JPS58122508A - Connecting method of optical fiber core - Google Patents

Abstract

PURPOSE:To prevent moisture from being left in melt-fixing connection parts of cores to improve the durability and the reliability of core connection, by connecting cores after subjecting prescribed lengths of both end parts, which should be connected, of optical fiber cores to the dehumidifying treatment preliminarily. CONSTITUTION:A coating layer 2 of an optical fiber core 1 consists of a secondary coating layer 2a consisting of nylon or the like and a primary coating layer 2b consisting of a silicone resin or the like. Before connecting cores 1, a prescribed length of end parts of coating layers 2 is heated to remove moisture contained in secondary coating layers 2a. Optical fiber strands 3 are exposed, and their both end faces are connected by melt-fixing, and an adhesive 7 is packed in a thermal contracting tube 4 which is inserted preliminarily, and the tube 4 is contracted by heating to make connection parts into one body. Thus, since moisture or the like is not left in melt-fixing connection parts of optical fiber cores 1, the reliability of connection is improved, and the increment of the transmission loss is prevented under a high water pressure of the deep sea.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a connecting method intended to improve the reliability of a connecting portion of optical fibers.

Compared to conventional metal transmission lines, optical fiber cables have a smaller diameter, are lighter, and are also more flexible, but they have too little mechanical strength to be used as optical signal transmission lines. There is also a high risk of damage or breakage. Therefore, it is common practice to provide a reinforcing coating layer on the outer surface of the optical fiber.

However, when connecting optical fibers having such coating layers, the reinforcing coating layer is removed and the optical fibers are fusion spliced, and the fusion splice and both ends of the spliced portion are connected. It has been practiced to form a reinforcing layer for reinforcing the optical fiber by integrating it with the coating layer of the optical fiber.

The conventional method for connecting optical fibers is to butt and bond the optical fibers in a groove formed in the center of the reinforcing body, and also bond the coating layer to the reinforcing body. The so-called groove reinforcement splicing method, the molding splicing method in which a reinforcing sleeve is provided to span the fusion spliced part and the coating layer at both ends, and the inside is molded with resin, or the fusion spliced optical fiber element is used. A heat-shrinkable tube reinforcement connection method in which a reinforcing stainless steel wire is twisted around the wire, a heat-shrinkable tube is placed over the coating layer at both ends of the connection, and the heat-shrinkable tube is heated and shrunk together with the adhesive filled inside to strengthen the wire. and so on.

However, when reinforcing and splicing under heated conditions, such as by molding resin molding splicing or heat shrink tube reinforced splicing, the exposed portion of the optical fiber must be cleaned immediately before fusion splicing. , and the moisture on the surface is removed by evaporation due to heating during fusing, whereas the secondary coating 1- (nylon, polyethylene, etc.) and the combination of the secondary coating layer and the primary coating layer (silicone resin, etc.) At the boundary part, as shown in FIG. 1, the moisture absorbed in the optical fiber core 1, mainly in the secondary coating layer 2a, becomes gas (water vapor) when the heat shrink tube 4 is heated and shrunk.
The durability and reliability of the connection portion decreases due to the residual moisture 8 generated by the volume expansion and being trapped inside. This moisture and air bubbles do not cause much of a problem under atmospheric pressure and around room temperature, but when there is a temperature change, the air bubbles expand and contract, leading to an increase in transmission loss. Further, according to the research conducted by the inventors, it has been found that under high water pressure, such as when used as a submarine optical cable, a significant property deterioration force acts, often leading to breakage.

The present invention solves such conventional drawbacks and provides a method for splicing optical fibers that can obtain a highly durable and reliable splice without residual moisture in the fusion splice of the optical fibers. For the purpose of providing. The structure of the present invention that achieves this object is to remove the coating layer of the optical fiber core wire, then fusion splice the optical fibers, and apply heating conditions to the fusion spliced portion and the coating layer at both ends thereof. When forming the reinforcing layer and making the connection, the coating layer at both ends of the fusion spliced portion is subjected to dehumidification treatment in advance.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

FIGS. 2(a) and 2(b) are a longitudinal cross-sectional view and a cross-sectional view when the reinforcing connection method using a heat-shrinkable tube is applied.

