JPH06308336A - Production of distributed refractive index type optical fiber - Google Patents

Abstract

PURPOSE:To provide the process for production of the distributed refractive index type optical fiber having practicability and a wide range of characteristics by packing a monomer having a specific value of the refractive index after polymn. curing and subjecting the monomers included between both phases to crossdiffusion, thereby making polymn. curing in the state of giving a refractive index distribution. CONSTITUTION:This distributed refractive index type fiber is constituted by molding a circular columnar pipe-shaped perform of a mixture composed of a polymer and monomer capable of forming a polymer having >=10000 poises viscosity and the refractive index n1 of the polymer after polymn. curing and packing the mixture composed of the polymer and monomer capable of forming the polymer having n2 (where n2>n1) refractive index of the polymer after the polymn. curing within this preform. The monomers included in both phase pipes are crossdiffused and are subjected to the polymn. curing in the state of having the refractive index distribution, by which this optical fiber is produced. The distributed refractive index type optical fiber produced in such a manner is reduced in diameter by stretching the fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a gradient index optical fiber having a wide optical transmission band which can be effectively used as an optical information communication medium and having a continuous refractive index distribution from a central portion toward an outer peripheral portion. It is a thing.

[0002]

2. Description of the Related Art As a method for producing an optical fiber having a refractive index distribution from the center to the outer periphery of a cylindrical body, a cylindrical tubular preform made of a mixture of a monomer and a polymer having different refractive indexes. The monomer in the columnar object is polymerized and cured in a state where the monomer is partially volatilized from the outer periphery of the columnar object, and the refractive index distribution is generated from the central portion of the columnar shaped object toward the outer peripheral portion. As described in JP-A-54-30301, a method for producing a gradient index optical fiber by polymerizing cylindrical preforms of a monomer mixture having different reactivity ratios, and JP-A-4-30301. As disclosed in Japanese Unexamined Patent Publication No. 97302, there is a method of producing a gradient index optical fiber by utilizing the difference in the diffusion rate of monomers in a cylindrical preform from a mixture of monomers having different molecular sizes.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the production of preforms, it is necessary to use a mixture of monomers with different reactivity ratios, or a mixture of monomers with different molecular sizes, and even with these monomer mixtures, a single amount that does not cause phase separation Since it is necessary to be a body mixture, the range of monomer combinations that can be used is limited, so the performance of the graded index optical fiber that can be produced is also limited. The characteristics of the rate distribution type optical fiber were still insufficient.

[0004]

Therefore, the present inventors have widened the range of monomer combinations that can be used and have a wider range of refractive index distribution than the conventional method for manufacturing a gradient index optical fiber. The present invention has been completed as a result of studies to find a method for producing a mold-type optical fiber, and the gist thereof is a polymer having a viscosity of 10,000 poise or more and a refractive index of the polymer after polymerization and curing is n _1. A cylindrical tubular preform is shaped with a mixture of a polymer and a monomer capable of forming, and the refractive index of the polymer after polymerization and curing is n ₂ (however, in this preform.
n ₂ > n ₁ ) A polymer that can form a polymer is filled with a mixture of the monomer and the monomer contained in both phases is mutually diffused to cure the polymer with a refractive index distribution. The present invention relates to a method of manufacturing a graded index optical fiber, and a method of manufacturing a graded index optical fiber in which the graded index optical fiber is drawn to have a smaller diameter.

Next, a preferable method for producing the gradient index optical fiber of the present invention will be described.

First, a cylindrical tubular preform is filled with a mixture of a monomer having a refractive index after polymerization of n ₁ and a photopolymerization initiator in a translucent circular tubular container, and Irradiating light from the outside of the tube container while rotating about the axis, from the outer peripheral surface side in the circular tubular container, gradually progress the polymerization toward the inside, the viscosity of the polymer composition in the desired thickness range from the outer peripheral wall surface. But
The photopolymerization is stopped at a point of 10,000 poises or more, and preferably cooled to allow the resin composition of 10,000 poises or less to flow out to obtain a cylindrical tubular preform. The molecular weight of the outer peripheral surface of the preform thus obtained is higher, and the viscosity becomes lower toward the inside. The viscosity of the cylindrical tubular preform is 70
By setting the porosity to 10,000 poises or less, more preferably 500,000 poises or less, the subsequent monomer diffusion treatment can be easily performed.

The above-mentioned cylindrical tubular preform can be carried out by using a cylindrical molding container as described above. However, a monomer obtained by adding a thermal polymerization catalyst or a photopolymerization catalyst to a cylindrical preform of 10,000 poise or more in advance is used. It may be produced by a method in which a polymer obtained by polymerizing a composition of a polymer and a monomer is extruded using a die or a nozzle, and then extrusion-molded into a hollow tubular body.

