JP2000347044A - Plastic optical fiber preform and production of plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic optical fiber preform which makes it possible to obtain nearly constant transmission loss along the longitudinal direction of a plastic optical fiber and a process for producing the plastic optical fiber. SOLUTION: The process for producing the plastic optical fiber 5 formed by coaxial superposition of resin bodies 1 and 2 having refractive indices varying from each other includes a stage for coaxially arranging the resin bodies 1 and 2 having the refractive indices varying from each other, a stage for heat treating the resin bodies 1 and 2 in such a manner that the volatile component contents in the resin bodies 1 and 2 attain <=1 wt.% and a stage for obtaining the preform 5 by thermally fusing the resin bodies 1 and 2. In such a case, the resin bodies 1 and 2 are heat treated before the thermal fusing of the resin bodies, by which the boundary irregularity along the longitudinal direction of the resin bodies 1 and 2 is sufficiently eliminated. The volatile components are sufficiently removed from the resin bodies 1 and 2 at the time of the thermal fusing and, therefore, the generation of the volatile components may be sufficiently prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical fiber preform and a method of manufacturing a plastic optical fiber, and more particularly, to a plastic optical fiber preform and a plastic optical fiber whose refractive index increases from the outside toward the center. The present invention relates to a method for manufacturing a fiber.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of manufacturing a solid plastic optical fiber preform by heating and fusing a hollow cylindrical body whose refractive index increases from the outside toward the center. (For example, Japanese Patent Laid-Open No.
No. 4). In Japanese Patent Application Laid-Open No. 5-107404,
While maintaining the inside of the hollow pipe in a reduced pressure state, the pipe is heated by passing it through a ring-shaped heating element, and continuously stretched from the lower part of the pipe, thereby forming a cylindrical plastic. A method for manufacturing an optical fiber preform is disclosed.

[0003]

However, if a cylindrical plastic optical fiber preform is manufactured by the above-described conventional manufacturing method, the plastic optical fiber obtained by drawing the preform will be stretched along its longitudinal direction. In some cases, the transmission loss was uneven.

The present invention has been made in view of such circumstances, and a plastic optical fiber preform and a method of manufacturing a plastic optical fiber capable of obtaining a substantially constant transmission loss along the longitudinal direction of the plastic optical fiber. The purpose is to provide.

[0005]

As a result of studying the above-mentioned conventional method for manufacturing a plastic optical fiber preform, the present inventors have obtained a constant transmission loss along the longitudinal direction of the plastic optical fiber preform. The cause was found to be due to irregularities in the interface of the fused surface. And we have:
As a result of further intensive research, before the heat fusion of the pipe-shaped body,
By heat-treating the pipe-shaped body so that the amount of volatile components in the pipe-shaped body is equal to or less than a predetermined value, the interface irregularity of the plastic optical fiber preform obtained by heat fusion can be sufficiently eliminated, and as a result, the plastic The inventors have found that the transmission loss of the optical fiber is substantially constant along the longitudinal direction, and completed the present invention.

That is, the present invention relates to a method of manufacturing a plastic optical fiber preform comprising a plurality of resin bodies having mutually different refractive indices overlapping each other coaxially, and comprising a plurality of cylindrical bodies having mutually different refractive indices. An arranging step of coaxially disposing the resin body, and a heat treatment step of heat-treating the resin body so that the amount of volatile components in the resin body is 0.1% by weight or less.
A step of thermally fusing the plurality of resin bodies to obtain a plastic optical fiber preform in which the plurality of resin bodies are coaxially overlapped with each other.

According to the present invention, by performing a heat treatment on the resin body before heat-sealing the resin body, interface irregularities in the resin body along its longitudinal direction are sufficiently removed. Further, at the time of heat fusion, since volatile components are sufficiently removed from the resin body before the heat fusion of the resin body, generation of volatile components can be sufficiently prevented. If the amount of volatile components in the resin body exceeds 0.1% by weight before the heat fusion of the resin body, the interface irregularities of the resin body cannot be sufficiently removed, and the interface between the resin bodies during the heat fusion of the resin body. Volatile components are easily generated.

