JPH0973029A - Metallic pipe type optical unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the side pressure that optical fibers receive within a metallic pipe and to prevent the optical fibers from moving in this metallic pipe by housing the plural optical fibers into the metallic pipe by placing these fibers longitudinally along the surface of buffer materials or spirally winding the fibers. SOLUTION: The plural coated fiber cords of the optical fibers 1 are disposed around the buffer materials 3 as interposing members by placing these coated fiber cords longitudinally along the buffer materials or spirally winding the coated fiber cords; further, the circumferences thereof are roughly wound with cords 4, by which an optical fiber unit is formed. One or plural pieces of such optical fiber units are housed into the metallic pipe 2 by having extra lengths. The buffer materials 3 are preferably colored in order to identify the optical fiber units. If the cords 4 consists of plural pieces, at least two pieces are made to wind in opposite directions. The buffer materials 3 have preferably water absorptivity. For example, foamed plastic cords are used for the buffer materials 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal tube type optical unit in which an optical fiber is housed in a metal tube.

[0002]

2. Description of the Related Art Since an optical fiber is weak in strength, a structure in which it is housed in a metal tube for use as an optical communication cable is conventionally known from Japanese Patent Laid-Open No. 148475/1994. .

FIG. 8 is a sectional structural view of a conventional general metal tube type optical unit. In the figure, 1 is an optical fiber and 2 is a metal tube. The optical fiber 1 is loosely housed in the internal space of the metal tube 2 with a gap. The internal space is filled with a low-humidity gas or is evacuated. Here, in order to guarantee the transmission characteristics and the reliability after the metal tube type optical unit is wired, it is important to provide the optical fiber 1 in the metal tube 2 with an appropriate extra length.

In the conventional metal tube type optical unit, the extra length of the optical fiber 1 is evenly provided over the entire length at the beginning of manufacture. However, since the optical fiber 1 is accommodated in the metal tube 2 with a loose gap, the optical fiber 1 is likely to move in the longitudinal direction due to various external forces and thermal history. As a result, a deviation of the extra length occurs, so that the optical fiber 1 is locally
Sagging occurs. In particular, when the optical fiber 1 is housed in the metal tube 2, the friction coefficient is smaller than that of the plastic coating, so that the excess length is likely to be unevenly distributed due to the movement of the optical fiber 1. As a result, there is a problem that bending loss increases due to the bending of the optical fiber 1.

Further, when a conventional metal tube type optical unit is used for an aerial cable, it is subject to vibration due to wind, but at this time, the optical fiber 1 can easily move in the metal tube 2 in the radial direction. Therefore, the collision with the inner wall of the metal tube 2 is repeated,
As a result, the lateral pressure is received from the metal tube 2 to increase the loss.
In particular, the metal tube 2 has a higher Young's modulus and is harder than a plastic tube, so that a larger loss increase occurs. Furthermore, when a plurality of optical fibers 1 are housed in the metal tube 2, the optical fibers 1 repeatedly collide with other optical fibers 1 and the lateral pressure is also received from the other optical fibers to increase loss.

When such a situation occurs, the transmission characteristics and the life of the optical fiber 1 are adversely affected, so that the conventional metal tube type optical unit has a problem in terms of guaranteeing the reliability after the overhead line.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and reduces the lateral pressure that the optical fiber receives in the metal tube and prevents the optical fiber from moving in the metal tube. It is an object of the present invention to provide a metal tube type optical unit capable of preventing an adverse effect on the transmission characteristics and life of the above.

[0008]

According to a first aspect of the present invention, in a metal tube type optical unit, a plurality of optical fibers are vertically attached or spirally wound on a buffer material and the periphery is roughly wound with a string. One or more optical fiber units are stored in the metal tube.

According to a second aspect of the invention, in the metal tube type optical unit according to the first aspect, the buffer material has a water absorbing property.

According to a third aspect of the invention, in the metal tube type optical unit according to the first or second aspect, the buffer material is colored.

According to a fourth aspect of the present invention, in the metal tube type optical unit according to any one of the first to third aspects, the buffer material has a void occupancy rate of 30 to 70%. It is a feature.

