JPH0593829A - Optical cable - Google Patents

Abstract

(57) [Abstract] [Purpose] When the optical cable is bent, the extension strain generated in the optical fiber is reduced, and a highly reliable multicore cable is realized. [Structure] A plastic spacer 2 accommodating an optical fiber ribbon 5 is gathered around the tension member 1 with its bottom portion in contact. Plastic spacer 2
Has a substantially U-shaped cross-section inside, and tensile strength members 3a, 3b, 3c are provided in the cross-section.
By providing the strength member, the residual elongation of the spacer due to the supply tension at the time of manufacturing the cable can be significantly reduced, and the effect of alleviating the strain due to the sliding of the spacer can be sufficiently exerted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an optical fiber tape core wire accommodated in a plastic spacer having a substantially U-shaped cross section, and a plurality of the plastic spacers are assembled around a tension member. It relates to the structure of an optical cable.

[0002]

2. Description of the Related Art Conventional optical cables usually employ a structure in which an optical fiber core wire or a unit in which a plurality of optical fibers are assembled is twisted around a tension member. For example, JP-A-55-45087. As described in Japanese Patent Laid-Open Publication No. JP-A No. 2003-187, there is also known an optical cable using a plastic spacer in which the inside of a cross section is substantially U-shaped and extruded. FIG. 3 is a sectional view thereof, in which 1 is a tension member, 2 is a plastic spacer, 6 is a press winding, 7 is a sheath, 8 is an optical fiber, and 9 is an optical fiber unit. In this optical cable, the optical fiber 8 or the optical fiber unit 9 is housed in a plastic spacer 2 having a substantially U-shaped cross section inside, and is further assembled around the tension member 1 and a tape is formed thereon. The press winding 6 and the sheath 7 are sequentially provided.

Such an optical cable has an excellent structure from the viewpoint of a larger number of cores and a smaller diameter than cables of other structures, but for example, several hundred cores or several hundreds of cores are used.
When it is attempted to realize an ultra-multifiber optical fiber such as 0 core, the outer diameter of the cable becomes a large diameter ranging from 30 to 40 mm. When the cable has a large diameter, the layer core diameter (distance from the center of the cable) of the optical fiber accommodated in the cable becomes larger than that of a conventional cable with a small number of cores. There is a problem that the elongation strain that the fiber receives becomes large.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a cable having a structure in which a plastic spacer for accommodating an optical fiber ribbon has a substantially U-shaped cross section and is assembled around a tension member. In order to realize a highly reliable multicore cable, it is possible to reduce the elongation strain generated in the optical fiber when the cable is bent.

[0005]

According to the present invention, an optical fiber ribbon is housed inside a plastic spacer having a substantially U-shaped cross section inside, and the bottom of the plastic spacer is a tension member at the center of the cable. In the optical cables arranged and assembled toward each other, the plastic spacer has a tensile strength member in its cross section.

[0006]

When the cable is bent, the optical fiber on the outer side of the bend from the center of the cable is subjected to extensional strain, and the optical fiber on the inner side is subjected to compressive strain. The maximum value of elongation strain is when the optical fiber is located on the outermost side of the bend. The distance from the cable center to the optical fiber is r,
Assuming that the cable bending radius is R, the maximum value of elongation strain is represented by an approximate value of E = r / R.

In an actual cable, the extension strain is relaxed by the slip of the optical fiber in the plastic spacer and the slip of the plastic spacer itself, and the extension strain is smaller than the maximum value obtained by the above equation.
The present invention is intended to reduce the strain applied to the optical fiber by increasing the effect of relaxing the extension strain due to the slip of the plastic spacer itself.

