JPS6147912A - Fiber unit for optical submarine cable - Google Patents

Abstract

PURPOSE:To obtain an optical fiber unit structure which can be manufactured continuously and easily, causes no water-run, and also is excellent in its handling property by constituting it so that one center supporting body and plural optical fiber core wires are embedded so as to make the whole surface contact to an ultraviolet hardening type resin. CONSTITUTION:The periphery of an optical fiber 1 is covered with a UV urethane resin layer 20 first, its periphery is covered with a UV epoxy resin layer 21, and also its periphery is covered with a thermoplastic resin layer 22 such as nylon, heitler, etc., and a core wire is formed thereby. Subsequently, a unit structure is formed by covering in advance the periphery of a center supporting body 8 of the same diameter as that of this core wire with a UV urethane resin layer 23, twisting together six core wires and collecting and placing them in its periphery, and packing its gap and periphery with a UV urethane resin 24 as a unit filling material. In such a way, by forming the unit filling material 24 and the covering 23 of the center supporting body 8 by the UV urethane resin of the same material, the resin layers 23, 24 are formed as one body, and the fiber core wire is embedded completely in the filling material 24.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to the structure of an optical fiber unit used in an optical submarine cable.

(Prior art and its problems) Optical fiber submarine cables have been designed for more than 20 years to avoid deterioration of the transmission characteristics and mechanical characteristics of the optical fiber, which is the transmission medium. Therefore, by housing the optical fiber in a water pressure structure, up to 800
The optical submarine cable structure protects the optical fiber from seawater pressure, which can reach atmospheric pressure.

Figure 1 shows a typical structural example of a conventional optical submarine cable.

In the figure, 1 is an optical fiber, 2 is a pressure-resistant structure, 3 is a tensile strength wire, 4 is a supply IE line, and 5 is an insulator such as polyethylene. In such an optical submarine cable, the optical fiber 1 is normally completely protected from moisture, but in the event of a failure such as the optical submarine cable being cut, seawater pressure of up to 800 atmospheres may be applied to the cable end. become,
If there is even a minute gap in the cross section of the cable, water leaks will occur in that gap. Generally, when an optical fiber is exposed to seawater, its mechanical strength deteriorates due to the action of Na ions and OH ions. In addition, the cable structure includes a feeder line 4 (Cu or A) as shown in Figure 1.
t), tensile strength wire 3 (piano wire), pressure layer 2 (At, Cu
or a combination of different metals such as Fe). When seawater enters the inside of such a cable, hydrogen gas is generated through an electrochemical reaction. Optical fibers have the property that when left in a hydrogen gas atmosphere, transmission loss increases significantly.

(MOCHIZUKI, K., NAMIHIRA
, Y, , and YAMAMOTO.

H: ” TRANSMISSION Loss I
NCREASE lN0PTICAL FIBRES
DUE To HYDROGEN PER Escape AT I
ON”, Electron, Lett, , 19
83, Vol, 19 A 18 pp, 743
(Refer to 745) As mentioned above, for optical submarine cables, it is important to protect the optical fiber from external pressure and to prevent seawater from entering the cable even in the event of a temporary failure. This is important for ensuring long-term transmission characteristics and mechanical strength. In order to satisfy these conditions, various housing structures have been adopted for housing the optical fiber 1 in the pressure-resistant structure 2. The optical fiber assembly housed within this pressure-resistant structure 2 is called a fiber unit.

FIG. 2 shows an example of the structure of a conventional fiber unit. In the figure, 1 is an optical fiber, 6 is a silicon buffer layer for protecting the optical fiber 1 from external forces, 7 is a nylon coating,
8 is a tensile strength wire for obtaining the tensile strength necessary for manufacturing the optical fiber unit, and 9 is a soft silicon filling material that completely fills the optical fiber unit. The multiple optical fibers 1 are twisted together at a constant pitch to prevent local distortion by fixing their mutual positional relationship, and to provide extra length that can follow the cable's elongation. It is embedded in material 9. In this structure, silicon acts as a buffer layer and is said to be extremely stable in terms of transmission and mechanical properties. In addition, the unit structure shown in Fig. 2 is a completely solid structure with no visible gaps, and when this unit is housed in the pressure-resistant structure 2, the locks are filled with sherry-like filler, etc. Measures were taken;
Even after converting to a cable, it still appears to have a complete structure.

