JPH07199013A - Optical cable and method for laying optical cable - Google Patents

Abstract

PURPOSE:To provide an optical cable having an excellent post-branching property and a method for laying the optical cable for the purpose of post-branching using this optical cable. CONSTITUTION:This optical cable is constituted by twisting plural optical fiber units 1 formed with primary sheaths having weatherability and tubes 6 to left- hand and right-hand lays around a tensile body 5 and coating the assembly with a secondary sheath 7. This secondary sheath 7 is provided with a score 8. The secondary sheath 7 is cut off from this score 8 and the tubes 6 are taken out and cut at the time of post-branching. The small number of fiber optical cable which is a size-reducing line is inserted therein and is merely required to be connected to other optical fiber in, for example, a connecting box. The other optical fiber units 1 are exposed at the post-branching point but are protected by the primary sheaths. The operation at the post-branching point is simple.

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 for 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 is 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 view of an example thereof. In the figure, 31 is a station, 32 is an underground cable, and 33, 34, 35.
Is a utility 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 wiring cables, 4
1, 42, 43 are connection boxes, 44, 45 are outdoor lines, 46,
47 is a subscriber. 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 pole installation type optical drop connection box 38 installed on the utility pole 33. From the optical drop connection box 38, the wiring cables 39 and 40 are sequentially connected to the area where the subscriber exists through the utility poles 34 and 35. Wiring cables 39, 40
Are supported by support wires stretched between electric poles, and are connected to each other by a connection box 41 in the electric pole 34, for example. The demanding subscriber 46 is withdrawn from the connection box 41 by the outdoor line 44. The withdrawal to the subscriber may be withdrawn from a connection box provided near the telephone pole, or may be withdrawn from a connection box 43 provided between the telephone poles 41 and 42 like the subscriber 47.
Of course, it is not necessary to have a connection box for each telephone pole,
In some cases, electric poles that are used only for retaining are placed.

As described above, the distribution cable is dropped to the subscriber in response to the demand. Conventionally, an optical cable used for the optical subscriber wiring system is, for example, Japanese Patent Laid-Open No. 4-37.
A multi-core optical cable as described in Japanese Patent No. 2917 is used. FIG. 11 is a sectional view thereof. In the figure, 51 is a tape core wire, 52 is a U-shaped spacer, 53 is a fitting spacer, 54 is a press winding, 55 is a tension member, and 56 is a sheath. The U-shaped spacer 52 is
It is formed of plastic so as to have a substantially U-shaped cross section, and accommodates a plurality of tape core wires 51 therein. The tape core wire 51 is, for example, one in which five optical fibers are arranged and integrated by an ultraviolet curable resin or the like. The spacers 52 are twisted so that their bottoms face the tension members 55 arranged in the center of the optical cable, or are arranged in parallel and assembled. The adjacent wall surfaces of the adjacent spacers are engaged with each other at the edge portions of both ends of the fitting spacer 53 to be connected and integrated, and then the press winding 54 and the sheath 56.
Has been applied. Adjacent U-shaped spacers 52 are integrated by fitting spacers 53, so that U-shaped spacers as a whole
The shaped spacer 52 is integrally fixed to the periphery of the tension member 55, and thus a single robust multi-core optical cable is formed.

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

The above concept was known from NTT Research Practical Report, Vol. 33, No. 3, No. 3 (1984), pages 116 to 129, etc., but conventionally, the development of optical terminals was not sufficient. And because the price was high,
The actual use of optical subscriber systems was extremely limited. For this reason, the work of connecting an optical cable from a multi-core optical cable to a small-core optical cable is a special construction with a low frequency, and workability and economic efficiency have not been a problem.

However, with the progress of the advanced information society in recent years, the time to realize the optical subscriber system is approaching,
Optical subscriber wiring systems are required to be economical, workable, and expandable. In particular, the demand for optical communication networks is not clear, and even if a connection box is installed to meet the initial demand and optical cables are laid, a new connection point will be created between connection points due to environmental changes in the vicinity. It is expected that a so-called post-branch will be required. In order to respond to 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 capable of sufficiently responding to 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. 12 (A) 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. 12 (B). The SZ twists in which the twisting direction is alternately inverted at every predetermined length are twisted and assembled. It is covered with a sheath 63. In such an optical cable, each optical fiber unit 61 can be pulled out by removing the sheath 63. The optical fiber unit 61 that has been pulled out can be cut to perform post branching.