In an optical cable in which the bottom of the plastic spacer, which is substantially U-shaped inside the cross section, is always arranged towards the tension member, the plastic spacer is always assembled around the tension member without twisting. There is a need. When an optical fiber ribbon is used for the purpose of increasing the number of cores, the outermost optical fiber ribbon is always on the outer side and the innermost fiber ribbon is always on the inner side. As a result, the twisting rate varies depending on the position of the tape core wire in the plastic spacer, which causes a difference in the length of the optical fiber tape core wire in the cable. For this reason, in the manufactured optical cable, in order to prevent the strain in the length direction from remaining in the optical fiber tape core wire, the steps of assembling the plastic spacers around the tension member and the optical guide in the groove of the plastic spacer are performed. It is necessary to tandemly perform the step of accommodating the fiber tape core wire on the same line. At this time, since the plastic spacers are supplied with the supply tension and gather around the tension member, the elongation strain determined by the supply tension remains in the plastic spacers. If the strain when the cable is bent is not taken into consideration, the residual elongation of the plastic spacer in the cable is not limited, but this is a problem from the viewpoint of the strain relaxation effect when the cable is bent.

The reason will be described. FIG. 2 shows the state of strain when the cable is bent. In the figure, 1 is a tension member and 2 is a plastic spacer. The shape of the plastic spacer 2 is simplified and only one is shown. When the cable is bent with a bending radius R, a portion outside the center line in the C direction receives a stretching force and an inside portion in the D direction receives a compressive force. Therefore, in the 1/2 pitch A region located outside the tension member 1, the plastic spacer 2 is subjected to elongation strain, and in the 1/2 pitch B region located inside the tension member 1, the plastic spacer 2 is compressed. Receive distortion. Here, when the plastic spacer 2 slips with respect to the tension member 1, the extension strain and the compression strain are canceled out, and the strain applied to the optical fiber housed in the plastic spacer 2 is relaxed.

However, if the plastic spacer 2 is subjected to a large residual elongation strain due to the supply tension, the compressive strain generated by bending at the inner half pitch is canceled by the residual elongation strain. Become. In that case, there is no compressive strain on the inner side that should cancel out the elongation strain received on the outer side, and the effect relaxed by the slip of the plastic spacer is reduced.

In the present invention, by adopting a structure having a tensile strength member in the cross section of the plastic spacer,
Residual elongation of plastic spacers caused by supply tension during cable manufacturing can be significantly reduced,
The problems described above can be solved. In addition, the strength members in the plastic spacer increase the force required to compress or stretch the plastic spacer, making it more slippery and more strain-relieving when the cable is bent. ..

Further, since the optical fiber is housed in the plastic spacer and the plastic spacer itself is twisted around the tension member with a certain curvature, when an extension strain is applied to the optical fiber, A force acts to move the optical fiber toward the center of the cable, and the optical fiber ribbon is subjected to lateral pressure from the bottom inside the plastic spacer. Therefore,
The lateral pressure can be reduced by reducing the elongation strain of the optical fiber during bending.

[0013]

1 is a sectional view of an embodiment of the optical cable of the present invention. In the figure, 1 is a tension member, 2 is a plastic spacer, 3a, 3b and 3c are strength members, 4 is a groove, 5 is an optical fiber tape core wire, 6 is a press winding, and 7 is a sheath. The inner side of the cross section of the plastic spacer 2 is substantially U-shaped. The U shape does not necessarily require that the lower surface is a curved surface portion. From the viewpoint of the accommodation of the optical fiber ribbon 5, the lower surface of the plastic spacer 2 is preferably flat. Also, the corners need not be square. Regarding the side surface, the shape is free and does not need to be a planar shape.

For the sake of explanation, the tensile strength members 3a and 3b are 2
The types are illustrated. 3a is a deformed strength member, and 3b is a circular strength member. Of course, only one of these may be used. Moreover, the position where it is arranged may be appropriate. Also, a plurality of lines may be provided on one surface. As for the cross-sectional shape of the tensile strength member, the deformed shape has a higher storage efficiency and is therefore advantageous in reducing the diameter of the cable.

