JP3247531B2 - Optical cable and method of laying optical cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical cable suitable for constructing an optical subscriber wiring system for distributing an optical communication network to each subscriber, and a method of laying the optical cable.

[0002]

2. Description of the Related Art Various methods have been proposed for constructing an optical communication network. Among them, it has been considered to construct an optical subscriber wiring system by distributing an optical communication network from a station to each subscriber like a conventional telephone.

FIG. 10 is a schematic diagram of one example. In the figure, 31 is a station, 32 is an underground cable, 33, 34, 35
Is a telephone pole, 36 is an optical underground connection box, 37 is an optical drop cable,
38 is an optical drop connection box, 39 and 40 are distribution cables,
1, 42, 43 are connection boxes, 44, 45 are outdoor lines, 46,
47 is a subscriber. The optical drop cable 3 connected from the station 31 through the underground cable 32 and the optical underground connection box 36
7 is connected to a light drop connection box 38 of a pole installation type installed on a utility pole 33. From the optical drop-down connection box 38, the cable is wired to the area where the subscriber is located via the distribution cables 39 and 40 and the telephone poles 34 and 35 sequentially. Distribution cable 39, 40
Are supported by a support wire stretched between telephone poles. For example, the telephone poles 34 are connected to each other by a connection box 41. The subscriber 46 who has generated the demand is debited from the connection box 41 by the outdoor line 44. The withdrawal to the subscriber may be withdrawn from the connection box provided near the telephone pole, or may be withdrawn from the connection box 43 provided between the telephone poles 41 and 42 like the subscriber 47.
Of course, there is no need to provide a connection box for each telephone pole,
In some cases, utility poles that perform only detention are arranged.

[0004] As described above, a distribution cable is dropped by a subscriber according to demand. Conventionally, as an optical cable used in an optical subscriber wiring system, for example, Japanese Patent Laid-Open No. Hei 4-37 is known.
A multi-core optical cable as described in JP-A-2917 is used. FIG. 11 is a sectional view thereof. In the figure, 51 is a tape core, 52 is a U-shaped spacer, 53 is a fitting spacer, 54 is a presser winding, 55 is a tension member, and 56 is a sheath. The U-shaped spacer 52
The cross section is formed to have a substantially U shape using plastic, and a plurality of tape cores 51 are accommodated therein. The tape core wire 51 is, for example, one in which five optical fibers are arranged and integrated with an ultraviolet-curable resin or the like. The spacer 52 is twisted so that the bottom thereof faces the tension member 55 arranged at the center of the optical cable, or is arranged in parallel and assembled. Adjacent wall surfaces of adjacent spacers are engaged with each other at edge portions of both ends of the fitting spacer 53 and connected to each other.
Is given. Adjacent U-shaped spacers 52 are integrated by fitting spacers 53 so that U
The shape spacer 52 is integrally fixed to the periphery of the tension member 55, so that a multi-core optical cable having one sturdy structure is formed.

On the other hand, as a so-called drop cable connected to a subscriber terminal, a small-fiber optical cable containing one or two optical cables is known. Therefore,
The optical subscriber system is constructed by dropping a low-fiber optical cable connected in series with the optical fiber in the multi-fiber optical cable as described above to the subscriber's house.

[0006] The above concept has been known from the NTT Research and Practical Use Report, Vol. 33, No. 3 (1984), pp. 116-129, etc., but conventionally, the development of optical terminals was not sufficient. Because of the fact that the price was high,
The actual use of optical subscriber systems has been extremely limited. For this reason, the construction such as the connection of an optical cable from a multi-core optical cable to a small-core optical cable is a low-frequency special construction, and the workability and economic efficiency have not been taken into consideration.

[0007] However, with the progress of the highly information-oriented society in recent years, the realization of optical subscriber systems is approaching.
Optical subscriber wiring systems are required to be economical, workable, and expandable. In particular, the demand for the optical communication network is not clear, and even if a connection box is provided to respond to the initially required demand and an optical cable is laid, a new connection point will be established between the connection points due to subsequent environmental changes. It is expected that a so-called post-branch will be required. In order to cope with this, it is necessary to take out a part of the optical cable from the middle of the laid optical cable and branch it, and there is no conventional optical cable that can sufficiently cope with this.

