JPH05119224A - Structure for connecting optical fiber covered with metallic pipe - Google Patents

Abstract

PURPOSE:To facilitate connection and to avert the stress concn. to a juncture by subjecting at least a part of the outside surface of a sleeve pipe to waving. CONSTITUTION:Both ends of the sleeve pipe 3 are connected by welding along the outer periphery of a covering metallic pipe 2 to form a welded juncture 4. The sleeve pipe 3 which is bridged in such a manner and is connected by welding at both ends forms the covering of the juncture 11. The metallic pipe 2 and the sleeve pipe 3 overlap on each other and form an overlap part 13 near the welded juncture 4. The overlap part 13 is less flexible than the metallic pipe 2. On the other hand, a corrugated part 12 is formed near the overlap part 13 and, therefore, the juncture 11 is more high flexible in this corrugated part 12. Then, the optical fiber covered with the metallic pipe including the juncture 11 is so constructued that the force to bend the fiber acts as the force to bend the corrugated part 12 and does not concentrate the stresses to the overlap part 13. The bending stresses acting on the welded juncture 4 and the overlap part 13 are absorbed by bending of the corrugated part 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal tube-coated optical fiber connecting structure in which an optical fiber element wire, an optical fiber code, an optical fiber cable and the like are housed in a metal tube, and particularly, the connection is easy. In addition, the present invention relates to a metal tube-coated optical fiber connection structure capable of avoiding stress concentration on the connection portion.

[0002]

2. Description of the Related Art In an optical fiber, strength is deteriorated by moisture when stress is applied, and when exposed to moisture, transmission loss may increase due to absorption of hydrogen. In order to address the problems caused by the environment in which it is used, maintain the strength and transmission characteristics of the optical fiber to improve long-term reliability, and to improve the mechanical strength, A metal tube coated optical fiber in which a core wire, an optical fiber code, an optical fiber cable or the like is housed in a metal tube may be used.

As a typical example of a metal tube-coated optical fiber, a metal tube-coated optical fiber in which an optical fiber core wire is housed in a commonly used metal tube is taken as an example, and its application example and connection structure will be described. To do.

An optical fiber composite submarine cable in which a metal tube-coated optical fiber is compounded with a submarine cable and the metal tube-coated optical fiber is laid using the submarine cable as a carrier has been put into practical use. When laying this optical fiber composite submarine cable for a long distance like a cross-strait crossing submarine cable, a unit length of submarine cable manufactured in a unit length of several km is successively connected with the same diameter. Then, the armored iron wire is wound on it as a protective coating, which is wound in a coil and stored in the hold of the laying ship, and is usually pulled out from the laying ship and laid on the seabed. In this case, it is necessary to connect the metal tube-coated optical fibers combined with the submarine cable so that the connecting portions have substantially the same diameter as the submarine cable connecting portion.

The metal tube coated optical fiber has been put to practical use for underwater exploration in addition to the optical fiber composite undersea cable. In this case as well, in order to take advantage of its small diameter and light weight, a joint box, etc. It is desirable to make a straight-line, same-diameter connection without using

Conventionally, in order to connect the metal tube-coated optical fibers with the same diameter, it is general to use the method shown in FIGS. That is, as shown in FIG. 4, the metal tube 2 of the optical fiber coated with a metal tube is stripped and removed, and as shown in FIG. 5, the sleeve tube 3 is fitted on one metal tube 2 side, The end faces of the fiber core wires 1 and 1 are connected to each other by fusion splicing or the like at the connection portion 1A. Next, as shown in FIG. 6, the sleeve pipe 3 is pulled back so as to cover the connecting portion 1A, and bridged between the respective ends of the metal pipes 2 and 2 that have been stripped off, as shown in FIG.
As shown in FIG. 7, both ends of the sleeve pipe 3 are welded to the metal pipes 2 and 2 by a welding machine 10 such as a laser beam welding machine.
It is fixed by 4 to obtain a connection structure as shown in FIG.

In addition to such a general connection structure, FIG.
As shown in Fig. 10, the sleeve pipe 3 is wire-drawn so that the outer periphery of the connection portion does not have a step as shown in Fig. 8. Furthermore, as shown in Fig. 10, the sleeve pipe 3 is a metal pipe. Two, two
It has been proposed to insert it into the inside of the, or a structure without overlapping as shown in FIG. However, in general, the simplest connection structure as shown in FIG. 8 is often used.

