JP2002040306A - Optical fiber cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber cable which hardly causes an increase in transmission loss even when trodden under a human foot or a leg of desk. SOLUTION: In this optical fiber cable in which a coated optical fiber 12 (or optical fiber tape core) and a tension line 14 are arranged in parallel and are covered with a sheath 16 en bloc, the width b in cross-section shape of the sheath 16 is larger than the thickness a and grooves 20 are formed on the center part in the width direction of the sheath 16 surface, the cross-section shape of the sheath 16 is made to be a rectangle having the grooves 20 and to be round on four corners and the ratio c/a of the length c of linear part in the thickness direction to the thickness a is made to be >=0.4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an optical fiber cable.

[0002]

2. Description of the Related Art In recent years, the construction of an optical subscriber line network has been rapidly progressing, and its area has been extended to inside buildings and general homes. Conventionally, as an optical fiber cable routed around a wall, floor, or desk in a user's home, FIG.
A cable as shown in FIG. (A)
Cable 10 comprises an optical fiber core 12 and two tensile wires 14
Are arranged in parallel such that the tensile strength wires 14 are located on both sides of the optical fiber core 12, and a flat batch coating 16 is applied.
In the cable 10 (B), an optical fiber ribbon 18 and two tensile wires 14 are arranged in parallel so that the tensile wires 14 are located on both sides of the optical fiber ribbon 18, and a flat batch coating 16 is applied. It was done.

[0003] In both cables, the width b of the cable cross section (the dimension in the direction in which the core wire and the tensile wire are arranged) is greater than the thickness a (the dimension in the direction perpendicular to the width direction), and the center of the surface of the coating 16 in the width direction. Is provided with a groove 20. The groove 20 is used for connecting the end of the cable 10 to an optical device or the like at the site so that the sheath 16 can be cut right and left so that the core wire 12 or 18 can be easily taken out.

[0004]

When an optical fiber cable is routed around a desk, it is expected that the optical fiber cable will be stepped on by the legs of the desk or human feet. Since this type of optical fiber cable is of a flat type, an external force caused by stepping on a leg of a desk or a human foot is usually applied in a thickness direction. As shown in FIG. 6, a human foot (shoes) or a leg 22 of a desk has an edge 24.
When an external force is applied to the coating 10 in the thickness direction, a slight bend M is generated in the portion of the coating 16 where the edge 24 is applied. Coating 16
When the bend M occurs, the bend m is also generated in the optical fiber core wire 12 (or the optical fiber tape core wire 18), which leads to an increase in transmission loss. In other words, the conventional optical fiber cable has a problem that transmission loss is likely to increase when a person steps on a human foot or desk with a leg or the like.

In view of the above problems, an object of the present invention is to provide an optical fiber cable in which an increase in transmission loss hardly occurs even when stepped on a human foot or a desk with a leg or the like.

[0006]

According to the present invention, as shown in FIG. 1, an optical fiber core wire 12 (or an optical fiber tape core wire) and a tensile wire 14 are arranged in parallel and collectively coated. 16 and the width b (dimension in the direction in which the core wire and the tensile strength line are aligned) of the cross-sectional outer shape of the coating 16 is larger than the thickness a (dimension in the direction perpendicular to the width direction), and the width direction center of the surface of the coating 16 In an optical fiber cable in which a groove 20 is provided,
The cross-sectional outer shape of the coating 16 is a rectangle having the groove and rounded at four corners, and the ratio c / a of the length c of the linear portion in the thickness direction of the coating surface to the thickness a is 0.4 or more. It is characterized by the following.

In order to suppress the slight bending of the coating 16 due to the application of an external force in the thickness direction to the flat optical fiber cable, the coating 16 may be made hard to bend. That is, covering
The bending stiffness of 16 may be increased. If the sectional outline of the coating 16 is formed as shown in FIG. 1, the coating having the sectional outline as shown in FIG.
Bending rigidity can be increased from 16. This effect can be confirmed from the calculation results of the simple models shown in FIGS.

That is, the conventional cable sheath shown in FIG. 5 is formed of a curved surface with rounded sides.
The cross-sectional shape can be approximated by an ellipse as shown in FIG. On the other hand, the coating of the cable of the present invention shown in FIG. 1 can be approximated by a rectangle as shown in FIG. If the thickness dimension a and the width dimension b are the same in both cases, the second moment of area is as follows. Elliptical second moment of area: (π / 64) × a ³ b Rectangular second moment of area: (1/12) × a ³ b Comparing these two moments of area, (π / 64) × Since a ³ b <(1/12) × a ³ b, it can be said that a rectangle is harder to bend than an ellipse.

