JPH10115752A - Optical fiber unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to drastically lessen the shrinkage of a buffer layer under a low-temp. environment and to suppress the increase of transmission loss in use at a low temp. by forming the buffer layer of a fiber layer exhibiting low shrinkability at a low temp. area. SOLUTION: This optical fiber cable 1 has a coated optical fiber 2, the buffer layer 3 covering the outer peripheral surface of this coated optical fiber 2 and an outer coating 4 covering the outer peripheral surface of the buffer layer 3. The buffer layer 3 is formed by using fibers which exhibit low shrinkability in a low-temp. area so as not to act the bending stress by shrinkage on the coated optical fiber 2 even if the optical fiber cable 1 is laid under the low-temp. environment. Aramid fibers having the low shrinkage particularly by a temp. change and high strength are preferably used as the material having such properties. The production thereof is executed by passing the coated optical fiber 2 through an extruder while placing the fibers constituting the buffer layer 3 along its longitudinal direction on the circumference thereof and extruding polyethylene(PE) to the circumference of the buffer layer 3, thereby coating the buffer layer. The PE is then foamed and cured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical fiber unit.

[0002]

2. Description of the Related Art In an optical fiber communication line network, when connecting a station to a subscriber (user), an optical fiber cable having a plurality of optical fiber units is used. As the optical fiber unit, generally, an optical fiber core wire in which foamed polyethylene is coated as an outer layer coating is used.

Incidentally, the optical fiber unit may be bent or twisted depending on the state of the wiring place. At this time, the optical fiber unit has a low resistance to lateral pressure since only the outer layer coating is applied directly to the optical fiber core. Therefore, the optical fiber core wire may be cut or the transmission loss may increase due to the lateral pressure or bending stress.

Therefore, in order to avoid the above-mentioned inconvenience, an optical fiber unit having a buffer layer made of nylon between the optical fiber core wire and the outer layer coating is used. That is, the optical fiber unit is formed by coating the outer peripheral surface of the optical fiber core wire with nylon as a buffer layer, and then coating it with foamed polyethylene. The optical fiber unit is provided with resistance to lateral pressure by the nylon buffer layer. For this reason, even in the state where side pressure, bending, and twisting are applied, it is possible to suppress cutting of the optical fiber core wire and increase in transmission loss.

[0005]

When the optical fiber cable is laid outdoors, for example, the optical fiber unit may be exposed to a low temperature depending on environmental conditions. In this case, nylon has a property of shrinking at a low temperature. Therefore, if the thickness of the nylon buffer layer of the optical fiber unit is not constant, there is a problem that the buffer layer contracts unevenly.

[0006] Non-uniform shrinkage in the nylon buffer layer can cause local microbends in the optical fibers, thereby increasing light transmission losses.
An object of the present invention is to solve the above-mentioned problems in the optical fiber unit and to provide an optical fiber unit that can suppress an increase in transmission loss even when used at a low temperature.

[0007]

In order to achieve the above object, an optical fiber unit according to the present invention comprises an optical fiber core, a buffer layer covering an outer peripheral surface of the optical fiber core, and an outer peripheral surface of the buffer layer. In the optical fiber unit provided with an outer layer covering the above, the buffer layer is a fiber layer exhibiting low shrinkage in a low temperature range.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the optical fiber unit of the present invention will be described with reference to FIG. The optical fiber unit 1 of the present invention includes an optical fiber core wire 2, a buffer layer 3 covering the outer peripheral surface of the optical fiber core wire 2, and an outer coating 4 covering the outer peripheral surface of the buffer layer 3. The optical fiber core 2 is
It has a core 2a, a clad 2b, and a protective layer 2c. For example, a core wire in which both the core 2a and the clad 2b are made of quartz and the protective layer 2c is made of an ultraviolet-curable resin can be given. Various types of cores such as single mode and multi mode are used depending on the application.

The buffer layer 3 is formed using a fiber having a low shrinkage property in a low temperature range so that a bending stress due to shrinkage is not applied to the optical fiber core 2 even when the optical fiber unit 1 is laid in a low temperature environment. Is done. Materials having such properties include, for example, aramid fiber, polyparaphenylene benzobisoxazole fiber, cotton fiber, polyester fiber and the like. In particular, it is preferable to use aramid fiber which has low elasticity due to temperature change and has high strength.

The outer coating 4 is formed to protect the optical fiber core wire 2 and to improve the transmission to the optical fiber transmission pipe used in the so-called collective drop cable. As a material of the outer layer coating 4, there is no difference from a conventionally used material, and for example, foamed polyethylene is used. Optical fiber unit 1 configured as above
Is manufactured as follows.

That is, the polyethylene is extruded around the buffer layer 3 by covering it with an extruder while the fibers serving as the buffer layer 3 are attached around the optical fiber core 2 in the longitudinal direction. Next, the polyethylene is foamed with a foaming agent or gas, and then cooled and cured. As described above, the optical fiber unit 1 of the present invention employs, as the buffer layer 3, a fiber layer exhibiting low shrinkage in a low temperature range. For this reason, when the optical fiber unit 1 is laid in a low-temperature environment such as a cold region or winter, low-temperature shrinkage that has occurred in the conventional nylon buffer layer is suppressed, and the occurrence of microbends in the optical fiber core 2 is suppressed. It is significantly reduced. Therefore, an increase in transmission loss is suppressed even in a low-temperature environment.

