thin film formed on the surface

Claims (1)

[Claims] 1. A quadratic nonlinear optical material having a repeating unit represented by the following general formula (1). [Chemical 1]