[0012]

According to the first aspect of the invention, the plurality of optical fibers are vertically mounted or spirally wound on the buffer material and housed in the metal tube. Therefore, the optical fibers do not contact each other. When the plurality of optical fibers are divided into a plurality of sets and each is a bundled optical fiber bundle, the plurality of sets of optical fiber bundles do not contact each other. As a result, it is possible to eliminate the lateral pressure generated between them, and also to reduce the lateral pressure between the optical fiber, the optical fiber bundle and the inner wall of the metal tube due to the cushioning property of the cushioning material. Furthermore, since an appropriate resistance is generated between the inner wall of the metal tube and the cushioning material, and between the cushioning material and the optical fiber or the optical fiber bundle, the optical fiber does not easily move within the metal tube even when an external force is applied. A uniform surplus length distribution can be maintained.

Further, according to the invention of claim 1,
Since it is an optical fiber unit that is roughly wound around a string, the above-mentioned effects can be maximized. For example, a method of applying a plastic coating instead of roughly winding with a string,
There is also a method of winding a cover tape to cover it. But,
In any case, when applying the coating, a pressing force acts in the central direction over the entire length of the optical fiber unit, and as a result, the buffer material at the center is tightened and the diameter thereof is reduced. as a result,
The cushioning material may not be able to maintain a sufficient cushioning effect after the metal tubular unit is manufactured. In particular, when a relatively thick buffer material is used, when the optical fiber unit is bent, a large extension strain is applied to the optical fiber on the outside of the bend, and a large compressive strain is applied to the optical fiber on the inside of the bend. At this time, with a structure in which the circumference is tightly covered with a coating, such as a plastic coating or a press-wrap tape,
Since the optical fiber cannot be easily moved, it is impossible to relax the extension strain and the compression strain applied to the optical fiber.

On the other hand, when the cord is roughly wound, the pressing force only acts on the portion where the cord and the optical fiber come into contact with each other, the cushioning effect of the cushioning material can be maintained, and the optical fiber unit is bent. The optical fiber can be easily moved even when it is broken.

When the optical fiber is spirally wound on the buffer material, the expansion of the optical fiber can be relaxed by reducing the diameter of the buffer material when the optical fiber unit is expanded.

According to the second aspect of the invention, since the cushioning material has a water absorbing property, it can have a water stopping property for preventing running water into the metal pipe.

According to the third aspect of the present invention, since the buffer material is colored, the optical fiber unit can be identified, and even if the number of coatings of the optical fiber itself is limited, the buffer material is limited. A specific optical fiber can be identified by its combination with the color. Therefore, it is possible to develop from a single-core type in which one optical fiber unit is accommodated to a multi-core type in which a plurality of optical fiber units are accommodated.

According to the invention of claim 4, according to claim 1,
In the metal tube type optical unit according to any one of items 1 to 3, since the void occupancy rate of the cushioning material is 30 to 70%, the effect of reducing the lateral pressure and the effect of suppressing the movement of the optical fiber in the metal tube can be greatly obtained. be able to.

[0019]

1 is a sectional structural view of the first embodiment of the present invention. In the figure, the same parts as those in FIG. 3 is a cushioning material and 4 is a string. A single buffer material 3 is used as an interposer, and a plurality of single-core wires of the optical fiber 1 are arranged vertically or spirally around the buffer material 3, and the periphery thereof is roughly wound with a string 4 to form an optical fiber unit. Has been formed. One or a plurality of the optical fiber units are housed inside the metal tube 2 with an extra length. The cushioning material 3 is preferably colored to identify the optical fiber unit. The string 4 may also be colored.

The optical fiber unit is roughly wound with one or a plurality of cords 4. In the case of a plurality of cords, at least two of the cords are wound in opposite directions, and the force with which the cord 4 tightens the optical fiber. To prevent an increase in transmission loss, and at the same time, when the string 4 loosens and breaks up at the terminal part, even if one string loosens and unwinds, the other one does not loosen. It is also possible to prevent deterioration of the discriminating property of the optical fiber unit due to the coloring of the cushioning material 3.