The present invention also relates to a method for producing a plastic optical fiber comprising a plurality of resin bodies having mutually different refractive indices overlapping each other coaxially, and comprising a plurality of cylindrical resin having mutually different refractive indices. Arranging the bodies coaxially, heat-treating the resin body so that the amount of volatile components in the resin body is 0.1% by weight or less, and drawing while thermally bonding the plurality of resin bodies. And obtaining a plastic optical fiber.

According to the present invention, by subjecting the resin body to heat treatment before the resin body is heat-sealed, interface irregularities in the resin body along its longitudinal direction are sufficiently removed. In addition, since the plurality of resin bodies are drawn simultaneously with the heat fusion, a plastic optical fiber can be obtained directly from the plurality of resin bodies arranged coaxially without passing through the form of the base material. For this reason, the number of steps required for manufacturing is reduced, and the production efficiency is improved. At this time, when the fusion bonding of the resin body is performed, the volatile component is sufficiently removed from the resin body before the thermal fusion of the resin body, so that the generation of the volatile component can be sufficiently prevented. Before the thermal fusion of the resin body, the amount of volatile components in the resin body is 0.1%.
When the content is more than 10% by weight, the irregularity of the interface between the resin bodies cannot be sufficiently removed, and volatile components tend to be generated at the interface between the resin bodies during the thermal fusion of the resin bodies.

The present invention also relates to a method of manufacturing a plastic optical fiber comprising a plurality of resin bodies having different refractive indices overlapping each other coaxially, wherein a plurality of cylindrical resin having different refractive indices are provided. A coaxial arrangement of the bodies, a heat treatment step of heat-treating the resin body so that the amount of volatile components in the resin body is 0.1% by weight or less, and a plastic light by heat-sealing the plurality of resin bodies. A fusion process of obtaining a fiber preform, and drawing a plastic optical fiber preform,
A drawing step of obtaining a plastic optical fiber in which a plurality of resin bodies are coaxially overlapped with each other.

According to the present invention, by subjecting the resin body to heat treatment before the resin body is heat-sealed, interface irregularities in the resin body along its longitudinal direction are sufficiently removed. During the thermal fusion of the resin body, the volatile component is sufficiently removed from the resin body before the thermal fusion of the resin body, so that the generation of the volatile component can be sufficiently prevented. When the plastic optical fiber preform thus obtained is drawn, a plastic optical fiber having a low transmission loss along the longitudinal direction and a constant plastic optical fiber is obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a plastic optical fiber according to the present invention will be described below with reference to the drawings. FIG.
FIG. 2 is a series of process diagrams of a method for manufacturing a plastic optical fiber (hereinafter, referred to as “POF”) preform.

In the production of POF, first, a POF base material is produced. In this case, first, a plurality of cylindrical resin bodies 1 and 2 are prepared, and as shown in FIG. 1A, these resin bodies 1 and 2 are arranged coaxially (arrangement step). At this time, a columnar resin body 3 may be prepared, and this resin body 3 may be inserted into the opening 2a of the innermost resin body 2 and arranged coaxially with the cylindrical resin bodies 1 and 2. . The resin bodies 1, 2, and 3 have different outer diameters, and the resin bodies 1, 2, and 3 are such that the outer diameter of the inner resin body is smaller than the inner diameter of the adjacent outer resin body. To place. Resin body 1,
Each of 2 and 3 has a constant refractive index, and the refractive index is set higher for the inner resin body.

The resin body can be molded by various molding methods such as an extrusion molding method. The cylindrical resin bodies 1 and 2 are preferably produced as follows.
That is, first, a plurality of cylindrical tubes having different inner diameters are prepared, and a polymerizable material having a different composition is charged into each of the cylindrical tubes. The polymerizable material contains at least one kind of monomer, a polymerization initiator and a chain transfer agent and / or a dopant. Thereafter, the cylindrical tube is moved to its central axis D
Heat the polymerizable material while rotating it around. Thus, a plurality of cylindrical resin bodies 1 and 2 having different outer diameters can be obtained. The cylindrical resin body 3 is, for example, a cylindrical resin body 2.
The opening 2a is decompressed while heating with a heater, the heat shrinkage of a heat shrinkable tube coated on the outside of the resin body 2 is used, or a polymerizable material is charged into the cylindrical tube, and the cylindrical tube is oiled. It can be obtained by heating in a bath or the like.