FIG. 12 is an explanatory view of another example of the conventional optical cable. In the figure, 61 is an optical fiber unit, 62 is a tensile strength wire, and 63 is a sheath. The optical cable shown in FIG. 12A has six optical fiber units 61 as cable members, and these six optical fiber units 61 are arranged around the tensile strength line 62 as shown in FIG. Are twisted into an SZ twist in which the direction of twist is alternately reversed every predetermined length, and are assembled. The upper part is covered by a sheath 63. In such an optical cable, each optical fiber unit 61 can be pulled out by removing the sheath 63. The pulled-out optical fiber unit 61 can be cut to perform a post-branch.

However, in the optical cable having such a structure, the sheath 6 is not damaged without damaging the internal cable member.
It is extremely difficult to remove 3. Further, when the SZ twisted cable member is opened, a portion where the cable member is exposed occurs in the laid cable, and this portion needs to be protected from external rainwater and dust. For this reason, it is necessary to provide waterproofing around many cable surfaces, and the work is very difficult. If this protection is inadequate, water vapor and water will often enter the gaps between the cable members, causing water to leak in the cable, reducing the strength of the optical fiber and reacting with the metal in the tensile strength material to release hydrogen gas. Then, there is a problem that the loss of the optical fiber is increased, or the invaded water freezes and applies a side pressure to the optical fiber, causing an increase in the loss in winter.

FIG. 13 is a sectional view of an example of a conventional coaxial cable. In the figure, 71 is a coaxial cable, 72 is a tensile strength wire, and 73 is a bind wire. The coaxial cable shown in FIG. 13 shows an example of a coaxial cable used for CATV. This coaxial cable has a structure in which an individual coaxial cable 71 and a tensile strength wire 72 are wound and integrated by a bind wire 73.

In this coaxial cable, the winding of the bind wire 73 is performed by rotating the reel around which the bind wire 73 is wound around the moving coaxial cable. In this operation, for example, while performing the operation of winding the bind wire 73 having a circumference of 5 cm, in order to manufacture a coaxial cable at 20 m / min, the bind wire 73 is operated at an extremely high speed of 400 times per minute.
It is necessary to rotate the winding reel. To perform this operation, the equipment becomes large and the cost increases. Alternatively, since the production speed must be reduced, productivity is reduced. Also, when the bind line 73 is cut at one place, the looseness of the bind line 73 propagates back and forth,
There is also a problem that the integrated structure of the coaxial cable is lost.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an optical cable having excellent post-branchability and a method of laying an optical cable for rear branching using the optical cable. The purpose is to do so.

[0013]

According to the first aspect of the present invention, at least two or more optical fiber units, each of which is individually provided with a weather-resistant jacket, are used as cable members and twisted into an SZ twist. An optical cable laid using a telephone pole, wherein the cable central portion is combined, a tensile member is linearly disposed on the cable central portion, and a secondary jacket is applied to the entire cable. Is characterized in that it has a cut in the longitudinal direction in a part thereof through the secondary jacket.

According to the second aspect of the present invention, at least two or more optical fiber units, each of which is individually weathered, are used as a cable member and twisted in an SZ twist to form a central portion of the cable. A secondary cable is provided on the whole by arranging a tensile strength member in a straight line, and the optical cable is laid using a utility pole. It has a cut which penetrates the secondary jacket.

According to a third aspect of the present invention, in the optical cable according to the first or second aspect, the strength member arranged linearly is arranged at the center of the cable member twisted in SZ twist. It is characterized by having.

According to a fourth aspect of the present invention, in the optical cable according to the first or second aspect, the strength member disposed linearly is disposed outside a central portion of the cable. Things.

According to a fifth aspect of the present invention, in the optical cable according to the first aspect, the cut is provided in a shape turning in one direction.

According to a sixth aspect of the present invention, in the optical cable according to the first aspect, the cut is provided in an SZ shape while changing the direction.

According to a seventh aspect of the present invention, in the optical cable according to any one of the first to sixth aspects, at least one hollow conduit is included as a cable member constituting the central portion of the cable. It is a feature.

In the invention according to claim 8, in the optical cable according to any one of claims 1 to 6, at least one hollow conduit is provided in parallel with the strength member arranged linearly. It is characterized by including.