When the optical fiber 1 is spirally wound on the buffer material 3, when the optical fiber unit is extended by external stress, the buffer material 3 is reduced in diameter, so that the twist radius of the optical fiber 1 is reduced. The extension of the optical fiber 1 can be relaxed. Moreover, since the optical fiber 1 is twisted by spiral winding, the bending characteristics are improved.

The optical fiber 1 has, for example, an outer diameter of 12
An optical fiber having an outer diameter of 0.25 mm, which is obtained by coating a 5 μm optical fiber glass with a primary coating layer of an ultraviolet curable resin,
Alternatively, an optical fiber having an outer diameter of 0.4 mm coated with a primary coating layer of silicone resin can be used, and the string 4 can be a cotton fiber bundle, a Kevlar (registered trademark) fiber bundle, or the like. As the metal tube 2, a stainless (SUS) tube or an aluminum tube can be used.

FIG. 2 is a sectional structural view of the second embodiment of the present invention. In the figure, the same parts as those in FIG. 8 and FIG. 5 is a string. In this embodiment, a plurality of optical fibers 1 are bundled by a string 5 similar to the string 4 to form an optical fiber bundle, and the optical fiber bundle has a plurality of optical fibers 1 around the buffer material 3 as an interposing body. They are arranged vertically or spirally. Further, the optical fiber unit is formed by further roughly winding the periphery thereof with a string 4. One or more optical fiber units are housed inside the metal tube 2.

FIG. 3 is a sectional structural view of the optical fiber composite overhead ground wire. In the figure, 11 is a metal tube type optical unit, 12 is a steel wire, and 13 is an aluminum wire. This figure explains an optical fiber composite overhead ground wire (OPGW) as a specific example of use of the metal tube type optical unit of the present invention. The metal tube type optical unit 11 has been described with reference to FIGS. 1 and 2, and has six steel wires 12 as conductor wire around the optical unit 11.
And a layer of twelve aluminum wires 13 around the layer. The metal tube type optical unit 11 has the same diameter as the steel wire 12 and the aluminum wire 13. Instead of the one shown in the figure, a metal tube type optical unit 1
Two layers of aluminum-coated steel wire may be twisted around 1.
The number and arrangement of the conductor wires are not limited to those shown in the figure. Further, one of the conductor wires in the conductor twisted wire layer and the metal tube type optical unit 11 may be replaced and arranged. further,
A plurality of metal tube type optical units 11 may be arranged.

The metal tube type optical unit is as it is,
Alternatively, an outer sheath may be provided around the metal tube 2 to form an optical cable, or a plurality of metal tube type optical units may be arranged around the central tensile body, and a sheath may be formed on the metal tube type optical unit to form an optical cable.

Next, specific examples of the present invention and test results will be described. In the first embodiment of the metal tube type optical unit described with reference to FIG. 1, the metal tube 2 is made of stainless steel (SU having an outer diameter of 3.2 mmφ and an inner diameter of 2.8 mmφ).
S) tubes were used. A foamed plastic string was used as the cushioning material 3, and six optical fibers were longitudinally attached to this, and the periphery thereof was roughly wound with a cotton thread of 225d. At this time, the void occupancy f of the cushioning material 3 is 60%. Using this metal tube type optical unit, the optical fiber composite overhead ground wire described with reference to FIG. 3 was prototyped and a vibration test was performed.

FIG. 4 is a sectional structural view of a metal tube type optical unit for a comparative sample. In the figure, the same parts as those of FIG. 1 and FIG. Compared with the metal tube type optical unit described with reference to FIG. 1, the buffer material 3 is not provided, and the string 4 is formed around the single fiber of the plurality of optical fibers 1.
And is roughly wound to form an optical fiber unit.
The comparative sample was manufactured by using the metal tube type optical unit shown in FIG. 4 under exactly the same conditions as the others, and this was also tested. The wavelength of light was 1.55 μm, and the initial light receiving level was −56.62 dBm. The test length is 30
m, vibration frequency is 30 Hz, and total vibration amplitude is 10 m
m, and the number of vibrations was 10 ⁷ or more.