However, since silicon (thermosetting silicone resin) is used for the buffer layer 6 and the filler 9, it has the following major drawback in terms of materials.

■Silicon essentially has no adhesion to organic materials other than silicon. Therefore, if seawater pressure is applied to the cross section of the fiber unit in the event of a failure, it is possible to prevent damage to the fibers between the optical fiber 1 and the silicon buffer layer 6 or between the silicon buffer layer 6 and the nylon coating 7.
Water running occurs between the seawater and the seawater, and the optical fiber 1 comes into direct contact with seawater.

- Since the primary coating of the optical fiber 1 is a soft silicone buffer layer 6, it breaks at around IKm in a high strength proof test. A large amount of tension is applied to optical submarine cables when they are installed or when they are recovered for troubleshooting. Most of this tension is applied to the tensile strength wire 3 of the cable, and it is thought that the fiber unit also needs to have a strength of 2% in terms of elongation strain, but this strength is not guaranteed in the structure of FIG. 2. In addition, 1 in the optical submarine cable system
The relay section will be about 50 km, but it was IK in the proof test.
Breaking at around m means that there are dozens of connection points in one relay section, and in terms of transmission characteristics and reliability,
Furthermore, the manufacturing process is also unfavorable.

■When thermosetting silicone resin is used as a unit filling material, there is a problem in continuous long unit manufacturing. It is necessary to heat the thermosetting resin in a state where the two liquids are mixed together. After the optical fiber core wires are twisted and assembled, the mixed resin is extruded through a die and passed through a heating zone.

In this case, it will take about a week to manufacture a unit with a length exceeding 50Kr+1, and if a failure occurs on the production line (for example, a power failure) and the line is stopped during this time, it will be heated and molded immediately. Parts of the unit located within the heating zone may become bent before being cured, resulting in manufacturing defects. Connections between units must be repaired without changing the outer diameter of the unit because the outer diameter of the unit is limited by the inner diameter of the cable pressure layer 2, but it is necessary to repair the 22) GC overlapping parts to be connected. connection is virtually impossible. Therefore, if such a failure occurs during manufacturing, the unit containing a large number of optical fibers must be remanufactured.
The economic loss is extremely large.

■If a soft unit filler material such as silicone resin is used as the unit filler material 9, a large lateral pressure will be applied to the unit in the lower layer during drum winding of a long unit of 50 km or more, resulting in unit deformation or microbending. There are problems such as occurrence. In addition, silicone resin has tackiness, so when supplying a drum-wound unit for making cables, the unit may get caught.

There is a risk of silicone peeling off in the cable manufacturing machine.

■Thermosetting silicone resin has the property of reacting with moisture in the air and generating hydrogen gas more easily than other resins when left for a long period of time, so it cannot be used in sealed structures such as submarine cables. This is extremely dangerous in terms of the aforementioned increase in transmission loss.

As another unit structure example, a structure as shown in FIG. 3 is considered. As a coating for the optical fiber 1, ultraviolet curing urethane or epoxy resin (UV
The inner layer 12 and the outer layer 1302 are coated with a hardening type) and made into a core wire. These six core wires are directly assembled around the center support 8, and the surrounding area is filled with a UV silicone resin body 10.
Furthermore, it has a structure in which the outer cover 11 is coated with UV urethane or UV epoxy resin.