The monomer is not particularly limited as long as it is transparent to transmitted light after polymerization. For example, methyl methacrylate, ethyl methacrylate, n-methacrylate
Propyl, i-propyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, phenyl methacrylate, 2,2,2-trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, 1,1-dihydroperfluoropropyl methacrylate, 1,1,1,2,3,3-hexafluorobutyl methacrylate,
2-perfluorooctylethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, methyl 2-fluoroacrylate, tetrafluoropropyl 2-fluoroacrylate, 2,2-fluoroacrylate 2, 2-bis (trifluoromethyl) propyl,
1,1,1,3,3,3-hexafluoroisopropyl 2-fluoroacrylate, 2,2-fluoroacrylic acid 2,
2,2-trifluoroethyl, 1,1-dihydroperfluoropropyl 2-fluoroacrylate, hexafluoroisopropyl 2-fluoroacrylate, nonafluoro t-butyl 2-fluoroacrylate, hexafluoroneopentyl methacrylate, styrene, Substituted styrene or a mixture thereof is used.

Examples of the polymerization initiator include benzoyl peroxide, acetyl peroxide, azobisisobutyronitrile,
Cumene hydroperoxide, t-butyl peroxide, di-t-butyl peroxide and the like are used,
As the chain transfer agent, for example, a mercaptan-based chain transfer agent such as n-butyl mercaptan, n-octyl mercaptan, and lauryl mercaptan is used. As the dopant, phenyl benzoate, benzyl benzoate, diphenyl phthalate, butyl benzyl phthalate, benzyl-n-butyl phthalate, dibenzyl terephthalate, triphenyl phosphate, tricresyl phosphate, tris (2-chloroethyl) phosphate , Biphenyl, diphenylmethane, diphenyl ether, diphenyl sulfide,
Benzyl phenyl ether, dibenzyl ether, dimethyl adipate, dibutyl adipate, dioctyl adipate, diisopropyl adipate, diadipate (2
-Ethylhexyl), dimethyl sebacate, dibutyl sebacate, dioctyl sebacate, di (2-sebacate)
Ethylhexyl), tri-n-butyl phosphate, trioctyl phosphate, tris (2-chloroethyl) phosphate, tris (fluoroalkyl) phosphate, dimethyl 1,4-cyclohexanedicarboxylate, 1,4-cyclohexanone-
Dimethyl 2,5-dicarboxylate, diglycidyl 1,2-cyclohexanedicarboxylate, diisobutyl sulfide, tetramethylene sulfone and the like are used.

If a plurality of resin bodies 1, 2, 3 are arranged coaxially, as shown in FIG.
Is performed (heat treatment step). By heat-treating the resin bodies 1, 2, and 3, volatile components in the resin bodies 1, 2, and 3 are sufficiently removed, and interface irregularities along the longitudinal direction of the resin bodies 1, 2, and 3 are sufficiently removed. Is done. Here, the heat treatment is performed so that the amount of volatile components in the resin bodies 1, 2, and 3 is 0.1% by weight or less. If the amount of volatile components in the resin bodies 1, 2, 3 exceeds 0.1% by weight, the interface irregularities of the resin bodies 1, 2, 3 cannot be sufficiently removed, and the heat of the resin bodies 1, 2, 3 cannot be removed. This is because volatile components are easily generated at the interface between the resin bodies during fusion. The amount of volatile components in the resin bodies 1, 2, and 3 can be measured using, for example, a thermogravimetric analyzer (TG). In the heat treatment, for example, the resin bodies 1, 2, and 3 arranged coaxially are held horizontally, and the resin bodies 1, 2, and 3 are inserted into the ring-shaped heater 4 from one end thereof while rotating around the central axis C thereof. Then, the heating can be performed by heating the other end of the resin bodies 1, 2 and 3 along the longitudinal direction.

