JPH0221561B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reinforcing a mold of a connecting portion of a glass optical fiber for light transmission having a plastic coating.

[Prior Art] Optical fibers generally have a plastic coating such as nylon, and conventionally, for example, as shown in FIG. Connected by fusion or the like. For reinforcement, this joint is covered with a reinforcing material such as a plastic tube that is the same as the above-mentioned plastic coating or can be welded, and is held down with an upper die 4a and a lower die 4b as shown in Fig. 2 until the temperature exceeds the melting point of the plastic. When heated, pressurized, molded, and cooled, the third
A joint integrally welded with the fiber coating as shown in the figure is obtained.

[Problems to be Solved by the Invention] However, in the conventional example described above, air in the space B may be trapped in the connecting portion during molding.
When thermal strain or mechanical force is applied to such a connection portion, stress concentrates on the bubble generation portion, which adversely affects the connection characteristics of the optical fiber.

Also, in particularly large portions of the bubble, the optical fiber may buckle, bend, or break.

The present invention eliminates the above-mentioned drawbacks and provides mold reinforcement for optical fiber connection parts, which makes it possible to obtain extremely reliable optical fiber connection parts with no air bubbles in the reinforcing material or between the reinforcing material and the optical fiber connection part. The purpose is to provide a method.

[Means for Solving the Problems] That is, the gist of the present invention is to provide a method for reinforcing an optical fiber core connection part using a heating mold using a nylon reinforcing material, in which the temperature distribution of the mold is such that the central part in the longitudinal direction is The temperature is the highest, and the temperature is lower toward both ends, and the difference between the highest and lowest temperatures is 30 to 70°C.

[Example] The configuration of the present invention will be specifically described with reference to FIGS. 4 to 7 showing one example.

In Figure 4, the mold reinforcing tube is
Plastic (nylon) three layers 6a, 6b, 6
c. It is composed of two layers of glass fibers 7a and 7b.

Here, the glass fiber is contained in order to improve the mechanical strength of the connection portion, and may be a glass powder or the like.

In this case, the tube can be covered with the optical fiber connector 2, and heat molded by the method shown in FIGS. 1 and 2 as described above. At this time, the mold 4 is
As shown in the figure, by providing a structure in which heat dissipation fins 8 are provided at both ends of the mold 40b, the temperature at both ends where the heat dissipation fins 8 are provided decreases, and therefore the temperature at both ends where the heat dissipation fins 8 are provided decreases.
By changing the size and shape of the heat dissipation fins 8, the temperature difference between the center and both ends can easily create a temperature gradient in which the temperature is highest in the center in the longitudinal direction and gradually decreases toward both ends. Easily adjustable. Incidentally, the mold 40a is also provided with heat dissipation fins 8. In this way, heat dissipation fins 8 are placed on both ends of the mold 4.
Since the temperature gradient as described above can be obtained by simply providing the mold, there is no need to forcefully cool the mold or provide a split heater or the like in the mold to control the temperature, and the operation is very simple.

FIG. 6 shows the formation of the mold 4 in the longitudinal direction. FIG. 3 is a diagram showing the relationship between temperature gradient and viscosity of plastic as a reinforcing material. As shown in Figure 5, when the length of the mold is l, the center is the reference point O, and both ends are l/2, the center O has the highest temperature,
A temperature gradient T is obtained in which both ends 1/2 have the lowest temperature. The temperature difference between the center O and both ends 1/2 is ΔT.
At this time, the viscosity η of the plastic reinforcing material is lowest at the center. Therefore, when the reinforcing material is molded, the central part of the reinforcing material softens first, and then the reinforcing material softens and melts toward both ends.

When a mold capable of forming such a temperature gradient is used to heat mold an optical fiber core connection portion covered with a reinforcing material, as shown in FIG. 7,
The composite tube deforms from the center, which is first softened, toward both ends, and the air in the space B is pushed out. If heating molding is continued, the entire reinforcing material will melt, and when it is cooled, no air bubbles will remain inside the reinforcing material or between the reinforcing material and the optical fiber core, and the reinforcing material and the plastic coating of the optical fiber will be welded together. A good optical fiber connection can be obtained.

In addition, in the experiments conducted by the present inventors when the reinforcing material was nylon, no cases were found where air bubbles were trapped in the connection part when the difference between the highest temperature and the lowest temperature of the temperature gradient ΔT was in the range of 30 to 70 degrees Celsius. A highly reliable connection was obtained.

However, at ΔT=20°C, the probability that bubbles with a diameter of 1 mm would occur was 7 out of 100 cases. In addition, if the temperature exceeds 70℃, the temperature at the edges of the mold will not rise above the melting point of nylon, or the center will become extremely hot.
The fiber may break due to the deterioration of the nylon.
Adversely affects optical transmission characteristics.

[Effects of the Invention] As explained above, the mold reinforcing method using the nylon reinforcing material of the present invention has the following remarkable effects.

(1) A temperature gradient was created in the longitudinal direction of the mold, with the highest temperature at the center and lower temperatures toward both ends, and the difference between the maximum and minimum temperatures of this temperature gradient was 30 to 70°C. Therefore, a mechanically strong, thermally stable, and reliable optical fiber connection part can be obtained without generating bubbles in the molded reinforced connection part and without any part where stress is concentrated due to thermal stress or the like.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of the conventional mold forming method, Figure 2
The figures are a sectional view taken along the line A-A' in Fig. 1, Fig. 3 is a plan view of a conventional mold reinforcing connection section, Fig. 4 is a sectional view showing a mold reinforcing tube used in an embodiment of the present invention, and Fig. 5. 6 is an explanatory diagram showing a mold used in one embodiment of the present invention, FIG. 6 is a diagram showing the relationship between temperature gradient and viscosity, and FIG. 7 is an explanatory diagram showing one implementation process of the present invention. 1a, 1b: plastic coated fiber, 2:
Optical fiber core wire (connection part), 3: plastic tube, 4a, 4b: mold, 5: mold reinforced connection part, 6a, 6b, 6c: plastic (nylon), 7a, 7b: glass fiber, 8: overflow, 40a, 40b: Molding mold.

Claims (1)

[Claims] 1. After removing the coatings from both ends of the two opposing plastic-coated optical fibers and connecting the exposed ends of the optical fibers, the connecting portions of the optical fibers are covered with a nylon reinforcing material. In a method of reinforcing by heat molding with a mold, heat dissipation fins are provided at both ends of the mold in the longitudinal direction, so that the temperature reaches the highest temperature in the center of the mold in the longitudinal direction, and the temperature decreases toward both ends. 1. A method for reinforcing a mold for an optical fiber connection part, characterized by applying a gradient and performing heat molding such that the difference between the maximum temperature and the minimum temperature of the temperature gradient is 30 to 70°C.