JPH09218312A - Production of preform for graded index plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a preform for a graded index plastic optical fiber having a refractive index distribution smooth in a radial direction and, in some cases, uniform in a longitudinal direction. SOLUTION: A plastic rod including a compd. having a high refractive index is swollen by the monomers forming the plastic of this rod. The monomers and the compds. having the high refractive index are diffused with each other in the rod. The diffused monomers and the monomers around the rod are then polymerized. In some cases, the monomers are polymerized while a monomer soln. contg. the compd. having the high refractive index at the time of producing the plastic rod.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a preform for a gradient index plastic optical fiber.

[0002]

2. Description of the Related Art Refractive index distribution type [GI (graded index)]
Mold] A method for manufacturing a preform for a plastic optical fiber is disclosed in JP-A-7-5329 and JP-A-7-533.
No. 1 publication. In these methods, in order to form a refractive index distribution, a plurality of solutions (coating solutions) having different refractive indexes are used, and the solutions are sprayed or coated. Since the solution does not flow, it must have a certain degree of viscosity, but it is difficult to apply a highly viscous solution uniformly. On the other hand, the viscosity that can be applied causes liquid sagging.

Further, since the viscosity of the solution affects the thickness of the formed layer, it is necessary to precisely adjust the viscosity. However, the viscosity should be constantly adjusted to be constant by evaporation of volatile components such as a solvent. It is difficult. Even if the coating or spraying conditions are controlled, it is very difficult to make the refractive index distribution uniform in the length direction and / or the radial direction. Moreover, it is difficult to completely remove the solvent and the like from the applied solution layer, and the solvent remaining in the preform forms bubbles in the drawing step. Moreover, bubbles are highly likely to be generated due to rapid evaporation of the solvent. These bubbles increase the transmission loss of the optical fiber. The residual solvent also increases the transmission loss.

Japanese Unexamined Patent Publication (Kokai) No. 7-13029 discloses a method of growing a graded index plastic optical fiber preform by spraying raw material vapors having different blending ratios and thus different refractive indexes onto the lower end portion of the support rod. Has been done. However, with this method, it is considered difficult to accurately control the thickness of each layer and form the refractive index distribution in a predetermined manner. A method of manufacturing a gradient index plastic optical fiber is described in Japanese Patent Application Laid-Open No. 7-27928. This method involves dispersing a refractive index distribution in a polymer molded product by diffusing a transparent non-polymerizable compound having compatibility with the polymer and a different refractive index into the transparent polymer molded product. To form. However, it is almost impossible to precisely control the refractive index distribution by diffusion. Since there is a part where the refractive index is low, or there is a boundary between the part where the refractive index is high and the part where the refractive index is low, a continuous refractive index distribution cannot be obtained. In addition, the plastic fiber must be heated to a high temperature for diffusion, which can cause the fiber to stretch or melt,
The fiber cannot be manufactured stably. Further, if the operation is performed under tension, the fiber may be cut due to the solvent crack.

Further, Japanese Patent Application Laid-Open No. 63-218903 discloses a method for manufacturing a synthetic resin optical transmission medium and an array. In this method, a monomer which forms a polymer having a refractive index different from that of the polymer is diffused in a base material made of a transparent network polymer. However, when the matrix polymer is reticulated, it has a drawback that it is difficult to stretch.

[0006]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a method capable of producing a gradient index plastic optical fiber preform having a radially smooth gradient index at a relatively low temperature. That is. A second object of the present invention is to provide a graded-index plastic optical fiber preform that has a uniform refractive index distribution in the radial direction and the longitudinal direction, does not increase transmission loss, and does not lower the transmission band. It is to provide a method that can be manufactured at a low temperature.

[0007]

According to the present invention, the above object is to provide a plastic rod containing a compound having a high refractive index,
For a gradient index plastic optical fiber comprising swelling with a monomer forming the plastic, diffusing the monomer and the compound having a high refractive index into each other in the rod, and polymerizing the diffused monomer and the monomer around the rod Method for producing preform, and polymerization of a monomer solution containing a compound having a high refractive index with stirring to form a plastic rod containing a compound having a high refractive index, and the plastic rod is swollen with a monomer forming the plastic. And a method for producing a preform for a gradient index plastic optical fiber, which comprises mutually diffusing the monomer and the compound having a high refractive index in a rod and polymerizing the diffused monomer and the monomer around the rod. You can

The plastic forming the optical fiber preform is preferably a colorless and highly transparent polymer. As a monomer giving such a polymer, the following methacrylic acid ester, acrylic acid ester,
Examples thereof include styrene compounds, fluorinated acrylic acid esters, fluorinated methacrylic acid esters, and the like: (a) Methacrylic acid ester and acrylic acid ester Methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate. , Benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, methyl acrylate, ethyl acrylate, t-butyl acrylate, etc .; (b) Styrene compounds styrene, α-methylstyrene, chlorostyrene, bromo Styrene, dichlorostyrene, dibromostyrene, etc .; (c) Fluorinated acrylic acid ester 2,2,2-trifluoroethyl acrylate, etc .; (d) Fluorinated ethyl methacrylate 1,1,2-trifluoroethyl methacrylate, etc. In the present invention, the refractive index can be adjusted by appropriately selecting and using one kind or two or more kinds from the above monomers.