However, in the optical cable having such a structure, the sheath 6 is kept without damaging the internal cable member.
Excluding 3 is extremely difficult. Further, when the SZ-twisted cable member is opened, a part where the cable member is exposed is generated in the laid cable, and it is necessary to protect this part from rainwater and dust in the outside world. For this reason, many cable surfaces have to be waterproofed, which makes the work extremely difficult. If this protection is inadequate, water vapor and water often enter the gaps between the cable members, causing water to enter the cable, reducing the strength of the optical fiber, and reacting with the metal in the strength member to release hydrogen gas. However, there is a problem that the loss occurs in the optical fiber, or the invading water freezes to apply lateral pressure to the optical fiber, causing an increase in loss in the 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 is 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 around a bind wire 73 and integrated.

In this coaxial cable, the bind wire 73 is wound by rotating the reel around which the bind wire 73 is wound around the moving coaxial cable. For example, in order to manufacture a coaxial cable at 20 m / min while performing a work of winding a bind wire 73 having a length of 5 cm, the work is performed at an ultra high speed of 400 times per minute.
It is necessary to rotate the winding reel. To perform this work, the equipment becomes large and the cost increases. Alternatively, the production speed must be reduced, resulting in a decrease in productivity. When the bind wire 73 is cut at one place, the looseness of the bind wire 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 an excellent post-branching property, and a method of laying an optical cable for the post-branching using the optical cable. That is the purpose.

[0013]

According to a first aspect of the present invention, at least two or more optical fiber units individually provided with a weather-resistant jacket are used as cable members and twisted into an SZ twist. An optical cable in which a cable central portion is also formed, and a tensile strength member is linearly arranged on the central portion of the cable, and a secondary jacket is applied to the entire cable. It is characterized by having a notch.

According to the second aspect of the present invention, at least two or more optical fiber units individually provided with a weather-resistant jacket are used as cable members, and the cable center portion is formed by twisting them together in an SZ twist. An optical cable in which a tensile strength member is linearly arranged on the whole and a secondary jacket is applied to the optical cable, and holes are intermittently provided in a part of the circumference of the secondary jacket in the longitudinal direction. It is characterized by that.

According to a third aspect of the present invention, in the optical cable according to the first or second aspect, the tensile strength member arranged in a straight line is arranged at the center of the cable member twisted into an SZ twist. It is characterized by being present.

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

According to a fifth aspect of the present invention, in the optical cable according to the first aspect, the cutout portion is provided so as to swivel in one direction.

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

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

According to an eighth aspect of the invention, in the optical cable according to one of the first to sixth aspects, at least one hollow pipe line is provided in parallel with the tensile strength member linearly arranged. It is characterized by including.

According to a ninth aspect of the present invention, in the method of laying an optical cable, after laying the optical cable according to the seventh or eighth aspect, the secondary jacket is formed from the notch or the opening at an arbitrary position. The optical fiber cable is cut out to take out the hollow pipe line, the hollow pipe line is cut and the optical cable is sent into the hollow pipe line, and the optical cable is laid between two cutting points or end portions. To do.

[0022]

According to the present invention, in the invention described in claim 1 or 2, since the secondary jacket of the optical cable is provided with the notch or the hole, the notch or the hole is provided at the time of the rear branch. By opening the secondary jacket from the opening, the cable can be easily taken out from the secondary jacket without damaging the center of the cable composed 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. Further, even if the secondary jacket is cut off for a required length, the gripping force at the center of the cable before and after it is not changed, and the looseness unlike the coaxial cable using the bind wire does not occur. Further, since each optical fiber unit is individually provided with a weather resistant jacket, waterproof protection at the time of rear branching should be performed for each individual optical fiber unit that has been dropped, and for other optical fiber units, etc. Work is easy because there is no need for waterproofing. Further, the water that has entered the cable member flows out through the notch or the opening of the secondary jacket, so that it does not collect in the optical cable. Even if the slightly remaining water is frozen in winter, the change in volume is partially absorbed by the opening of the notch or the opening, and the lateral pressure applied to the optical fiber unit is almost zero.