[0012]

【Example】

Example 1 Core diameter: 9.5 (μm), clad diameter: 125
Aramid fiber (Kevlar fiber manufactured by DuPont) 11 on the outer peripheral surface of a quartz single-mode optical fiber core (μm).
An optical fiber unit was prepared in which two 40-denier fibers were vertically attached to the outer peripheral surface of the optical fiber core to form a buffer layer, and the outer peripheral surface of the buffer layer was further coated with polyethylene foam as an outer layer coating.

Then, the optical fiber unit was placed in a thermostat, and the temperature conditions were changed to determine the transmission loss (dB / km) at each temperature. The result is shown in FIG. At a temperature of 25 ° C., the optical fiber unit is
The length corresponding to the longitudinal direction of the optical fiber unit is 10
It was sandwiched between two metal plates of 0 (mm) and a load of 500 (N), that is, a lateral pressure was applied, and the transmission loss in this state was determined. The results are shown in Table 1. Table 1 also shows the transmission loss when no side pressure was applied to the optical fiber unit (temperature: 25 ° C.).

Here, the transmission loss was obtained as follows. First, one end of an optical fiber unit having a total length of L ₁ (m) was connected to a light source, and the other end was connected to a power meter to measure light power P ₁ (dB). Next, the power P ₀ (dB) is similarly obtained for the optical fiber unit having a total length of 2 (m).
Was measured. From this result, the transmission loss A is given by the following equation: A =
It was calculated from (P ₁ −P ₀ ) / (L _1-2 ) × 1000.

The light at this time has a wavelength of 1.
Light of 55 (μm) was used. Comparative Example 1 A transmission loss at each temperature and a transmission loss in a state where a lateral pressure was applied were determined in the same manner as in Example 1 except that a nylon coating was applied to the outer periphery of the optical fiber as a buffer layer. . The results are shown in FIG.

Comparative Example 2 The procedure of Example 1 was repeated, except that the foamed polyethylene was directly coated on the optical fiber without providing the buffer layer.
The transmission loss at each temperature and the transmission loss with the side pressure applied were determined. The results are shown in FIG.

[0017]

[Table 1] The following is clear from FIG. 2 showing the relationship between the temperature and the transmission loss.

First, the transmission loss of the optical fiber unit of Example 1 including the buffer layer formed by using aramid fiber exhibiting low shrinkage at a low temperature hardly changes even when the temperature decreases. That is, the transmission loss at −25 ° C. is 0.21 (dB / km), and the difference (increase in the transmission loss) from the transmission loss (0.20 (dB / km)) at 25 ° C. is 0.01 (dB). (dB / km), which is extremely small, indicating that the composition has excellent low-temperature resistance.

This is because the buffer layer employed in the present invention hardly shrinks at a low temperature, so that stress is not applied to the optical fiber and the occurrence of microbending can be suppressed. Also, from the results in Table 1, the transmission loss of the optical fiber unit of Example 1 when the side pressure was applied was 0.2 (dB / km), which was different from the transmission loss when the side pressure was not applied. Is 0 (dB / km), which indicates that the transmission loss does not increase even when the lateral pressure is applied.

This is because the buffer layer is resistant to lateral pressure. On the other hand, in the case of the optical fiber unit of Comparative Example 1 including the nylon buffer layer, from the results shown in Table 1, the transmission loss under the state where the lateral pressure was applied was 0.2 (dB / k).
m), and the difference from the transmission loss when no side pressure is applied is 0 (dB / km), indicating that the transmission loss does not increase even when the side pressure is applied. That is, the nylon buffer layer exhibits resistance to lateral pressure.

However, as is apparent from the results shown in FIG. 2, the transmission loss increases as the temperature decreases.
This is because the nylon buffer layer shrinks with a decrease in temperature, thereby applying stress to the optical fiber core and generating microbending. In addition, in the case of the optical fiber unit of Comparative Example 2 having no buffer layer, as is clear from FIG. 2, the increase in transmission loss due to the decrease in temperature is smaller than that of Comparative Example 1. This is because the nylon buffer layer does not intervene.

However, as is apparent from the results in Table 1, the transmission loss under the condition where the lateral pressure is applied is 0.30 (dB).
/ Km), and the difference (increase) from the transmission loss when the side pressure is not applied is 0.10 (dB / km), and the increase in the transmission loss when the side pressure is applied is often large. Recognize.
This is because resistance to lateral pressure is low because no buffer layer is provided.

It goes without saying that the optical fiber unit 1 of the present invention may be used for a so-called collective drop cable.

[0024]

As is apparent from the above description, the optical fiber unit of the present invention has a fiber layer which exhibits low shrinkage in a low temperature range as a buffer layer. It is remarkably reduced, can suppress an increase in transmission loss when used at low temperatures, and has excellent low-temperature resistance.

Further, when the buffer layer is formed by using aramid fiber as the fiber having low shrinkage in a low temperature range, the aramid fiber has high strength, which also contributes to improvement in tensile strength of the optical fiber unit.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a relationship between temperature and transmission loss.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical fiber unit 2 optical fiber core 2 a core 2 b clad 2 c protective layer 3 buffer layer 4 outer layer coating

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuo Hokari, Inventor, Nippon Telegraph and Telephone Corporation 3-9-1, Nishishinjuku, Shinjuku-ku, Tokyo (72) Inventor Shinichi Furukawa 3-192, Nishishinjuku, Shinjuku-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. An optical fiber unit comprising an optical fiber core, a buffer layer covering an outer peripheral surface of the optical fiber core, and an outer layer coating covering an outer peripheral surface of the buffer layer. An optical fiber unit comprising a fiber layer exhibiting low shrinkage in a region.