According to a ninth aspect of the present invention, in the method for laying an optical cable, after laying the optical cable according to the seventh or eighth aspect, the secondary jacket is cut off from the cut at any position. The method is characterized in that a conduit is taken out, the hollow conduit is cut, an optical cable is sent into the inside, and an optical cable is laid between two cutting points or end portions and the cutting point.

[0022]

According to the present invention, in the invention as set forth in claim 1 or 2, since the secondary jacket of the optical cable is provided with a cut which penetrates the secondary jacket, the cut is made at the time of rear branching. By opening the secondary jacket from the cut, it is possible to easily remove the cable from the secondary jacket without damaging the center of the optical fiber unit having the individual sheath. Since the cable members are twisted in the SZ twist, it is easy to separate the individual optical fiber units.
Also, even if the secondary jacket is cut over a required length, there is no change in the gripping force at the center of the cable before and after the secondary jacket, and the loosening unlike a coaxial cable using a bind wire does not occur. Furthermore, since each optical fiber unit is individually provided with a weatherproof jacket, waterproof protection at the time of rear branching may be performed for each optical fiber unit that has been drawn down, and other optical fiber units etc. Since there is no need for waterproofing, the work is easy. Further, the water that has entered the cable member flows out of the cut through the secondary jacket to the outside, and does not accumulate in the optical cable. Even if a small amount of remaining water freezes in winter, the change in volume is absorbed by the opening of the jacket at a part of the cut, and there is almost no side pressure applied to the optical fiber unit.

According to the third aspect of the present invention, since the tensile member is disposed at the center of the cable member, it is easy to twist the cable member into SZ twist. In addition, since the tensile strength member is located near the center of the secondary jacket having a cut in the sheath over the entire length or intermittently, all the cable members pass over the tensile strength once during the twisting pitch. become. For this reason, there is an advantage that the problem that the cable member comes off from the cut is less likely to occur. For this reason, it is effective when used for a cable that is laid in a relatively long span or a cable that is laid in a place where the wind is strong and where there is a lot of vibration. Further, since the outer diameter of the optical cable is a perfect circle, a long optical cable can be stably wound around the drum.

According to the fourth aspect of the present invention, by arranging the strength member outside the center of the cable, the strength member can be easily gripped from the outside. For this reason,
It is useful when, for example, laying an optical cable, using a number of electric poles, grasping a tensile member for each electric pole, and changing the laying direction of the optical cable. Also, when the connection box is hung for the rear branch, the work of fixing to the tensile strength member or the like can be easily performed. Also, because the vertical direction is clear,
A cut can be provided in the vicinity of the strength member, that is, on the upper side or side surface of the optical cable, and it is possible to prevent the cable member from falling off due to its own weight in the downward direction.

According to the fifth aspect of the present invention, since the cut provided in the secondary jacket is formed to have a spiral shape swiveling on the cable in one direction, the weight of the cable central portion with time increases. Therefore, there is no problem that the notch portion opens due to creep. Similarly, in the invention described in claim 6, since the cut provided in the secondary jacket is provided in the SZ shape,
Breaks are difficult to open due to the weight of the cable center. The inventions described in claims 5 and 6 are particularly effective when the center of the cable is heavy.

According to the invention as set forth in claim 7, the cable member includes at least one hollow conduit,
According to the eighth aspect of the present invention, by including at least one hollow conduit in parallel with the tensile strength member, it is possible to provide a more excellent degree of freedom in post-branchability.

That is, as in the ninth aspect of the present invention, after the optical cable is laid, the secondary jacket is cut off from the cut at the point where the post-branch is necessary, and the hollow conduit is taken out. A pipe is cut open, and an optical cable with a small number of fibers is passed through the pipe, and an optical fiber is guided and connected to a connection box on the office side. If a low-fiber-count optical cable is used in common with the drop line, connection of the optical fiber at the rear branch point is not always necessary, and the rear branch connection box provided at the rear branch point does not have to worry about water infiltration into the cable. It can be.
In this way, it is possible to easily perform the post-branching operation.

Further, in the invention according to claim 7, by including the hollow conduit in the center of the cable, the appearance of the entire cable is excellent, and the cross section close to a perfect circle can be maintained. Can be wound around. On the other hand, in the invention according to claim 8, since the hollow conduit is straight when the cable is laid, the optical cable having a small number of fibers can be easily drawn therein. It is particularly advantageous when used for long optical cables.

