JPS597361B2 - fiber optic submarine cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cable structure suitable for a long-distance optical fiber submarine cable in the field of optical 15-fiber communication using a low-loss optical fiber as a transmission medium.

Optical fibers have features such as low loss, broadband properties, non-inductive properties, and light weight, so they are very advantageous as broadband transmission media.

For this reason, attempts are being made in various fields to convert optical fibers into cables for high-capacity communications, and there are also reports of several applications of optical fibers to submarine cables, focusing on their broadband and low-loss characteristics. has been done. 25 For example, according to ``Submarine Cable'' published in Japanese Patent Publication No. 51-99032, the structure is as shown in FIG.

FIG. 1a shows an example of a cable structure using a single pressure-resistant pipe characterized by its small diameter. Four optical fiber core wires 30 in which the coating 2 is applied to the optical fiber bare wire 1 and two feeder lines 7 in which the insulation layer 9 is applied are gathered around the tension member 8, and the surroundings are covered with the heat insulating layer 3, This prevents heat from being transmitted to the optical fiber during pipe formation. The outside of the optical fiber is covered with a pressure buffer layer 4 to prevent local pressure from being applied to the optical fiber, and a pressure-resistant pipe 5 protects them. 6 is protective plastic.

Figure 1b shows a cable in which the units of a are assembled 1|.

A tension member 10 is placed in the center, and six pressure-resistant pipes 11 are gathered around it 2 and fixed with plastic 12. It is covered with a waterproof layer 13 and further protected with plastic 14. In addition, if the power supply line is placed outside the high-pressure pipe in the unit shown in Figure 1a, please refer to Figure 1c.
The configuration is as follows. Reference numeral 15 is a power supply line, and other than that, the structure is the same as that shown in FIG. 1b.

This cable is now used as a long-distance submarine cable21,
In this case, in a structure in which the power supply line is inside a pressure-resistant pipe as shown in FIG. 1a or b, the pressure-resistant pipe must have a very large diameter.

The reason for this is, for example, when considering a submarine cable system connecting Japan and Hawaii, the power supply voltage required to transmit 12,000 telephone lines is 0.5Ω, assuming the voltage required for one repeater is 32V. 165 even when using a feeder line with a relatively small resistance value of /Icm.
00V (transmission speed 400Mbit/s, 2 systems, number of relays 248), even if copper is used as the feeder line, the thickness needs to be 6.64m1L, and if you put this in a pressure-resistant pipe together with the optical fiber,! This is because in order to withstand water pressure at a depth of 8,000 meters, the inner diameter of the pipe must be at least ten millimeters, and the wall thickness of the pipe must be about 5 mm.

This is no longer a small-diameter pipe, and therefore it does not lose the advantage of pipe manufacturing, which is easy to manufacture due to its small diameter as claimed in this earlier invention (in this earlier invention, it is molded using a rollformer). be exposed. In fact, it is extremely difficult to manufacture thick-walled pipes using the forming method specified in this prior invention. Therefore, it is extremely difficult to realize a long-distance deep-sea submarine cable with this structure.
Next, in the structure shown in FIG. 1c, the power supply line extends outside the pressure-resistant pipe, so there is no need for the power supply line inside the pipe.

However, in this case as well, in addition to the optical fiber, a heat insulating layer and a pressure buffer layer are required inside the pipe. In particular, the heat insulating layer is very important because it prevents heat from being transferred to the optical fiber during pipe manufacturing, and it must have a sufficient heat insulating effect. Therefore, when these are placed in a pipe together with several optical fibers, it is difficult to make the inner diameter 1 mm as described in this prior invention, and a large inner radius is required, which inevitably results in The wall thickness becomes thicker, and in this case as well, it becomes difficult to manufacture the pipe using the molding method.

Furthermore, considering that the cable as a whole will be laid in the deep sea at a depth of 8,000 m, not only the power supply line but also the tension member will be quite thick.