The amount of volatile components in the resin bodies 1, 2, 3 is 0.1
In order to make the weight% or less, the heat treatment temperature in the resin bodies 1, 2, and 3 is preferably not less than (the fusion temperature of the resin bodies 1, 2, and 3) ℃. Below this temperature, interface irregularities along the longitudinal direction of the resin bodies 1, 2, and 3 cannot be sufficiently removed, and volatile components are easily generated at the interface between the resin bodies when the resin bodies 1, 2, and 3 are thermally fused. Tend to be. Here, the fusion temperature of the resin bodies 1, 2, and 3 refers to the temperature at which the resin bodies are thermally fused together. In addition, the heat treatment temperature is set for the resin body 1,
Although it differs depending on the material constituting 2,3, it is preferable that it is not more than (fusing temperature of resin bodies 1,2,3 + 50) ° C, and it is not more than the fusing temperature of resin bodies 1,2,3. More preferred. (Fusing temperature of resin bodies 1, 2, 3 + 50) ° C
When the ratio exceeds 1, the materials constituting the resin bodies 1, 2, 3 tend to start to decompose. Further, the heat treatment time of the resin bodies 1, 2, and 3 is preferably 10 minutes or more and 60 minutes or less. When the heat treatment time is out of the above range, interface irregularities occur along the longitudinal direction of the resin bodies 1, 2, and 3, and volatile components are generated at the interface between the resin bodies during thermal fusion of the resin bodies 1, 2, and 3. Tends to be easier. Further, from the viewpoint of heating uniformly along the circumferential direction, the resin bodies 1, 2, 3 are preferably rotated around the central axis C, and the rotation speed is preferably 1
0 to 300 rpm.

When the heat treatment is completed in this way, FIG.
As shown in (c), the plurality of resin bodies 1, 2, and 3 are thermally fused at a fusion temperature (fusion step). Resin bodies 1, 2, 3
The fusion temperature varies depending on the material constituting the resin body, but is usually 150 to 250C. Here, the heat treatment of the resin bodies 1, 2, and 3 can be performed using a heating furnace or an infrared ray generating device such as an infrared ray heater that generates infrared rays. Of these, an infrared ray generating device (not shown) is used. It is preferable to carry out. When infrared rays are used, each of the resin bodies can be uniformly heated, and the resin bodies 1 and 2 can be heated in a short time.
This is because a few fusions can be completed. As the infrared rays, those having a wavelength of usually 1 to 100 μm, preferably 5 to 15 μm are used. From the viewpoint of increasing the roundness of the obtained POF preform 5, the resin bodies 1, 2, 3 are preferably rotated around the central axis C. The rotation speed is usually 10 to 100 rpm. Further, it is preferable to heat-bond the resin bodies while reducing the pressure in the gap between the resin bodies and the opening 2a of the innermost resin body 2. At this time, the pressure between the gaps between the resin bodies and the opening 2a (fused portion) of the innermost resin body 2 is usually set to 0 to 1 with respect to the external pressure.
The pressure is reduced in the range of 0000 Pa. Thus,
A cylindrical POF base material 5 in which the resin bodies 1, 2, 3 are coaxially overlapped is obtained (see FIG. 1D).

When the resin bodies 1, 2, 3 are heat-fused in this manner, a plurality of cylindrical resin bodies 1, 2 having different refractive indices are formed in advance. At the time of thermal fusion, the reaction near the interface between the resin bodies is sufficiently prevented regardless of the type of the material constituting the resin bodies 1, 2, and 3, and the formation of a single polymer domain is suppressed. For this reason, the occurrence of white turbidity in the obtained POF base material 5 is sufficiently prevented. Also, in the previous heat treatment step, the resin body 1,
Since the volatile components in 2 and 3 have already been sufficiently removed, it is possible to sufficiently prevent the generation of bubbles due to the volatile components. Further, since the interface irregularities of the resin bodies 1, 2, and 3 are sufficiently removed, interface irregularities do not occur in the POF base material 5.