[0029]

FIG. 1 is a sectional view showing a first embodiment of an optical cable according to the present invention. In the figure, 1 is an optical fiber unit,
2 is a slot, 3 is a tape core, 4 is a primary jacket, 5 is a tensile member, 6 is a tube, 7 is a secondary jacket, and 8 is a cut. The optical fiber unit 1 is provided with four slots 2, and each of the slots 2 is provided with a core ribbon 3 and covered with a primary jacket 4. The primary jacket 4 has weather resistance, and the optical fiber unit 1 is configured to be able to be laid as it is. Five optical fiber units 1 and one tube 6 are twisted in SZ twist around the strength member 5 and covered with a secondary jacket 7. This 2
A cut 8 is provided in the secondary jacket 7. The cut 8 penetrates the secondary jacket 7.

The optical cable shown in FIG. 1 is an example, and the number of optical fiber units 1 and tubes 6 to be twisted is
Number of slots 2 in optical fiber unit 1, slot 2
The number of cores and the like of the tape core wires 3 arranged inside are arbitrary. It can be configured without using the tube 6. However, as will be described later, by arranging the tube 6 and using it, the post-branch can be easily performed.

In the optical cable shown in the first embodiment, the tensile member 5 is arranged at the center of the cable member. This makes it easy to twist the cable members into SZ twist. Further, since the cable member is held between the strength member 5 and the secondary jacket 7, it is difficult for the cable member to fall off from the cut of the secondary jacket. For this reason, cables that lay relatively long spans, strong winds,
It is effective when used for a cable laid in places where there is a lot of vibration. Further, since the outer diameter of the optical cable is a perfect circle, a long optical cable can be stably wound around the drum.

FIG. 2 is an explanatory view of the shape of the cut in the first embodiment of the optical cable of the present invention. As the cut 8 provided in the secondary jacket 7, various shapes can be considered. For example, as shown in FIG. 2A, a structure in which a cut 8 is provided intermittently in the secondary jacket 7 can be employed. FIG.
As shown in (B), a cut 8 can be spirally formed in the secondary jacket. Or, as shown in FIG.
A cut 8 can be provided in the SZ shape. Such a cut 8 can be manufactured, for example, by rotating a crosshead having a C-shaped discharge die and alternately rotating in the forward and reverse directions when applying the secondary jacket 7 to the optical cable. it can. By manufacturing in this manner, a speed of 50 m is higher than that of the conventional binding wire shown in FIG.
Per minute. The break 8 is, for example,
When the outer shape of the secondary jacket 7 is 40 mm, it can be formed with a width of 4 mm and a pitch of about 400 mm. In either structure, after cutting one portion of the secondary jacket 7, the secondary jacket 7 can be easily opened in the side direction, and the secondary jacket 7 can be easily cut off for rear branching. It is.

In the configuration shown in FIGS. 2 (B) and 2 (C), there is a problem that the cut 8 is opened due to the weight of the central portion of the cable over time as compared with the case where the cut is simply provided in the longitudinal direction. Does not occur. Therefore, it is particularly effective when the center of the cable is heavy.

As a specific optical cable in the above-mentioned first embodiment, for example, an optical cable having an outer diameter of 1.1 × 0.4 mm is used.
Four pieces of core tape are housed in four 1.3 mm wide x 2.0 mm deep slots cut into nylon rods with a diameter of 10 mm, and a polyethylene sheath is applied to an outer diameter of 12 mm. Fiber unit. Five optical fiber units and one polyethylene tube having an outer diameter of 12 mm and an inner diameter of 10 mm were placed around a strength member made of a polyethylene-coated steel stranded wire having a diameter of 12 mm at a pitch of 40 mm.
The cable core was manufactured by twisting SZ at 0 mm and an inversion angle of 275 °. A secondary jacket having an outer diameter of 40 mm and a continuous cut having a width of 4 mm is applied to the lower surface. As a result, an optical cable having an initial number of cores of 320 can be produced.