Therefore, according to this structure, since the thick feeder line and the thick tension member are arranged in a line, the cable diameter becomes thick and it is difficult to bend in that direction, which is a major drawback in terms of economy and installation. . Furthermore, since the optical fiber is not located at the center of the cable, there is a loss in length due to the helical pitch, making it uneconomical. Therefore, it is difficult to manufacture a long-distance deep-sea submarine cable with this structure, and it is not suitable for both economical and installation considerations. In addition, Tokukai Sho 5
No. 1-1121342 has an example of a structure called "optical fiber cable" as shown in FIG. 2. Here, 16 is an optical fiber core wire, 17 is a space or a jelly-like substance, 5 is a pressure-resistant pipe,
18 is a soft plastic or rubber, 10 is a tension member, and 19 is a cable jacket. In this structure, when the power supply line is also used as a pressure-resistant pipe, the power supply line has a large diameter as described above, so the pressure-resistant pipe has a thick wall. Law (
It is difficult to manufacture using the pipe extrusion method or the same molding method as the "submarine cable" mentioned above. The same applies when the power supply line is inside the pipe. If the feeder line is outside the pipe, the structure will be similar to that shown in Figure 1c, so if you look at the entire cable, it will be used as a long-distance deep-sea submarine cable for the same reason as in Figure 1c. is not suitable. In this way, the conventional optical fiber submarine cable structure uses pressure-resistant pipes by extrusion method or molding method using a wall former, so it is heated during the production of the pressure-resistant layer, and external forces are also applied, which has a negative impact on the optical fiber. You will end up losing the money.

Therefore, when manufacturing pipes, it is desirable to be able to manufacture a long pressure-resistant layer with a thick wall and a small diameter without applying heat or external force. This is difficult with conventional cylindrical tube manufacturing methods. The present invention focuses on these points, and uses a thick pressure-resistant layer that protects the optical fiber from external pressure, is easy to manufacture, does not require heating, and does not suffer from external forces, thereby simplifying the cable structure. In addition, it is easy to implement measures to prevent failures by installing a waterproof dam inside the pressure-resistant layer or filling with a highly viscous liquid to prevent seawater from entering. It provides an economical optical fiber submarine cable. The present invention will be explained in detail below using the drawings.

FIG. 3 shows a typical structural example of a voltage-resistant layer according to the present invention.
Figure 3a shows a pressure-resistant material divided into several equal parts and combined to form a single pressure-resistant layer. In this example, the number of divisions is three. This is because in the case of an even number of divisions such as 2 divisions (half ring) or 4 divisions, after the cable is made, the mating surfaces of the individual pieces are located on both sides of the same diameter when viewed from the center of the pressure layer, and the external force causes each division to In contrast, when the cable is divided into odd numbers, each piece has a wedge-shaped cross section, and the mating surfaces of the pieces are not located on the same diameter, which prevents the wedge effect from occurring when water pressure is applied to the cable. This has the effect of maintaining the cylindrical shape normally by mutually adjusting the positions of the individual pieces. However, when the number of divisions is large, it becomes difficult to maintain the required strength and precision for each individual piece and form it into a normal cylindrical shape during manufacturing, so the optimal number of divisions is 3, which is the minimum odd number of divisions. be. In this structure, a single cylindrical pressure-resistant layer is formed by continuously aligning deformed wires 20 having fan-shaped cross sections around the optical fiber core wire 16. This pressure-resistant layer material is one that can withstand seawater pressure in the deep sea (for example, 800 atmospheres at a depth of 8000 m). When these pieces are fitted together, each piece may be provided with a groove and a matching protrusion to prevent relative displacement between the pieces, as shown in FIG. 3b. Further, it is also possible to manufacture a thick pressure-resistant layer in a multilayer structure as shown in FIG. 3c. It is conceivable to fix the joints of each piece with adhesive in order to provide adhesion to each piece of the pressure-resistant layer, but it is also possible to wrap the combined pressure-resistant layer with aluminum tape or the like and fix it. can. Since each divided piece 20 of these pressure-resistant layers has exactly the same shape, the irregularly shaped wire can be manufactured simply and economically because a long round wire can be drawn by drawing a fan-shaped die.

In addition, when manufacturing such a pressure-resistant layer, the required pressure-resistant characteristics are obtained by crimping each divided element to each other, so the relative position of each divided piece of the pressure-resistant layer is firmly fixed in the process. Since there is no need to apply heat, there is no need for a heat insulating layer, and there is no need for an optical fiber coating.
7 heat-713-・Sokasho-ei f-Homare Tate Rokushin Ichijima 儫 6 does not cause any adverse effects on the transmission characteristics of the optical fiber. Further, even if mechanical bending, twisting, etc. occur randomly in the cable, since each divided piece has the same shape, an equal force is applied to each piece, so that no part of the cable is likely to break. If an accident were to occur and the submarine cable was damaged during or after it was laid, seawater would seep into the pressure-resistant layer, making it necessary to replace the entire relay section.

In order to avoid this, the present invention can employ a structure in which waterproof dams are provided at appropriate intervals within the pressure-resistant layer. This means that even if the pressure layer is damaged due to an accident, only that dam section needs to be replaced. FIG. 4 shows the state of the dam installed within the pressure-resistant layer. Pressure-resistant layer 23
The optical fiber core wire 16 is housed inside, and dams 22 are provided at appropriate intervals using adhesive or the like. Now, when the water pressure applied to the pressure layer is Pe, and the inner diameter of the pressure layer is r, the required length l of the dam is calculated using the following formula. Here, τs is the shearing force per unit area between the adhesive and the inner surface of the pressure-resistant layer.