FIG. 5 is a vibration resistance characteristic diagram for explaining the result of the vibration test. The horizontal axis represents the number of vibrations and the vertical axis represents the transmission loss. Light wavelength is 1.55 μm, initial received light level is -5
It was set to 6.62 dBm. The transmission loss variation of the optical fiber composite overhead ground wire using the metal tube type optical unit of the present invention is 0.01 dB within the measurement accuracy as indicated by a black circle in the figure.
In contrast, the comparative example using the optical unit without the cushioning material 3 has a maximum loss increase of 0.2 dB / Length as indicated by a white circle in the figure.

The results of this experiment show that the cushioning material 3 reduces the side pressure due to the collision between the inner wall of the metal tube 2 and the optical fiber 1, or between the optical fibers 1, and
It is well shown that the resistance between the cushioning material 3 and the inner wall of the metal tube 2 has the effect of suppressing the movement of the optical fiber 1.

However, in order to bring out the above-mentioned two effects of the cushioning material 3, it is desirable to define the range of the void occupancy f. In order to confirm this point experimentally, the void occupancy f of the cushioning material 3 is changed from 0% to 25%, 50%, 70%.
%, 90%, 95%, 6 levels were changed to fabricate an optical fiber composite overhead ground wire.

FIG. 6 is a characteristic diagram of initial transmission loss characteristics and vibration resistance characteristics when the void occupancy rate is changed. The horizontal axis represents the void occupancy f of the cushioning material 3, and the vertical axis represents the initial transmission loss characteristics and the maximum value of transmission loss increase. The maximum value of the increase in transmission loss indicates the vibration resistance. Regarding the initial transmission characteristics, as indicated by the black circles in the figure, the loss increases when the void occupancy f of the cushioning material 3 becomes 70% or more, whereas the maximum value of the transmission loss increase is the white circles in the figure. As shown, the void occupancy f is 30
It will increase if it becomes less than%. The comparative example using the optical unit without the cushioning material 3 corresponds to the void occupancy f = 0%.

The fact is that if the cushioning material 3 is overfilled, the optical fiber 1 is pressed into the metal tube 2 by the cushioning material 3, and the optical fiber 1 is constantly subjected to lateral pressure from the inner wall of the metal tube 2. It also means that there is a problem that it becomes difficult to move on the cushioning material 3.

On the contrary, when the space occupancy ratio f of the buffer material 3 is small, the resistance force between the optical fiber unit and the inner wall of the metal tube 2 becomes small, and the degree of freedom of the optical fiber unit becomes large. Therefore, when some kind of external force is applied to the metal tube type optical unit, the optical fiber unit moves in the metal tube 2, and the extra length of the optical fiber unit becomes non-uniform in the longitudinal direction, which causes bending loss. Increase occurs. Also, when vibration is applied to the metal tube type optical unit,
Since the collision force between the optical fiber unit and the inner wall of the metal tube becomes large, the lateral pressure cannot be absorbed by the cushioning material, and the loss increases.

From the above-mentioned examination results, if the void occupancy f of the cushioning material 3 is specified to be 30 to 70%, it is possible to bring out the effect of the present invention to a great extent.

Further, a buffer material 3 in which a hydrolyzate of an acrylonitrile graft polymer having water absorbency was applied to the buffer material 3 of the prototype described above was manufactured as a trial and a running test with a water head length of 1.0 m was conducted. When the running water length was measured after 1 day, 3 days, and 10 days, it was proved that the running water length did not change even after 10 days after reaching 3 m after 3 days, and that the water stopping property was sufficient.

Here, the void occupancy f of the cushioning material 3 will be supplemented. The void occupancy f is represented by the area occupied by the cushioning material 3 with respect to the area obtained by removing the occupied cross-sectional area of the optical fiber 1 from the internal cross-sectional area of the metal tube 2 on the cross section of the metal tube 2. Expressed by a formula, the void occupancy f = the cross-sectional area of the cushioning material / (the cross-sectional area inside the metal tube−the cross-sectional area occupied by the optical fiber) × 100 [%].

