JPS58150904A - Submarine optical fiber cable - Google Patents

Abstract

PURPOSE:To suppress the elongation of a cable when it is laid or lifted up at a deep-sea part by using aluminum for internal layer and an external layer pressure-tight pipe. CONSTITUTION:The optical fibe cable consists of an optical fiber core 1, center base 2, buffer layer 3, internal layer pressure-tight pipe 9 of aluminum, steel stranded wire 5 made of piano wire 5, and external layer pressure-tight pipe 10 of aluminum, and the steel stranded wire 5 is sealed by the external layer pressure-tight pipe 10. Further, an insulating layer 7 made of low-density polyethylene is arranged around the pipe; and a sheath made of high-density polyethylene containing carbon black is further arranged around it. Consequently, the pressure-tight pipe is made thin in an area selected according to pressure-tightness and manufacture, so the underwater weight of the cable is reduced to suppress the elongation of the cable when it is or lifted up at a deep-sea part.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to submarine optical fiber cables used in the field of submarine optical communications.

Compared to conventional electrical communication, optical communication allows signal transmission lines to be significantly lighter, heavier, and smaller, so development is progressing in all forms of communication.
As a link to this, research is being conducted on submarine optical fiber cables to replace submarine coaxial cables. FIG. 1 shows a cross-sectional view of a conventional submarine optical fiber cable. Optical fiber core 1
are arranged around the center support 2, and are housed in an internal pressure-resistant pipe made of steel via a buffer layer 8. A stranded steel wire 5 is wound around the internal pressure-resistant tube 4, and the tube is further sealed with a pressure-resistant vibro made of external steel. Further, a layer of an insulator (low density polyethylene) 7 is formed around it, and an outer cover (high density polyethylene) 8 is further formed around it. Because of this structure, the weight of the copper material of the pressure-resistant vibro has a large effect on the underwater heavy line of the cable, and the cable elongation during installation and salvage in deep sea areas is extremely large, resulting in a water depth of 5 QtIQ. When installed at a depth of 11 mm or more, the required elongation of the optical fiber during the screening test is 2% or more, which is a low price that is difficult to achieve for long fibers.

The present invention is characterized by using aluminum as the material of the inner pressure-resistant pipe.The purpose of the present invention is to reduce the need for submerged submarine optical fiber cables underwater by making the material of the inner pressure-resistant pipe aluminum. The objective is to suppress the elongation of the cable during operation, thereby suppressing the breakage of the optical fiber.

The elongation of submarine optical fiber cables during installation and salvage depends on the cable's placement in the water, and therefore the elongation cannot be reduced simply by increasing the cross-sectional area of the central tensile strength member of the cable. To reduce elongation, without changing the tensile stiffness of the cable,
It is effective to reduce the underwater mW of the cable.

Figure 2 shows the relationship between the elongation of a conventional submarine optical fiber cable and the tensile rigidity of the central tensile strength member. In Figure 2, the total q value "L!", which takes into account the copper yielding phenomenon of pressure-resistant pipes, is indicated by a line, but the trends between the calculated values and the experimental values are the same, and the tensile rigidity decreases due to the copper yielding phenomenon. The calculated value of the tensile stiffness of only the steel stranded wire is shown by the broken line, but as the elongation strain increases, the experimental value approaches this value and is almost dominated by the tensile stiffness of only the steel stranded wire. Therefore, in the region of large strain, it is only necessary to consider the tensile stiffness of the steel strands.In this case, the elongation ε of the cable is determined by the following formula (Reference: IEE Proceedings
vol, l 28-H, A6″Design an
dOharaacteristics of Subma
line 0ptical 0ableN, Kojim
a et al+) εzαρh (1+A'ρ'/A+')/βEt(1
) However, α is the coefficient related to installation and salvage, β is the tensile stiffness correction coefficient of the tensile strength member, h is the water depth, Et is the second coefficient of the tensile strength member, A′ is the cross-sectional area of the pressure-resistant pipe, and ρ′ is the underwater density of the pressure-resistant pipe. , A is the cross-sectional area of the tensile strength member, and ρ is the density of the tensile strength member in water.

As shown in equation (1), when a pressure-resistant pipe is placed underwater, A'
It is closely related to the elongation during installation and lifting in the form of ρ′. As shown in equation (1), the density ρ of the tensile strength member is
, the elongation ε will be small if a material with a Chang Young's modulus E is used.

