JP2910306B2 - Pneumatic light transmission cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic light transmission cable constructed by inserting an optical fiber unit under pressure into a tube using an air flow.

[0002]

2. Description of the Related Art A method of constructing an optical fiber cable by inserting an optical fiber unit or an optical fiber alone into a previously laid tube using an air flow is described in Japanese Patent Publication No. 22921/1990. However, this publication does not consider the relationship between the configuration of the tube and the structure of the optical fiber unit inserted therethrough. Thereafter, as described in "Preliminary Proceedings of the 1990 IEICE National Convention" B-667, Kanzaki et al. "Air Blown Transmission to Twisted Pipes", as a conduit for inserting an optical fiber unit, Although there is a report using a helical conduit, no consideration is given to the relationship with the structure of the optical fiber unit.

A conventional optical fiber unit for pneumatic feeding is
Since the tube was developed on the premise that it is fed to a tube line having a straight line and several bent portions, the tube assembled in a spiral has a radius of curvature of 200 cm.
When used for a tube conduit having the following bent portions, there is a problem that the insertion capacity is greatly reduced.

[0004] This is because, during the insertion of the optical fiber unit, the optical fiber unit is bent into a helical shape, so that a large amount of pumping energy is consumed even in a portion where the pipeline is laid in a straight line. Therefore, it can be said that a conventional optical fiber unit having a large bending rigidity is disadvantageous for a spiral pipe.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a radius of curvature of 200c.
Provided is a pneumatic light transmission cable which is realized by using an optical fiber unit having an improved insertion ability in a pneumatic light transmission cable configured to be pressure-pushed and inserted into a spiral tube pipe having a bent portion of m or less by pneumatic pressure. It is intended to do so.

[0006]

According to a first aspect of the present invention, there is provided an optical fiber unit comprising a plurality of optical fibers in a tube pipe which is spirally disposed and has a bent portion having a radius of curvature of 200 cm or less. In the pneumatic light transmission cable configured to be inserted by using a flow, the optical fiber unit may be configured such that an optical fiber constituting the optical fiber unit or a subunit including a plurality of optical fibers has a twist pitch shorter than a helical pitch of the tube conduit. While being twisted, the twist direction is characterized by being opposite to the spiral direction of the tube conduit. The invention according to claim 2 is the air pressure transmission cable according to claim 1. The tube line is characterized in that a plurality of tube lines are twisted.

[0007]

When the optical fiber unit is inserted into the tube, the optical fiber unit is bent in the helical direction of the tube as it is inserted. At this time, the lower the bending rigidity of the optical fiber unit, the higher the insertion capability. As the optical fiber unit according to the present invention is inserted into the tube,
Because the tip gradually rotates in the twisting direction of the tube,
The twist of the optical fiber or the subunit is loosened, and the bending rigidity is reduced.

On the other hand, when the twisting direction of the optical fiber or the subunit is the same as that of the tube, the twisting is tightened by rotating the tip of the optical fiber unit in the twisting direction of the tube, the bending rigidity is increased, and the insertion capacity is reduced. Causes a decline. In addition, an optical fiber unit that does not twist an optical fiber or subunit will cause the outer optical fiber or subunit to stretch and bend when it is bent, so that the bending rigidity will increase and, similarly, the insertion capacity will increase. It is disadvantageous because it decreases.

[0009]

FIG. 1 is a sectional view of an embodiment of the optical fiber unit of the present invention. In the figure, 1 is an optical fiber, 2 is a tear string, 3 is an inner layer coating, and 4 is an outer layer coating. In this embodiment, a total of seven optical fibers 1 and one tear string 2 are twisted, an inner coating 3 is put thereon, and an outer coating 4 is applied to form an optical fiber unit. Have been. The direction of twist is opposite to the direction of twist of the tube line through which this unit is inserted, and the pitch of twist is smaller than the pitch of twist of the line.

FIG. 2 is a sectional view of another embodiment of the optical fiber unit of the present invention. In the figure, 1 is an optical fiber, 2 is a tear string, 3 is an inner layer coating, 4 is an outer layer coating, 5 is a subunit, and 6 is an inner layer coating. In this embodiment, the optical fiber unit is composed of three subunits 5. Each of the subunits 5 is composed of six optical fibers 1 and one tear cord 2 in total, as described in FIG. The optical fiber 1 and the tear string 2 in the subunit are twisted as in FIG. 1, but need not necessarily be twisted. The three subunits 5 are twisted in a direction opposite to the twisting direction of the tube conduit through which this unit is inserted, and the twisting pitch is
This value is smaller than the twist pitch of the pipeline.

