JPH09133820A - Manufacture of preform for gradient index plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture the preform for the gradient index optical fiber which has a constant refractive index distribution both and radially. SOLUTION: First molten plastic having a 1st refractive index is poured into the center part of a cylindrical metal mold which has at least two concentric partitions inside, and the innermost partition is removed after the 1st plastic is cooled and hardened. Then 2nd molten plastic having a 2nd refractive index is poured into between the 1st plastic part in the center and the next partition and the circumferential partition are removed after the 2nd plastic is cooled and hardened. Then the pouring of next plastic, cooling and hardening, and the removal of a partition are repeated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method of manufacturing a preform for a gradient index plastic optical fiber,
More specifically, the present invention relates to a method for manufacturing a plastic optical fiber preform by sequentially molding a plurality of melts of plastics having different refractive indexes into concentric circles.

[0002]

2. Description of the Related Art Refractive index distribution type [GI (graded index)]
[Type] Plastic A method for manufacturing a plastic for an 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.

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.

Another method for producing a graded index plastic optical fiber plastic is disclosed in Japanese Patent Laid-Open No. 7-2792.
No. 84 is described. This method, by diffusing a transparent non-polymerizable compound having a different refractive index, which is compatible with the polymer, into a molded product of the transparent polymer,
A refractive index distribution is formed in the polymer molding. However, it is almost impossible to precisely control the refractive index distribution by diffusion.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel method for producing a preform for a graded index plastic optical fiber whose graded index distribution is constant in the longitudinal and radial directions.

[0007]

In order to solve the above-mentioned problems, the present invention provides a first mold having a first refractive index at the center of a cylindrical mold having at least two concentric partitions therein.
After the plastic melt is poured and the first plastic melt is cooled and solidified, the innermost partition is removed, and then the second plastic part is inserted between the first plastic part in the center and the next partition.
A second plastic having a refraction index of, a second plastic is cooled and solidified, and then the surrounding partition is removed, and then the next plastic is poured, cooling and solidification and removal of the partition are repeated. A method of manufacturing a preform for a distributed plastic optical fiber is provided.

The mold used in the manufacturing method of the present invention comprises two or more partitions whose cross sections are concentric circles.
It has it inside the mold. Thus, the mold interior has a central cylindrical portion and at least two compartments surrounding it. The number of this section is appropriately selected according to the distribution of the refractive index and is usually 2 to 9, preferably 3 to 6. The thickness of each plastic layer may be appropriately set based on the diameter of the obtained preform and the stretching ratio when manufacturing the optical fiber.

The mold is made of metal, preferably stainless steel, and the peripheral wall of the mold and the inner surface of the partition are preferably well polished. With this alone, the partition can be easily removed from the cooled and solidified plastic, but if the inner surface is plated with chrome or laminated with a film of fluororesin (polytetrafluoroethylene or the like), the releasability is improved.

The plastic used in the present invention may be the plastic used in conventional plastic optical fibers, for example, a polymer based on methyl methacrylate or benzyl methacrylate is preferably used. Further, monomers such as styrene and vinyl acetate can also be used.

In order to adjust the refractive index of plastics, it is sufficient to use a base monomer and a comonomer having a refractive index different from that of the base, and change the polymerization ratio thereof.
For example, benzyl methacrylate (refractive index 1.592)
(Note that the refractive index indicates the refractive index of a homopolymer.) Methyl methacrylate (refractive index 1.492) is copolymerized at various ratios to obtain refractive indices of 1.592 and 1.4.
It is possible to produce plastics which have changed between 92 and.

In another method, plastics having different refractive indexes may be prepared by adding a compound that changes the refractive index to the base plastic in various proportions. Further, two or more kinds of plastics having different refractive indexes can be blended and used in various ratios.

In the manufacturing method of the present invention, first, the melt of the first plastic having the first refractive index is injected into the center of the mold, and after holding the pressure, it is cooled and solidified. Then remove the innermost partition. Next, a melt of the second plastic having the second refractive index is injected between the central plastic cylinder and the second partition, and after holding the pressure, it is cooled and solidified, and the second partition is removed. A preform is molded by sequentially repeating the series of operations of injecting the plastic melt, cooling and solidifying, and removing the partition toward the outside.

[0014]

EXAMPLES Next, the present invention will be specifically described by showing Examples. Example 1 Purified methyl methacrylate and benzyl methacrylate were used in the proportions shown in Table 1 below, with 0.5% by weight of benzoyl peroxide as a polymerization initiator and 0.2% by weight of n-butyl mercaptan as a chain transfer agent. After addition, polymerization was carried out in a nitrogen atmosphere at 40 ° C. for 20 hours, and then heat treatment was carried out at 100 ° C. for 20 hours to produce 5 kinds of plastics.

[0015]

[Table 1] Plastics Methacrylic acid Methacrylic acid Refractive index number Benzyl (vol%) Methyl (vol%) 1 100 0 1.568 2 82 18 1.554 3 57 43 1.535 4 21 79 1.508 5 0 100 100.492

180 to 20 plastics 1 as the core
After melting at 0 ° C., pouring into the center of the mold, holding the pressure, cooling and solidifying, the innermost partition was removed. Next, between the center plastic rod and the second partition, the plastic 2 was melted and injected at 180 to 200 ° C., and after the pressure was maintained, it was cooled and solidified, and then the second partition was removed.
Plastics 3 to 5 were concentrically molded in the same procedure to obtain a preform having a diameter of 20 mm. The diameter of the central rod is 4.0 mm, and the thickness of the layers of plastics 2-5 are 1.8 mm, 1.6 mm and 1.6 mm, respectively.
And 3.0 mm. When the refractive index distribution was measured, the distribution was as shown in FIG.

[0017]

According to the present invention, it is possible to easily manufacture a preform for a plastic fiber having a refractive index distribution type in which the refractive index distribution is uniform both in the longitudinal direction and in the radial direction.

[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 first mold having a first index of refraction at the center of a cylindrical mold having at least two concentric partitions therein.
After the plastic melt is poured and the first plastic melt is cooled and solidified, the innermost partition is removed and then the second plastic part is inserted between the first plastic part in the center and the next partition.
A second plastic having a refraction index of, a second plastic is cooled and solidified, and then the surrounding partition is removed, and then the next plastic is poured, cooling and solidification and removal of the partition are repeated. Manufacturing method of preform for distributed plastic optical fiber.