JPS61200515A - All uv resin coated optical fiber - Google Patents

Abstract

PURPOSE:To prevent the exertion of a side pressure to an optical fiber at a low temp. by coating >=2 layers of UV resins on an optical fiber, setting the Young's modulus and coefft. of linear coefft. of the 1st layer coating in a prescribed range and specifying the thickness of each layer so as to satisfy prescribed conditions. CONSTITUTION:>=2 layers of coatings 21, 22...2n of the UV resin are formed on the optical fiber 10 and the Young's modulus E1 and coefft. alpha1 of linear expansion of the 1st layer 21 are so set as to attain E1<En and alpha1>alphan as compared to the effective Young's modulus En and the coefft. alphan of linear expansion of the entire part of the coatings 22-2n of the 2nd and subsequent layers. The thickness of the layers 21-2n is so specified that the sum total of the stresses in the radiation direction to be exerted to the fiber 10 is made zero. The outside diameter 2b of the coating 21 of the 1st layer is so determined as to satisfy the following equation for the above-mentioned purpose: 2b=2a/{1-2(1-upsilon1)R}<1/2>, where upsilon1 is the Poisson ratio of the coating 21 of the 1st layer, 2a is the diameter of the fiber 10 and R is the ratio of the integrated value of alphan and alpha1 over a desired temp. range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] This invention uses UVMiI resin (ultraviolet curable resin) in all layers of the coating. This relates to an all-UVZ fat-coated optical fiber.

[Prior Art and Background of the Invention] Some all-UV resin-coated optical fibers experience a significant increase in loss at low temperatures, depending on their coating structure. For example, the loss at -409C is several tens of dB higher than at 20C.

This phenomenon is due to the material properties of the coating (Young's modulus, Poisson's ratio,
(linear expansion coefficient, etc.), structure, coating conditions, etc.

The increase in loss is caused by microbends being applied to the optical fiber for some reason.

It is known that shrinkage in the axial direction of the optical fiber causes an increase in loss due to the low-temperature characteristics of the conventionally used core wire having a three-layer coating structure of silicone resin and nylon.

However, the low-temperature characteristics of an all-UV resin-coated optical fiber are different from those of conventional fibers in terms of the mechanism of increase in loss.

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

Therefore, it is an object of the present invention to provide an all-UV resin-coated optical fiber configured so that no lateral pressure is applied to the optical fiber at low temperatures.

[Means for solving problems] The present invention is as shown in FIGS. 1 and 5.

(1) Coating two or more layers of UV resin on the optical fiber,
And the Young's modulus E1 of the first layer coating 21 is the Young's modulus E2 of the second layer coating 22 or the entire coating 21 of the second layer or more.
, 22--2n is smaller than the effective Young's modulus En (i.e., E<El or El<En).
(2) The linear expansion coefficient α1 of the first layer coating 21 is the same as the linear expansion coefficient α2 of the second layer coating 22 or the effective coefficient of the entire coating of the second layer and above. is larger than the linear expansion coefficient αn (i.e.,
αl〉α2 or α,〉αn), and (3) the thickness of each layer is regulated so that the sum of radial stress applied to the optical fiber due to temperature change becomes zero. shall be.

[Explanation] A case where the coating has two layers will be explained.

In FIG. 1, 10 is an optical fiber, 21 is a coating,
22 is a secondary coating. Also, E1 Young's modulus of Knee-method coating El Young's modulus of second-order covering νX Poisson's ratio of second-order covering ν2 Poisson's ratio of second-order covering α1 Linear expansion coefficient of second-order covering α2 : Linear expansion coefficient a of second-order covering : Radius of optical fiber. Radius of secondary coating C: Radius of secondary coating.

(1) Regarding E, < El 2. In the case of conventional silicone resin and nylon coating, as a rule of thumb, E 1
<< E 2 was used to improve the lateral pressure characteristics.

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

(2) Concerning α,>α2 When the knee method coating and secondary coating contract at low temperature, if α plate=α2, the contraction force becomes lateral pressure and is transmitted to the optical fiber.

However, since α1>α2, the -method coating shrinks more than the secondary coating. Also, E is <El.

Therefore, it becomes as follows (Figure 2).

If the legal covering (i21) and the secondary covering 22 are not adhered at the boundary, a gap will be created between them, and the inner diameter of the legal covering will also be reduced.

However, since the primary coating and the secondary coating are bonded and integrated, the primary coating 21 contracts with respect to the interface with the secondary coating 22. Therefore, at the interface between the optical fiber coating 21 and the optical fiber 10, a tension force toward the secondary coating side 22 acts.

- If 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 secondary coating 22
The contraction force of the optical fiber is balanced, and the stress applied to the optical fiber becomes zero.

(3) Once the materials of the primary coating and secondary coating are determined for the thickness of each layer, the thickness of each layer at which the stress applied to the optical fiber becomes zero can be determined experimentally or by the calculations described below.

This is what is stated in claim 1.