This relationship is shown in FIG. 5 for a water depth of 8000 m. In the figure, the horizontal axis represents the inner diameter of the pressure-resistant layer, and the vertical axis represents the required dam length. The parameter is the allowable shearing force, and it can be seen that the larger the allowable shearing force, the shorter the dam length. τs between normal epoxy adhesive and metal is 0
．． 5k9/M7l-0.7k9/Md, so when the internal diameter of the pressure layer is 4 mm, a dam length of 20 mm is sufficient. In this way, the dam is very easy to manufacture because it only needs to be very short. It is also possible to seal a liquid having an appropriate viscosity inside this pressure-resistant layer under an appropriate pressure. This makes it possible to relieve the external pressure applied to the pressure-resistant layer, apply uniform pressure to the optical fiber, prevent microbending from occurring, and prevent seawater from entering in the event of breakage. FIG. 6 shows a typical embodiment of a long-distance submarine cable using the pressure-resistant layer described above.

In the figure, 1 is an optical fiber wire, and 2 is a coating. 23
is a voltage-resistant layer, which can also be used as a power supply line.

Reference numeral 10 is a tension member for applying tension to the cable when the cable is laid or pulled up, and reference numeral 24 is an insulator made of, for example, polyethylene.

Now, the inner diameter of the pressure-resistant layer 23 is r, the wall thickness is t, and the yield strength is λ.

When a compressive force of Pe is applied to the pressure-resistant layer, the relationship between the minimum thickness of the pressure-resistant layer and the yield strength is given by the following equation. Here K is a safety factor.

At Pe2 8kg/Md (equivalent to 8000m depth) (
The results of equation 2) are shown in FIG.

The horizontal axis of the figure is the yield strength of the voltage-resistant layer, and the vertical axis is the ratio of the internal radius of the voltage-resistant layer to the minimum wall thickness. The parameter is the safety factor, and from this figure it can be seen that if the safety factor is 2, a material with a yield strength of 40 kg/Md or more is required. Table 1, which describes the cable dimensions when a high-strength Al alloy (equivalent to 2014) is used as this material, shows the physical properties of this Al alloy. Applying the tensile strength in Table 1 as the yield strength,
According to FIG. 7, t/r=0.68.

If, for example, four optical fibers are inserted into the pressure-resistant layer (for 12,000 lines, two systems are required at 400 Mbit/s), the inner diameter of the voltage-resistant layer is 4 mTL, which corresponds to the amount of light, so the minimum voltage-resistant layer thickness is 1.36 mm. . Next, if you use this as a feeder line, it will be 0.5Ω/ICI! In order to have a resistance of l, the inner diameter is 4m71L and the wall thickness is 3.6L according to the resistivity shown in Table 1.
It turns out that mm is sufficient. This sufficiently satisfies the requirements for a pressure-resistant layer. Therefore, the size of the pressure-resistant layer is an inner diameter of 4m77! By setting the outer diameter to 11.2 mm, it can function as both a power supply line and a voltage-resistant layer. Next, 8
When a cable is laid or salvaged from the seabed at a depth of 1,000 m, the tension that the tension member should have is the underwater weight of the entire cable from the seabed to the laying ship. The thickness of the cable is determined by the thickness of the insulating layer covering the outside of the voltage-resistant layer.
When polyethylene is used as an insulating layer, the dielectric strength of polyethylene is shown in FIG. The horizontal axis is the power supply voltage, and the vertical axis is the polyethylene thickness. A, b, and c each have the minimum corona resistance voltage of 1414V/M7! L1 average value 2121V
/Mm and maximum 2828V/M7! It is L. Since power is supplied from both terminals, the thickness of polyethylene required for a withstand voltage of 8250 V is 6 even in the case of polyethylene with the minimum corona withstand voltage.
7 nm is sufficient. Therefore, it can be seen that the outer diameter of the entire cable is about 25 mm. If a strand of steel wire is used for the tension member, the underwater weight of the cable can be calculated and the required cross-sectional area of the strand can be determined.
If the structure is as shown in FIG. 6, the outer diameter of each strand should be 2.54 m71 L. This strand can be easily realized using conventional techniques. Additionally, cables using such thick pressure-resistant layers generally have the disadvantage of being difficult to bend.

