JP2539599B2 - All UV resin coated optical fiber - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an all-UV resin coated optical fiber which uses a UV resin (ultraviolet curable resin) for all layers of the coating.

[Background of the Invention and Background of the Invention] For general optical fiber cables for communication, -40 ° C to +60
It is required to maintain stable transmission characteristics without loss fluctuation under the temperature condition of ° C. The all-UV resin-coated optical fiber has no problem in the high temperature region of the above range, but there is one that causes a significant loss increase at low temperature depending on the coating concept. For example, the loss at -40 ℃
Some increase by several tens of dB more than at 20 ° C.

This phenomenon depends on the material properties of the coating (Young's modulus, Poisson's ratio, linear expansion coefficient, etc.), structure, and coating conditions.

The increase in loss is caused by giving a microbend to the optical fiber for some reason.

It has been known that the low temperature characteristic of the core wire of the three-layer coating structure of the silicone resin and nylon, which has been conventionally used, causes the axial shrinkage of the optical fiber to increase the loss.

However, the low-temperature characteristics of the all-UV resin coated optical fiber differ from the conventional one in the mechanism of loss increase.

As a result of investigating the low temperature characteristics of the all-UV resin coated optical fiber with various coating structures, it was found that the lateral pressure on the optical fiber due to the radial contraction of the UV coating is a major cause of the increase in loss at low temperature. .

If the radial contraction is uniform, the microbend does not occur. However, in the actual coating, various nonuniformities are considered to exist in the longitudinal direction and the radial direction, which causes the coating to contract nonuniformly, resulting in microbends in the optical fiber and increased loss.

Therefore, it is an object of the present invention to provide an all-UV resin-coated optical fiber configured so that lateral pressure is not applied to the optical fiber in the radial direction at a low temperature.

[Means for Solving the Problems] Normally, when UV resin is sequentially coated in a multilayer form on an optical fiber, adjacent layers are adhered and coated in an integrated state. Therefore, according to the present invention, as shown in FIG. 1 and FIG. 5, (1) two or more layers of UV resin are coated on the optical fiber in a state where the adjacent layers are adhered and integrated, and The Young's modulus E ₁ of the coating 21 of the first layer is smaller than the Young's modulus E ₂ of the coating 22 of the second layer or the effective Young's modulus En of the entire coating 21,22 -2-n of the second layer or more. (Ie E ₁
<E ₂ or E ₁ <En) for all UV resin coated optical fibers, (2) The linear expansion coefficient α ₁ of the first layer coating 21 is the linear expansion coefficient α of the second layer coating 22. The effective linear expansion coefficient of the entire coating of _two or more second layers is larger than αn (that is, α ₁
> Α ₂ or α ₁ > αn), and (3) the radial contraction force of the coating of the first layer and the radial contraction force of the coating of the second layer or the second layer or more due to temperature change. The thickness of each layer is specified such that the total radial stress applied to the optical fiber due to temperature change becomes zero by balancing the effective radial contraction force of the entire coating of Characterize.

[Explanation] The case where the coating has two layers will be described.

In FIG. 1, 10 is an optical fiber, 21 is a primary coating, 22
Is the secondary coating. E ₁ : Young's modulus of primary coating E ₂ : Young's modulus of secondary coating ν ₁ : Poisson's ratio of primary coating ν ₂ : Poisson's ratio of secondary coating α ₁ : Linear expansion coefficient of primary coating α ₂ : Secondary coating Coefficient of linear expansion a: radius of optical fiber b: radius of primary coating c: radius of secondary coating.

₍₁₎ E 1 <about to E _2: If the coating of the conventional silicone resin nylon, heuristically in the E ₁ << E _2, was with the aim of improving the lateral pressure property.

This idea is inherited in the case of all UV resin coated optical fibers and is also described in the published literature.

(2) Regarding setting α ₁ > α ₂ : When the primary coating and the secondary coating shrink at low temperature, if α ₁ =
If it is α ₂ , the contracting force becomes lateral pressure and is transmitted to the optical fiber.

However, because of α ₁ > α ₂ , the primary coating shrinks more than the secondary coating. Also, E ₁ <E ₂ . So it looks like this (Fig. 2).

If the primary coating 21 and the secondary coating 22 are not adhered at the boundary, a gap is created between them and the inner diameter of the primary coating is also reduced.

However, in the case of an all-UV resin-coated optical fiber, the primary coating 21 and the secondary coating 22 are bonded and integrated, and since the primary coating 21 has a smaller elastic coefficient than the secondary coating 22 (is easily deformed). The primary coating 21 shrinks with reference to the boundary surface with the secondary coating 22. For that purpose, the primary coating 21 and the optical fiber are
At the interface with 10, tension acts toward the secondary coating side 22.

When the thicknesses of the primary coating and the secondary coating, that is, the values of b and c are appropriate, the tension of the primary coating 21 and the contracting force of the secondary coating 22 are balanced and the stress applied to the optical fiber becomes zero. Become.

(3) Thickness of each layer: When the material for the primary coating and the material for the secondary coating are determined, the contracting force of the primary coating and the contracting force of the secondary coating are balanced and the optical fiber is experimentally or by the following calculation. It is possible to obtain the thickness of each layer at which the stress applied to is zero.

This is what is stated in claim 1 of the appended claims.

Generally, a material that satisfies E ₁ << E ₂ is selected. Then, as will be described later, the stress applied to the optical fiber can be made zero by simply determining the thickness of the primary coating.

[Calculating the thickness of each layer by calculation] When the stress applied to the surface of the optical fiber when the primary coating and the secondary coating contract is Pa, from the theory of shrink fit (material mechanics), Can be expressed as Where t ₀ is room temperature and t ₁ is the temperature under consideration (eg −20 ° C.).

Also, A and B are Is.

