JP3006493B2 - Metal tube type light unit - Google Patents

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 the optical fiber is housed in a metal tube for use as an optical communication cable is conventionally known in Japanese Patent Application Laid-Open No. Hei 6-148475. .

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 accommodated in the inner space of the metal tube 2 in a state of being loose and having a gap. The internal space is filled with a low humidity gas or is evacuated. Here, it is important to provide the optical fiber 1 in the metal tube 2 with an appropriate extra length in order to guarantee the transmission characteristics and reliability after the metal tube type optical unit is wired.

[0004] In the conventional metal tube type optical unit, the surplus length of the optical fiber 1 is provided uniformly over the entire length at the beginning of manufacture. However, since the optical fiber 1 is loosely housed in the metal tube 2 with a gap, the optical fiber 1 easily moves in the longitudinal direction due to various external forces and heat histories. As a result, a deviation of the extra length occurs, so that the optical fiber 1
Sag 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 extra length is likely to be unevenly distributed by the movement of the optical fiber 1. As a result, there is a problem that the 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 overhead cable, the optical fiber 1 can easily move in the radial direction within the metal tube 2 under the vibration caused by wind. Therefore, the collision with the inner wall of the metal tube 2 is repeated,
As a result, the lateral pressure is applied from the metal tube 2 to increase the loss.
In particular, since the metal pipe 2 has a higher Young's modulus and is harder than the plastic pipe, a greater increase in loss occurs. Further, when a plurality of optical fibers 1 are accommodated in the metal tube 2, collision with another optical fiber 1 is repeated, and a side pressure is applied from the other optical fiber to increase the loss.

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

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made to reduce the lateral pressure of an optical fiber in a metal tube and to suppress 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 transmission characteristics and life of the optical unit.

[0008]

According to the 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 surrounded by a plurality of strings. One or a plurality of optical fiber units which are roughly wound and in which at least two of the plurality of strings are wound in the opposite direction are housed in a metal tube. .

According to a second aspect of the present invention, in the metal tube type optical unit according to the first aspect, the occupation ratio of the gap of the cushioning material is 30 to 70%.

[0010]

[0011]

[0012]

According to the first aspect of the present invention, an optical fiber unit in which a plurality of optical fibers are vertically wound or spirally wound on a buffer material and roughly wound with a plurality of strings is housed in a metal tube. I have. Further, at least two of the plurality of strings are wound in the opposite direction. For this reason, the optical fiber is located on the cushioning material, so that the lateral pressure can be reduced, and the lateral pressure between the optical fiber, the optical fiber bundle and the inner wall of the metal tube can be reduced 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 hardly moves in the metal tube even when an external force is applied. A uniform extra length distribution can be maintained.

Further, according to the first aspect of the present invention,
Since the optical fiber unit is roughly wound around with a cord, the above-described effects can be obtained to the maximum. For example, instead of roughly winding with a string, a method of applying a plastic coating,
There is also a method in which a winding tape is wound and coated. But,
In any case, when the coating is applied, a pressing force acts toward the center over the entire length of the optical fiber unit, and as a result, the center cushioning material is tightened and the diameter thereof is reduced. as a result,
After the manufacture of the metal tube unit, the cushioning material may not be able to maintain a sufficient cushioning effect. In particular, when a relatively thick cushioning material is used, when the optical fiber unit is bent, a large extension strain is applied to the optical fiber outside the bend, and a large compression strain is applied to the optical fiber inside the bend. At this time, with a structure that completely covers the periphery tightly with a coating, such as a plastic coating or holding tape,
Since the optical fiber cannot be easily moved, extension strain and compression strain applied to the optical fiber cannot be reduced.

On the other hand, when roughly wound with a string, only a pressing force is applied to a place where the string and the optical fiber are in contact with each other, the cushioning function of the cushioning material can be maintained, and the optical fiber unit is bent. The optical fiber can be easily moved when it is moved.

In the case where the optical fiber is spirally wound on the cushioning material, the elongation of the optical fiber can be reduced by reducing the diameter of the cushioning material when the optical fiber unit is extended.

[0016]

[0017]

According to the invention described in claim 2, according to claim 1
In the metal tube type optical unit described in (1), since the void occupancy of the cushioning material is 30 to 70%, the effect of reducing the side pressure and the effect of suppressing the movement of the optical fiber in the metal tube can be brought out greatly.