Further, the cylindrical P obtained in this manner is obtained.
The OF base material 5 is disposed vertically, and the lower end of the POF base material 5 is heated and melted for drawing (drawing step). In drawing, the heating furnace temperature at the time of drawing is usually 150 to 250 ° C., and the drawing speed is usually 1 to 10 m / min. Drawing is performed using, for example, a drawing apparatus 6 shown in FIG. In this drawing apparatus 6, the POF base material 5 is inserted from the lower end side into an upper opening 10a formed in a case 11, the lower end of which is placed in a heating furnace 7, heated and melted, and a take-up reel 8 is provided. By
The molten portion is drawn out through the lower opening 10b of the case 11. Thus, a POF 9 in which the plurality of resin bodies 1, 2, 3 are coaxially overlapped is obtained.

Next, a second embodiment of the method for producing a POF of the present invention will be described.

As shown in FIG. 3, the method for manufacturing a POF base material according to the present embodiment includes a plurality of resin members 1 and 2 arranged coaxially.
After the heat treatments 2 and 3, the POF 9 is obtained by drawing while the resin bodies 1, 2 and 3 are heat-fused to obtain a POF 9, which is different from the POF manufacturing method of the first embodiment. By simultaneously fusing and drawing the resin bodies 1, 2, 3 as described above, the plurality of resin bodies 1, 2, 3 arranged coaxially directly without passing through the form of the POF base material. POF9 can be obtained. For this reason,
The time required for manufacturing is reduced, and the production efficiency is improved.

During the heat treatment of the resin bodies 1, 2, 3
The heat treatment temperature of the resin bodies 1, 2, and 3 is preferably at least (the fusion drawing temperature of the resin body−30) ° C. or more. The fusion drawing temperature refers to a temperature at which the resin bodies 1, 2, 3 are drawn while being fused, and is usually 150 to 250 ° C.
It is. The heat treatment temperature of the resin bodies 1, 2, 3
Although it differs depending on the material constituting 2,3, it is preferable that the temperature is not more than (the fusion drawing temperature of the resin bodies 1,2,3 + 50) ° C, and is not more than the fusion drawing temperature of the resin bodies 1,2,3. Is more preferable. If (the fusion drawing temperature of the resin bodies 1, 2, 3 +50) ° C is exceeded, the decomposition of the material constituting the resin bodies 1, 2, 3 tends to start. In addition, the resin bodies 1, 2,
The heat treatment time of No. 3 is preferably 10 minutes or more and 60 minutes or less. If the heat treatment time is out of the above range, the resin body 1
In Examples 2 and 3, the interface irregularities along the longitudinal direction cannot be sufficiently removed, and air bubbles due to volatile components tend to be generated during thermal fusion of the resin bodies 1, 2, and 3.

The present invention is not limited to the first and second embodiments. For example, in the first and second embodiments described above, the heat treatment step is performed after the step of arranging the resin body, but the arrangement step may be performed after the heat treatment step of the resin body.

Hereinafter, the contents of the present invention will be described more specifically with reference to examples.

[0027]

(Example 1) First, an outer diameter of 35 mm and an inner diameter of 28 mm
mm, 50 cm long cylindrical clad part, outer diameter 26
A cylindrical first core having a diameter of 20 mm, an inner diameter of 20 mm and a length of 50 cm, and a cylindrical second core having a diameter of 18 mm and a length of 50 cm were separately prepared.

Here, the clad portion was manufactured as follows. That is, a glass cylindrical tube for centrifugal molding having an inner diameter of 35 mm and a length of 50 cm was horizontally arranged, and lids were attached to both ends thereof. Then, 216 ml of the polymerizable solution was charged into the cylindrical tube with the lid having the opening formed therein sealed with a rubber elastic ring for sealing. Examples of the polymerizable solution include methyl methacrylate (MMA) and 2,2,2-trifluoroethyl methacrylate (3FM
A) is contained in a volume ratio of MMA: 3FMA = 1: 1, and further 100 parts by weight of MMA, 0.5 parts by weight of di-t-butyl peroxide (PBD) as a polymerization initiator, and a chain transfer agent N-butyl mercaptan as (n-
BM) to which 0.15 part by weight was added. Thereafter, the cylindrical tube was passed through a ring heater to 85 ° C from outside.
Around the central axis of the cylindrical tube while heating for 20 hours at 1500r
The solution was polymerized by rotating at a rotation speed of pm. Thus, a cylindrical clad portion was obtained.