[0008]

In the conventional structure described above, when bending is applied near the connecting portion (for example, when the connecting portion is wound on a bobbin, a bent cable laying loop is used).
In the connection structure shown in FIGS. 8 and 10, the bending rigidity differs between the metal pipe 2 and the sleeve pipe 3, so that stress is not applied to the welded portion 4. concentrate. Therefore, if the bending diameter is small or repeated bending is applied, cracks may occur. On the other hand, the connection structure shown in FIG. 9 and FIG.
Since the bending rigidity of the sleeve pipe 3 can be made substantially equal, stress is less likely to concentrate on the welded portion 4, but the connecting structure of FIG. 9 uses the latter half split die to make the sleeve pipe 3 have the same diameter. Rework to drop off is required. Further, in the connection structure of FIG. 11, since the slitted sleeve pipe 3 is fitted into the connection portion to have the same diameter, the slit portion must be further welded after the metal pipe 2 and the sleeve pipe 3 are welded. This is both time consuming and laborious. In this way, the connection structure lacking in simplicity is particularly problematic when the connection work is performed in the field.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems, and to provide a connection structure for a metal tube-coated optical fiber which is easy to connect and which can avoid stress concentration on the connection portion.

[0010]

In order to achieve the above object, the present invention is one in which at least a part of the outer surface of the sleeve pipe is corrugated.

Further, the corrugated shape of the corrugated processing applied to the sleeve tube is made spiral along the tube axis.

[0012]

With the above structure, the metal tube between the connecting ends of the metal tube-coated optical fiber is peeled off to connect the optical fibers to each other, and then the sleeve tube fitted to the outer peripheral portion of the metal tube end is provided. When the lead-out ends are welded and connected so as to cover the exposed portion of the optical fiber so as to cover it, the optical fiber is continuously coated. Such a connection is easily achieved.

When the metal tube coated optical fiber having the connection structure thus formed is laid in the bent portion, the sleeve tube is corrugated near the welded connection portion, and the wavy portion is formed. Has flexibility, stress concentration on the connection portion due to bending can be avoided.

Further, since the corrugated shape of the corrugated processing applied to the sleeve tube has a spiral shape along the tube axis, better flexibility can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the metal tube-coated optical fiber 15 is provided at the axial center of a metal tube 2 made of stainless steel or the like in which the single-fiber optical fiber 1 forms the metal tube coating layer 16. Besides stainless steel, copper, aluminum, titanium or the like may be used. Metal tube coated optical fibers 1, 1 connecting end 11a
At, the metal tube 2 is peeled off to expose the connection ends of the optical fibers 1 and 1. A sleeve pipe 3 having a predetermined length for covering the connecting portion 11 is fitted to the end of the metal pipe 2 on one side. The sleeve tube 3 is preferably made of the same material as the metal tube 2. Sleeve tube 3
In the vicinity of both end portions, a corrugated portion 12 is formed in which the diameter expansion and the diameter reduction of the pipe diameter are alternately repeated along the axial direction by corrugation processing.

FIG. 2 shows a structure in which the connection ends of the optical fibers 1 and 1 are connected to each other by fusion splicing or the like. Also, FIG.
Shows a state in which the sleeve tube 3 is drawn out on the connection portion 1A of the optical fibers 1 and 1 so as to cover it, and the ends of the metal tubes 2 and 2 are bridged. As shown in FIG. 3, both ends 3a, 3a of the sleeve pipe 3 are covered metal pipes 2, 2.
Are welded and connected along the outer periphery of to form a welded connection portion 4. For this welding, fusion welding (laser welding, light beam
Welding, Tiguak welding, electronic beam welding, etc.) and brazing (solder, silver brazing, etc.) can be used. The sleeve pipe 3 thus bridged and welded at both ends forms a coating of the connecting portion 11.

As shown in FIG. 3, in the vicinity of the welded connection portion 4, the metal pipes 2, 2 and the sleeve pipe 3 overlap each other,
The overlapping portion 13 is formed. These overlapping portions 13 are less flexible than the metal tubes 2 and 2. On the other hand, since the corrugated portion 12 is located near the overlapping portion 13, the connecting portion 1
1 has a large flexibility in the wavy portion 12. Therefore, the metal tube-coated optical fiber 15 including the connection portion 11 has a structure in which the force for bending the same acts as the force for bending the wavy portion 12, and the stress is not concentrated on the overlapping portion 13.

Although the corrugated shape of the corrugated portion 12 is such that the diameter of the pipe is enlarged and the diameter of the pipe is alternately reduced along the axial direction, if it is formed in a spiral shape, it is twisted. It is more preferable because it is also effective.

Next, operation of the embodiment will be described.

