JPH0560954A - Fine diameter optical fiber - Google Patents

Abstract

PURPOSE:To obtain a fine diameter optical fiber having sufficient mechanical strength and little in increase of transmission loss caused by lateral pressure. CONSTITUTION:In the fine diameter optical fiber having <=230mum outside diameter and provided with an inner covering layer and an outer covering layer made from an ultraviolet curing resin on an optical fiber having 125mum outside diameter, the resin having 0.8-2.5 product of Young's modulus E1 (kg/mm<2>) and area of cross section of the outer covering layer S (mm<2>) is used for the outer covering layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-diameter optical fiber core wire having an outer diameter of 230 μm or less, which is used for a high-density multi-core optical cable or the like.

[0002]

2. Description of the Related Art Conventionally, in an optical fiber core wire using an optical fiber made of silica glass, in order to protect the optical fiber from impact and secure reliability, the optical fiber has an inner layer coating made of an ultraviolet curable resin. A structure with an outer coating is used. Young's modulus is different between the inner layer coating and the outer layer coating, and a soft material is used for the inner layer coating and a hard material is used for the outer layer coating. This coating structure protects the optical fiber by receiving an external force with a hard outer layer coating and making it difficult to transmit the external force to the optical fiber with a soft inner layer coating. The conventional optical fiber core wire has an outer diameter of 400 μm by applying the above two-layer coating to an optical fiber with an outer diameter of 125 μm.
The size of 250 μm is generally used.

[0003]

In recent years, along with the remarkable expansion and diversification of communication demand, the demand for high-density multi-core optical cables has increased, and the optical fiber cores constituting the optical cables maintain the current reliability. Therefore, it is desired to further reduce the diameter.

If the outer diameter of the optical fiber is not changed in order to reduce the diameter of the optical fiber, there is no other method than to reduce the coating thickness. If the coating thickness is reduced, the conventional coating structure is used. Was weakened and peeled off easily, and there was a problem in terms of reliability due to deterioration of screening and increase of lateral pressure loss.

[0005]

The present invention provides a small-diameter optical fiber core wire that solves the above problems.
The configuration is as follows: In a small-diameter optical fiber core with an outer diameter of 230 μm or less, which is obtained by applying an inner layer coating made of UV-curable resin and an outer layer coating to a quartz glass optical fiber with an outer diameter of 125 μm.
A resin having a product E ₁ × S of the Young's modulus E ₁ (kg / mm ² ) and the cross-sectional area S (mm ² ) of the outer layer coating in the range of 0.8 to 2.5 is used for the outer layer coating material. It is a thing. It is desirable to use a resin having a Young's modulus E ₂ (kg / mm ² ) of 0.3 or less for the inner layer coating material.

[0006]

The present invention is applied to a small-diameter optical fiber core wire having an outer diameter of 230 μm or less. Conventionally, such a small-diameter optical fiber core cannot be put to practical use because the coating layer is too thin and screening deterioration, increase in loss due to lateral pressure, or peeling of the coating easily occurs, but it cannot be used practically. It has been experimentally confirmed that these problems can be overcome by using a resin whose Young's modulus E ₁ has the above relationship with the cross-sectional area S of the outer layer coating. It was experimentally confirmed that when a resin having the above Young's modulus is used for the inner layer coating material, a small-diameter optical fiber core wire with little loss increase due to lateral pressure can be obtained.

[0007]

EXAMPLES Examples of the present invention will be described in detail below on the basis of test production and test results. The Young's modulus E ₂ of all the inner layer coating materials used in Experiments 1 to 5 is 0.3 kg / mm ² .

Experiment 1 A quartz glass single mode optical fiber having an outer diameter of 125 μm was drawn, an inner layer coating made of an ultraviolet curable resin was applied immediately after the drawing, and an outer layer coating made of an ultraviolet curable resin was further applied thereon. The optical fiber core wires having the outer diameter of the inner layer and the outer diameter of the outer layer shown in Table 1 were each manufactured in a length of 5000 m.

Since the optical fiber core is broken if the strength of the optical fiber is not sufficient, a screening test in which a stress load of 0.6% is applied to the entire manufacturing length was performed, and the number of breaks at that time was measured. The results are shown in Table 1.

[0010]

[Table 1]

From these results, it was found that it is desirable to make the coating layer thinner in the thin optical fiber core wire, but the number of breaks increases when the outer diameter of the optical fiber core wire becomes 230 μm or less.

Experiment 2 Since the number of breaks depends on the outer layer coating, as shown in Table 2, four kinds of ultraviolet rays having different Young's moduli are provided on the outer side of the inner layer coating made of an ultraviolet curable resin having an outer diameter of 180 μm. An outer layer coating made of a curable resin was applied, optical fiber cores with an outer diameter of 200 μm were manufactured for 5000 m each, and the same test as Experiment 1 was conducted. As a result, as shown in Table 2, it was found that the number of breaks decreased as the Young's modulus of the outer coating material increased.