[0019]

FIG. 1 is a sectional structural view of a 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. With a single cushioning material 3 as an intervening body, a plurality of single-core fibers of the optical fiber 1 are arranged around this around in a longitudinally attached or spirally wound manner, and the periphery thereof is roughly wound with a cord 4 to form an optical fiber unit. Is formed. One or a plurality of the optical fiber units are housed inside the metal tube 2 with an extra length. It is desirable that the cushioning material 3 is colored to identify the optical fiber unit. The string 4 may also be colored.

The optical fiber unit is roughly wound around a plurality of cords 4. At least two of the cords are wound in opposite directions to suppress the force by which the cords 4 tighten the optical fiber, thereby preventing an increase in transmission loss. At the same time as the string 4
If one string is loosened and loosened, even if one string is loosened and unwound, the other one can be prevented from being loosened, and the discrimination of the optical fiber unit due to the coloring of the buffer material 3 is prevented. Can also.

When the optical fiber 1 is spirally wound on the buffer material 3, when the optical fiber unit is stretched by external stress, the diameter of the buffer material 3 is reduced, so that the twist radius of the optical fiber 1 is reduced. The elongation of the optical fiber 1 can be reduced. Further, since the optical fiber 1 is twisted by helical winding, the bending characteristics are improved.

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

FIG. 2 is a sectional structural view of a 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 this optical fiber bundle is It is arranged vertically or spirally wound. Further, the periphery thereof is roughly wound around the string 4 to form an optical fiber unit. 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 FIG. 1 and FIG. 2, and six steel wires 12
And a layer of 12 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, metal tube type light unit 1
A two-layer twist of an aluminum-coated steel wire may be applied around 1.
The number and arrangement of the conductor strands are not limited to those shown. Further, one of the conductor strands in the conductor stranded 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 used as it is.
Alternatively, an optical cable may be formed by providing an outer sheath around the metal tube 2, or a plurality of metal tube type optical units may be arranged around the central tensile member, and a sheath may be provided thereon 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 has a stainless steel (SU) having an outer diameter of 3.2 mm and an inner diameter of 2.8 mm.
S) A tube was used. As the cushioning material 3, a foamed plastic string was used. Six optical fibers were vertically attached to the string, and the periphery thereof was roughly wound with a 225d cotton thread. At this time, the space occupation ratio f of the cushioning material 3 is 60%. Using this metal tube type optical unit, an 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 drawing, the same parts as those in FIG. 1 and FIG. Compared with the metal tube type optical unit described with reference to FIG. 1, there is no cushioning material 3 and a string 4
To form an optical fiber unit.
The comparative sample was a prototype produced using the metal tube type optical unit shown in FIG. 4 under the same conditions except for the above, and this was also tested. The light wavelength was 1.55 μm, and the initial light receiving level was −56.62 dBm. Test length is 30
m, vibration frequency is 30 Hz, and total vibration amplitude is 10 m
m and the number of vibrations were 10 ⁷ times or more.

FIG. 5 is a vibration resistance characteristic chart for explaining the results of the vibration test. The horizontal axis is the number of times of vibration, and the vertical axis is the transmission loss. The light wavelength is 1.55 μm and the initial light receiving level is -5.
It was set to 6.62 dBm. The transmission loss fluctuation of the optical fiber composite overhead ground wire using the metal tube type optical unit of the present invention is within 0.01 dB within the measurement accuracy as shown by a black circle in the figure.
In contrast, in the comparative example using the optical unit without the buffer material 3, the loss increased by 0.2 dB / Length at the maximum as shown by the white circle in the figure.

The results of this experiment show that the buffer 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
This clearly shows that the effect of suppressing the movement of the optical fiber 1 due to the resistance between the cushioning material 3 and the inner wall of the metal tube 2 has appeared.

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 was increased from 0% to 25%, 50%, 70%.
%, 90%, and 95%, and prototypes of optical fiber composite overhead ground wires were performed with six levels changed.

