JP2002372653A - Optical fiber unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the increase of transmission loss at a low temperature without the occurrence of microbends in consequence of the shrinkage of the respective members of an optical fiber unit in coated optical fibers constituting the optical fiber unit even when the optical fiber unit is placed under a low- temperature environment of about -20 deg.C. SOLUTION: The volumetric shrinkage percentage with a temperature change from +15 to -20 deg.C of the coated optical fibers of a tight type optical fiber unit formed by intertwining a plurality of the coated optical fibers 2, 2 and 2 around a central tension member 1 and disposing an integrating material 3 consisting of a UV curing resin thereon is confined to <=0.05%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical fiber unit, and more particularly to an optical fiber unit for an optical submarine cable.

[0002]

2. Description of the Related Art As an optical fiber unit used for an optical submarine cable or the like, a tight type structure as shown in FIG. 1 is known. In FIG. 1, reference numeral 1 denotes a center tension member made of copper-plated steel wire, glass fiber reinforced plastic (FRP), or the like. Around the center tension member 1, a plurality of optical fiber cores 2, 2,... The fiber cores 2, 2,... Are integrated. Such an optical fiber unit is provided with various coatings thereon to form an optical cable such as an optical submarine cable.

The optical fiber core 2 has a diameter of 12 mm.
An optical fiber having a diameter of 250 to 400 μm, in which a 5 μm bare optical fiber is provided with primary and secondary coating layers made of an ultraviolet curable resin, is mainly used. In addition, a soft ultraviolet curable resin having a Young's modulus of 0.1 to 5 kg / mm ² is mainly used for the integrated material 3 from the viewpoint of productivity and the like.

In order to manufacture such an optical unit, a plurality of optical fiber cores 2, 2,... Are twisted on a central tension member 1, and these are fed into a coating die to form an integrated material 3.
This is performed by a method of applying an ultraviolet-curable resin to be applied, and sending the ultraviolet-curable resin to an ultraviolet irradiating device, where the resin is irradiated with ultraviolet rays to cure the applied ultraviolet-curable resin.

In recent years, optical submarine cables have been using optical amplifiers to amplify optical signals for ultra-long distance transmission. For this reason, an optical fiber having a large effective area of its core is being used as an optical fiber so that a nonlinear effect does not occur even if a large optical power is input to the optical fiber serving as a transmission path. However, in an optical fiber having a large effective area of the core, the bending loss increases,
It is known that microvent sensitivity is increased.

[0006] In the above-mentioned optical fiber unit having a tight structure using an optical fiber having a large effective area and a high microbend sensitivity, the small bending caused by the contraction stress of the optical fiber unit at low temperatures. Even if a small amount of microbends occur in the optical fiber, the bending loss increases and the transmission loss increases.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress the increase in transmission loss at low temperatures even in a tight-type optical fiber unit using an optical fiber having high microbend sensitivity. It is to make.

[0008]

The object of the present invention is to reduce the temperature of the optical fiber core constituting the optical fiber unit from + 15 ° C. to −15 ° C.
This is possible by setting the volumetric shrinkage rate accompanying a temperature change up to 20 ° C. to 0.05% or less.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The optical fiber unit according to the present invention is, for example, an optical fiber unit having a tight structure as shown in FIG. 1 and having a volume shrinkage rate of 0.05 as a temperature change from + 15 ° C. to −20 ° C. % Or less. In the present invention, the volume shrinkage of the optical fiber core is determined by measuring the volume (V ₁ ) at a temperature of 15 ° C. and the volume (V ₁ ) at a temperature of −20 ° C. of a certain length of the optical fiber core present in the optical fiber unit. ₂ ) and the difference (V ₁ −V ₂ ) at 15 ° C.
And defined as a percentage divided by the volume at (V ₁ ).

In practice, the volumetric shrinkage can be calculated from a change in temperature of the refractive index or a change in strain of the bare optical fiber in the optical fiber unit. The volume shrinkage of such an optical fiber core is set to 0.05
% Or less can be achieved by individually optimizing various parameters such as the Young's modulus and the linear expansion coefficient of the integrated material 3 and the Young's modulus and the linear expansion coefficient of the coating layer of the optical fiber 2. .