FRP, Kevlar, piano wire, etc. are effective as low-density rK% high Young's modulus materials, but the material for the tensile strength body should be selected in consideration of power supply to the repeater, cable sinking speed, economic efficiency, and connection workability. It is necessary to select a metal material, and piano wire is the most suitable material considering these points.

In addition, for pressure-resistant pipes, the shape A'ρ' is related to the elongation during installation and salvage, so for pressure-resistant pipes, if the density is low and the cross-sectional area is made small, it has the effect of suppressing elongation. Recognize.

For this reason, removing the inner or outer layer of pressure-resistant pipes will result in
Although it can be expected that the elongation characteristics of the cable will be improved, the effect cannot be expected to be very great due to the following discussion.

Figure 3 shows a cross-sectional view of a submarine optical fiber cable with the outer layer pressure-resistant vibrator removed. The tensile strength body is made by twisting the steel wires of the inner and outer layers oppositely and removing the untwisting of the clay strands when tension is applied. A comparison is shown in Figure 4. The elongation of the cable during installation and lifting depends on how the cable is placed in the water, so the normalized tension is calculated using the value obtained by removing the tension by placing the cable in the water on the horizontal axis. Here's a comparison. As shown in FIG. 4, contrary to expectations, when the pressure-resistant pipe is 1M, it stretches more easily. This is because displacement in the plane diameter direction of the tensile strength member when tension is applied affects elongation in the longitudinal direction, making it easier to elongate. However, if there are pressure-resistant pipes in the inner and outer layers, the structure is such that the outer layer pressure-resistant pipes are sinked, so the initial deformation caused by springback in the rear direction of the tensile strength body can be removed when sinking the outer layer pipes, and the steel strands are It is possible to bring out the tensile rigidity of the wire itself.

This effect appears as the effect of β in equation +11, and estimated from the experimental results, the outer layer pipe? r: 0.5 in β in case of removed alternate twist, β-+1.0 in case of sinking with outer layer pipe, and effect of removing outer layer pressure vibrator in case of alternate twist tensile strength body with outer layer pressure vibrator removed. Rather than sinking the tensile strength member, the effects of deterioration factors on the structure of the tensile strength member become more significant. For this reason,
A pressure-resistant vibrator is placed on the inner and outer layers, and a cable with good structure and elongation properties can be achieved by sinking with the outer layer pressure-resistant vibrator.

Based on the above discussion, pressure-resistant pipes are placed in the inner and outer layers,
A pressure-resistant pipe made of a material with a low density is effective, but if you look for a metal with a low density in consideration of manufacturability and economy, aluminum is the most suitable.

FIG. 5 shows an embodiment of the present invention in consideration of the above considerations.

In Fig. 5, 1 is an optical fiber core, 2 is a central support, 8 is a buffer layer, 9 is an aluminum inner layer pressure-resistant pipe, 5
0 is a steel stranded wire made of piano wire, and 0 is a structure in which the steel stranded wire 5 is sealed with an aluminum outer layer pressure-resistant vibrator. Further, an insulating layer 7 made of low-density polyethylene is arranged around the insulating layer 7, and an outer cover made of high-density polyethylene mixed with carbon black is further arranged around the insulating layer 7.

Next, when aluminum is used, the lateral pressure resistance and water pressure resistance are lower than those of copper, so a certain degree of wall thickness is required from the viewpoint of pressure resistance. Lateral pressure resistance strength F. The relationship between and the structure of the pressure-resistant pipe is given by the following equation.

(Reference: Institute of Electronics and Communication Engineers technical report os-so-194
[Design of submarine optical fiber cable (Part 2) Kojima et al.] However, σb is the breaking stress of aluminum (kg/mm
2) t is the wall thickness of the vibrator (Al111, r is the average height (mm) of the pressure-resistant pipe, and is the distance between the center of the vibrator and the center of the vibrator's wall thickness. Calculated value and experimental value shown in equation (2) A comparison is shown in Figure 6.The diagonal line indicated by the straight line in Figure 6
The second value indicates that the calculated value and the experimental value agree.

As described above, it can be seen that the lateral pressure resistance strength of the pressure pipe can be well estimated using equation (2).

In addition, Fig. 7 shows a comparison of the lateral pressure resistance strength of the inner layer vibrator and the lateral pressure resistance strength of a composite structure made of 1711i steel stranded wire and outer layer pipe. It can be seen that the improvement is over 40%. Therefore, assuming that the lateral pressure resistance strength will increase by 40% due to the combined effect, the lateral pressure resistance strength F of the composite vibrator can be estimated using the following formula: nF -1,4F0t3) The required lateral pressure strength during installation and salvage is 6 kg/mm
Since the following equation holds true:

1r>6+Jcs+/fight) (4) When this lateral pressure strength is satisfied, the water pressure resistance strength is 1 (l
It has been experimentally confirmed that the cable satisfies the water pressure of 10,000 m or more in terms of seawater pressure, indicating that it can be installed in any sea area.