FIG. 7 is a sectional structural view of a metal tube type optical unit of another specific example of the prototype. The above formula will be described using this specific example. In the figure, the same parts as those in FIG. 8, FIG. 1 and FIG. Metal tube 2
For this, a stainless (SUS) tube having an outer diameter of 3.2 mmφ and an inner diameter of 2.8 mmφ was used. As the cushioning material 3, a foamed plastic string having a cross-sectional diameter of 1.6 mm was used. The optical fiber 1 has an outer diameter of 0.
A 25 mm optical fiber was used. The periphery of the six optical fibers 1 is bundled by a string 5 of cotton thread of 225d to form an optical fiber bundle, and four optical fiber bundles are vertically arranged around the cushioning material 3 and arranged. An optical fiber unit is formed by roughly winding the periphery of the cotton thread string 4 of 225d. One optical fiber unit is housed inside the metal tube 2.

Applying the above equation to this specific example,
Vacancy occupancy f = (π × 1.6 × 1.6 / 4) / (π ×
(2.8 × 2.8 / 4-0.25 × 0.25 / 4 × 2
4)) × 100 [%] = 40.4 [%]. In this specific example, there is one optical fiber unit, but when there are two optical fiber units as shown in FIG. 1, the cross-sectional area of the buffer material and the occupied cross-sectional area of the optical fiber in the above equation are , Which is twice as large as that in the case of one optical fiber unit.

The value of the cross-sectional area of the cushioning material 3 is the metal tube 2
It was calculated from the diameter of the cross section measured in a state where the optical fiber was not wound yet and the tension was not applied in the longitudinal direction before being housed in. In the state of being housed in the metal tube 2 as shown in FIG. 7, the cross-sectional area of the buffer material 3 contracts in the radial direction by the tightening force of the optical fiber 1. However, since there is no large numerical difference in any cross-sectional area, the value of the cross-sectional area was obtained by the above-described measurement from the viewpoint of ease of measurement.

[0040]

As is apparent from the above description, according to the present invention, the side pressure received by an optical fiber in a metal tube, for example, the side pressure generated between the inner wall of the metal tube and another optical fiber can be reduced, and There is an effect that the movement of the fiber in the metal tube can be suppressed. Therefore, under severe conditions, it is very effective when used for an optical fiber housing portion of an optical fiber composite overhead wire, such as an optical fiber composite overhead power line and an optical fiber composite overhead wire, which requires reliability.

[Brief description of drawings]

FIG. 1 is a sectional structural view of a first embodiment of the present invention.

FIG. 2 is a sectional structural view of a second embodiment of the present invention.

FIG. 3 is a cross-sectional structure diagram of an optical fiber composite overhead ground wire.

FIG. 4 is a sectional structural view of a metal tube type optical unit for a comparative sample.

FIG. 5 is a vibration resistance characteristic diagram for explaining the results of a vibration test.

FIG. 6 is a characteristic diagram of initial transmission loss characteristics and vibration resistance characteristics when the void occupancy rate is changed.

FIG. 7 is a sectional structural view of a metal tube type optical unit of another specific example of the prototype.

FIG. 8 is a sectional structural view of a conventional general metal tube type optical unit.

[Explanation of symbols]

1 ... Optical fiber, 2 ... Metal tube, 3 ... Buffer material, 4, 5 ...
String, 11 ... Metal tube type optical unit, 12 ... Steel wire, 13 ... Aluminum wire.

Claims (4)

[Claims] 1. An optical fiber unit in which a plurality of optical fibers are vertically attached or spirally wound on a cushioning material, and the periphery is roughly wound with a string, and one or more optical fiber units are housed in a metal tube. This is a metal tube type optical unit. 2. The metal tube type optical unit according to claim 1, wherein the buffer material has a water absorbing property. 3. The metal tube type optical unit according to claim 1, wherein the buffer material is colored. 4. The void occupancy of the cushioning material is 30 to 70.
%, The metal tube type optical unit according to any one of claims 1 to 3.