Providing the straight portions P (planes) on both side surfaces of the coating 16 as in the cable of the present invention makes the cross-sectional profile of the coating close to a rectangle, so that the conventional cross-sectional profile is almost elliptical. Bending rigidity can be improved by coating. Therefore, it is possible to suppress the bending of the optical fiber core fiber or the optical fiber tape core fiber, and to suppress an increase in transmission loss.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail in comparison with a conventional cable. An optical fiber cable according to the present invention shown in FIG. 1 and a conventional optical fiber cable shown in FIG. In both cables, the thickness a of the sheath cross-sectional shape is 1.
8 mm, the width b was 3.0 mm, and the coating 16 was made of polyethylene. The optical fiber core wire was a steel wire having a diameter of 0.25 mm, and the tensile strength wire 14 was a steel wire having a diameter of 0.4 mm.

As the cables of the present invention, four types of cables having different lengths c of the straight portions P in the thickness direction of the coating surface were manufactured. In order to make the length c of the straight portion P different, specifically, the radius of curvature r of the rounded corners was adjusted. The larger the value of r, the smaller the length c of the straight portion P. The conventional cable is when r = 1 / 2a. The four types of cables of the present invention are as follows. Type 1: c = 0.34mm c / a = 0.19 r = 0.73mm Type 2: c = 0.74mm c / a = 0.41 r = 0.53mm Type 3: c = 1.14mm c / a = 0.63 r = 0.33mm Type 4 : C = 1.34 mm c / a = 0.74 r = 0.23 mm On the other hand, the conventional cable has c = 0 mm r = 1 / 2a =
0.9 mm.

With respect to these five types of cables, to examine the increase in transmission loss when an external force is applied in the thickness direction,
A lateral pressure test as shown in FIG. 3 was performed. This test is a side pressure plate
This is a test for applying a lateral pressure to the cable 10 at 26. The side pressure plate 26 had a length L of a side pressure application portion (flat surface) of 25 mm, a radius of curvature R of curved surfaces at both ends of 5 mm, and an applied load W of 1200 N. wavelength
At 1.55 μm, a change in transmission loss was measured when no load was applied and when a load was applied.

FIG. 4 shows the measurement results. Compared with the conventional cable, the increase in the transmission loss is small even in the type 1 cable, and it can be seen that a certain effect is exhibited. Here, the effect of suppressing the increase in transmission loss is sufficiently recognized, and if the increase in transmission loss that does not pose a problem in practical use is considered to be 0.1 dB or less, it can be seen that the cables of types 2 to 4 satisfy this. The transmission loss increase of the cables of types 2 to 4 is 23.5% or less of the conventional cable. From this result, c
/ A was 0.4 or more.

FIG. 4 shows that as the value of c / a approaches 1, the increase in transmission loss due to lateral pressure can be reduced. However, it was found that when c / a = 1, the four corners of the coating cross section were angular, so that burrs tended to remain on the corners after the cable was manufactured, and the corners were easily damaged during cable handling. If burrs are left on the corners or scratched,
It is considered that the cable is liable to be caught at the portion when the cable is laid, which may easily hinder the cable laying. In order to confirm this point by experiment, a cable having no rounding at the four corners of the coating cross section (a cable having a cross section as shown in FIG. 2B) and a cable of the type 4 of the present invention (a cable having the smallest r) were produced. Laying experiment. The laying test is 11mm inside diameter and length
This shows the probability of successful installation when three cables are passed through a 50m pipe. Table 1 shows the experimental results.

[0015]

[Table 1]

From the results shown in Table 1, it can be seen that making the corners round is effective in preventing troubles during installation.

[0017]

As described above, according to the present invention, it is suitable for wiring in a house or a building where the increase in transmission loss can be sufficiently suppressed even when stepped on by human feet or legs of a desk. A simple optical fiber cable can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an optical fiber cable according to the present invention.

FIG. 2A is an explanatory view showing a conventional cable approximate calculation model, and FIG. 2B is an explanatory diagram showing a cable approximate calculation model of the present invention.

FIG. 3 is an explanatory view of a lateral pressure test method.

FIG. 4 is a graph showing the results of a lateral pressure test of the cable of the present invention and a conventional cable.

FIGS. 5A and 5B are cross-sectional views each showing a conventional cable.

FIG. 6 is an explanatory diagram showing a state when the optical fiber cable is trampled by an object having an edge.

[Explanation of symbols]

 10: Optical fiber cable 12: Optical fiber core wire 14: Tensile wire 16: Coating 18: Optical fiber tape core wire 20: Groove

Claims (1)

[Claims] An optical fiber or an optical fiber tape and a tensile strength wire are arranged in parallel and coated in a lump, and the width b (dimension in the direction in which the core wire and the tensile strength wire are arranged) of the cross section of the coating is a thickness. a (dimension in the direction perpendicular to the width direction) is larger than a (width in the direction perpendicular to the width direction), and a groove is provided at the center in the width direction of the coating surface. An optical fiber cable having a rectangular shape, wherein a ratio c / a of a length c of a linear portion in a thickness direction of the coating surface to the thickness a is 0.4 or more.