FIG. 3 is a sectional view showing a second embodiment of the optical cable of the present invention. In the figure, the same parts as those in FIG. 9 is an intermediate | middle material. In this embodiment, a plurality of optical fiber units 1 and a tube 6
Are twisted in an SZ twist around the intermediate member 9 to form a cable central portion. Outside the center of the cable, tensile strength members 5 are arranged in parallel, and a secondary jacket 7 is applied to form an optical cable. As the intermediate member 9, for example, a member made of polyester terephthalate can be used. A cut 8 is provided in a part of the secondary jacket 7. The tube 6 may not be provided, or a configuration having a plurality of tubes may be employed.

Also in this optical cable, the post-branch can be easily performed using the cut 8. Further, since the strength member 5 has a convex shape, it is easy to grip the strength member 5 at the time of laying. The installation direction can be easily changed, for example, by changing the installation direction. Further, when the connection box is provided at the rear branch point after the installation of the optical cable, it is easy to suspend the connection box on the tensile strength member. In the optical cable having such a configuration, since the vertical direction is clear, the vicinity of the tensile strength member 5, that is,
Cuts can be made on the upper and side surfaces of the optical cable,
It is possible to prevent the cable member from falling off due to its own weight in the downward direction.

FIG. 4 is a sectional view showing a third embodiment of the optical cable of the present invention. Reference numerals in the figure are the same as those in FIG. In this embodiment, the optical fiber unit 1 is twisted SZ around the tensile strength member 5 to form a cable center portion, a tube 6 is arranged in parallel with this, and a secondary jacket 7 is applied to form an optical cable. are doing. A cut 8 is provided in a part of the secondary jacket 7, and a rear branch can be easily performed by using the cut 8. Further, in the optical cable having such a configuration, the transmission resistance is reduced, for example, the maximum value is reduced to 1/3 as compared with the insertion resistance when a small-fiber-count cable is pushed into the optical cable shown in the first embodiment. Has the effect of being done. A plurality of tubes 6 may be arranged in parallel with the cable center. Of course, the tube 6 may be arranged at the center of the cable.

Next, the rear branching of the above-described optical cable will be described based on a specific example. 5 is an explanatory diagram of an example of laying an optical cable, FIG. 6 is an explanatory diagram of a specific example of a sheath cutting tool and an example of its use, and FIG. 7 is an explanatory diagram of an example of a state after branching at a rear branch point. . In the figure, 11 is an optical cable, 12 is a utility pole, 13 is a clamp, 14 is a rear branch point, 15 is a sheath cutting tool, 16 is a handle, 17 is a blade, 18 is a guide, 19 is a binding wire, 20 is an airtight closure, 21 Is a rear branch cable. An optical cable 11 is laid between two utility poles 12 having a clamp 13 at a certain height. For example, the clamp 13 can be arranged at a position at a height of 5 m of the utility pole 12. The distance between the poles of the utility pole 12 can be, for example, 50 m. The optical cable 11 is fixed by a clamp 13. It is assumed that the rear branch is performed at the rear branch point 14 between the two electric poles 12.

At the time of branching, first, a certain length including the rear branch point 14 is set.
Next, cut the jacket. For cutting the secondary jacket, it is convenient to use a sheath cutting tool as shown in FIG. In the example of the sheath cutting tool shown in FIG. 6A, a handle 16 is provided on one of two convex portions of a U-shaped blade 17, and the other is used as a guide 18. When cutting the secondary jacket, handle 1
6, the guide 18 is inserted into a cut provided in the optical cable 11 as shown in FIG.
The secondary jacket can be cut in a circumferential shape by drawing along the outer shape of (1). In addition, the break is
In the case of intermittently provided as shown in (A),
The connection part of the cut can be cut similarly. Then, the cut may be opened to remove the secondary jacket from the center of the cable. At this time, at the end of the part excluding the secondary jacket,
It is covered by the secondary jacket, and since this secondary jacket does not loosen, the twisting structure is suppressed and fixed.
The twist is not disturbed.

As described above, by cutting the secondary jacket using the cut, the cable member such as an optical fiber unit or a tube having an individual sheath in the optical cable can be easily removed from the secondary jacket without damaging the cable member. Can be taken out. Since the cable members are twisted in SZ twist, it is easy to separate the individual optical fiber units, and the extra length can be taken.

