JPH01270017A - Optical cable - Google Patents

Abstract

PURPOSE:To suppress the strain of optical fibers generated by a cable body to a small level by providing a cushion layer to the outside circumference of an assembly formed by doubling and twisting optical fiber units around the outside circumference of a central tensile body and armoring an top winding tape and sheath thereon. CONSTITUTION:The plural tape-like optical fibers 3 are housed in the spiral grooves provided on the optical fiber of grooved fibers 2 of the units 10 and the cushion layer 1 is provided on the outside circumference of the assembly formed by doubling and twisting and the units 10 around the outside circumference of the central tensile body 8. The tightening force of the top winding tape 6 or the armor of the unit assembly part to the inner side of the sheath 7 is absorbed by the deformation of the cushion layer 1 and the transmission of the external force to the units 10 is obviated by providing the cushion layer 1 adjacently to the outside circumference of the assembly in such a manner and, therefore, the generation of a large strain in the units 10 is prevented when the cable is bent. The strain applied on the optical fibers in consequently small and the long-term reliability of the optical fiber strength after laying of the cable is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a high-density optical fiber cable used in an optical communication network, and in particular, the present invention relates to a high-density optical fiber cable used in an optical communication network. In an optical cable that has a structure in which an optical fiber unit containing tape-shaped optical fiber cores is twisted around the outer periphery of a central tensile strength member, and an upper tape and an outer sheath are applied to the outer periphery of the unit assembly part, when the optical cable is bent, The present invention relates to an optical cable structure that can suppress strain applied to the fiber and has excellent long-term reliability of optical fiber strength after installation of the optical cable.

(Prior Art) Conventionally, there have been so-called layered optical fiber cables (hereinafter referred to as optical cables) in which single optical fibers are twisted around the outer periphery of a central tensile strength member, and optical fiber cables in which single optical fibers are twisted together. In so-called unit-type optical cables in which optical fiber units are further twisted around a central tensile strength member, a cushion layer may be provided between the outside of the portion where the optical fibers are arranged and the jacket. The structure in which this cushion layer is provided is such that the external force applied to the optical cable is directly transmitted to the optical fiber, so that uneven bending will not increase the transmission loss of the optical fiber or cause mechanical strength deterioration or breakage of the optical fiber. The cushion layer absorbs the deformation of the jacket due to external force, making it difficult for the external force to be transmitted to the part where the optical fiber is arranged.

However, a plurality of tape-shaped optical fiber cores (hereinafter referred to as tape core fibers) are formed in the grooves of a grooved core body 2 that incorporates a unit center tensile strength member 4 having a spiral groove on the outer periphery, the cross-sectional structure of which is shown in FIG. ) 3, and the optical fiber units 10 with the unit upper tape 5 applied to the outer periphery are twisted and assembled around the outer periphery of the central tensile strength member 8, and the unit assembly part upper tape 6 and the outer sheath 7 are attached to the assembly. In the so-called tape slot unit type optical cable, the optical fiber is housed in the groove of the grooved core 2 in the form of a tape core 3, so the optical cable receives external force, and the external force is Even if the external force is transmitted to the tlI structure, the deformation of the grooved core 2 is extremely small, so there is almost no need to consider that the external force will be transmitted to the optical fiber in the groove. In this way, in addition to the fact that the cushion layer has no effect on tape slot unit type optical cables, the provision of a cushion layer also increases the outer diameter and weight of the cable body (as a result, conventional A cushion layer is not provided in tape slot unit type optical cables.

[Problem to be solved by the invention]

Optical cables are partially bent when they are installed outdoors in conduits, overhead or directly buried, or when they are routed indoors. When this bending is applied, elongational strain or compressive strain is applied to the optical fiber.

It is necessary to suppress elongation strain and compressive strain because elongation strain causes a decrease in the strength of the optical fiber over time, and compressive strain causes buckling of the optical fiber and thus increases transmission loss.

For example, when using an optical fiber that has passed a 0.5% Bruch test for 20 years, the probability of breakage is 11000K.
In order to reduce the bending point to 1% or less, the bending point should be 1/1% of the total length
100, it is necessary to suppress the maximum strain due to bending to 0.25% or less. In tape slot unit type optical cables, the strain that occurs in the optical fiber due to cable bending is thought to be due to the following two factors.