Further, the first core portion was manufactured as follows. That is, a glass cylindrical tube for centrifugal molding having an inner diameter of 26 mm and a length of 50 cm is horizontally arranged, lids are attached to both ends thereof, and the lid having an opening formed therein is sealed with a rubber elastic ring for sealing. 135 ml of the polymerizable solution was charged into the cylindrical tube. As this polymerizable solution, MMA: 3FMA = volume ratio of MMA: 3FMA =
3: 1 and further based on 100 parts by weight of MMA,
What added 0.5 part by weight of PBD and 0.15 part by weight of n-BM was used. Thereafter, the polymerizable solution was polymerized by rotating the cylindrical tube around the center axis of the cylindrical tube for centrifugal molding at a rotation speed of 1500 rpm while heating the cylindrical tube at 85 ° C. for 20 hours from the outside through a ring heater. Thus, a cylindrical first core portion was obtained.

On the other hand, the second core portion was manufactured as follows. That is, a lid was attached to one end of a cylindrical tube having an inner diameter of 18 mm and a length of 60 cm, and a polymerizable solution was placed in the cylindrical tube for 160 minutes.
ml. As the polymerizable solution, MMA100
The one to which 0.5 parts by weight of PBD and 0.15 parts by weight of n-BM were added to parts by weight was used. Thereafter, the cylindrical tube was set in an oil bath and heated at 85 ° C. for 20 hours to polymerize the polymerizable solution. Thus 18mm in diameter,
A cylindrical second core portion having a length of 50 cm was obtained.

The clad part thus obtained, the first
The core part and the second core part were arranged coaxially and horizontally. One end of each of the clad portion, the first core portion, and the second core portion is sealed with Teflon tape, and in this state, the clad portion, the first core portion, and the second core portion are rotated around their central axes at 30 rpm. 200 ℃
For 10 minutes. Before and after this heat treatment, a part of each of the clad part, the first core part, and the second core part was sampled, and the TG-DTA device (Mac S
using TG-DTA2020S manufactured by Science Co., Ltd.
The amounts of volatile components in the clad portion, the first core portion, and the second core portion were measured. Table 1 shows the results. Note that T
G-DTA measurement was performed under a nitrogen atmosphere under a sample weight of 10.0 m.
g, at a heating rate of 10.0 ° C./min.

[0032]

[Table 1]

Subsequently, a gap between the clad portion and the first core portion and a gap between the first core portion and the second core portion are reduced by 30 mmH ₂ O.
Held. Then, the clad portion, the first core portion, and the second
While rotating the core at 30 rpm, the core was moved in the horizontal direction at a speed of 1 mm / min along the longitudinal direction of the clad, and heated at 200 ° C. for 400 minutes using an electric heater. In this way, the cladding part and the first core part, and the first core part and the second core part, which are adjacent to each other, were thermally fused to obtain a cylindrical plastic optical fiber preform having an outer diameter of 32 mm. No white turbidity was observed in the plastic optical fiber preform thus obtained.

Next, the plastic optical fiber preform was drawn using a drawing apparatus shown in FIG. 2 to obtain a plastic optical fiber having a diameter of 0.75 mm. The temperature of the heating furnace during drawing was controlled at 230 ° C., and the drawing speed was 1 m /
Minutes. Then, the plastic optical fiber is cut to prepare a plurality of plastic optical fibers having a length of 50 m. For each of these plastic optical fibers, a white light source (AQ-4303B, manufactured by Ando Electric Co., Ltd.) and a spectrum analyzer (Ando) Electric company, AQ-631
5B) was used to measure the transmission loss for 650 nm light. As a result, the transmission loss was less than 180 dB / km for each plastic optical fiber, and was almost constant. From this fact, by setting the amount of volatile components in the clad portion, the first core portion, and the second core portion to 0.1% by weight or less by the heat treatment, the transmission loss along the longitudinal direction of the plastic optical fiber becomes substantially constant. It turned out to be.

Comparative Example 1 A cylindrical plastic optical fiber was produced in the same manner as in Example 1, except that the heat treatment temperature of the clad portion, the first core portion and the second core portion, which were coaxially arranged, was 150 ° C. A base material was produced. In the production of the plastic optical fiber preform, the amounts of volatile components before and after the heat treatment of the clad portion, the first core portion, and the second core portion were measured in the same manner as in Example 1. Table 1 shows the results.