When the metal tube coated optical fiber 15 having the connecting portion 11 is laid in a bent portion or the like, a bending force is applied to the connecting portion 11. In FIG. 3, assuming that a bending force is applied in a direction of extending the upper portion and compressing the lower portion, the wavy portion 12 formed by corrugation processing.
Expands at the top and compresses at the bottom. Thus the wavy portion 1
The bending stress applied to the welded connection portion 4 and the overlapping portion 13 is absorbed by the bending of 2.

Next, specific examples of the present invention will be shown.

In the metal tube coated optical fiber 15 shown in FIGS. 1 to 3, as the optical fibers 1 and 1, a single mode optical fiber coated with an ultraviolet curable resin (hereinafter referred to as UV resin) and having an outer diameter of 0.4 mm is used. The outer diameter is 0.9 mm, the inner diameter is 0.7 mm, and the length of each metal tube is 2 k.
Two metal tube-coated optical fibers 15 were obtained using a stainless steel (SUS304) tube of m.

On the other hand, the sleeve pipe 3 has an outer diameter of 1.2 m.
A stainless steel (SUS304) tube having a diameter of 1.0 mm, an inner diameter of 1.0 mm, and a length of 1200 mm is used, and a pitch of 1 from a position of 20 mm to a position of 50 mm from both ends of this sleeve pipe 3.
Corrugation was performed using a swaging machine at mm to give flexibility.

The metal tubes 2 and 2 were cut and removed up to 650 mm from the ends to expose the optical fibers 1 and 1 as shown in FIG. 1, while the sleeve tube 3 was fitted to the end of the metal tube 2.
Here, the reason why the optical fibers 1 and 1 are exposed by 500 mm or more is to obtain the length necessary for performing the pull-off test of the optical fiber connection portion.

Next, as shown in FIG.
The terminals are fused and connected, and the connecting portion 1A is recoated with the UV resin.

Next, the sleeve pipe 3 is changed from the state shown in FIG.
Then, the end portion was fitted into the covered metal tube 2 on the other side. Then, both ends of the sleeve pipe 3 and the metal pipe 2 are connected to a laser beam (YAG laser) welding machine 10
The welded portion 4 was welded and fixed. Here, the welding conditions are: metal tube coated optical fiber rotation speed: 1 rpm, laser
The power was 0.4 J and the pulse interval was 2 seconds. Under this condition, the internal temperature of the metal tube 2 of the welded portion 4 was 120 ° C. at maximum, and no deterioration of the optical fiber coating material was observed.

The connection structure formed as described above is
It was found that the stress is not concentrated by bending and the tensile strength is the same as in the conventional case.

[0029]

The present invention exerts the following excellent effects.

(1) Since stress is not concentrated by bending, damage during installation and transportation is prevented.

(2) Connection is easy as before, and no additional process or special tool is required.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one of the connecting steps of one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing one of the connecting steps of the embodiment of the present invention.

FIG. 3 is a sectional view showing an embodiment of the present invention.

FIG. 4 is a cross-sectional view showing one of connection steps of a conventional example.

FIG. 5 is a cross-sectional view showing one of connection steps of a conventional example.

FIG. 6 is a cross-sectional view showing one of connection steps of a conventional example.

FIG. 7 is a cross-sectional view showing one of connection steps of a conventional example.

FIG. 8 is a cross-sectional view showing a conventional example.

FIG. 9 is a cross-sectional view showing a conventional example.

FIG. 10 is a cross-sectional view showing a conventional example.

FIG. 11 is a cross-sectional view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 1A connection part 2 Metal tube 3 Sleeve tube 4 Weld connection part 15 Metal tube coating optical fiber 16 Metal tube coating layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tatsuo Teraoka, Inventor Tatsuo Teraoka 5-1-1, Hidaka-cho, Hitachi, Ibaraki Hitachi Cable Ltd., Optro System Research Laboratories (72) Inventor, Yasutoshi Yoshie 1-chome, Marunouchi, Chiyoda-ku, Tokyo No. 1 and 2 inside Nippon Steel Tube Co., Ltd.

Claims (2)

[Claims] 1. A metal tube coated with an optical fiber housed in a metal tube, the metal tubes of the connecting ends are removed, and the optical fibers exposed from the ends of the metal tube are connected to each other. A sleeve tube is coated on the connection part of the optical fiber together, and at least the outer surface of the sleeve tube is provided in a connection structure of a metal tube-coated optical fiber in which both ends of the sleeve tube are welded to the both metal tubes. A metal tube-coated optical fiber connection structure characterized in that a corrugated part is applied. 2. The connection structure of a metal tube-coated optical fiber according to claim 1, wherein the corrugated shape of the corrugated processing applied to the sleeve tube is a spiral shape along the tube axis.