The advantage of this structure is that the manufacturing speed is fast because all the coating is done with UV resin. However, in this unit, the core wires (1°12, 13) are first attached directly to the center support 8.
Because the core wires are gathered together, it is difficult to completely fill the space between the core wires and the support 8 with resin, and because the core wires are in contact with other core wires and the center support 8, there is no resin on that surface. is not filled,
Water running can occur here when there is a cable failure. In addition, since the unit filler material is UV, it is still a silicone resin, so it does not have adhesive strength with other resins, and has no adhesive strength between it and the outer sheath 11 and the fiber core wires (1, 12, 13).
) will definitely cause water running. To prevent this,
When the unit filler 10 is filled with other W resin, such as UV-curing urethane or UV-curing epoxy resin,
It is true that water running between the outer sheath and the core wire can be prevented, but on the other hand, the degree of adhesion between the core wire and the solid material at the end of the unit is so excellent that it becomes impossible to separate the core wires. This makes terminal work such as connection to a repeater extremely difficult. Furthermore, U
A problem with V-resin core wires is that it is difficult to color them for identification.

Furthermore, it has been reported that the mechanical strength of UV-coated core wires deteriorates due to the influence of moisture.

(Objective and Summary of the Invention) In order to solve the problems of the prior art as described above, the present invention provides an optical fiber unit structure that is easy to manufacture continuously, has no water holes, and is easy to handle. It is.

In order to achieve this object, the present invention provides a core wire by coating a thermoplastic resin around a wire coated with a UV curing resin,
For example, six core wires are placed around the center support, which has been previously coated with UV-curable resin and whose outer diameter is larger than the outer diameter of the core wire, and is completely filled with the same type of UV-curable resin as the coating of the center support. It has a unit structure like this.

(Structure of the invention) The present invention will be explained in detail below.

In the present invention, the periphery of the optical 7-eyeper 1 is first coated with a UV urethane resin layer 20, and the periphery thereof is coated with a UV epoxy resin layer 21. Furthermore, a thermoplastic resin layer 22 such as nylon or Hytrel is coated around the core wire to form a core wire. The periphery of the center support 8, which has approximately the same diameter as this core wire, is coated in advance with a UV urethane resin layer 23, and the six core wires described above are twisted together, assembled, and arranged around the center support 8, and the space between and around the center support 8 is covered with a UV urethane resin layer 23. It has a unit structure filled with UV urethane resin (same as 23) 24 as a unit filler.

In the same figure, 207 series resin is preferable as the primary coating material of the optical fiber 1, and the secondary coating 21 as the outer layer is made of resin of several kg/sa'' to several tens of kilograms in order to improve the lateral pressure characteristics of the optical fiber.
A UV epoxy resin or a UV urethane resin having a Young's modulus of approximately g/J is desirable. Around it is nylon,
It is coated with a thermoplastic resin layer 22 such as Noritrel, and has a three-layer structure as a whole.

This thermoplastic resin layer 22 must not melt at a temperature of 150° C. applied to the unit when covering an insulating material such as polyethylene during cable manufacture. In addition, in order to improve the lateral pressure characteristics of the Noah 1 bar, the Young's modulus is 50~
It needs to be about 100 Kg/m2, and nylon or I-Ytrel are suitable. The center support 8 takes charge of the tension during the unit manufacture, and also takes charge of the retention tensile strength when the unit is tied to the cable at the end in order to eliminate slippage between the unit and the cable after the unit is made into a cable. A hard steel wire or the like is mainly used for this. This wire diameter is related to the rigidity of the entire unit and is preferably approximately the same diameter as the fiber core wire. By coating the periphery of this center support 8 with a UV urethane resin layer 23 in advance and making the outer diameter slightly thicker (the wire width is also slightly thicker, when six fiber core wires are arranged around this core), , Fino (the core wires or the fiber cores and the center support 8 do not come into direct contact with each other, making it possible to fill the gaps between them with the unit filler without any gaps. In this case, the unit filler 24 and the center By making the covering 23 of the support 8 from the same material of UV urethane resin, 23 and 24 are integrated, and the fiber core wire is completely embedded in the unit filler 24.This unit filler 24 It is desirable to use a UV resin having a Young's modulus of 0.5 to 10 Kg/M'' in consideration of lateral pressure characteristics and elongation characteristics.