Further, the plastic optical fiber preform was drawn in the same manner as in Example 1, and the diameter was 0.75.
mm plastic optical fiber was obtained. This plastic optical fiber was cut to prepare a plurality of plastic optical fibers having a length of 50 m. Transmission loss was measured for each of these plastic optical fibers in the same manner as in Example 1. As a result, the transmission loss is different for each plastic optical fiber, and their values are between 150 and 350 d.
It took B / km and varied considerably. From this, it was found that the transmission loss of the plastic optical fiber was considerably uneven along its longitudinal direction.

(Example 2) The clad part, the first core part, and the second core part manufactured in the same manner as in Example 1 are coaxially and horizontally arranged, and in this state, the same as in Example 1 is performed. The heat treatment of the clad part, the first core part and the second core part was performed. Before and after this heat treatment, a part was taken from each of the clad part, the first core part and the second core part, and the amount of volatile components was measured in the same manner as in Example 1. Table 1 shows the results.

Subsequently, the clad portion, the first core portion, and the second core portion are arranged vertically, and the gap between the clad portion and the first core portion and the gap between the first core portion and the second core portion are set to 30 mmH.
_It was kept at 2O. Then, the clad part, the first core part, and the second core part were lowered at a speed of 1 mm / min along their longitudinal directions, and the drawing was performed at the same drawing temperature and drawing speed as in Example 1. . Thus, a plastic optical fiber having an outer diameter of 0.75 mm was obtained.

By cutting the plastic optical fiber, a plurality of plastic optical fibers having a length of 50 m are prepared.
For each of those plastic optical fibers,
Transmission loss was measured in the same manner as in Example 1. as a result,
Transmission loss is 180d for each plastic optical fiber
B / km or less. From this fact, by setting the amount of volatile components in the clad portion, the first core portion, and the second core portion to 0.1% by weight or less by the heat treatment, the transmission loss along the longitudinal direction of the plastic optical fiber becomes substantially constant. It turned out to be.

(Embodiment 3) At the time of heat fusion, the clad portion, the first core portion, and the second core portion, which are coaxially arranged, are 3 m apart.
m / min, and heated in the same manner as in Example 1 except that the clad portion, the first core portion, and the second core portion were heated by an infrared heater that generates infrared rays having a wavelength of 8 to 15 μm. A POF base material was obtained. The volatile component amounts of the clad portion, the first core portion, and the second core portion before and after the heat treatment were measured in the same manner as in Example 1. Table 1 shows the results.

Further, when the obtained POF base material was observed, no bubbles were observed in the POF base material. From this fact, even if the moving speed at the time of heat fusion is increased by performing the fusion using far infrared rays by reducing the amount of the volatile component to 0.1% by weight or less by the heat treatment, the generation of the bubbles due to the volatile component is performed. It has been found that heat fusion can be performed while preventing the formation of a POF base material in a short time.

Comparative Example 2 Example 3 was repeated except that the thermal fusion of the clad portion, the first core portion and the second core portion was performed with an electric heater instead of the far infrared heater, and the fusion temperature was set at 180 ° C. In the same manner as in the above, the clad portion, the first core portion and the second core portion were thermally fused. As a result, there were portions that could not be fused in the clad portion, the first core portion, and the second core portion after the thermal fusion. The cladding before and after the heat treatment,
The amounts of volatile components in the first core portion and the second core portion were measured in the same manner as in Example 3. Table 1 shows the results.

Example 4 A POF base material was obtained in the same manner as in Example 1 except that the clad, the first core, and the second core were heat-treated at 180 ° C. for 60 minutes. Then, in the same manner as in Example 1, the volatile component amounts of the clad portion, the first core portion, and the second core portion before and after the heat treatment were measured. Table 1 shows the results.