The plastic spacers 2 are gathered around the tension member 1 with their bottoms in contact with each other.
In the U-shaped groove 4 inside the optical fiber tape core wire 5
Are stored in a stacked state. A press winding 6 is provided on the outer circumference of the plastic spacer 2 accommodating the optical fiber ribbon 5, and a sheath 7 made of vinyl chloride, polyethylene or the like is provided on the press winding 6.

An optical cable having the structure described with reference to FIG. 1 was prototyped, and the effect of reducing strain due to bending was confirmed. Glass FR
An optical cable having an outer diameter of 25 mm was experimentally manufactured by using a polyethylene spacer having a tensile strength member 3a made of P and a polyethylene spacer having no tensile strength member. The optical fiber ribbon used was a 4-fiber ribbon having a thickness of 0.4 mm and a width of 1.0 mm, and three tape fibers were accommodated in the groove of each spacer. After fixing both ends of this optical cable, it was wound around a mandrel with a diameter of 400 mm by 360 °, and at that time, the maximum elongation strain value that the optical fiber receives was
It measured using the phase difference measuring method. As a result, the maximum elongation strain of the optical fiber housed in the polyethylene spacer of the conventional structure having no strength member was 0.20%, whereas it was housed in the polyethylene spacer having the strength member made of glass FRP. The maximum elongation strain of the conventional optical fiber was 0.13%, confirming the relaxation effect of the present invention.

Further, the supply tension at the time of manufacturing the cable is 3
Elongation strain was measured as kg. The elongation strain remaining in the plastic spacer was almost 0% in the plastic spacer having the strength member, whereas it was 0.4% in the plastic spacer having no strength member.
In addition, in the above-mentioned Example, although the cable structure of 1 layer twist of 1-6 arrangement | positioning was demonstrated, in order to implement | achieve multi-core, 1-10-15 arrangement | sequence, 1-6-12 arrangement | sequence, etc. Needless to say, the structure in which the plastic spacers are twisted together can be adopted.

[0018]

As is apparent from the above description, according to the present invention, by using a plastic spacer having a substantially U-shape inside the cross section and having a tensile strength member in the cross section, When the optical cable is bent, the plastic spacer itself easily slides and moves, so that the elongation strain applied to the optical fiber is relaxed.

Generally, the laid cable has bent portions at fixed intervals in order to fix the cable in the manhole, but if the elongation strain of the optical fiber due to bending becomes large, the breaking life of the optical fiber becomes short, The reliability will be reduced. The present invention makes it possible to realize a highly reliable cable.

Further, since the tension of the plastic spacer supply can be set higher than before when the cable is manufactured, not only the conventional difficult tension control that requires low tension and high accuracy is not required, but also the tension can be increased. , It becomes possible to stably gather the plastic spacers around the tension member.

Furthermore, since the elongation strain of the optical fiber when it is bent is reduced, the lateral pressure applied to the optical fiber can be reduced, and an optical cable having excellent bending characteristics is realized from the viewpoint of transmission loss. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of an optical cable of the present invention.

FIG. 2 is an explanatory view of the operation of the present invention.

FIG. 3 is a sectional view of an example of a conventional optical cable.

[Explanation of symbols]

 1 Tension Member 2 Plastic Spacers 3a, 3b, 3c Strength Member 4 Groove 5 Optical Fiber Tape Core Wire 6 Pressing Winding 7 Sheath

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Ishikawa 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Nobumasa Nirazawa 1-tani, Taya-cho, Sakae-ku, Yokohama, Kanagawa Denki Kogyo Co., Ltd. Yokohama Works (72) Inventor Masakazu Watanabe 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Denki Kogyo Co., Ltd. Yokohama Works (72) Inventor Shigeru Tomita 1-1-1 Uchisaiwaicho, Chiyoda-ku, Tokyo No. 6 Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. An optical fiber ribbon is housed inside a plastic spacer having a substantially U-shaped cross section, and the bottom of the plastic spacer is arranged and assembled toward a tension member at the center of the cable. In the optical cable, the plastic spacer has a strength member in its cross section.