JPH0332763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an optical waveguide using a polymeric material, and more specifically, uses a laser or the like to apply thermal energy to an amorphous substance to generate a difference in thermal history.
This relates to an optical waveguide that utilizes a high refractive index difference.

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 to practical use. For example, even in the case of photopolymerized methyl methacrylate, which has the smallest 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
The purpose is to provide a polymer optical waveguide that has relatively low optical loss from visible to near-infrared regions, can easily create a homogeneous and wide-area thin film, can obtain a high refractive index difference, and can be easily written. There is a particular thing.

That is, the present invention is composed of a copolymer of vinylidene cyanide represented by the following formula and another vinyl compound, vinylidene compound, or diene, The present invention also relates to a polymer optical waveguide characterized in that the optical waveguide circuit is formed by partially heat-treating the parts to produce parts having 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 its esters, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, Fluorinated ethylene, butadiene, chlorobutadiene, isobutylene, maleic anhydride, acrylonitrile, α-chloroacrylonitrile,
Examples include methyl vinyl ketone, vinyl isobutyl ether, and cyanoacrylates. It is also possible to chemically modify a part or all of the ester compound after polymerization, such as hydrolysis.

The mole composition ratio of vinylidene cyanide and other monomers in the copolymer is 0.5 to 1.5:1, preferably 0.8:1 to 1.2:1, particularly preferably 1:1 alternating copolymerization. Consolidation 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,
Polymerization can be carried out by applying heat in the presence of a radical initiator such as α,α'-azobisisobutyronitrile.

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 heat-treated 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, the difference in density between polystyrene cooled at 1°C/3 minutes and glass obtained by cooling it at 1°C/1 day is approximately 0.18%. The difference in density between glass and polystyrene is only about 0.6% (Polymer Journal, 2, 644 (1971)).
The difference in refractive index based on this density difference is about 0.001 between those cooled at a slow rate of 1°C/day and those cooled rapidly, and has not been used as a material for forming optical waveguides. Ta.

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 along with this, 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 desired shape such as a film, sheet, or monofilament. Further, the optical waveguide can be constructed of a single phase of the copolymer of the present invention, but it can also be used 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 above the glass transition point and then slowly or rapidly cooled to a uniform state. Then, after irradiating laser light, high frequency, ultrasonic waves, etc. to partially raise the temperature to above the glass transition point so that the refractive index of the position where the waveguide circuit is to be written changes with respect to the surrounding area, it is rapidly cooled or By slow cooling, a heat history different from that in the pretreatment is provided to form portions with different refractive indexes, and writing is thereby performed.

Therefore, the 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 a temperature above the glass transition point using a heating furnace or a laser beam, etc. After that, it is cooled slowly or at a temperature slightly lower than the glass transition point, generally 3 to 50 degrees below the glass transition point.
The heat treatment is carried out at a temperature lower than 5°C, preferably 5 to 15°C. 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 heating the optical waveguide-forming material of the present invention above the glass transition temperature to cause a transition, this must be taken 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 when the composition ratio is 0.5:1 to 1.5:
In the case of 1, it is about 0.003 to 0.03. This value is
This is extremely large compared to polystyrene under the same conditions, which has 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
3 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 is incident from the waveguide circuit end face 4, the waveguide circuit 3
Since the refractive index of the light is higher on the outside, the light can be guided while being confined within the waveguide circuit, and can be split into two lights and emitted from the ends 5 and 5' of the two waveguide circuits. .

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

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto in any way.

Example 1 A film (glass transition point: 175°C) of an alternating copolymer of vinylidene cyanide and vinyl acetate was prepared,
This film was heated to 180°C and then rapidly cooled. This quenched film was partially heated to 160°C and kept at 160°C for 24 hours.
After being kept at ℃, the refractive index of the obtained film was measured. 160 compared to the part quenched at 180℃
The refractive index of the part heat-treated for 24 hours at °C is approximately 0.7.
% has increased. These heat treated films are re-180
The refractive index of the product heated to ℃ for a short time and then rapidly cooled is 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 A quenched film of the same alternating copolymer of vinylidene cyanide and vinyl acetate as in Example 1 was heat treated at 180° C. and 200° C. for 1 hour under 4000 atmospheres, and then cooled and depressurized. The refractive index of the obtained film is 180
1.5141 for those treated at ℃ and 1.5213 for those heat treated at 200℃, and 180℃ and 200℃ at normal pressure.
The refractive index was approximately 1.7 to 2.2% higher than that of the more rapidly cooled film. These films were heated to 180°C at normal pressure, except for the optical waveguide part that was created inside these films.
An optical waveguide was obtained by heating to ℃ and then rapidly cooling.

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

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

[Brief explanation of drawings]

FIG. 1 is a perspective view of one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Base material, 2... Polymer film, 3... Optical waveguide circuit, 4, 5, 5'... End surface of the waveguide circuit.

Claims (1)

[Scope of Claims] Consisting of a copolymer of vinylidene cyanide represented by the following formula and another vinyl compound, vinylidene compound or diene, A polymer optical waveguide characterized in that an optical waveguide circuit is formed by partially heat-treating the portions to produce portions having different refractive indexes.