According to the third aspect of the present invention, the strength member is arranged at the center of the cable member, so that the cable member can be easily twisted into the SZ twist. In addition, since the strength member is located near the center of the secondary jacket that has cuts in the jacket over the entire length or intermittently, all cable members must pass over the strength member once during the twisting pitch. become. For this reason, there is an advantage that the problem that the cable member falls off from the break hardly occurs. Therefore, it is effective when used for a cable laid in a relatively long span or a cable laid in a place where wind is strong and there is a lot of vibration. Moreover, since the outer diameter of the optical cable is a perfect circle, the long optical cable can be stably wound around the drum.

According to the fourth aspect of the invention, the strength member is arranged outside the center of the cable, so that the strength member can be easily gripped from the outside. For this reason,
This is useful when, for example, a large number of electric poles are used to hold the strength member for each electric pole at the time of laying the optical cable to change the laying direction of the optical cable. Further, even when the connection box is hung down for the purpose of rear branching, it is possible to easily perform the fixing work to the strength member and the like. In addition, since the vertical direction is clear, notches and openings can be provided near the strength member, that is, on the upper and side surfaces 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. is there.

According to the fifth aspect of the present invention, since the notch portion provided in the secondary jacket is configured to have a spiral shape that swivels on the cable in one direction, the central portion of the cable changes with time. Due to the weight of, the problem of opening the notch due to creep does not occur. Similarly, in the invention according to claim 6, 2
Since the notch provided in the next jacket is provided in the SZ shape, it is difficult for the cut to open due to the weight of the center of the cable.
The invention described in claims 5 and 6 is particularly effective when the center of the cable is heavy.

According to the invention described in claim 7, at least one hollow conduit is included as the cable member, and
According to the invention described in claim 8, by including at least one hollow conduit in parallel with the tensile strength member, it is possible to give a further excellent degree of freedom to the post-branching property.

That is, as in the invention described in claim 9, after the optical cable is laid, the secondary jacket is cut out from the notch or the opening at a point where a rear branch is required, and the hollow conduit is cut. Then, the hollow conduit is cut open, an optical cable with a small number of fibers is sent through the hollow conduit, and the optical fiber is guided to the connection box on the station side. If the optical fiber cable with a small number of fibers is also used as the drop line, it is not always necessary to connect the optical fiber at the rear branch point, and the rear branch connection box provided at the rear branch point does not have to worry about flooding the cable, so it is lightly packaged. It can be anything. In this way, it becomes possible to easily perform the work of the post-branch.

Further, in the invention according to claim 7, since the hollow pipe is included in the central part of the cable, the appearance of the whole cable is excellent, and in order to maintain a cross section close to a perfect circle, it is densely packed in the bobbin. Can be wrapped around. On the other hand, in the invention described in claim 8, since the hollow conduit becomes linear when the cable is laid, it is possible to easily pull in the optical fiber having a small number of fibers into the hollow conduit. It is particularly advantageous when used for a long optical cable.

[0029]

1 is a sectional view showing a first embodiment of an optical cable of the present invention. In the figure, 1 is an optical fiber unit,
2 is a slot, 3 is a tape core wire, 4 is a primary jacket, 5 is a strength 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, a tape core wire 3 is arranged in each slot 2, and is covered with a primary jacket 4. The primary jacket 4 has weather resistance, and the optical fiber unit 1 can be installed as it is. Five optical fiber units 1 and one tube 6 are twisted into an SZ twist around the tensile strength member 5 and covered with a secondary jacket 7. This 2
A cut 8 is provided in the next 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,
Number of slots 2 in the optical fiber unit 1, slot 2
The number of cores of the tape core wire 3 arranged inside is arbitrary. It is also possible to configure without using the tube 6. However, as will be described later, by disposing the tube 6 and using it, the post-branching can be easily performed.