After removing the secondary jacket, the optical cable unit or the tube twisted in SZ twist is opened outward, the necessary optical cable unit is further opened, and the necessary fiber can be taken out and branched. For example, in the optical cable shown in FIG. 1, four four-core tapes housed in one slot can be taken out from one of the five optical fiber units and can be branched off. These four-core tapes are connected to the post-branch cable 21, and the connection points are air-tightly hardened by an air-tight closure 20 using a curable resin. The portion excluding the secondary jacket for the rear branch may be twisted as before and fixed using the bind wire 19. This state is shown in FIG. Further, by taking out the tube disposed in the optical cable and connecting the optical fiber cable having a small number of fibers passed through the tube to the rear branch cable 21, the rear branch can be performed.

At this time, since each optical fiber unit is individually provided with a weather-resistant primary jacket, waterproof protection at the time of rear branching may be performed for each of the dropped optical fiber units. The other optical fiber units do not need to be waterproof. Thus, the post-branching operation can be easily performed. After the work, the water that has entered the cable member flows out of the cut of the secondary jacket to the outside, and does not accumulate in the optical cable. Even if a small amount of remaining water freezes in winter, the change in volume is absorbed by the opening of the jacket at the cut, and there is almost no side pressure applied to the optical fiber unit.

FIG. 8 is an explanatory view of an example of a method of laying a small number of cables, and FIG. 9 is a cross-sectional view of an example of a small number of cables to be laid. In the figure, the same parts as those in FIG. 22 is a connection box, 23 is a tube, 2
Reference numeral 4 denotes a cable for a drawdown line, reference numeral 25 denotes a cable having a small number of fibers, and reference numeral 26 denotes a connection box to be dropped. As shown in FIG. 8A, the cable 11 is laid using a utility pole 12, and is connected to another cable in a connection box 22.

First, at the rear branch point 14, the secondary jacket is cut open to take out the tube 23 by the above-described rear branch method. The tube 23 is cut, and as shown in FIG.
4 to form a continuous conduit. As shown in FIG. 8C, a small-fiber-count cable 25 is pushed into the drawn-down conduit cable 24. As the small-fiber-count cable 25 to be pushed, for example, an optical cable having a cross-sectional shape as shown in FIG. 9 can be used. Specifically, the outer diameter is 0.9m
m, one around the single core, and six 1-6 around it
Array, polyethylene sheath on outer circumference, outer diameter 4m
m can be used. This small-fiber-count cable 25 can be pushed over 100 m into the tube in the optical cable shown in the first embodiment.

The small-fiber-count cable 25 is pushed into the connection box 22. From the open portion of the tube 23 in the connection box 22, the terminal of the small-fiber-count cable 25 is taken out, and predetermined fibers are connected in the connection box 22. On the other hand, as shown in FIG.
It is connected to an optical cable on the terminal side in a withdrawal destination connection box 26 provided at the withdrawal destination. As described above, by using the low-fiber-count cable in common with the drop line, it is not always necessary to connect the optical fiber at the rear branch point.
Also, the rear branch connection box provided at the rear branch point may be lightly mounted since there is no fear of water infiltration into the optical fiber unit. In this way, it is possible to easily perform the post-branching operation.

Separate the drawing line from the optical cable passing through the tube 23 and connect the drawing destination connection box 26 to the optical cable 11.
It can also be placed on top. In the drop-down connection box 26, the terminal on the drop-down destination side of the cable having a small number of fibers is connected to the drop-down cable. The connection box 26 used at this time is a connection box 2 installed at the time of laying at the optical cable connection point.
What is necessary is just to use the thing similar to 2.

In the above-described transmission of the small-fiber-count cable, the cable is transmitted from the rear branch point to the connection box, but may be transmitted from the branch point to the branch point. In addition, other than the pushing method, other methods such as pressure feeding by gas can be used as the passing method.

As described above, by using the tube arranged in the optical cable, a wider degree of freedom can be given to the post-branching and the construction method.

[0049]

As is apparent from the above description, according to the present invention, after the optical cable is laid using the telephone pole, the post-branch can be easily performed, and the optical fiber units can be individually separated from the weather resistance. By being covered
The waterproof protection at the time of the rear branch may be performed for each of the optical fiber units that have been drawn down, and the other optical fiber units and the like do not need to be waterproofed, so that the work is easy. Furthermore, since the water that has entered the cable member flows out of the cut through the secondary jacket, it does not accumulate in the optical cable. There is an effect that the side cover is absorbed by the opening of the jacket at the cut, and there is almost no side pressure applied to the optical fiber unit. INDUSTRIAL APPLICABILITY The optical cable of the present invention is useful when used in a distribution network in which a rear branch point needs to be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the optical cable of the present invention.