The monomer to be filled in the above-mentioned tubular container may be composed of a monomer and a photopolymerization initiator,
When photopolymerization is performed while rotating the container in this state, the photopolymerization efficiency is not very good. In order to shorten the photopolymerization step, the monomer is thermally or photopolymerized to form a polymer-monomer mixture having a viscosity of about 10,000 poise or less, and the gel effect in the photopolymerization step is obtained. It is good to use effectively.

In the hollow portion of the cylindrical tubular preform obtained as described above, a monomer capable of forming a polymer having a refractive index of n ₂ , more preferably a viscosity of 5,000 poises or less, preferably 1,000 poises or less Fill the monomer-polymer mixture,
By interdiffusion of the monomer between the central layer and the outer layer, by photopolymerization in the state of having a refractive index distribution,
The gradient index optical fiber which is the object of the present invention can be obtained.

In order to further reduce the diameter of this gradient index optical fiber, it can be produced by stretching the optical fiber by ordinary thermal stretching, and far infrared rays are preferably used as a heat source.

When a cylindrical tubular preform is produced, several types of monomers or a polymer mixture of monomers and polymers are prepared, and the above procedure is repeated to obtain the refractive index distribution of the obtained optical fiber. It can approach the ideal quadratic curve.

As the curable substance which can be used in the practice of the present invention, a radically polymerizable vinyl monomer or a composition comprising the monomer and a polymer soluble in the monomer can be used. , Specific examples of the monomer include methyl methacrylate, styrene, chlorostyrene, vinyl acetate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, 2,2,3,3,4,4, Fluorinated alkyls such as 5,5-octafluoropentyl (meth) acrylate, 2,2,3,3,4,4-hexafluorobutyl (meth) acrylate and 2,2,2-trifluoroethyl (meth) acrylate (Meth) acrylate, ethyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, hydroxyalkyl (meth) acrylate, alkylene glycol di (meth) acrylate In addition to trimethylolpropane di- or tri (meth) acrylate, pentaerythritol di-, tri- or tetra (meth) acrylate, diglycerin tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, diethylene glycol bisallyl carbonate, fluorine Alkylene glycol poly (meth) acrylate and the like.

These monomers can be used alone or in a composite state. Further, although it may be used in the state of a monomer, as a composition for forming an outer layer, a thermal polymerization catalyst is added to these monomers to perform heat polymerization, and the viscosity is about 10,000 poise or less, a monomer mixture. It is preferable to use as. If the viscosity is too high, an optical distortion may occur or an inconvenient bubble may be involved when the composition is filled in the cylindrical tube, which is not preferable.

Examples of thermal polymerization initiators for curing these monomers include 2,2'-azobisisobutyronitrile, 1,1'-azobiscyclohexanecarbonitrile,
Azo compounds such as 2,2′-azobis- (2,4-dimethylvaleronitrile), and di-t-butylperoxide, dicumyl peroxide, di-t-butylperphthalate, di-t-butylperacetate , Organic peroxides such as di-t-amyl peroxide are used.

Further, as the photopolymerization initiator, benzophenone, benzoin alkyl ether, 4'-isopropyl-
2-Methyl-propiophenone, 1-hydroxycyclohexyl phenyl ketone, benzyl methyl ketal, 2,2-diethoxyacetophenone, chlorothioxanthone, thioxanthone compounds, benzophenone compounds, 4-dimethylaminoethyl benzoate, 4-dimethylamino Examples include isoamyl benzoate, N-methyldiethanolamine, triethylamine and the like.

Examples of the light source for irradiating ultraviolet rays include a carbon arc lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a low pressure mercury lamp, a chemical lamp, a xenon lamp and a laser beam.

The gradient index plastic optical fiber obtained by the present invention can be made into an optical fiber having an arbitrary smaller diameter by heat drawing the plastic optical fiber.

The performance of the optical fiber of the present invention was evaluated by measuring the transmission loss and the transmission band. The transmission loss was measured by using a white light source as a light source, injecting light from one end of the fiber, and reading the absolute intensity of light emitted from the other end for each wavelength with a spectrum analyzer. To measure the transmission band of an optical fiber, a laser diode with a wavelength of 670 nm is used as a pulse light source, and a Picosec pulse generator manufactured by Hamamatsu Photonics Co., Ltd. is used as a driving device to generate light at intervals of 10 MHz, and the light is made incident on the fiber and emitted. Was detected by using a sampling head manufactured by Hamamatsu Photonics Co., Ltd. for light reception and AD conversion, and using a sampling oscilloscope manufactured by Hamamatsu Photonics Co., Ltd. for Fourier transform of the measured waveform. The frequency was converted by Fourier transform of the obtained waveform to obtain a frequency that attenuated by 3 dB, and this was used as a transmission band.