Generally, materials are selected such that E, <<E2, but in this case, as will be described later, the stress applied to the optical fiber can be reduced to zero simply by determining the thickness of the -order coating.

[How to determine the thickness of each layer by calculation] - From the theory of shrink fit (material mechanics), assuming that Pa is the stress applied to the surface of the optical fiber when the primary coating and secondary coating contract.

It can be expressed as Here, to is room temperature and tl is the temperature under consideration (eg -20°C).

Also, A and B are It is.

Since it is sufficient that P a = O(3) at a low temperature, equation (4) is obtained from equations (1) and (3).

When A/B is executed using equation (2), 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, determined from equations (4) and (5).

In addition, in this case, E, << E, , so
The value of 2b is largely independent of the value of 2C.

In addition, FIG. 4 shows the values obtained from equations (4) and (5). The relationship between the edge linear expansion coefficient ratio and the optimum outer diameter 2b of the primary coating is shown.

Once the materials for the primary coating and secondary coating are determined, the thickness of each layer can be determined using one or more relationships.

[Especially regarding the case of EI x E2] Under the condition of E, << E2, equation (5) becomes, and from equation (8), the outer diameter 2b of the -th order coating is.

becomes.

This is what is stated in the second claim.

[When the coating has two or more layers] As shown in FIG. 5, when the coating has n layers, the above E2.
If the effective values En, νn, αn from the first layer 2n to the secondary coating 22 are considered instead of ν2 and α2, the rest can be processed in the same manner as above.

[Example] Three types of optical fibers having coating structures as shown in Table 1 below were fabricated, and the temperature characteristics of the loss increase were measured. The results are shown in Figure 6 (20°C standard).

#1 fiber showed a large increase in loss at low temperatures, but
Fibers #2 and #3 showed no increase in loss even at low temperatures.

Table 1 The properties of these UV resins are shown in Table 2 below.

Table 2 In addition, the above A1. A7. In addition to resin B, commercially available coating materials include DeSoto In
c, “Desolite J 950x030, 950x”
065. Same 950x041. Same 950x069, same 9
50x071, and the company's [Desolai N 950x044, 950xlO1, 950x
042. The same 950xlOO can be used, respectively.

1 Effect of the invention] An optical fiber is coated with two or more layers of UV resin, and the Young's modulus of the first layer is equal to or greater than the Young's modulus of the second layer or the effective of the entire coating of 2N or more. In an all-UV resin-coated optical fiber that is made smaller than the Young's modulus, the linear expansion coefficient of the first layer coating is the linear expansion coefficient of the second layer coating or the effective linear expansion coefficient of the entire coating of the second and higher layers. The thickness of each layer is set to be larger than the expansion coefficient, and the thickness of each layer is specified so that the sum of radial stress applied to the optical fiber due to temperature changes becomes zero, so the lateral pressure applied to the optical fiber can be reduced to zero. You will be able to do this.

That is, one of the very major causes of increased loss at low temperatures can be eliminated.

[Brief explanation of drawings]

Fig. 1 is a detailed explanatory diagram of the present invention; Fig. 2 is an explanatory diagram of the case of contraction; Fig. 3 is a relationship line between the optimal primary coating outer diameter and the secondary coating outer diameter without applying pressure to the optical fiber. 4 is a diagram showing the relationship between the ratio of the optimum outer diameter of the coating and the coefficient of linear expansion when no pressure is applied to the optical fiber. FIG. 5 is an explanatory diagram when the coating has three or more layers, and FIG. 6 is a diagram showing the temperature characteristics in the example. lO: Optical fiber 21 primary coating 22 secondary coating

Claims (2)

[Claims] (1) Coating two or more layers of UV resin on the optical fiber,
In an all-UV resin coated optical fiber, the Young's modulus of the first layer coating is smaller than the Young's modulus of the second layer coating or the effective Young's modulus of the entire coating of the second layer or more, the first layer The linear expansion coefficient of the coating is larger than the linear expansion coefficient of the second layer coating or the effective linear expansion coefficient of the entire second or higher coating, and the radius applied to the optical fiber due to temperature change is An all-UV resin-coated optical fiber characterized in that the thickness of each layer is regulated so that the sum of directional stresses is zero. (2) The Young's modulus of the first layer coating is significantly smaller than the Young's modulus of the second layer coating or the effective Young's modulus of the entire second or higher layer coating, and The all-UV resin-coated optical fiber according to claim 1, wherein the outer diameter 2b is expressed by the following formula. 2b=2a/{√[1-2(1-ν_1)]R} 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,
The linear expansion coefficient of the second layer coating is α_2, and the effective linear expansion coefficient of the entire second layer and higher coatings is αn, t_0 is room temperature,
When t_1 is the temperature under consideration, R is a numerical value expressed as ▲There are mathematical formulas, chemical formulas, tables, etc.▼ or ▲There are mathematical formulas, chemical formulas, tables, etc.▼.