JPS5838902A - Optical fiber submarine cable - Google Patents

Abstract

PURPOSE:To avert direct contacting of tensile wires with an optical fiber unit and to protect the optical fiber unit against side pressure by covering the optical fiber unit with a thick-walled small diameter pipe using a plastic material of high tensile strength. CONSTITUTION:A tensile wire 1 is provided at the center of a cable, and the circumference thereof is enclosed with a cushion body 3 consisting of a material having small Young's modulus such as silicone rubber or elastomer. Optical fibers 2 are disposed at a constant interval in the body 3 so as not to contact with each other, whereby an optical fiber unit is constituted. The optical fiber unit is stored in a plastic pipe 4 and the outside circumference of the unit is in tight contact with the pipe 4. Tensile wires 5 are aggregated on the outside circumference of the pipe 4 in tight contact therewith. A metallic tube 6 of copper or aluminum is formed on the outer side of the wires 5, and a PE insulator 7 is formed by extrusion molding on the outside circumference of the tube 6. If necessary, an external jacket 8 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical submarine cable using optical fibers.

Optical submarine cable systems using optical fibers are expected to be significantly more economical than conventional coaxial systems, so their development is actively progressing, and various proposals for optical submarine cable structures are being prototyped and tested. has been done.

Currently being tried are: 1. Directly assembling tensile strength wires on top of an optical fiber assembly called an optical fiber unit, optical fiber core, etc.; 2. The two main plans are the overturning plan and the plan for ■, butt pipe.

Welded pipes, three-part collecting pipes, etc. are being prototyped and evaluated.

The above-mentioned method (2) in which the tensile strength wires are directly assembled on the optical fiber unit requires high-level manufacturing because hard tensile strength wires such as piano wire must be precisely assembled on the same circumference on the soft optical fiber unit. It requires technology and also has no odor after manufacturing.

However, when a large tension is applied to the cable or high water pressure is applied, the piano wire holds down the optical fiber unit, causing microbending in the optical fiber and increasing optical fiber loss.

On the other hand, the plan (2), in which the optical fiber unit is housed in a metal tube, has an inner diameter of 3 to 4 tubes, although the drawbacks of the plan D are eliminated.
Thick IWr! Due to the high level of manufacturing technology needed to manufacture thick-walled metal tubes with a diameter of about Compared to the above plan (■), the manufacturing process is increased, which is not desirable in terms of making the cable economical.

The present invention solves the above-mentioned drawbacks of the prior art and provides an optical fiber submarine cable that is easy to manufacture in long lengths and is economical.

The present invention avoids direct contact of the tensile strength wire with the optical fiber unit by covering the optical fiber unit with a thick-walled, small-diameter tube made of plastic material with high tensile strength, and also prevents the optical fiber unit from coming into contact with the optical fiber unit from lateral pressure. It is characterized by protection.

By extrusion molding this plastic tube onto an optical fiber unit, a long tube without any connections can be realized with good manufacturability, making it possible to make the cable lighter and more economical.

Examples of the present invention will be described in detail below.

Figure 1 shows a specific example of the present invention, in which a tensile strength wire 1 necessary for manufacturing an optical fiber unit is provided at the center of the cable.
It is surrounded by a buffer body 3 made of a material with a small Young's modulus, such as silicone rubber or elastomer, and optical fibers 2 are arranged within this buffer body 3 at regular intervals so as not to come into contact with each other. These tensile strength lines 1. Optical fiber 2. The buffer bodies 3 are collectively referred to as an optical fiber unit.

This optical fiber unit is protected by a buffer body 3 to prevent microbending from occurring when an external force is applied to the optical fibers 2, and the optical fibers 2 are assembled in a spiral shape in the length direction. When the cable is stretched, the optical fiber 2 moves toward the center of the cable, which has the effect of relieving the tension applied to the optical fiber 2. The outer diameter of the unit is 4 to 5 m.