The optical fiber core wires 1 that are connected to each other are coated with a secondary coating layer 2a made of nylon or polyethylene/carbonate, and a primary coating layer 2b made of silicone resin, and the coating layer 2 is removed to expose the optical fibers 3. The end face of the optical fiber element 11M3 is fusion spliced, but before exposing the optical fiber cable 3, the part exposed during fusion splicing and the part where the reinforcing heat shrink tube 4 spans the coating layer 2 are shown. The coating layer 2 is dehumidified.

This dehumidification treatment is carried out by heating the outer surface of the secondary coating layer 2a at a temperature below the softening point of the board material. As a result, the moisture absorbed by the secondary coating layer 2a is removed by evaporating outward in the radial direction, and the moisture in the boundary layer between the secondary coating layer 2a and the primary coating layer 2b is removed from the optical fiber core 1. is removed by evaporation from the axial cross section of the

The heating time in this case varies depending on the thickness and material of the coating layer 2, but it has been experimentally found that the coating layer 2 can be sufficiently removed in several minutes.

After removing the moisture in this way, the coating layer 2 is removed to expose the optical fiber 3, the exposed portion is cut to a predetermined length, the cut rings are butted together, and fusion spliced using a discharge heating welding device or the like. do. Thereafter, for reinforcement, the heat-shrinkable tube 4, which has been passed through the optical fiber core 1 in advance, is moved to the fusion splicing section 5 so that it straddles the coating layer 2 at both ends of the fusion splicing section 50. In this case, in order to further strengthen the reinforcement, the stainless steel wire 6 is inserted into the heat shrink tube 4 along with the original fiber wire 3, and an adhesive 7 such as EVA is applied.
is filled. Thereafter, the heat-shrinkable tube 4 is heat-shrinked to integrate and reinforce the negative connection portion 5 and the covering layer 2.

When heating the heat-shrinkable tube 4, the moisture in the coating layer 2 is dehumidified beforehand, so that it does not remain inside the heat-shrinkable tube 4.

Figure 3 shows the experimental results of the transmission loss and water pressure characteristics of the joints when optical fiber cores immersed in water at room temperature and atmospheric pressure are connected by the method of the present invention and by the conventional method. It is a graph.

When the connection method of the present invention is adopted, as shown by the curved line, no moisture or air bubbles are generated in the connection portion, and the connection loss (per connection) is extremely stable against water pressure. On the other hand, as shown by curve B, the connection made by the conventional connection method had a loss greater than 10 times that of the method of the present invention, and was also irreversible and unstable with respect to water pressure.

Incidentally, the dehumidification treatment can also be carried out by reducing the pressure to a vacuum state at room temperature without heating, and in this case, it is suitable for a coating layer having a low softening point. Further, in the above embodiment, a reinforcing connection method using a heat-shrinkable tube has been described, but it can be applied to any case where a reinforcement j- is formed under heating conditions (for example, a molding connection method, etc.) and is extremely effective.

As specifically explained above in conjunction with the embodiments, according to the present invention, moisture may remain in the connection portion of the optical fiber core wire,
Optical fiber cores can be connected without creating bubbles.

Therefore, the connection part has excellent durability and reliability, and increases in transmission loss are avoided, especially when used in places with large temperature changes or under high water pressure such as in deep seas hundreds to thousands of meters deep. It can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a reinforced joint using a conventional heat-shrinkable tube, and FIGS. 2(a) and (b) are longitudinal cross-sectional views of a reinforced joint using a heat-shrinkable tube and The cross-sectional view and FIG. 3 are graphs showing the relationship between transmission loss and water pressure characteristics at the connection portion of the optical fiber core. In the drawings, 1 is an optical fiber core, 2 is a coating layer, 3 is an optical fiber wire, 4 is a heat shrink tube, 5 is a fusion splicing part, 6 is a stainless steel wire, and 7 is an adhesive. Figure 1 Figure 2 (0) (b)

Claims (1)

[Claims] After removing the coating layer of the optical fiber core wire, the optical fiber wire is fusion spliced, and a reinforcing layer is formed on the fusion spliced portion and the coating layer at both ends thereof under heating conditions. A method of connecting optical fiber cores that requires the following steps in advance.