JP3003304B2 - Optical fiber cable and method of laying optical fiber 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 fiber cable laid by a gas flow and a method of laying an optical fiber cable.

[0002]

2. Description of the Related Art An example of an optical fiber cable laid by a gas flow is shown in FIG. (A) The figure is a side view,
(B) is a sectional view. In the figure, 1 is an optical fiber cable, 2 is an optical fiber, 3 is a primary coating, and 4 is a secondary coating. In this example, seven optical fibers 2 are twisted, a primary coating 3 is put thereon, and the optical fiber cable is further covered with a secondary coating 4 to form an optical fiber cable. Since the coating thickness of the primary coating 3 and the secondary coating 4 is constant over the longitudinal direction of the cable, the outer diameter of the optical fiber cable 1 is changed in the longitudinal direction as shown in the side view of FIG. On the other hand, it is uniform.

[0003] In general, when gas flows into a pipe, a continuous pressure distribution is generated in the pipe from the gas supply side to the open side, but the pressure gradient is close to the supply side. As small.

On the other hand, as described in Japanese Patent Publication No. 22921/1990, compressed air or the like is supplied from one end of a pre-installed pipeline to flow gas toward the other end.
A method of laying an optical fiber cable by this gas flow is known. Fiber optic cables are provided with a traveling force by the pressure gradient of the gas stream. This force is related to the magnitude of the pressure gradient and the outer diameter of the optical fiber cable, and is larger as the pressure gradient is larger and as the outer diameter of the optical fiber cable is larger. Therefore, when an optical fiber cable having a uniform outer diameter is pumped, the advancing force given to the optical fiber cable is minimized at the gas supply end, and the entire optical fiber cable travels at the gas supply end. And a large advancing force due to a large pressure gradient near the open side of the pipeline, that is, at the distal end side, has not been utilized.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical fiber cable as a whole by increasing a minimum value of a traveling force which governs the progress of the optical fiber cable. It is an object of the present invention to provide an optical fiber cable and a method for laying an optical fiber cable, which can dramatically improve the advancing power as a cable.

[0006]

According to a first aspect of the present invention, there is provided an optical fiber cable laid using a gas flow, wherein the outer diameter of the optical fiber cable extends from the leading end to the end in the traveling direction at the time of laying. Is continuously or stepwisely increased over the entire length, and the invention according to claim 2 is directed to an optical fiber cable laid using a gas flow, wherein The outer diameter of the optical fiber cable is uniform from the front end to the end toward the middle, and the outer diameter of the optical fiber cable increases continuously or stepwise from the middle to the rear end. Things. According to a third aspect of the present invention, in the method for laying an optical fiber cable,
An optical fiber cable whose outer diameter continuously or stepwise increases over the entire length from the front end side to the end side in the traveling direction at the time of laying is laid using a gas flow. Item 4 is a method for laying an optical fiber cable, wherein the outer diameter of the optical fiber cable is uniform from the leading end to the middle in the traveling direction at the time of laying, and the optical fiber extends from the middle to the rear end. An optical fiber cable in which the outer diameter of the cable is increased continuously or stepwise is laid using a gas flow.

[0007]

In general, when a gas flows in a pipe, the pressure distribution P (l) in the pipe is represented by L as the pipe length and P as the gas supply pressure.
_{When IN} , the pressure at the time of gas release is P _OUT , and the distance from the gas supply end is l,

[0008]

(Equation 1)

## EQU1 ## This is shown graphically in FIG.
become that way. On the other hand, the advancing force F (l) of the optical fiber cable pumped by the gas flow has a gas pressure gradient dP /
dl, outer diameter d ₁ of optical fiber cable, inner diameter d _{2 of} pipe
Related to

[0010]

(Equation 2)

## EQU1 ## From the formula and the formula, the traveling force at the point of the distance l is

[0012]

(Equation 3)

Is rewritten as: And d ₁ , d ₂ ,
If P _IN and P _OUT are all graphed as constants, the diagram shown in FIG. 3 is obtained.

FIG. 3 shows that, as described above, the advancing force of the optical fiber cable at the gas supply side end of the conduit is the smallest. When the outer diameter of the optical fiber cable is increased from the front end side to the end side in the traveling direction at the time of laying, a portion having a larger outer diameter has a larger advancing force than a portion having a smaller outer diameter. As shown, in the gas supply side end and in the vicinity of the region where the traveling force is small, the traveling force can be increased to provide a more uniform traveling force in the longitudinal direction of the optical fiber cable. Since the minimum value a of the traveling force is larger than the minimum value b of the traveling force in the case of the conventional optical fiber cable having a uniform outer diameter,
The traveling force of the entire optical fiber cable can be greatly improved.