FIG. 6 is a characteristic diagram of the initial transmission loss characteristic and the vibration resistance characteristic when the gap occupancy is changed. The horizontal axis represents the air gap occupation ratio f of the buffer material 3, and the vertical axis represents the initial transmission loss characteristics and the maximum value of the transmission loss increase. The maximum value of the transmission loss increase indicates the vibration resistance. As shown by the black circles in the figure, the initial transmission characteristics show that the loss increases when the void occupation ratio f of the buffer material 3 becomes 70% or more, whereas the maximum value of the transmission loss increase is shown by the white circles in the figure. As shown, the void occupancy f is 30
%, It increases. Note that 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, In addition, it means that there is a problem that it is difficult to move on the cushioning material 3.

Conversely, when the gap occupation ratio f of the cushioning member 3 is small, the resistance between the optical fiber unit and the inner wall of the metal tube 2 is reduced, and the degree of freedom of the optical fiber unit is increased. Therefore, when some 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. 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 examination results, when the void occupation ratio f of the cushioning material 3 is specified to be 30 to 70%, it is possible to bring out the function and effect of the present invention significantly.

Further, a buffer material 3 in which a hydrolyzate of an acrylonitrile graft polymer having a water absorbing property was applied to the buffer material 3 of the above-mentioned prototype was produced as a trial, and a water running test with a water head length of 1.0 m was performed. The water running length after 1 day, 3 days, and 10 days was measured. After reaching 3 m in 3 days, the water running length did not change even after 10 days, demonstrating that it had sufficient water stopping properties.

Here, a supplementary description will be given of the void occupation ratio f of the cushioning material 3. The void occupancy f is expressed by an area occupied by the cushioning material 3 with respect to an area obtained by subtracting an occupied cross-sectional area of the optical fiber 1 from a cross-sectional area inside the metal pipe 2 on a cross-section inside the metal pipe 2. When expressed by the equation, the space occupancy ratio f = cross-sectional area of buffer material / (cross-sectional area inside metal tube−cross-sectional area occupied by 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 equation 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
A stainless steel (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.
An optical fiber of 25 mm was used. The six optical fibers 1 are bundled around a 225d cotton thread string 5 to form an optical fiber bundle, and four of the optical fiber bundles are vertically arranged around the cushioning material 3 and arranged. The periphery of the optical fiber unit is roughly wound around a 225d cotton thread string 4 to form an optical fiber unit. One optical fiber unit is housed inside the metal tube 2.

By applying the above equation to this specific example,
Void 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, the number of optical fiber units is one. However, in the case where the number of optical fiber units is two as shown in FIG. , Respectively, is twice as large as the case of one optical fiber unit.

The value of the cross-sectional area of the cushioning material 3 is
Before being housed in the optical fiber, the optical fiber was not wound yet, and was obtained from the diameter of the cross section measured in a state where tension was not applied in the longitudinal direction. When housed in the metal tube 2 as shown in FIG. 7, the cross-sectional area of the cushioning material 3 contracts in the radial direction due to the tightening force of the optical fiber 1. However, since there is no significant difference in numerical values regardless of the cross-sectional area, the value of the cross-sectional area was determined 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 applied to the optical fiber in the metal tube, for example, the side pressure generated between the inner wall of the metal tube and another optical fiber can be reduced, and the light pressure can be reduced. There is an effect that movement of the fiber in the metal tube can be suppressed. Therefore, it is very effective when used in an optical fiber housing section of an optical fiber composite overhead line such as an optical fiber composite overhead transmission line and an optical fiber composite overhead ground wire, which require reliability under severe conditions.

[Brief description of the 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 sectional structural view 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 illustrating the results of a vibration test.

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

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

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

[Description of Signs] 1 ... optical fiber, 2 ... metal tube, 3 ... buffer, 4,5 ...
String, 11: metal tube type light unit, 12: steel wire, 13: aluminum wire.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-333432 (JP, A) JP-A-62-194209 (JP, A) JP-A-6-160679 (JP, A) 181906 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/44 H01B 11/22

Claims (2)

(57) [Claims] 1. A plurality of optical fibers are vertically wrapped or spirally wound on a cushioning material, and a plurality of optical fibers are roughly wound around a plurality of strings, and at least two of the plurality of strings are oppositely wound. A metal tube type optical unit, wherein one or a plurality of wound optical fiber units are housed in a metal tube. 2. The void occupancy of the cushioning material is 30 to 70.
%. The metal tube type optical unit according to claim 1, wherein