In the optical cable shown in the first embodiment, the strength member 5 is arranged at the center of the cable member. This makes it easy to twist the cable members into an 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 out from the cut of the secondary jacket. For this reason, the cables used for laying relatively long spans, strong winds,
It is effective when used for a cable laid in a place with a lot of vibration. Moreover, since the outer diameter of the optical cable is a perfect circle, the 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. Various shapes can be considered as the cut 8 provided in the secondary jacket 7. For example, as shown in FIG. 2 (A), the secondary jacket 7 may be provided with intermittent cuts 8. Also, FIG.
As shown in (B), it is possible to make a spiral cut 8 in the secondary jacket. Alternatively, as shown in FIG.
The break 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 way, compared with the conventional binding wire winding shown in FIG.
It is possible to manufacture in excess of / 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 any structure, after cutting the secondary jacket 7 at one location, the secondary jacket 7 can be easily opened in the lateral direction, and cutting of the secondary jacket 7 for post-branching is simple. Is.

In the configuration shown in FIGS. 2 (B) and 2 (C), there is a problem that the break 8 opens 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 happen. Therefore, it is particularly effective when the center of the cable is heavy.

As a concrete optical cable in the above-mentioned first embodiment, for example, an outer diameter of 1.1 × 0.4 mm 4
Four core tapes are put into a nylon rod with a diameter of 10 mm and placed in four slots with a width of 1.3 mm and a depth of 2.0 mm, and a polyethylene primary coating is applied up to an outer diameter of 12 mm. A fiber unit was used. Five optical fiber units and one polyethylene tube having an outer diameter of 12 mm and an inner diameter of 10 mm were provided around a tensile strength member made of a polyethylene-coated steel stranded wire having a diameter of 12 mm, with a pitch of 40 mm.
A cable core was manufactured by SZ twisting at 0 mm and a reversal angle of 275 °. A secondary jacket having an outer diameter of 40 mm and having continuous cuts with a width of 4 mm is applied to the lower surface. As a result, an optical cable with an initial number of fibers of 320 can be created.

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 interposer. In this embodiment, a plurality of optical fiber units 1 and tubes 6 are used.
Is twisted into an SZ twist around the interposer 9 to form a cable center portion. A tensile strength member 5 is arranged in parallel outside the central portion of the cable, and a secondary jacket 7 is applied to form an optical cable. As the interposer 9, for example, one made of polyester terephthalate can be used. Further, a cut 8 is provided in a part of the secondary jacket 7. The tube 6 may not be provided, or may be configured to have a plurality of tubes.

Also in this optical cable, the branching can be easily performed by using the break 8. In addition, since the portion of the strength member 5 is convex, it is easy to grip the portion of the strength member 5 at the time of laying. The installation can be easily performed by changing the installation direction of the. Furthermore, even when the connection box is provided at the rear branch point after the optical cable is laid, it is easy to hang the connection box on the 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,
You can make a cut on the top or side of the optical cable,
It is possible to prevent the cable member from slipping down due to its own weight.

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 into an SZ twist around the tensile strength member 5 to form a cable central portion, a tube 6 is arranged in parallel with this, and a secondary jacket 7 is applied to form an optical cable. is doing. A cut 8 is provided in a part of the secondary jacket 7, which can be used to easily perform a post-branch. Further, in the optical cable having such a configuration, the transmission resistance is reduced, for example, it becomes 1/3 at the maximum value as compared with the pushing resistance when pushing the cable with a small number of cores into the optical cable shown in the first embodiment. Is effective. A plurality of tubes 6 may be arranged in parallel with the central portion of the cable. Of course, the tube 6 may be arranged in the center of the cable.