Firstly, as the optical fiber unit itself expands and contracts, the optical fibers housed in the unit also expand and contract at the same time, resulting in distortion.Secondly, the curvature of the unit changes, causing the grooves in the grooved core to It is a strain that occurs in an optical fiber housed in a groove due to a change in helical length relative to its original state.

Therefore, in order to suppress the distortion of the optical fiber caused by cable bending, it is necessary to reduce the distortion caused by the expansion and contraction of the optical fiber itself, the distortion of the optical fiber caused by the change in the helical length of the groove, or both. It is necessary to consider the following.

In tape slot unit type optical cables, several studies have been made regarding the latter factor, that is, the strain caused in the optical fiber due to changes in the helical length of the groove. Dimensions are specified. However, little consideration is given to the former strain caused in the optical fiber due to expansion and contraction of the optical fiber itself.

[Means to solve the problem]

The present invention is a tape-slot unit type optical cable that solves the conventional problems, suppresses the strain applied to the optical fiber when bending the optical cable, and has excellent long-term reliability of the optical fiber strength after installation. This is an assembly in which an optical fiber unit in which a plurality of tape-shaped optical fiber cores are housed in the grooves of a grooved core having a spiral groove on the outer periphery is twisted and assembled around the outer periphery of a central tensile strength member. An optical cable having a structure in which the outer periphery of the optical cable is covered with a wrap-around tape and a sheath, characterized in that a cushion layer is provided on the outer periphery of the aggregate, and in particular, a cushion layer is provided in contact with the outer periphery of the aggregate. Moreover, it is characterized by a structure in which a cushion layer is arranged between the upper tape and the sheath.

[For production]

The present invention relates to an optical fiber unit (hereinafter referred to as the unit) in a tape slot unit type optical cable.
By providing a cushion layer around the outer periphery of the assembled assembly, when the upper tape of the unit assembly part or the outer sheath is tightened, the force is absorbed by the deformation of the cushion layer, and these Since the tightening structure prevents external force from being transmitted, it allows the unit to move easily, prevents large distortions in the unit when the cable is bent, and reduces the distortion applied to the optical fiber. This aims to improve the long-term reliability of the optical fiber strength after installation.

In tape slot unit type optical cable,
One of the causes of distortion that occurs in optical fibers due to cable bending is the expansion and contraction of the unit body, as described above. This local expansion and contraction of the unit main body is caused by friction between the unit and the central tensile strength member that twists and arranges the units around the outer periphery, and by friction between the unit and the central tensile strength member that twists the units around the outer periphery of the central tensile strength member. It is held by friction between the upper tape and the unit.

In other words, the manufacturing residual strain of the unit is ε1, the equivalent modulus of elasticity in the longitudinal direction of the unit is Eu, the cross-sectional area of the unit is S, the coefficient of static friction between the unit and the central tensile member is μm, and the effect of the upper tape and outer cover on the unit per unit is The force per length is T, the coefficient of static friction between the upper tape and the unit is μ2,
Assuming that the curvature of the unit is 1/r, the maximum static friction force F that this unit receives can be expressed by the following equation (1).

F=μlEu5εu/ru+(μ, +μz)T(ε,≧
-ε, ) (1) a F=-μ2E, S・εu /ru” (μ, 10μ2)T
(εb×ε,)+1)b Therefore, the strain ε of the unit when the cable is bent.

Unless it satisfies the following equation (2), the local strain generated in the unit will not become uniform in the longitudinal direction.

On the other hand, when a cushion layer is provided, the force between the upper tape of the unit gathering part or the sheath of the outer cover and the unit is absorbed by the cushion layer deforming, so the strain εゎ of the unit is calculated by the following formula (3)% By satisfying the formula (%), the unit moves in the longitudinal direction and localized strain is alleviated. From equations (2) and (3), since strain relaxation occurs even in the bright case, localized strain is smaller when a cushion layer is provided, and therefore, as described above, the strain generated in the optical fiber is also smaller. Examples will be described below based on the drawings.

〔Example〕

FIG. 1 shows a cross-sectional structure of an embodiment of the optical cable of the present invention. The same reference numerals as in FIG. 2 indicate the same parts.