Since Pa = 0 (3) at low temperature, it is necessary to obtain the equation (4) from the equations (1) and (3).

When A / B is executed using the equation (2), the equation (5) is obtained.

FIG. 3 shows the relationship between the outer diameter 2c of the secondary coating and the optimum outer diameter 2b of the primary coating, which is obtained from equations (4) and (5).

In this case, since E ₁ << E ₂ , the value of 2b hardly depends on the value of 2c.

Further, FIG. 4 shows the relationship between the linear expansion coefficient ratio and the optimum outer diameter 2b of the primary coating, which is obtained from the equations (4) and (5).

When the materials for the primary coating and the secondary coating are determined, the thickness of each layer can be determined using the above relationship.

[Especially for E ₁ << E ₂ ] Under the condition of E ₁ << E ₂ , the formula (5) is From equation (6), the outer diameter 2b of the primary coating is Becomes

This is what is stated in claim 2.

[When the coating has two or more layers] As shown in FIG. 5, when the coating has n layers, the above E ₂ , ν
_If the effective numerical values from the n-th layer 2n to the secondary coating 22, En, νn, and αn, are considered instead of ₂ and α2, the subsequent processing can be performed in the same manner as described above.

[Examples] Three types of optical fibers having coating structures as shown in the following Table 1 were prototyped, and the temperature characteristics of increased loss were measured. The results are shown in Fig. 6 (20 ° C standard).

The # 1 fiber showed a large loss increase at low temperatures,
The fiber of # 2 and # 3 did not increase loss even at low temperature.

The characteristics of these UV resins are shown in Table 2 below.

In addition to the above-mentioned A ₁ , A ₂ and B resins, as commercially available, the primary coating material is “Desolite” 950x030, 950x065, 950x041, 950x069,
950x071 and the company's "Desolite" 950x044, 950x101, 950x042, and 950x100 can be used as the secondary coating materials.

EFFECTS OF THE INVENTION The present invention has found that in the case of an all-UV resin-coated optical fiber, the lateral pressure on the optical fiber due to the radial contraction of the coating is a major cause of the increase in loss at low temperatures (new to natural phenomenon. It is a technical issue (purpose) to prevent lateral pressure from being applied to the optical fiber in the radial direction at low temperature based on the recognition.

Then, two or more layers of UV resin are coated on the optical fiber in a state in which the adjacent layers are bonded and integrated.
In the all-UV resin coated optical fiber, the Young's modulus of the coating of the first layer is smaller than the Young's modulus of the coating of the second layer or the effective Young's modulus of the entire coating of the second or more layers. The coefficient of linear expansion of the coating of the second layer is larger than the coefficient of linear expansion of the coating of the second layer or the effective coefficient of linear expansion of the entire coating of the second or more layers, and the radial expansion of the coating of the first layer due to temperature change. By balancing the shrinkage force with the radial shrinkage force of the coating of the second layer or the effective radial shrinkage force of the entire coating of the second layer and above, the radial stress applied to the optical fiber by the temperature change. Since the thickness of each layer is regulated so that the sum of the above is zero, even if the coating of each layer contracts at low temperature, radial side pressure is not applied to the optical fiber, and therefore the loss at low temperature is reduced. Eliminate the major causes of increase be able to.

[Brief description of drawings]

FIG. 1 is an explanatory view of a cross section of the present invention, FIG. 2 is an explanatory view when contracting, and FIG. 3 is a relational diagram of an optimum primary coating outer diameter and a secondary coating outer diameter where pressure is not applied to the optical fiber. FIG. 4 is a diagram showing the relationship between the optimum primary coating outer diameter where pressure is not applied to the optical fiber and the ratio of the linear expansion coefficient. FIG. 5 is an explanatory diagram when the coating has three or more layers. 4 is a diagram showing temperature characteristics in FIG. 10: Optical fiber 21: Primary coating 22: Secondary coating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Araki 1440 Rokuzaki, Sakura City Fujikura Electric Cable Co., Ltd.Sakura Plant (72) Inventor Michio Akiyama 1440, Rokuzaki Sakura City Fujikura Electric Cable Co., Ltd.Sakura Plant (56) References JP-A-59-217653 (JP, A) Actually developed 58-188606 (JP, U)

Claims (2)

(57) [Claims] 1. An optical fiber is coated with two or more layers of UV resin in a state in which the adjacent layers are bonded and integrated, and the Young's modulus of the coating of the first layer is the same as that of the second layer. In an all-UV resin-coated optical fiber in which the Young's modulus of the coating or the effective Young's modulus of the entire coating of the second layer or more is smaller than the linear expansion coefficient of the coating of the first layer The coefficient of expansion is larger than the effective linear expansion coefficient of the entire coating of the second layer or more, and the radial contraction force of the coating of the first layer due to temperature change and the radial contraction force of the coating of the second layer By balancing the contraction force or the effective radial contraction force of the entire coating of the second layer and above, the thickness of each layer is adjusted so that the total radial stress applied to the optical fiber due to temperature change becomes zero. All-UV resin coating, characterized by being specified Fiber. 2. The Young's modulus of the coating of the first layer is significantly smaller than the Young's modulus of the coating of the second layer or the effective Young's modulus of the entire coating of the second layer and above, and The all-UV resin-coated optical fiber according to claim 1, wherein the outer diameter 2b of the coating is represented by the following formula. Where 2a is the diameter of the optical fiber, ν ₁ is the Poisson's ratio of the first layer coating, and the linear expansion coefficient of the first layer coating is α ₁ ,
When the linear expansion coefficient of the coating of the second layer is α ₂ , the effective linear expansion coefficient of the entire coating of the second layer and above is αn, t ₀ is room temperature, and t ₁ is the temperature under consideration, R is , It is a numerical value represented by.