FIG. 2 is an explanatory diagram of a shape of a cut in the first embodiment of the optical cable of the present invention.

FIG. 3 is a sectional view showing a second embodiment of the optical cable of the present invention.

FIG. 4 is a sectional view showing a third embodiment of the optical cable of the present invention.

FIG. 5 is an explanatory diagram of an example of laying an optical cable.

FIG. 6 is an explanatory view of a specific example of a sheath cutting tool and an example of its use.

FIG. 7 is an explanatory diagram of an example of a state after a branch at a rear branch point.

FIG. 8 is an explanatory diagram of an example of a laying method of a cable having a small number of fibers.

FIG. 9 is a cross-sectional view of an example of a small-fiber-count cable to be laid.

FIG. 10 is a schematic view of an example of an optical subscriber wiring system.

FIG. 11 is a sectional view of a conventional multi-core optical cable.

FIG. 12 is an explanatory diagram of another example of the conventional optical cable.

FIG. 13 is a sectional view of an example of a conventional coaxial cable.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber unit 2 Slot 3 Tape core wire 4 Primary jacket 5 Tensile body 6 Tube 7 Secondary jacket 8 Cut 9 Intermediate material 11 Optical cable 12 Power pole 13 Clamp 14 Rear branch point 15 Sheath cutting tool 16 Pattern 17 Blade 18 Guide DESCRIPTION OF SYMBOLS 19 Bind wire 20 Airtight closure 21 Rear branch cable 22 Connection box 23 Tube 24 Pull-down pipeline cable 25 Small-fiber-count cable 26 Drop-down destination connection box

Continuation of the front page (72) Inventor Shigekazu Hayami 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation Examiner Eiichi Yoshida (56) References JP-A-1-257807 (JP, A) JP-A-50-144451 (JP, A) Japanese Utility Model Application No. 5-29010 (JP, U) Japanese Utility Model Application No. Hei 2-19001 (JP, U) Japanese Utility Model Application Laid-open No. Hei 2-13211 (JP, U) (58) (Int.Cl. ⁷ , DB name) G02B 6/44 G02B 6/46

Claims (9)

(57) [Claims] An optical fiber unit having at least two optical fiber units, each of which is individually provided with a weatherproof jacket, is used as a cable member and twisted in an SZ twist to form a cable central portion,
An optical cable, in which a tensile member is linearly disposed and a secondary jacket is entirely provided, and laid by using a power pole, and a part of the secondary cable in a longitudinal direction is provided on a part of the circumference of the secondary jacket. An optical cable having a cut through the secondary jacket. 2. A cable center part comprising at least two or more optical fiber units individually coated with a weather-resistant jacket as a cable member and twisted in SZ twist.
An optical cable which is provided with a secondary sheath entirely by arranging a tensile strength member in a straight line and laid by using a power pole, and which is intermittently longitudinally interposed on a part of the periphery of the secondary sheath. An optical cable having a cut through the secondary jacket. 3. The strength member disposed in a straight line,
The optical cable according to claim 1, wherein the optical cable is arranged at a center of the cable member twisted in a Z twist. 4. The optical cable according to claim 1, wherein the strength members arranged linearly are arranged outside a central portion of the cable. 5. The optical cable according to claim 1, wherein the cut is provided in a shape turning in one direction. 6. The cut is made by changing the direction while changing the direction.
The optical cable according to claim 1, wherein the optical cable is provided in a shape. 7. The optical cable according to claim 1, wherein the cable member constituting the cable center includes at least one hollow conduit. 8. The optical cable according to claim 1, further comprising at least one hollow conduit in parallel with the strength member arranged in a straight line. 9. After laying the optical cable according to claim 7 or 8, the secondary jacket is cut off from the cut at any position to take out the hollow conduit, and cut the hollow conduit. A method for laying an optical cable, comprising: sending an optical cable into the inside; and laying the optical cable between two cut points or end portions and the cut point.