Further, the obtained POF base material was drawn in the same manner as in Example 1 to obtain a POF having a diameter of 0.75 mm.
F was obtained. The POF was cut to prepare a plurality of 50 m-long POFs, and the transmission loss was measured for each of the POFs in the same manner as in Example 1. As a result, the transmission loss is 180 dB / km for each POF.
It was below. From this, the amount of volatile components in the clad portion, the first core portion, and the second core portion was reduced to 0.
It has been found that by setting the content to 1% by weight or less, the transmission loss becomes substantially constant along the longitudinal direction of the POF.

[0045]

As described above, according to the plastic optical fiber preform and the method for manufacturing a plastic optical fiber of the present invention, each of the resin bodies is heat-treated before the resin body is thermally fused. Since the interface irregularities along the longitudinal direction are sufficiently removed in the above, the plastic optical fiber obtained by drawing the preform can have a substantially constant transmission loss along the longitudinal direction.
In addition, the heat treatment of the resin body sufficiently removes volatile components in the resin body and can sufficiently prevent the generation of volatile components during thermal fusion of the resin body. Thus, the transmission loss of the plastic optical fiber obtained can be reduced.

[Brief description of the drawings]

FIG. 1 is a series of process drawings of a method for producing a plastic optical fiber preform of the present invention.

FIG. 2 is a sectional view showing an apparatus for drawing a plastic optical fiber preform.

FIG. 3 is a partial cross-sectional front view showing a state in which a clad portion, a first core portion, and a second core portion are drawn by fusion as one step of one embodiment of the method for manufacturing a plastic optical fiber of the present invention. .

[Explanation of symbols]

1, 2, 3 ... resin body, 5 ... plastic optical fiber preform, 9 ... plastic optical fiber.

Claims (8)

[Claims] 1. A method of manufacturing a plastic optical fiber preform comprising a plurality of resin bodies having mutually different refractive indices overlapping each other coaxially, wherein a plurality of cylindrical resin bodies having mutually different refractive indices are provided. An arranging step of coaxially arranging; a heat-treating step of heat-treating the resin body so that the volatile component amount in the resin body is 0.1% by weight or less; A fusion step of obtaining a plastic optical fiber preform in which the resin bodies are coaxially overlapped with each other. 2. The plastic optical fiber preform according to claim 1, wherein in the arranging step, a columnar resin body is arranged in an opening of an innermost resin body of the plurality of resin bodies. Manufacturing method. 3. In the heat treatment step, the resin body is heated at a temperature equal to or higher than (the fusion temperature of the resin body−30) ° C.
The method for producing a plastic optical fiber preform according to claim 1 or 2, wherein the heat treatment is performed for 0 minutes or more. 4. The method for producing a plastic optical fiber preform according to claim 1, wherein in the fusing step, the resin body is heat-treated with infrared rays. 5. A method for manufacturing a plastic optical fiber comprising a plurality of resin bodies having mutually different refractive indices overlapping each other coaxially, wherein a plurality of cylindrical resin bodies having mutually different refractive indices are coaxially formed. A heat treatment step of heat-treating the resin body so that the amount of volatile components in the resin body is 0.1% by weight or less; and drawing while thermally bonding the plurality of resin bodies. And fusing a wire to obtain a plastic optical fiber in which the plurality of resin bodies are coaxially overlapped with each other. 6. The plastic optical fiber according to claim 5, wherein, in the disposing step, a columnar resin body is disposed in an opening of an innermost resin body of the plurality of resin bodies. Method. 7. The heat treatment step, wherein the heat treatment is performed on the resin body at a temperature of (the fusion drawing temperature of the resin body−30) ° C. or more for 10 minutes or more. Manufacturing method of plastic optical fiber. 8. A method of manufacturing a plastic optical fiber comprising a plurality of resin bodies having mutually different refractive indices overlapping each other coaxially, wherein a plurality of cylindrical resin bodies having mutually different refractive indices are coaxially formed. A heat treatment step of heat-treating the resin body so that the amount of volatile components in the resin body is 0.1% by weight or less; and a plastic optical fiber obtained by heat-sealing the plurality of resin bodies. A fusion step of obtaining a base material, and a drawing step of drawing the plastic optical fiber preform to obtain a plastic optical fiber in which the plurality of resin bodies are coaxially overlapped. Manufacturing method of plastic optical fiber.