The diameter f of the fiber unit is limited by the inner diameter of the cable pressure-resistant layer 2, and must be slightly smaller than this. The diameter C of the fiber core is limited by the size that allows six cores to be stably arranged in this unit, and when the unit diameter is about 3 mm, the core diameter C is 0.6 to 0.9 μ. At this time, the diameter d of the center support 8 is also approximately 0.6-0.9Ilj, and the covering outer diameter e needs to be larger than d by 0.1-0.2IIj. The glass outer diameter a of the fiber 1 is generally 125 μm, and the outer diameter of the two-layer coating is about 0.4 au+.

(Effects of the Invention) By adopting such a unit structure, continuous production of long pieces becomes possible. Since the outer cover of the unit is made of UV resin, even if trouble occurs during manufacturing and the line is stopped, the UV
Since the resin will not harden unless it is irradiated with an ultraviolet lamp, there is no problem with the pot life of the resin. Furthermore, since the resin can be cured in an irradiation time of 1 second or less, there is no need for a wide heating zone unlike in the case of thermosetting resins, and the resin can be cured immediately after extrusion through a die. Therefore, even in the event of a power supply problem, there is no deformation of the unit due to curing failure, and continuous production is possible by restarting the unit as it is, which has an extremely large economical effect.

Next, this unit is completely filled with no gaps.
Also, since no silicone resin is used, water leakage can be completely prevented. As a result of the actual prototype, 700
Even against atmospheric pressure, the water tank was completely unresponsive.

Furthermore, since the core wire is coated with nylon or the like having a high Young's modulus, it has high rigidity and is easy to handle. Furthermore, since the fiber core and the unit filler material have different material properties at the terminal, they can be separated, and nylon or the like can be easily colored, providing excellent identification. Furthermore, coating the UV resin with a thermoplastic resin such as nylon or Hytrel improves water resistance. This means that if a bare fiber coated with only UV urethane resin is left in water for a month, its breaking strength will deteriorate by about half, but a fiber coated with Hytrel around it will show almost no deterioration in experiments under the same conditions. This is clear from the results.

In addition, this unit has a large Young's modulus throughout to suppress deformation, and the material closest to the optical fiber has a small Young's modulus to suppress microbending.
Even when winding a continuous length of 0 km, there is no increase in shear loss or flattening of the unit due to lateral pressure, and the unit structure is extremely reliable.

Moreover, by not using silicone resin, H2
There is almost no gas generation and the transmission characteristics are extremely stable.

By adopting such a unit structure, the present invention has excellent long-length continuous production, mechanical stability, and optical stability, and is also easy to handle in terminals and has excellent water resistance characteristics in the event of failure. It is possible to realize an extremely reliable unit with excellent performance.

[Brief explanation of the drawing]

1 is a cross-sectional view showing an example of the structure of an optical submarine cable to which the present invention is applied, FIG. 21 is a cross-sectional view showing an example of the structure of a conventional optical fiber unit, and FIG. 4 is a cross-sectional view showing an example of the structure of a conventional optical fiber unit. It is a front view. 1... Optical fiber, 2... Pressure-resistant layer, 3.8...
- Tensile strength wire, 4... Power supply line, 5... Insulator, 6... 7 Recon buffer layer, 7... Nylon coating, 8... Center support, 9... Silicon filler, 10...Nilicon resin body, 11...Outer cover,
12... Inner layer, 13... Outer layer, 20... UV urethane resin layer, 21... UV epoxy resin layer (outer layer coating), 22... Thermoplastic resin layer, 23... UV urethane resin Layer 24...UV urethane resin layer (unit filling material).

Claims (3)

[Claims] (1) When a plurality of optical fibers are twisted together at a constant pitch around one center support, the center support and the plurality of optical fibers cover the entire surface. A fiber unit for an optical submarine cable configured to be embedded in an ultraviolet curable resin so as to be in contact with the ultraviolet curable resin. (2) The fiber unit for an optical submarine cable according to claim 1, wherein the center support and the optical fiber core are coated with an ultraviolet curable resin layer in advance. (3) The optical fiber core wire is constructed by applying a primary coating of an ultraviolet curable resin and a secondary coating of a thermoplastic resin to an optical fiber strand. The fiber unit for optical submarine cable according to item 2.