JPH09178959A - Production of preform for distributed refractive index plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a preform which does not require the removal of a solvent and has a smooth refractive index distribution in a radial direction by applying a polymer which forms a clad and a solvent prepd. by dissolving a compd. for refractive index adjustment into a monomer constituting the polymer around a rod. SOLUTION: The polymer forming the clad and the solvent prepd. by dissolving the compd. for refractive index adjustment into the monomer constituting the polymer are applied around the plastic rod and the monomer is polymerized by irradiation with radiation or by heating. The soln. of the compsn. changed in refractive index is then applied thereon and the monomer is polymerized. the procedure is repeated. The plastic for forming the preform is preferably a colorless polymer having high transparency. The monomers to yield such polymer include methacrylate and styrene compds. The compd. for refractive index adjustment includes hexyl acetate, bis(2-methyl hexyl) phthalate, etc.

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 suitable for high speed optical communication.

[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. In addition, the plastic fiber must be heated to a high temperature for diffusion, but when heated to a high temperature, the fiber is stretched or melted, so that the fiber cannot be stably manufactured. 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 It is an object of the present invention to provide a method for producing a preform for a gradient index plastic optical fiber having a smooth gradient refractive index distribution in the radial direction, which does not require solvent removal. Is.

[0007]

According to the present invention, the above object is to provide a solution of a polymer forming a clad and a compound for adjusting the refractive index in a monomer constituting the polymer around a plastic rod. It can be solved by a method for producing a gradient index plastic optical fiber, which comprises coating and polymerizing a monomer.

The plastic forming the optical fiber preform is preferably a colorless and highly transparent polymer. Examples of the monomer that gives such a polymer include the following methacrylic acid esters, styrene compounds, fluorinated acrylic acid esters, and fluorinated methacrylic acid esters: (a) Methacrylic acid ester Methyl methacrylate , Ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, 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. In order to ensure transparency, it is preferable to use one kind of monomer.

When only one type of monomer is used, a refractive index adjusting compound having a refractive index difference from the polymer of at least 0.02 is used, and the total refractive index is adjusted by the concentration of the compound. As the compound for adjusting the refractive index, a compound which is non-polymerizable, has good compatibility with the monomer and the polymer, and has a high boiling point, for example, a boiling point of 200 ° C. or higher is preferable. When using a low refractive index compound, the concentration of the low refractive index compound is increased from the center to the outside, and conversely, when using a high refractive index compound, the concentration is decreased.

As such a compound for adjusting the refractive index,
Base monomers from hexyl acetate, bis (2-methylhexyl) phthalate, sebacate ester (eg dibutyl sebacate), adipate ester (eg dihexyl adipate), dimethyl phthalate, benzyl benzoate, diphenyl sulfide, etc. 1 depending on the type of
One kind or two or more kinds are selected.

When two or more kinds of monomers are used, it is preferable to select monomers having different refractive indexes and having similar reactivity ratios. However, when two or more kinds of monomers are copolymerized, the transmission loss increases due to the phase separation due to the microscopic non-uniform structure. Therefore, it is preferable to use only one type of monomer and a non-polymerizable refractive index adjusting compound.

A solution in which a polymer and a compound for controlling the refractive index are dissolved in a monomer is applied around the rod, and the monomer is polymerized by an appropriate means depending on the kind of the monomer, for example, irradiation with radiation (ultraviolet rays) or heating. Let Then, a solution having a composition with a different refractive index is applied to polymerize the monomer.
Repeat this procedure. In the case of heating, it is not necessary to raise the temperature so as to melt the polymer, and the polymerization is carried out within the temperature range below the glass transition point and the temperature at which the polymerized layer is dissolved in the monomer.

The solution containing the polymer and the compound for controlling the refractive index can be prepared by dissolving the polymer polymerized in advance and the compound for controlling the refractive index in the monomer, but the compound for controlling the refractive index is dissolved in the monomer. Then, the monomers may be partially polymerized, for example 50 to 70%, to form a polymer in solution. The latter method is preferred for obtaining a highly pure solution. If the viscosity of the solution is too low, dripping and nonuniformity of the coating film occur. On the other hand, if the viscosity is too high, it becomes difficult to apply it to the rod surface. Therefore, the viscosity is preferably 5000
It is in the range of 100,000 poise.

Finally, a fluororesin having a low refractive index is laminated as a cladding layer to complete the preform.

According to the manufacturing method of the present invention, when the solution is applied to the plastic rod, the plastic of the rod or the previously formed polymer layer is partially swollen by the monomer, and the refractive index adjusting member is directed toward the center of the rod. Since there is no diffusion between the layers, there is no boundary in the concentration of the compound for adjusting the refractive index, and the refractive index distribution becomes smooth. Further, since the solvent is not used, it is not necessary to remove the solvent, so there is no problem caused by the removal of the solvent found in the prior art.

[0016]

EXAMPLES Example 1 Methyl methacrylate to benzoyl peroxide (polymerization initiator)
To add 0.3% by weight and 0.2% by weight of n-butyl mercaptan (chain transfer agent), polymerize in a cylindrical polymerization tube previously purged with nitrogen gas at 60 ° C. for 20 hours, and further to complete the polymerization. At 90 ° C for 10 hours and 110 ° C for 1 hour
Heated after 10 hours. This was extruded at a melting temperature of 190 ° C. to obtain a center rod having a diameter of 4 mm. Separately, 0.5% benzoyl peroxide (polymerization initiator) in methyl methacrylate
% By weight and n-butyl mercaptan (chain transfer agent)
0.2 wt% was added, and polymerization was carried out at 60 ° C. in a reaction vessel filled with nitrogen gas. When the polymerization rate reached 60%, heating was stopped to stop the polymerization. During the coating process below, in order to change the refractive index, dibutyl sebacate was added at a constant rate,
The concentration in the solution was changed from 0% by volume to 25% by volume.

The rotating center rod was coated with the first gel solution which gives the polymer having the lowest refractive index, and was irradiated with ultraviolet rays in a nitrogen atmosphere to be polymerized. The gel solution was applied so that the diameter was increased at a rate of 1 mm / hour while proceeding with polymerization by ultraviolet rays. After 4 hours, the supply of the gel solution was stopped and the polymerization was continued for 3 hours. Then, the product rod was heated from 60 ° C. to 110 ° C. to complete the polymerization.

An optical fiber was manufactured by drawing the obtained rod. When the refractive index of the obtained optical fiber was measured by an interference microscope, the refractive index distribution was smooth as shown in FIG.

[0019]

According to the production method of the present invention, since a monomer is used as a solvent of a polymer solution and the monomer is polymerized and used as a component of a rod, it is not necessary to remove the solvent and the refractive index distribution It is also easy to control.

[Brief description of the drawings]

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

Claims (1)

[Claims] 1. A gradient index type which comprises coating a solution of a polymer for forming a clad and a compound for controlling the refractive index in a monomer constituting the polymer around the plastic rod, and polymerizing the monomer. Manufacturing method of plastic optical fiber.