[0019]

EFFECTS OF THE INVENTION According to the present invention, the drawback of producing a graded index plastic optical fiber by the conventional method, that is, the type of usable monomer is limited, is improved. A monomer can be used as a raw material, and a gradient index plastic optical fiber having a wider range of properties can be manufactured.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0021]

Example 1 100 parts by weight of 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate (refractive index after polymerization 1.397), 2,
2'-azobis- (2,4-dimethylvaleronitrile) 0.04 parts by weight and 1-hydroxycyclohexyl phenyl ketone 0.2 parts by weight were mixed, and after nitrogen substitution, the mixture was heated at 65 ° C for 60 minutes. The tube was filled. Then 3
After irradiating light for 20 minutes while rotating the cylindrical tube at a distance of 10 cm from this fluorescent lamp (40 cm, 20 W) and cooling in cold water for 5 minutes, the low-viscosity material on the center side of the circular tube was discharged (effluent The viscosity was 900 poise). In the hollow portion of the cylindrical tube generated by this, 100 parts by weight of 2,2,2-trifluoroethyl methacrylate (refractive index 1.413 after polymerization), 2,2'-azobis- (2,
4-Dimethylvaleronitrile) 0.04 parts by weight and 1-hydroxycyclohexyl phenyl ketone 0.2 parts by weight are mixed, the atmosphere is replaced with nitrogen, and then the mixture is heated at 65 ° C. for 45 minutes and filled with 25 parts by weight.
It was allowed to stand for 28 minutes at 28 ° C. Then, light is irradiated for 70 minutes while rotating the circular tube 10 cm away from the three fluorescent lamps, and the diameter is 1 cm,
A columnar cured product having a length of 70 cm was obtained. This cylindrical cured product,
A fiber with an outer diameter of 0.8 mm was created by performing thermal drawing while indirectly heating in a cylindrical heating cylinder set at 200 ° C, and the transmission loss and transmission band were measured. As a result, the transmission loss was 95 dB / km and the transmission band was 350 MHz · km.

[0022]

Example 2 100 parts by weight of methyl methacrylate (refractive index after polymerization 1.489), 0.02 part by weight of 2,2'-azobis- (2,4-dimethylvaleronitrile) and 0.2 part by weight of 1-hydroxycyclohexylphenylketone were used. After mixing and purging with nitrogen, 65
The one heated at 45 ° C. for 45 minutes was filled in a polyethylene cylindrical tube. Next, 10cm from 3 fluorescent lamps (40cm, 20W)
After irradiating with light for 20 minutes while rotating the circular tube separately and cooling in cold water for 5 minutes, the low-viscosity material on the central side of the circular tube was discharged (the viscosity of the effluent was 800 poise). In the hollow part of the resulting cylindrical tube, 100 parts by weight of benzyl methacrylate (refractive index 1.568 after polymerization), 0.04 parts by weight of 2,2'-azobis- (2,4-dimethylvaleronitrile), 1-hydroxycyclohexylphenyl After mixing with 0.2 part by weight of ketone and purging with nitrogen, heat the mixture for 60 minutes at 65 ° C and fill it for 15 minutes.
It was left still at 30 ° C. Then, light was irradiated for 60 minutes while rotating the cylindrical tube at a distance of 10 cm from the three fluorescent lamps to obtain a cylindrical cured product having a diameter of 1 cm and a length of 70 cm. This cylindrical cured product is
A fiber with an outer diameter of 1.0 mm was created by heat drawing while indirectly heating in a cylindrical heating cylinder set at 50 ° C.
Transmission loss and transmission band were measured. As a result, the transmission loss was 200 dB / km and the transmission band was 320 MHz · km.

[0023]