For example, when the Young's modulus of the integrated material 3 is increased, the volume shrinkage tends to decrease, and when the linear expansion coefficient of the integrated material 3 is decreased, the volume shrinkage tends to decrease. Also, when the Young's modulus of the coating layer of the optical fiber core wire 2 is increased, the volume shrinkage tends to decrease, and when the linear expansion coefficient of the coating layer is reduced, the volume shrinkage tends to decrease. By appropriately determining these parameters in consideration of such a tendency, optimization is possible.

However, the optical fiber unit as a whole needs to satisfy not only the temperature characteristics but also many mechanical characteristics such as lateral pressure, bending, water pressure, tension and the like at the same time. The above parameters should be optimized.

The bare optical fiber forming the optical fiber 2 is not particularly limited, but preferably has a core effective area of 70 μm ² or more from the viewpoint of suppressing non-linear effects. Even in an optical fiber unit using a bare optical fiber having high microvent sensitivity, an increase in transmission loss at low temperatures can be suppressed.

In such an optical fiber unit, even if the integrated material 3 shrinks at a low temperature, little bending of the fiber axis of the optical fiber core 2 hardly occurs. For this reason, microbending does not occur in the optical fiber core wire 2 and bending loss does not increase and transmission loss does not increase. Therefore, even when a bare optical fiber having a large effective area of the core and a high microbend sensitivity is used as the bare optical fiber forming the optical fiber core 2, transmission loss does not increase at low temperatures.

Hereinafter, specific examples will be described. An optical fiber unit having a tight structure shown in FIG. 1 was manufactured. As an optical fiber core wire, a diameter 4 in which a primary coating layer and a secondary coating layer made of an ultraviolet curable resin are provided on a bare optical fiber having a diameter of 125 μm.
A thing of 00 μm was prepared. As the bare optical fiber, a single mode fiber for 1.55 μm having an effective cross-sectional area of 80 μm ² was used.

By changing the Young's modulus of the coating layer of the optical fiber core and the integrated material, the temperature of the optical fiber core is + 15 ° C.
0.03 volumetric shrinkage with temperature change from
%, 0.05%, 0.08%, and 0.1%. The low-temperature characteristics of these optical fiber units were evaluated.

The low temperature characteristic is +15 of the optical fiber unit.
It is evaluated by the difference between the transmission loss of the optical fiber core at -20 ° C. and the transmission loss at −20 ° C., and the difference is 0 to −10 mdB.
/ Km or less was judged to be acceptable. All transmission losses are measurements at a wavelength of 1.55 μm. Table 1 shows the results.

[0018]

[Table 1]

From Table 1, it can be seen that by setting the volume shrinkage of the optical fiber core to 0.05% or less, the temperature change from −15 ° C. to −15 ° C.
It is apparent that the amount of increase in transmission loss at 20 ° C. can be reduced to 0 mdB / km or less, and increase in transmission loss can be prevented.

[0020]

As described above, in the optical fiber unit of the present invention, this optical fiber unit is -2.
Even in a low-temperature environment of about 0 ° C., the microbend generated in the optical fiber core due to contraction of various members constituting the optical fiber unit becomes extremely small, and transmission loss is reduced. Does not increase. Therefore, even when a bare optical fiber having a large effective area of the core and a high microbend sensitivity is used, the increase in transmission loss can be suppressed to an extremely low level.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an optical fiber unit having a tight structure according to the present invention.

[Explanation of symbols]

1: Central tension member, 2: Optical fiber core, 3:
Integrated material.

Continued on the front page (72) Inventor Takeshi Shimichi, 1440, Mukurosaki, Sakura-shi, Chiba Prefecture Inside Fujikura Sakura Office, Ltd. Reference) 2H001 BB06 DD04 KK06 KK08 KK22 MM09 PP01 4G060 AA12 AA19 AC02 AD22 AD43

Claims (1)

[Claims] 1. A tight-type optical fiber unit comprising a plurality of optical fiber cores twisted around a central tension member, and an integral material made of an ultraviolet curing resin is provided thereon. An optical fiber unit characterized in that a volume shrinkage rate accompanying a temperature change from 15 ° C. to −20 ° C. is 0.05% or less.