[0013]

[Table 2]

Experiment 3 Since the number of breaks depends on the Young's modulus of the outer coating material, it is presumed that it is also affected by the cross-sectional area of the outer coating material. Therefore, as shown in Table 3, four types of optical fiber core wires with different cross-sectional areas of the outer layer coating were used as the outer layer coating material with Young's modulus of 15
It was manufactured by using 0 kg / mm ^{2 of} an ultraviolet curable resin, and the same test as Experiment 1 was performed. As a result, as shown in Table 3,
It was found that the number of breaks also depends on the cross-sectional area of the outer layer coating, and when the Young's modulus of the outer layer coating material is low, the number of breaks increases as the cross-sectional area of the outer layer coating decreases.

[0015]

[Table 3]

From the above results, the relationship between the Young's modulus of the outer layer coating and the product E ₁ × S of the cross-sectional area and the number of breaks was examined, and FIG.
It was found that there was a correlation between the two, and when the product E ₁ × S of Young's modulus and cross-sectional area exceeded 0.8, almost no fracture occurred. Therefore, if a resin having a Young's modulus E ₁ of 0.8 / S or more is used for the outer layer coating material, a small-diameter optical fiber core wire having excellent screening strength can be manufactured.

Experiment 4 The optical fiber core wire is required to have not only strength characteristics but also excellent lateral pressure characteristics in order to suppress an increase in transmission loss during cable formation. Therefore, in order to investigate the lateral pressure characteristics of the thin optical fiber core wire, the sample No. 2 to 12 small-diameter optical fiber cores are placed on a plastic bobbin with a body diameter of 160 mmφ and tension is 40
The increase in transmission loss at a wavelength of 1.55 μm when wound with g was measured. The results are shown in Table 4, and E ₁ ×
It was observed that when the value of S was large, the increase in transmission loss was also large.

[0018]

[Table 4]

Experiment 5 Therefore, various small diameter optical fiber core wires having different values of E ₁ × S shown in Table 5 were newly manufactured, and the lateral pressure characteristics were examined under the same conditions as in Experiment 4. The results are shown in Table 5.

[0020]

[Table 5]

The results of Experiment 4 and Experiment 5 are shown in a graph of FIG. From these results, it was found that when the product E ₁ × S of the Young's modulus and the cross-sectional area of the outer layer coating increases, the lateral pressure characteristics tend to deteriorate, and especially E ₁ × S is 2.
It can be seen that when it exceeds 5, lateral pressure characteristics are significantly deteriorated. Therefore, in order to maintain the lateral pressure characteristic at a good level, the value of E ₁ × S must be 2.5 or less.

From the above results, in order to obtain a small-diameter optical fiber core wire having both excellent strength and lateral pressure characteristics, the product E ₁ × S of Young's modulus and cross-sectional area of the outer layer coating can be set within the range of 0.8 to 2.5. I understand that it is good.

Experiment 6 While further studying the lateral pressure characteristics of the small-diameter optical fiber core, the lateral pressure characteristics of the small-diameter optical fiber core are not limited to the above-mentioned E ₁ × S value, but also the inner layer coating. It was found that the Young's modulus of the product also had an effect. Therefore, as shown in Table 6, E ₁
Various small-diameter optical fiber core wires having a constant value of × S and different Young's moduli E ₂ of the inner layer coating material were made on a trial basis, and the lateral pressure characteristics were examined under the same conditions as in Experiment 4. The results are shown in Table 6 and FIG.

[0024]

[Table 6]

From these results, Young's modulus E _{2 of the} inner layer coating material
It can be seen that the transmission loss increases remarkably when the value exceeds 0.3 kg / mm ² . Therefore, in order to obtain a small diameter optical fiber having excellent lateral pressure characteristics, it is desirable to set the Young's modulus E ₂ of the inner layer coating material to 0.3 or less.

[0026]

As described above, according to the present invention, it is possible to obtain a small-diameter optical fiber core wire having an outer diameter smaller than that of the prior art and having sufficient strength and lateral pressure characteristics. Can greatly contribute to the realization of.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the Young's modulus and cross-sectional area product E ₁ × S of the outer layer coating of a small-diameter optical fiber and the number of breaks during a screening test.

FIG. 2 is a graph showing the relationship between the product E ₁ × S of Young's modulus and cross-sectional area of the outer layer coating of the small-diameter optical fiber and the increase in transmission loss due to lateral pressure.

FIG. 3 Young's modulus E of the inner layer coating of a small-diameter optical fiber
₂ is a graph showing the relationship between ₂ and the increase in transmission loss due to lateral pressure.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keigo Maeda 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Shuji Okakawa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Akihiro Otake 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Shigeru Tomita 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A small-diameter optical fiber core having an outer diameter of 230 μm or less obtained by applying an inner layer coating made of an ultraviolet curable resin and an outer layer coating to a silica glass optical fiber having an outer diameter of 125 μm,
A resin having a product E ₁ × S of the Young's modulus E ₁ (kg / mm ² ) and the cross-sectional area S (mm ² ) of the outer layer in the range of 0.8 to 2.5 is used for the outer layer coating material. Small diameter optical fiber core. 2. Young's modulus E ₂ (kg / mm ² ) is applied to the inner layer coating material.
2. The small-diameter optical fiber core wire according to claim 1, characterized in that a resin having a value of 0.3 or less is used.