JPS6073602A - Optical waveguide of polymer - Google Patents

Abstract

PURPOSE:To facilitate writing by partially heat treating a copolymer consisting of specified vinylidene cyanide and a vinyl compound, other vinylidene compound or diene to form an optical waveguide. CONSTITUTION:A copolymer consisting of vinylidene cyanide represented by formula I and a vinyl compound, other vinylidene compound or diene is partially heat treated to form an optical waveguide which is different from other part in refractive index. For example, a substrate 1 of ''Pyrex'' glass or the like having a low refractive index is covered with a copolymer film 2, and an optical waveguide 3 is formed in the film 2. When light is introduced into the waveguide 3 from an end 4, the light is guided through the waveguide 3 in a trapped state because the waveguide 3 has a higher refractive index than the outside, and it emerges dividedly from ends 5, 5' of the waveguide 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an optical waveguide using a polymer material, and more specifically, uses a laser or the like to apply thermal energy to an amorphous material to create a difference in thermal history, thereby increasing refraction. This invention relates to optical waveguides that utilize index differences.

Polymer materials are attracting attention as materials for optical waveguides because they can be easily fabricated into homogeneous, wide-area thin films with relatively low loss in the visible to near-infrared range. However, as there is currently no way to obtain a high difference in refractive index, this method has not been put into practical use. For example, even in the case of photopolymerized methyl methacrylate, which has a small optical loss and the largest change in refractive index, the change in refractive index is about 0.1%, which is not practical for forming optical waveguides.

The present invention was made in view of the current situation, and its purpose is to have relatively low optical loss from the visible to near-infrared regions, to facilitate the production of homogeneous and wide-area thin films, and to be able to obtain a high refractive index difference. The object of the present invention is to provide a polymer optical waveguide that can be easily written.

That is, the present invention is composed of a copolymer of vinylidene cyanide represented by the following formula and other vinyl compounds, vinylidene compounds, or dienes, AN CH2=C C=N and partially heat-treated. The present invention relates to a polymer optical waveguide characterized in that the optical waveguide circuit is formed by forming portions with different refractive indexes.

Next, the present invention will be explained in detail. The polymer compound used as a material for forming an optical waveguide in the present invention is obtained by copolymerization or alternating copolymerization of vinylidene cyanide and other vinyl compounds, vinylidene compounds, or dienes.

Other vinyl compounds, vinylidene compounds, and dienes include styrene, dichlorostyrene, acrylic acid and its esters, methacrylic acid and its esters, vinyl alcohol and hiscoesters, vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride. Examples include ethylene trifluoride, butadiene, chlorobutadiene, isobutylene, maleic anhydride, acrylonitrile, α-chloroacrylonitrile, methyl vinyl ketone, vinyl isobutyl ether, and cyanoacrylates.

For ester compounds, it is also possible to chemically modify part or all of them after polymerization, such as hydrolysis.

The compositional ratio of vinylidene cyanide and other monomers in the copolymer is in the range of 0.5:1 to 1.5:1, preferably 0.8:1 to 1.2:, and particularly Preferably, a 1:1 alternating copolymer is used.

The polymerization of the above monomer can be carried out using a method known as a method for polymerizing this type of monomer, in the coexistence of a radical initiator such as α,α'-azobisisoputiloni, or Polymerization can be carried out by applying heat in the absence of coexistence.

As the means, emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, etc. can be adopted, but preferably, the monomer is dissolved in a solvent such as toluene or a mixed solvent of toluene and hexane, and then the polymerization is carried out. This is done by collecting the polymer that precipitates as the process progresses.

Normally, when an amorphous polymer is heat-treated at a temperature slightly lower than its glass transition temperature, a glassy polymer with higher density can be obtained than when it is heated at a temperature higher than its glass transition temperature and then rapidly cooled. . This phenomenon is called volume relaxation phenomenon.

That is, when a material that has been heated to a temperature higher than the glass transition temperature and then rapidly cooled is subjected to heat treatment at a temperature approximately 10° C. lower than the glass transition temperature, the density gradually increases and approaches a certain equilibrium value. Furthermore, when the heat-treated material is heated to a temperature higher than the glass transition temperature and then rapidly cooled, the density returns to approximately the value before the heat treatment, and this change in density is reversible.

Similar density differences are observed between samples cooled quickly and slowly from temperatures above the glass transition temperature. Even if the cooling rate is the same, there is a difference between cooling from a temperature higher than the glass transition temperature under high pressure to below the glass transition temperature and then returning to normal pressure, and one from a temperature higher than the glass transition temperature at normal pressure. A similar density difference is observed between cooled samples. All of these phenomena originate from the fact that glass transition is a relaxation phenomenon.

This density difference is usually very small. For example, polystyrene is 1
The difference in density between the glass obtained when cooled at ℃/3 minutes and when cooled at 1℃/day-5= is about 0.18%, and when cooled at 1℃/3 minutes under normal pressure and 600 atm. The difference in density of the glass obtained with polystyrene is only about 0.6% (Potimer Journat, !, 644 (
1971)). The difference in refractive index based on this density difference is 1°C/
The difference between those cooled at a slow rate of one day and those cooled quickly is only about 0.001, and so it has not been used as a material for forming optical waveguides in the past.

In the present invention, by making vinylidene cyanide into a copolymer with other monomers, this density difference is much larger than that of ordinary amorphous polymers, and accordingly, the refractive index is large enough to be used as an optical waveguide. This made it possible to obtain the difference.

The material for forming an optical waveguide of the present invention is molded into a film, sheet, monofilament, or other shape depending on the purpose. Although the optical waveguide can be constructed from a single phase of the copolymer of the present invention, it can also be constructed by laminating the copolymer of the present invention with a base material such as fused silica.