FIG. 3 shows an example of a pipeline. In the figure, 7 is a tube, 8 is a covering, and 9 is a power cable. The tube 7 provided with the coating 8 is twisted together with the three-phase power cable 9. These may be further provided with a suitable coating.

The optical fiber unit described with reference to FIG. 1 or 2 is inserted into such a conduit to form an optical fiber cable. In order to insert the optical fiber unit into the tube 7, it is necessary to reduce the bending rigidity in the tube spiral direction. For this purpose, it is effective to twist an optical fiber or an optical fiber subunit constituting the optical fiber unit. Moreover, since the twist pitch is shorter than the twist pitch of the tube and the twist direction is opposite to the twist direction of the tube, rigidity at the time of insertion can be reduced.

In order to confirm the effect of the present invention, ten kinds of optical fiber units shown in FIG. The pipe used was a spiral-shaped polyethylene tube having an outer diameter of 8 mm and an inner diameter of 6 mm. The spiral shape of the tube has a twist pitch of 830 mm, the core diameter of the tube is 46 mm, and the twist direction is right.

Of the ten types of optical fiber units, N
o. 1 to No. Reference numeral 5 denotes an optical fiber coated with an outer diameter of 250 μm, one of which is arranged at the center and six of which are arranged around the optical fiber.
m is further covered with an outer layer of high-density foamed polyethylene to have an outer diameter of 2 mm, and has the same structure as that of FIG. The twist pitch of the optical fiber is shown in FIG.
As shown in FIG.

No. 6-No. In No. 10, three of the above-described polypropylene inner layer coatings were used as subunits. This was twisted at the pitch shown in FIG. 4, overlaid with an inner layer coating of polypropylene to a diameter of 2.5 mm, and coated with high density foamed polyethylene to an outer diameter of 4 mm. This is a structure similar to that of FIG.

FIG. 5 shows the insertion characteristics of the ten types of optical fiber units shown in FIG. The compression pressure of the air used for insertion is 5 kg / cm ² in gauge pressure. The length of the tube fed by pressure is no. 1 to No. No. 5 is 600 m;
6-No. 10 is 300 m.

As can be seen from the results, it was confirmed that the insertion capability was particularly high when the twisting direction of the tube and the optical fiber or the subunit were opposite and the twisting pitch was equal to or less than the twisting pitch of the tube. did it.

As a conduit to which the present invention can be applied, as shown in FIG. 3, a tube is twisted, for example, when an optical fiber unit is inserted after a power cable and a tube are combined and laid. Effective for pipelines. Further, not only when a tube is combined with another cable but also when a cable is formed by bundling a plurality of tubes, the tube is often twisted in order to increase the flexibility of the cable. The optical fiber unit according to the present invention is effective for such a pipeline.

[0019]

As is apparent from the above description, according to the present invention, the optical fiber or the subunit constituting the optical fiber unit is twisted in a direction opposite to the spiral direction of the tube line, and the twist pitch Is smaller than the helical pitch of the tube conduit, there is an effect that it is possible to provide a pneumatic light transmission cable with improved insertion capability.

[Brief description of the drawings]

FIG. 1 is a sectional view of one embodiment of an optical fiber unit of the present invention.

FIG. 2 is a sectional view of another embodiment of the optical fiber unit of the present invention.

FIG. 3 is an example of a pipeline to which the present invention is applied.

FIG. 4 is an explanatory diagram of characteristics of an optical fiber unit used in an experiment.

FIG. 5 is an explanatory diagram of an experimental result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Tear string 3 Inner layer coating 4 Outer layer coating 5 Subunit 6 Inner layer coating

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/46

Claims (2)

(57) [Claims] 1. A helical arrangement having a radius of curvature of 200 cm
In a pneumatic light transmission cable constructed by inserting an optical fiber unit composed of a plurality of optical fibers by using an air flow into a tube conduit having the following bent portion, the optical fiber unit comprises an optical fiber Alternatively, a subunit composed of a plurality of optical fibers is twisted at a twist pitch shorter than the spiral pitch of the tube line, and the twist direction is opposite to the spiral direction of the tube line. Pneumatic light transmission cable. 2. The pneumatic light transmission cable according to claim 1, wherein a plurality of tube lines are twisted in the tube line.