EXAMPLE 3 60 parts by weight of 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 40 parts by weight of methyl methacrylate (refractive index 1.436 after copolymerization), 2,2'-azobis -(2,4-Dimethylvaleronitrile) 0.04 parts by weight and 1-hydroxycyclohexyl phenyl ketone 0.2 parts by weight were mixed, and after nitrogen substitution, what was heated at 60 ° C for 70 minutes was filled in a polyethylene cylindrical tube. . Next, 3 fluorescent lights (40 cm, 20
Light was irradiated for 30 minutes while rotating the circular tube at a distance of 10 cm from W), cooled in cold water for 5 minutes, and then the low-viscosity material on the central side of the circular tube was discharged (the viscosity of the effluent was 1050 poise). ).
In the hollow part of the cylindrical tube generated by this, 50 parts by weight of benzyl methacrylate, 50 parts by weight of methyl methacrylate, 2,2'-
Azobis- (2,4-dimethylvaleronitrile) 0.04 parts by weight,
After mixing with 0.2 part by weight of 1-hydroxycyclohexyl phenyl ketone, purging with nitrogen, and heating at 60 ° C for 90 minutes, 30 parts by weight of 2,2,2-trifluoroethyl methacrylate was added and mixed (copolymerization The subsequent refractive index of 1.502) was filled and the mixture was allowed to stand at 30 ° C. for 20 minutes. Then from three fluorescent lamps
Light was irradiated for 60 minutes while rotating the cylindrical tube at a distance of 10 cm to obtain a cylindrical cured product having a diameter of 1 cm and a length of 60 cm. This cylindrical cured product was subjected to thermal drawing while being indirectly heated in a cylindrical heating cylinder set at 200 ° C. to prepare a fiber having an outer diameter of 0.7 mm, and the transmission loss and the transmission band were measured. As a result, the transmission loss was 190 dB / km and the transmission band was 330 MHz · km.

[0024]

Example 4 100 parts by weight of methyl methacrylate (refractive index after polymerization 1.489), 0.04 parts by weight of 2,2′-azobis- (2,4-dimethylvaleronitrile), and 0.2 parts by weight of 1-hydroxycyclohexylphenylketone were used. After mixing and purging with nitrogen, 60
What was heated at 0 ° C. for 20 minutes was filled in a polyethylene cylindrical tube. Next, 10cm from 3 fluorescent lamps (40cm, 20W)
After irradiating with light for 25 minutes while rotating the circular tube separately and cooling in cold water for 5 minutes, the low viscosity substance on the center side of the circular pipe was allowed to flow out (viscosity of the effluent was 700 poise). In the hollow part of the resulting cylindrical tube, 30 parts by weight of benzyl methacrylate and 70 parts by weight of methyl methacrylate (refractive index after copolymerization
1.513) was mixed with 0.04 parts by weight of 2,2'-azobis- (2,4-dimethylvaleronitrile) and 0.2 parts by weight of 1-hydroxycyclohexyl phenyl ketone, and after substituting with nitrogen, 25 at 60 ° C.
After heating for one minute, it was filled and left standing at 28 ° C. for 10 minutes. Subsequently, while the cylindrical tube was rotated 10 cm away from the three fluorescent lamps, the cylindrical tube was irradiated with light for 20 minutes, cooled in cold water for 5 minutes, and then the low-viscosity material on the center side of the cylindrical tube was similarly discharged (effluent. Had a viscosity of 900 poise). In the hollow part of the cylindrical tube generated by this, 70 parts by weight of benzyl methacrylate, 30 parts by weight of methyl methacrylate (refractive index 1.5443 after copolymerization), 2,2'-
Azobis- (2,4-dimethylvaleronitrile) 0.04 parts by weight,
After mixing with 0.2 part by weight of 1-hydroxycyclohexyl phenyl ketone and purging with nitrogen, what was heated at 60 ° C. for 30 minutes was filled and left standing at 28 ° C. for 20 minutes. Subsequently, light was irradiated for 65 minutes while rotating the cylindrical tube at a distance of 10 cm from the three fluorescent lamps to obtain a cylindrical cured product having a diameter of 1 cm and a length of 70 cm. The cylindrical cured product was thermally stretched while being indirectly heated in a cylindrical heating cylinder set at 250 ° C. to prepare a fiber having an outer diameter of 0.75 mm, and the transmission loss and the transmission band were measured. As a result, transmission loss is 185 dB / km, transmission band is 380 MHz.
It was km.

Front Page Continuation (72) Inventor Yoshihiro Uozu 20-1 Miyukicho, Otake, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory

Claims (2)

[Claims] 1. A polymerization-cured polymer in a cylindrical tubular preform made of a mixture of a polymer and a monomer, which has a viscosity of 10,000 poise or more and has a refractive index of n ₁ after the polymerization and curing. It is characterized by being filled with a monomer having a refractive index of n ₂ (where n ₂ > n ₁ ) afterward, allowing the monomers contained in both phases to mutually diffuse, and polymerizing and curing with a refractive index distribution. And a method of producing a graded index optical fiber. 2. A cylindrical tubular preform made of a mixture of a polymer and a monomer, the viscosity of which is 10,000 poise or more, and the refractive index of the polymer after polymerization and curing is n _1. N ₂ (where n ₂ > n ₁ ) is filled with a mixture of a monomer and a polymer, and the monomers contained in both phases are interdiffused to give a cylindrical body a refractive index distribution. A method for producing a graded-index optical fiber, which comprises stretching a columnar material that has been polymerized and cured in step 1.