The optical fiber unit is housed in an extruded plastic tube 4 surrounding the unit.
The outer periphery of the unit and the plastic tube 4 are in close contact. As the plastic material, thermoplastic materials such as polycarbonate and polyethylene, which are easy to manufacture into tubes, are used. Tensile strength wires 5 are closely assembled around the outer periphery of the plastic tube 4 as shown in FIG. In this case, when the tensile strength wires 5 are arranged without any gaps on the same circumference, the plastic tube, 4
The diameter of the plastic tube and the tensile strength wire are selected so that there is no space between the tensile strength wire 5 and the plastic tube 4.

A metal tube 6 made of copper or aluminum is formed on the outside of the tensile strength wire 5, and the metal tube 6 is inserted between the tensile strength wires 5 through a die to create a stable structure. A polyethylene insulator 7 is extruded on the outside of the metal cheapo, and an external jacket 8 is provided if necessary.

Furthermore, if it is necessary to improve the waterproofness of the optical fiber 2, waterproof material such as polypropylene is added between the outer periphery of the optical fiber unit and the plastic tube 4, and between the plastic tube 4 and the tensile strength wire 5, or both. The optical submarine cable, which can be filled with an admixture, is thus easy to manufacture and does not require the manufacture of small-diameter metal tubes, and maintains high water pressure resistance due to the collecting pipe of the tensile strength wires 5. Therefore, it is important that the tensile strength lines are precisely arranged on the same circumference, as shown in an enlarged view in FIG.

When repairing an optical submarine cable, the cable is pulled up from 8,000 meters of deep sea and held on a cable ship for a long time, and several tons of tension is applied to the cable, so it is necessary to lay the cable on the cable ship. Large lateral pressure is applied on the mechanism.

When applying lateral pressure in the direction of arrow A to the optical submarine cable, Figure 3
As shown in (a), the polyethylene insulator 7 is deformed,
A gap as shown at 10 in FIG. 3 is created between the metal tube 6 and the polyethylene insulator 7, and the metal Q-Pro is deformed into a slightly elliptical shape.

In the optical submarine cable according to the present invention provided with the plastic tube 4, when the lateral pressure is removed, the elastic force of the polyethylene insulator 7 and the plastic tube 40 acts as shown by arrow A2 as shown in FIG. 3(b), making the cross section of the metal tube 6 circular. For restoration, the tensile strength lines 5 are arranged on the same circumference.

That is, when the cable is put into the water and high water pressure is applied, the large lateral pressure is removed, and the cable has a circular cross section, so it can withstand high water pressure. Cable repairs in deep sea areas are extremely rare, and such large lateral pressures are not normally applied during cable installation.

By protecting the optical fiber unit with a plastic tube, the present invention has the ability to restore the cable shape against large lateral pressure that occurs extremely rarely, without damaging the cable's original water pressure resistance. This provides an economical optical submarine cable that is lightweight and easy to manufacture.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a partially enlarged cross-sectional view of an optical fiber submarine cable according to the present invention, and FIG.
(a) and (b) are cross-sectional views for explaining the influence when lateral pressure is applied to the optical fiber submarine cable according to the present invention. l...center tensile strength line, 2...optical fiber, 3...
Buffer body, 4... plastic tube, 5... tensile strength wire,
6...Metal tube, 7...Polyethylene insulator,
8...External jacket, 10...Void. Patent applicant Kokusai Telegraph Kiwa Co., Ltd. Agent Otsuka 1 person from outside the university

Claims (1)

[Claims] (1) An optical fiber unit in which at least one optical fiber is embedded in a buffer with a small Young's modulus, a plastic tube surrounding the optical fiber unit tightly or via a waterproof mixture, and the surroundings of the plastic tube. A tensile strength wire layer that is assembled in close contact with or through a waterproof mixture, a metal tube that is placed in close contact with the periphery of the tensile strength wire layer, and an insulator layer that is placed around the outer periphery of the metal tube. Fiber optic submarine cable.