Such a monomer is preferably radical-polymerized in the presence of a compound having a refractive index higher than that of the polymer, preferably a non-polymerizable compound, and molded to produce a preform rod. Such compounds are highly compatible with the monomers and polymers and preferably have a high boiling point, for example 200 ° C. or higher. It also preferably has a refractive index at least 0.02 higher than the polymer.

Examples of such high refractive index compounds include hexyl acetate, bis (2-methylhexyl) phthalate, dimethyl phthalate, benzyl benzoate, and diphenyl sulfide, depending on the type of plastic. Two or more types are selected.

A compound having a high refractive index and a monomer are mixed,
If it is polymerized as it is, the high refractive index compound may not be uniformly dispersed in the plastic rod. If the high-refractive-index compound is non-uniformly dispersed, the solubility of the monomers may partially differ, and the refractive index distribution of the resulting preform may be disturbed in the length direction or transmission loss may increase. . Further, the molecular weight becomes non-uniform in the length direction of the rod, which may cause disorder of the refractive index distribution and increase of transmission loss. Also, the disorder of the refractive index distribution leads to a reduction in the transmission band.

Therefore, in one form of the present invention, a monomer solution containing a high refractive index compound is polymerized while stirring in a vertical container to form a plastic rod. The stirring may be performed by any method as long as the monomer solution can be uniformly stirred.For example, a method of rotating a magnetic stirrer provided in the container with a magnet from the outside of the container, or putting a rotary blade in the container It can be carried out by a method of taking out the rotor blades when the solution has a predetermined viscosity.

Next, when the obtained plastic rod is dipped in the monomer to swell, the high refractive index compound in the rod diffuses toward the periphery of the rod, and the monomer diffuses toward the center. As a result, a refractive index distribution that is high at the center and decreases toward the periphery is formed in the radial direction of the rod, and therefore the plastic rod can be suitably used as a preform for manufacturing a gradient index optical fiber.

The monomer diffused in the rod and the monomer around the rod are polymerized to complete the preform. The polymerization can be promoted by heating, irradiation with radiation (for example, irradiation with ultraviolet rays) or the like depending on the type of the monomer. In the case of heating, it is not necessary to raise the temperature so that the polymer melts, and the polymerization can be performed at a relatively low temperature at which the monomer does not volatilize.

[0015]

Example 1 Purified methyl methacrylate (MMA) and benzyl benzoate (BEN) were mixed at a weight ratio of 5: 1, and 0.5% by weight of azoisobutyronitrile (AIBN) was used as a polymerization initiator.
And n-butyl mercaptan 0.2 as a chain transfer agent
0% by weight was added to 40 in a cylindrical polymerization tube with an inner diameter of 12 mm.
Polymerization was performed at 48 ° C for 48 hours. The obtained polymer was in a slightly soft state because it contained benzyl benzoate. This was molded by holding it in the center of a cylindrical polymerization container having an inner diameter of 18 mm.

0.4% by weight of AIBN and a chain transfer agent n
-Butyl mercaptan Methyl methacrylate added with 0.15% by weight is put into a cylindrical container having an inner diameter of 18 mm,
The obtained plastic rod was immersed at 35 ° C. for 24 hours to be swollen.

The monomers in the swollen plastic rod and the surrounding monomers were polymerized by gradually heating from 35 ° C. and heating at 95 ° C. for 20 hours and then 110 ° C. for 10 hours. Since the monomer was polymerized without moving in the rod, the rod solidified to form the core portion while maintaining the concentration gradient of benzyl benzoate. Further, the monomer in the cylindrical container around the rod was also polymerized to form a clad. When the distribution state of the refractive index was measured by an interference microscope, it was found to have a refractive index distribution as shown in FIG.