Formula (2), +4. ), the following relationship can be obtained between the structure and material strength of the inner layer pressure-resistant vibrator.

, );j, 1JIK9/mm41hJ For the inner layer pressure-resistant pipe, if a thinner wall thickness is selected in the region that satisfies formula (5) and in consideration of manufacturing aspects, 1 elongation characteristics can be improved.

Regarding the outer layer vibrator, since the outer layer pipe alone hardly contributes to the pressure resistance strength, it is better to consider the tJBe property and the sinking thickness of the steel stranded wire, and select the thinner thickness.

FIG. 8 shows the relationship between the required screening strength of a cable designed in this design area and a conventional cable using copper. As shown in Figure 8, conventional cables have a water depth of 50 mm.
(If applied to l When using an optical cable, the required screening strength is approximately 1.0 to 1.2%, which is the required value for a long optical fiber that can be achieved in reality. A submarine optical fiber cable can be realized.

Furthermore, even if the outer layer pipe is made of copper in order to reduce corrosion by seawater, the effect of improving elongation characteristics will be slightly reduced, but a considerable effect can be expected as shown by the broken line in FIG. 8.

As explained above, in the submarine optical fiber cable of the present invention, aluminum is used for the inner layer pressure-resistant pipe and the outer layer pressure-resistant pipe, and the thinnest wall thickness is selected from the viewpoint of pressure resistance and manufacturing. It is possible to create a cable that can significantly reduce the need to be placed underwater and greatly suppress cable elongation during installation and salvage in deep sea areas.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the structure of a conventional high-bottom optical fiber cable, Figure 2 is a diagram showing the relationship between the strength and stiffness of a conventional submarine center tensile strength body, and Figure 8 is an outer layer pipe. 4 is a comparison diagram of the elongation characteristics of the cable shown in FIG. 1 and the cable shown in FIG. 3, and FIG. 5 is a cross-sectional view showing the structure of a submarine optical fiber cable of the present invention. 6 is a diagram showing the relationship between calculated values and experimental values of lateral pressure strength, and Figure 7 is a diagram showing the effect of improving lateral pressure strength by using a composite structure.
FIG. 8 is a diagram comparing and showing the results of required screening tests for various submarine optical fiber cables. ■... Optical fiber core wire, 2... Center support, 3...
・Buffer layer, 4. ...Pressure pipe (inner layer copper pipe), 5...
・Steel stranded wire, 6...Pressure resistant pipe (outer layer copper vibe), 7
... Insulator (low-density polyethylene), 8 ... Outer cover (high-density polyethylene), 9 ... Aluminum inner layer pipe, 10 ... Aluminum outer layer pressure-resistant pipe.・ 12 Katsu'IL f) Extension 3° (%) Fig. 3 Fig. 4 Force/underwater medium weight (Ksu Fig. 5 Fig. 6 Fig. 7 Vibrator's 9. Shape (m effort rM value) (Kμ7) Figure 8, Iku Political situation (Kria) Continuation of page 1 0 Inventor Momokibata Nippon Inuyo Submarine Electric Cable Co., Ltd., 1-16-10 Dogenzaka, Shibuya-ku, Tokyo Inventor Person: Shigeru Tanaka, Sumitomo Electric Industries, Ltd., 5-15 Kitahama, Higashi-ku, Osaka, Japan Applicant: Nippon Inuyo Submarine Cable Co., Ltd., 1-16-10 Dogenzaka, Shibuya-ku, Tokyo Applicant: Sumitomo Electric Industries, Osaka 5-15-20 Kitahama, Higashi-ku, Ichiha

Claims (1)

[Claims] L: an optical fiber support in the center, a plurality of optical fiber cores arranged around it, a buffer layer arranged around its outer periphery,
Furthermore, it is composed of a pressure-resistant pipe made of aluminum placed around the outside.The wall thickness of this aluminum pipe is t (mm), the distance between the center of the pipe and the center of the wall thickness is r (tomo), and the breaking stress of the aluminum is σb. Select a wall thickness t within a range of 1, then seal the stranded steel wires with a pipe made of aluminum or copper, and set the thickness to the thinnest thickness within the range that can be manufactured. A submarine optical fiber cable characterized by a copper pipe surrounded by plastic.