When writing an optical waveguide circuit on the optical waveguide forming material of the present invention, the molded optical waveguide forming material is heated to above the -H glass transition point and then slowly or rapidly cooled to a uniform state. After pre-treatment, irradiating with the following to partially raise the temperature to above the glass transition point, and then rapidly or slowly cooling it, giving it a different thermal history than the pre-treatment and having a different refractive index. A portion is formed by which writing is performed.

Therefore, preliminary treatment is performed to give a thermal history that is in contrast to the thermal history during writing, and when rapidly cooling during writing, the optical waveguide forming material is heated to above the glass transition point in a heating furnace or with a laser beam. This is followed by slow cooling or heat treatment at a temperature slightly lower than the glass transition point, generally 3 to 50°C, preferably 5 to 15°C lower than the glass transition point. Slow cooling or heat treatment under pressure can also be carried out.

On the other hand, when slow cooling is performed during writing, rapid cooling is performed during preliminary processing.

Glass transition usually occurs over a wide range of temperatures.

Therefore, when the optical waveguide forming material of the present invention is heated to a temperature higher than the glass transition temperature to induce a transition, it is necessary to take this into consideration.

Generally, heating during pretreatment or writing is preferably performed at a temperature of 5° C. or higher, preferably 10° C. or higher, above the glass transition temperature. There is no particular upper limit to the temperature, and the temperature is below the decomposition temperature of the optical waveguide forming material.

The written optical waveguide circuit is normally stored at a temperature lower than the glass transition point by 30° C. or more, preferably 50° C. or more.

The difference in refractive index due to history difference depends on the type and composition ratio of the monomer copolymerized with vinylidene cyanide, and the conditions for providing history, but it is 0 when the composition ratio is 0.5:1 to 1.5 = 1. It is about .003 to 0.03. This value is extremely large compared to polystyrene under the same conditions, which produces a refractive index difference of only 0.001.

A specific example of the present invention is shown in FIG.

1 may be a base material having a low refractive index, such as Pyrex glass or fused silica. 2 is a polymer film made of the copolymer of the present invention, and 3 is an optical waveguide circuit formed in the polymer film 2. In an optical waveguide having such a structure, for example, when light enters from the end face 4 of the waveguide circuit, since the refractive index of the waveguide circuit 3 is higher than that of the outside, the light remains confined within the waveguide circuit and is guided. However, the light can be divided into two light beams and emitted from the ends 5.5' of the two waveguide circuits.

The following explanation will focus on alternating copolymers of vinylidene cyanide and other heptamers; however, if the composition ratio is within the above-mentioned range, a difference in refractive index will occur that can be used relatively easily as an optical waveguide. The present invention is not limited in any way by the following description.

Next, the present invention will be explained by examples, but the present invention is not limited thereto in any way.

Example 1 Alternating copolymerization of vinylidene cyanide and vinyl acetate - An integral film (glass transition point: 175°C) was prepared, and this film was heated to 180°C and then rapidly cooled. This quenched film was partially heated to 160° C., kept at 160° C. for 24 hours, and then the refractive index of the film obtained by quenching was measured. The refractive index of the portion heat-treated at 160° C. for 24 hours was approximately 0.7% higher than that of the portion rapidly cooled at 180° C.

When these heat-treated films were heated again to 180° C. for a short time and then rapidly cooled, the refractive index was approximately 1.4892, and the change in refractive index due to rapid cooling and heat treatment was reversible. Even after heat treatment for about 2 hours, the refractive index increased by about 0.33%, which was a very large change compared to ordinary amorphous polymers.

Example 2 The same quenched films of vinylidene cyanide and vinyl acetate alternating copolymers as in Example 1 were each heated at 4000 atm.
After being heat treated at 80°C and 200°C for 1 hour, it was cooled and the pressure was removed. The refractive index of the obtained film was 1.5141 when treated at 180°C, and 1 when heat treated at 200°C.
．． 5213, and the refractive index was about 1.7 to 2.2% higher than that of films rapidly cooled from 180°C and 200°C at 10-normal pressure. An optical waveguide was obtained by heating the film to 180° C. at normal pressure, excluding the portion of the optical waveguide formed in these films, and then rapidly cooling the film.

Example 3 Refractive index of a film of an alternating copolymer of vinylidene cyanide and methyl methacrylate (glass transition point: 148°C), which was rapidly cooled from 175°C in the same manner as in Example 1 and then heat-treated at 140°C for 24 hours. was measured. The refractive index of the sample heat-treated at 140°C for 24 hours was about 0.4% higher than that of the sample rapidly cooled from 175°C. This change was also reversible, and the refractive index after heating to 175° C. again and then rapidly cooling was 1.5174.

Example 4 Refractive index of a film of an alternating copolymer of vinylidene cyanide and vinyl benzoate (glass transition point: 175°C), which was rapidly cooled from 190°C in the same manner as in Example 1 and then heat-treated at 160°C for 24 hours. was measured. The refractive index of the sample heat-treated at 160°C for 24 hours was about 0.3% higher than that of the sample rapidly cooled from 190°C. Furthermore, the change in refractive index due to rapid cooling and heat treatment was reversible as in Example 1.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an example of an integrated body of the present invention. 1...Base material, 2...Polymer membrane 3...
... Optical waveguide circuit 4.5.5' ... Waveguide circuit end face patent applicant
Mitsubishi Yuka Co., Ltd. 1) Seizo agent Patent attorney Hidetoshi Furukawa (and 1 other person)

Claims (1)

[Claims] Consisting of a copolymer of vinylidene cyanide represented by the following formula and other novinyl compounds, vinylidene compounds, or dienes, C3N CH2=C -EN and partially heat-treated. A polymer optical waveguide characterized in that an optical waveguide circuit is formed by forming portions with different refractive indexes.