Next, the rear branch of the above-mentioned optical cable will be described based on a specific example. FIG. 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 its usage example, and FIG. 7 is an explanatory diagram of an example of a state after branching of 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 bind wire, 20 is an airtight closure, 21 Is a rear branch cable. An optical cable 11 is laid between two electric poles 12 having a clamp 13 at a certain height. For example, the clamp 13 can be arranged at a position where the height of the electric pole 12 is 5 m. Moreover, the distance between the poles of the electric pole 12 can be set to, for example, 50 m. The optical cable 11 is fixed by a clamp 13. It is considered that the post-branch is performed at the post-branch point 14 in the middle of the two electric poles 12.

At the time of branching, first, a certain length including the post-branch point 14 is set, and two points are set at two positions on both sides thereof.
Next cut the outer jacket. For cutting the secondary jacket, it is convenient to use a sheath cutting tool as shown in FIG. 6 (A). In the example of the sheath cutting tool shown in FIG. 6A, the handle 16 is provided on one of the two convex portions of the U-shaped blade 17, and the other is used as the guide 18. When cutting the secondary jacket, handle 1
6 and insert the guide 18 into the cut provided in the optical cable 11 as shown in FIG.
By drawing along the outer shape of 1, the secondary jacket can be circumferentially cut. In addition, the break is shown in Figure 2.
In the case of intermittent provision as shown in (A),
The connection part of the break can be similarly cut. After that, a cut is 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 does not loosen, so the twisted structure is suppressed and fixed,
The twist is not disturbed.

As described above, by cutting the secondary jacket using the cuts, the secondary jacket can be easily formed without damaging the cable member such as the optical fiber unit or the tube having the individual sheath inside the optical cable. You can take it out. Since the cable members are twisted in the 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 tube twisted into the SZ twist can be opened to the outside and the required optical cable unit can be further opened to take out the required fiber and branch it. For example, in the optical cable shown in FIG. 1, it is possible to take out four four-core tapes stored in one slot of one of five optical fiber units and branch them later. These four-core tapes are connected to the rear branch cable 21, and the connection point is airtightly hardened by an airtight closure 20 using a curable resin. The portion excluding the secondary jacket for post branching may be twisted as before and fixed using the bind wire 19. This state is shown in FIG. It is also possible to carry out post-branching by taking out the tube arranged in the optical cable and connecting the optical cable having a small number of fibers, which is sent through the tube, to the post-branching cable 21.

At this time, since each optical fiber unit is individually provided with a primary jacket having weather resistance, waterproof protection at the time of post-branching may be performed for each optical fiber unit that has been dropped. , Other optical fiber units, etc. do not need to be waterproof. In this way, the post-branching work can be easily performed. After the work, the water that has entered the cable member flows out through the cuts in the secondary jacket, and therefore does not collect in the optical cable. Even if the slightly remaining water is frozen in winter, the change in volume is partially absorbed by the opening of the notch or the opening, and the lateral pressure applied to the optical fiber unit is almost zero.

FIG. 8 is an explanatory view of an example of a method of laying a cable with a small number of cores, and FIG. 9 is a sectional view of an example of a cable with a small number of cores to be laid. In the figure, parts similar to those in FIG. 22 is a connection box, 23 is a tube, 2
Reference numeral 4 is a drop conduit cable, 25 is a cable with a small number of cores, and 26 is a connection box for the drop destination. 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 and the tube 23 is taken out by the above-described rear branch method. The tube 23 is cut, and as shown in FIG. 8 (B), the drop conduit cable 2 that connects with the drop destination.
4 to form a continuous conduit. As shown in FIG. 8 (C), the cable 25 with a small number of cores is pushed into the drop conduit cable 24. As the small number of cables 25 to be pushed in, for example, an optical cable having a sectional shape as shown in FIG. 9 can be used. Specifically, the outer diameter is 0.9 m
1 centered around 7 single-core wires of m and 6 around it 1-6
Arranged, polyethylene sheath on the outer circumference, outer diameter 4 m
What was set to m can be used. The small number of cables 25 can be pushed into the tube in the optical cable shown in the first embodiment for 100 m.

The small number of cables 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 pushed-in small number of cables 25 is taken out, and predetermined fibers are connected in the connection box 22. On the other hand, the terminal of the withdrawal destination, as shown in FIG.
The connection is made with the optical cable on the terminal side in the withdrawal destination connection box 26 provided at the withdrawal destination. In this way, by making the cable with a small number of fibers common to 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 concern about water ingress to the optical fiber unit. In this way, it becomes possible to easily perform the work of the post-branch.