[0015]

1 is an explanatory view of an embodiment of an optical fiber cable according to the present invention. FIG. 1 (A) is a side view, and FIG. 1 (B) is a cross-sectional view on the front end side in the traveling direction. In the figure, 1 is an optical fiber cable, 2 is an optical fiber, 3 is a primary coating, and 4 is a secondary coating. The side view exaggerates the ratio of the longitudinal direction to the diameter. In this embodiment, as in FIG. 8, seven optical fibers are twisted and a primary coating and a secondary coating are applied thereon. The structure is not limited to a structure in which all seven fibers are made of optical fibers, and may include a tensile strength fiber, a tear string, or the like. The outer diameter of the optical fiber cable 1 is larger on the terminal side (right side in the figure) than in the front side (left side in the figure) in the traveling direction at the time of laying, and the outer diameter changes continuously in the longitudinal direction. ing. When this optical fiber cable is pressure-fed, it proceeds in the direction of the arrow shown in the figure.

FIG. 5 shows an embodiment in which the outer diameter of the secondary coating is changed as a method of changing the outer diameter of the optical fiber cable. (A) is a side view, (B) is a cross-sectional view on the front end side in the traveling direction, and (C) is a cross-sectional view on the terminal end side. In the figure, the same parts as those in FIG.
The secondary coating 4 was formed by extrusion coating of a synthetic resin, and the extrusion diameter was continuously changed. The outer diameter of the primary coating 3 is
It is uniform in the longitudinal direction.

The outer diameter of the primary coating 3 may be changed in the longitudinal direction so that the secondary coating 4 has a uniform thickness.
The thickness of both coatings may be varied. Further, the coating is not limited to two layers, and one or three or more coating layers may be formed.

The change in the outer diameter may be over the entire length of the optical fiber cable or only a part thereof. Also,
The change in the longitudinal direction is not necessarily continuous, but may be a stepwise change.

FIG. 6 is a side view of an optical fiber cable according to an embodiment in which a part of the optical fiber cable 1 has a uniform outer diameter and the outer diameter changes partway.

FIG. 7 is a side view of the optical fiber cable of the embodiment in which the outer diameter of the optical fiber cable 1 is changed stepwise.

[0021]

As is apparent from the above description, according to the present invention, the minimum traveling force that governs the progress of the entire optical cable can be increased, so that there is an effect that the traveling ability of the entire optical cable can be improved. In particular, it is extremely effective when laying a series of pipes in a long distance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of an optical fiber cable of the present invention.

FIG. 2 is a diagram showing a pressure distribution in a pipeline.

FIG. 3 is a diagram illustrating a traveling force of a conventional optical fiber cable.

FIG. 4 is a diagram illustrating a traveling force in an embodiment of the optical fiber cable of the present invention.

FIG. 5 is an explanatory view of another embodiment of the optical fiber cable of the present invention.

FIG. 6 is a side view of an embodiment in which the outer diameter of the optical fiber cable is changed in the middle.

FIG. 7 is a side view of an embodiment in which the outer diameter of the optical fiber cable is changed stepwise.

FIG. 8 is an explanatory diagram of an example of a conventional optical fiber cable.

[Explanation of symbols]

 1 Optical fiber cable 2 Optical fiber 3 Primary coating 4 Secondary coating

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/46 H02G 1/08

Claims (4)

(57) [Claims] In an optical fiber cable laid using a gas flow, the outer diameter of the optical fiber cable increases continuously or stepwise over the entire length from the front end side to the end side in the traveling direction at the time of laying. An optical fiber cable characterized in that: 2. In an optical fiber cable laid using a gas flow, the outer diameter of the optical fiber cable is uniform from the front end side to the end side in the traveling direction at the time of laying, and from the middle to the rear end. An optical fiber cable, wherein the outer diameter of the optical fiber cable increases continuously or stepwise. 3. An optical fiber cable whose outer diameter continuously or stepwise increases over the entire length from the front end side to the end side in the traveling direction at the time of laying is laid using a gas flow. How to lay an optical fiber cable. 4. The outer diameter of the optical fiber cable is uniform from the front end side to the end side in the traveling direction at the time of laying, and the outer diameter of the optical fiber cable is continuous or stepwise from the middle to the rear end. A method of laying an optical fiber cable, which comprises laying an increasing number of optical fiber cables using a gas flow.