Reference numeral 1 denotes a cushion layer according to the present invention, and in this embodiment, it is located between the unit 10 and the upper tape 5 of the unit gathering portion.

As the cushion layer 1, yarns of thermoplastic plastics such as polypropylene, aramid fibers, urethane foam, etc. are used.

Next, a tape according to the present invention having the cross-sectional structure shown in FIG.
An example in which a slot unit type optical cable was specifically produced as a prototype will be described.

Each of the units 10 has five spiral grooves, and two GT 4-fiber tape cables 3 are housed in each groove.

Five units are twisted and assembled around a central tensile strength member 8 with an outer diameter of 5.8 mmφ, and a 2 mm thick
A cushion layer 1 made of polypropylene is provided.

The upper tape 6 of the unit gathering part has a structure in which two sheets of nonwoven fabric are wound horizontally, and a PE sheath 7 as an outer covering is applied to the outer periphery.

A 500 m optical cable with the above-mentioned structure was fabricated, and 3 wooden samples were cut out with a length of 10 m from an arbitrary part. Sample No.
1 to No. 3 were created.

Created sample No. 1. No, 'l, No
, 3 around mandrels with diameters of 600 mmφ and 400 mmφ, and by monitoring the optical path length of the optical fiber in each wrapped state using the phase method,
The maximum strain caused in the optical fiber due to bending of the cable body was measured.

For comparison, we fabricated an optical cable with the same unit structure and unit assembly structure as in this example, and a conventional structure without the cushion layer shown in Figure 2, which was the same as the sample in this example. Comparative examples having the same number of lengths were prepared, and the maximum strain caused in the optical fiber due to bending of the cable body was measured under the same conditions as for the sample of this example.

Table 1 shows the configurations of the sample of this example and a comparative example of conventional structure.

Further, Table 2 shows a comparison of the maximum strain measurement results due to cable bending of the optical fibers described above. As can be seen from these results, the sample according to the example of the present invention had a maximum strain of 70% or less compared to the comparative example having a conventional structure. This means that under normal conditions, the probability of breakage during use will be less than 1/1000 compared to conventional products.

Table 1 Table 2 In the example, an example was explained in which the cushion layer was provided in contact with the outer periphery of the assembly, but an optical fiber in which the cushion layer was provided between the upper tape of the unit assembly part and the sheath was fabricated. Similar results were obtained when the maximum bending strain was measured.

〔Effect of the invention〕

As explained above, in the tape slot unit type optical cable of the present invention, the units are twisted and assembled around the outer periphery of the central tensile strength member, and the units are twisted and assembled around the outer periphery of the central tensile strength member, and the upper tape and sheath are connected to the outer periphery of the assembly or the upper tape and sheath By having a structure with a cushion layer between the cable and the cable, the strain caused in the optical fiber due to bending of the cable body can be suppressed to a minimum, thereby improving the transmission characteristics and external pressure resistance characteristics of a tape slot unit type optical cable. Improvements have been made, particularly in terms of long-term reliability of optical fiber strength.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of an optical cable according to the present invention. FIG. 2 is a cross-sectional structural diagram of a conventional optical cable. DESCRIPTION OF SYMBOLS 1... Cushion layer, 2... Grooved core body, 3... Tape core wire, 4... Unit center tensile strength body, 5... Unit upper winding tape, 6... Unit gathering part upper winding tape , 7... Sheath, 8... Central tensile strength body, 10...
Unit patent applicant Sumitomo Electric Industries, Ltd. (1 other person) Agent Patent attorney Kugobe Tamamushi Cross-sectional structure of the optical cable of the present invention Fig. 1 Fig. 2 Cross-sectional structure of the conventional optical cable

Claims (3)

[Claims] (1) An optical fiber unit in which a plurality of tape-shaped optical fibers are housed in the grooves of a grooved core with a spiral groove on the outer periphery is twisted and assembled around the outer periphery of a central tensile strength member. What is claimed is: 1. An optical cable having a structure in which an upper tape and a sheath are used as an exterior covering, characterized in that a cushion layer is provided on the outer periphery of the aggregate. (2) The optical cable according to claim 1, wherein the cushion layer is arranged in contact with the outer periphery of the aggregate. (3) The optical cable according to claim 1, wherein the cushion layer is arranged between the upper tape and the sheath.