The allowable bending radius of this cable is determined by the outer diameter of the voltage-resistant layer, the Young's modulus of the voltage-resistant layer material, and the stress allowed in the voltage-resistant layer. In the case of Figure 6, if the proof stress in Table 1 is used as the allowable stress, the value is 0.987 m. Become. It can be seen that this satisfies the conditions for cable installation (allowable bending radius of approximately 1.5 m).
Although the structure described above serves both as a voltage-resistant layer and a power supply line, it is also possible to provide the voltage-resistant layer with the function of a tension member by using a material with high tensile strength for the voltage-resistant layer.

FIG. 9a shows an embodiment of a structure that functions as both a voltage resistance layer and a tension member. In the figure, 16 is a cored optical fiber, and 25 is a voltage-resistant layer and a tension member. 15 is a power supply line, and 24 is an insulating layer.

Further, as shown in FIG. 9b, by selecting an appropriate material, it is possible to create a structure that functions as a voltage-resistant layer, a power supply line, and a tension member. After all, when such a structure is adopted, the structure can be simplified because the breakdown voltage layer and the power supply line or tension member can be made the same.

Furthermore, since the optical fiber is located at the center of the cable, it is most protected from external forces, and since there is no need to wind it in a spiral shape, the optical fiber length can be kept at the shortest length, making it safe and economical. Furthermore, by selecting the material, the allowable bending radius of the cable can be adjusted to meet the conditions during installation, making it extremely practical. Since the feeder line and tension member become thicker, the cable structure can be simplified by using the thick pressure-resistant layer of the present invention, which is divided into three equal parts in the axial direction, instead of the conventional small-diameter pipe. .

This cylindrical pressure-resistant layer can be manufactured into irregularly shaped wires from each round wire by drawing a fan-shaped die, and can be manufactured by simply combining them, so that a thick layer can be obtained very easily. Furthermore, since no heating is required during manufacturing, there is no need for a heat insulating layer and there is no adverse effect on the transmission characteristics of the optical fiber. Also,
Since the cross-sectional shapes of the divided pieces are congruent, each piece receives an equal force from an external mechanical force, thereby preventing any portion from becoming easily broken. Furthermore, in case a submarine cable is damaged, installing a dam within the pressure-resistant layer or injecting viscous material can prevent seawater from entering and shorten the time required for repair. Economical. By placing this three-part cylindrical pressure-resistant layer at the center of the optical fiber submarine cable, the voltage-resistant layer can also function as a power feeder or a tension member.
A long-distance, deep-sea optical fiber submarine cable with a simple structure and excellent mechanical properties can be realized.

[Brief explanation of the drawing]

Figures 1A, b, c and 2 are cross-sectional views of typical embodiments of conventional fiber optic submarine cables; Figure 3A, b, c
is a cross-sectional view showing a typical structural example of a pressure-resistant layer according to the present invention,
FIG. 4 is a vertical cross-sectional view showing the state of the waterproof dam in the pressure-resistant layer according to the present invention, FIG. 5 is a characteristic diagram showing the relationship between the inner diameter of the pressure-resistant layer and the minimum required length of the dam, and FIGS. 6 and 9A. , b is a cross-sectional view showing a typical embodiment of the optical fiber submarine cable of the present invention, FIG. 7 is a characteristic diagram showing the relationship between the yield strength of the voltage-resistant layer and the required minimum voltage-resistant layer thickness, and FIG. 8 is the power supply voltage. It is a characteristic diagram showing the required wall thickness of polyethylene for. DESCRIPTION OF SYMBOLS 1... Optical fiber wire, 2... Coating layer, 3... Heat insulation layer, 4... Pressure buffer layer,
5...Pressure pipe, 6...Protective plastic, 7...Power supply line, 8...Tension member for optical fiber, 9... ...Insulating layer, 1
0... Cable tension member, 11...
...Pressure-resistant pipe single wire, 12...Fixing plastic, 13...Waterproof layer, 14...
Waterproof layer protection plastic, 15... Power supply line,
16... Optical fiber core wire,) 17...
- Space or jelly-like substance, 18... Soft plastic or rubber, 19... Cable jacket, 20... Pressure-resistant layer division piece, 22...
Waterproof dam, 23...Pressure layer, 24...
- Insulating polyethylene, 25... Voltage-resistant layer and tension member, 26... 5... Voltage-resistant layer and tension member and power supply line.

Claims (1)

[Claims] 1. In an optical fiber submarine cable that uses a low-loss optical fiber as a transmission medium, three irregularly shaped metal wires having equal cross-sectional shapes and fan-shaped shapes are combined to form at least one light beam in the center. 1. An optical fiber submarine cable comprising a cylindrical pressure-resistant layer configured to have an optical fiber accommodation space with a circular cross section for accommodating a fiber in the center of the cable. 2. The optical fiber submarine cable according to claim 1, wherein the metal material is a good electrical conductor.