Example 2 Purified MMA and BEN were mixed at a weight ratio of 5: 1, and 0.1% by weight of AIBN as a polymerization initiator and 0.12% by weight of n-butyl mercaptan as a chain transfer agent were added, and the mixture was stood upright. In a glass cylindrical closed polymerization container (outer diameter 21 mm, inner diameter 18 mm) held in an oxygen-free atmosphere at 100
Polymerized at ° C. During the polymerization, the solution was stirred at about 1000 rpm by a magnetic stir bar provided at the bottom of the vessel. The rotation was stopped when the viscosity reached 1000 poise. As a stirrer, a Teflon (registered trademark) -coated cylindrical magnet having a diameter of 3 mm and a length of 6 mm was used.

The inner diameter of an MMA containing 0.1% by weight of di-t-butyl peroxide (perbutyl D) and 0.15% by weight of the chain transfer agent n-butyl mercaptan. The obtained plastic rod was immersed in a cylindrical cylindrical container of mm for 24 hours at room temperature to be swollen.

The monomer in the swollen plastic rod and the surrounding monomer were polymerized by gradually heating from room temperature and heating at 95 ° C. for 20 hours and then at 110 ° C. for 10 hours. Since the monomer was polymerized without moving in the rod, the rod solidified to form the core portion while maintaining the concentration gradient of benzyl benzoate. Further, the monomer in the cylindrical container around the rod was also polymerized to form a clad.

The gradient index plastic optical fiber preform thus manufactured was molded into a fiber by drawing by heating and melting, and the transmission loss and the transmission band of the fiber were measured. Transmission loss is measured from one fiber to 10
20 fibers with a length of m are cut out and 10m each
Was measured by a cutback of 1 m. The loss values of 20 fibers were compared. As a result, the average loss value was 157 dB / km, and the change in loss value in the length direction (max-min 16 dB / km) was ± 8 dB / km. The transmission band was 2 GHz · 100 m.

Example 3 Purified MMA and diphenyl sulfide in a weight ratio of 5: 1
, 0.1% by weight of AIBN as a polymerization initiator and 0.12% by weight of n-butyl mercaptan as a chain transfer agent were added, and a cylindrical cylindrical polymerization vessel made of glass (outer diameter 21 mm, inner diameter 18 mm) held in a standing state Polymerization was performed at 110 ° C. in an oxygen-free atmosphere. During the polymerization, the solution was stirred at about 800 rpm with a 10 mm diameter screw blade. The rotation was stopped when the viscosity reached 5000 poise.

MMA containing 0.1% by weight of di-t-butyl peroxide (perbutyl D) and 0.15% by weight of a chain transfer agent, n-butyl mercaptan, was placed in a cylindrical container having an inner diameter of 27 mm and obtained. The plastic rod was immersed at room temperature for 24 hours to allow it to swell.

The monomer in the swollen plastic rod and the surrounding monomer were polymerized by gradually heating from room temperature to 95 ° C. for 20 hours and then 110 ° C. for 10 hours. Since the monomer was polymerized without moving in the rod, the rod solidified to form the core portion while maintaining the concentration gradient of diphenyl sulfide. Further, the monomer in the cylindrical container around the rod was also polymerized to form a clad.

The gradient index plastic optical fiber preform thus manufactured was molded into a fiber by drawing by heating and melting, and the transmission loss and the transmission band of the fiber were measured in the same manner as in Example 2. As a result, the average loss value was 140 dB / km, and the change in loss value in the length direction was also ± 7 dB / km. Also, the transmission band is 2 GHz
・ It was 100 m.

[0026]

According to the manufacturing method of the present invention, a gradient index plastic optical fiber preform having a smooth gradient index distribution in the radial direction can be manufactured at a relatively low temperature. Since the monomer is used as the swelling liquid, the problem of "solvent removal" found in the prior art using a solvent does not occur. Furthermore, when the monomer solution is polymerized while stirring to produce a plastic rod, the refractive index distribution type plastic has a uniform refractive index distribution in the radial direction and the length direction, does not increase the transmission loss, and does not lower the transmission band. An optical fiber preform is obtained.

[Brief description of drawings]

FIG. 1 is a view showing a refractive index distribution of a preform for a plastic optical fiber obtained in Example 1.

Claims (2)

[Claims] 1. A plastic rod containing a compound having a high refractive index is swollen by a monomer forming the plastic, the monomer and the compound having a high refractive index are mutually diffused in the rod, and the diffused monomer and the surroundings of the rod. A method for producing a preform for a gradient index plastic optical fiber, which comprises polymerizing the above monomer. 2. A polymer solution containing a compound having a high refractive index is polymerized with stirring to form a plastic rod containing a compound having a high refractive index, and the plastic rod is swollen with a monomer forming the plastic, In which the monomer and the high refractive index compound are mutually diffused,
A method for producing a preform for a gradient index plastic optical fiber, which comprises polymerizing a diffused monomer and a monomer around a rod.