The drop line is separated from the optical cable that passes through the tube 23, and the connection box 26 for the drop destination is connected to the optical cable 11.
It can also be installed on top. In this drop-down destination connection box 26, the terminal on the drop-down destination side of the cable with a small number of cores is connected to the drop-down cable. The drop-off connection box 26 used at this time is the connection box 2 installed at the time of installation at the optical cable connection point.
The same one as in 2 may be used.

In the above-described transmission of the small number of cables, the transmission is made from the rear branch point to the connection box, but it may be made from the branch point to the branch point. Further, as a method of feeding, other than pushing in, other methods such as pressure feeding by gas can be used.

As described above, by using the tube arranged in the optical cable, it is possible to give a wider degree of freedom to the post-branching and the construction method.

[0049]

As is apparent from the above description, according to the present invention, there is an effect that post branching can be easily performed after the optical cable is laid. The optical cable of the present invention is
It is useful when used in a wiring network where a rear branch point needs to be provided.

[Brief description of drawings]

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

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

FIG. 3 is a cross-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 a usage example thereof.

FIG. 7 is an explanatory diagram of an example of a state after branching of a post branch point.

FIG. 8 is an explanatory diagram of an example of a method of laying a cable with a small number of cores.

FIG. 9 is a cross-sectional view of an example of a cable with a small number of fibers to be laid.

FIG. 10 is a schematic diagram 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 cross-sectional view of an example of a conventional coaxial cable.

[Explanation of symbols]

 1 Optical fiber unit 2 Slot 3 Tape core wire 4 Primary jacket 5 Strength member 6 Tube 7 Secondary jacket 8 Cut 9 Intermediary material 11 Optical cable 12 Utility pole 13 Clamp 14 Rear branch point 15 Sheath cutting tool 16 Handle 17 Blade 18 Guide 19 Bind wire 20 Airtight closure 21 Rear branch cable 22 Connection box 23 Tube 24 Dropping conduit cable 25 Small number of cables 26 Dropping connection box

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigekazu Hayami 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (9)

[Claims] 1. A cable central part is formed by twisting at least two optical fiber units individually provided with weather resistant jackets as cable members, and twisting them into an SZ twist.
An optical cable in which a tensile strength member is linearly arranged and a secondary jacket is applied to the whole, and a notch portion is provided in a longitudinal direction in a part of the circumference of the secondary jacket. Optical cable characterized by. 2. A cable center portion is formed by twisting at least two or more optical fiber units individually provided with a weather-resistant jacket as cable members, and twisting them into an SZ twist.
An optical cable in which a tensile strength member is linearly arranged on the whole of which is provided with a secondary jacket, and an opening is intermittently provided in a longitudinal direction in a part of the circumference of the secondary jacket. An optical cable that is characterized by 3. The tensile strength member linearly arranged is S
The optical cable according to claim 1 or 2, wherein the optical cable is arranged at the center of the cable member twisted into a Z twist. 4. The optical cable according to claim 1, wherein the strength members arranged in a straight line are arranged outside the central portion of the cable. 5. The optical cable according to claim 1, wherein the cutout portion is provided in a shape that turns in one direction. 6. The cutout portion is formed by changing the direction of the cutout S.
The optical cable according to claim 1, wherein the optical cable is provided in a Z shape. 7. The optical cable according to claim 1, wherein at least one hollow conduit is included as a cable member that constitutes the central portion of the cable. 8. The optical cable according to claim 1, further comprising at least one hollow pipe line in parallel with the tensile strength member arranged in a straight line. 9. After laying the optical cable according to claim 7 or 8, the secondary jacket is cut out from the notch or the opening at an arbitrary position to take out the hollow conduit, A method of laying an optical cable, characterized in that the optical fiber is cut by cutting the pipe and sending the optical cable to the inside thereof, and laying the optical cable between two cut points or ends and the cut points.