JPH05281431A - Coated polarization maintaining optical fiber - Google Patents

Abstract

PURPOSE:To obviate the peeling of a coating layer and to improve a polarization maintaining characteristic at a low temp. by successively coating the surface of a bare optical fiber with a cushion layer, an adhesive layer and a protective layer. CONSTITUTION:The surface of the bare polarization maintaining optical fiber 1 is coated with the cushion layer 4. This cushion layer 4 consists of a synthetic resin having low elasticity ranging from 0.01 to 0.4kg/mm<2>, a small coefft. of thermal expansion ranging from 0.1 to 5.0X10<-4> and about 20 hardness and suppresses the microbending by shrinkage of the coating. The surface of the cushion layer 4 is coated with the adhesive layer 5. This adhesive layer 5 consists of a synthetic resin having the elasticity ranging from 0.1 to 0.6kg/mm<2>, the coefft. of thermal expansion ranging from 0.1 to 10X10 and about 30 hardness and having the good adhesiveness to the cushion layer 4 and the protective layer 6. This layer prevents the low-temp. deterioration of the coated optical fiber based on the peeling of the two layers 4, 6 at the time of high load. The surface of the adhesive layer 5 is coated with the protective layer 6. The protective layer 6 consists of a synthetic resin having the elasticity ranging from 50 to 200kg/mm<2>, the coefft. of thermal expansion ranging from 0.5 to 10X10<-4> and about 40 hardness and plays the role of improving the side pressure characteristic of the coated optical fiber and protecting the fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved polarization-maintaining optical fiber core wire, and more particularly to a polarization-maintaining optical fiber core wire coating structure for use as a sensing coil in a sensor such as an optical fiber gyroscope. Regarding improvement.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional polarization-maintaining optical fiber core wire coating structure has an inner layer on the bare optical fiber 1 as in the case of a normal optical fiber coating structure used for communication. 2 and the outer layer 3 are coated in this order in two layers. Of these, the inner layer 2 is coated for the purpose of suppressing the occurrence of microbending caused by the contraction of the coating of the polarization-maintaining optical fiber core wire at a low temperature, and therefore a material having a relatively low Young's modulus is used. The outer layer 3 is coated for the purpose of improving the lateral pressure characteristic of the polarization-maintaining optical fiber core and protecting the polarization-maintaining optical fiber core, so that a material having a relatively high Young's modulus is used. The inner layer 2 and the outer layer 3 are usually coated simultaneously with the drawing of the bare optical fiber 1.

As a material used for the inner layer 2 and the outer layer 3, there is a combination of modified silicone for the inner layer 2 / silicone for the outer layer 3 and urethane acrylate for the inner layer 2 / epoxy acrylate for the outer layer 3. However, since the silicone has a small coefficient of thermal expansion and the Young's modulus does not increase even at low temperatures, the polarization-maintaining optical fiber core wire coated with the combination of has good temperature characteristics, but tackiness appears on the surface. However, there is a drawback that it is difficult to make a coil. Further, the coating materials of the combination have a large coefficient of thermal expansion, and the Young's modulus rapidly increases at low temperature. Therefore, the polarization-maintaining optical fiber core wire coated with the combination of polarization-maintaining fiber at the low temperature of -20 ° C or lower. There is a drawback that the characteristics are significantly deteriorated.

On the other hand, a coil fiber for an optical fiber gyroscope is required to have good polarization maintaining characteristics, especially in the range of −65 ° C. to 100 ° C. Therefore, the polarization-maintaining optical fiber core wire coated with the combination of is not suitable as a coil fiber for an optical fiber gyroscope. Therefore, as the coil fiber for the optical fiber gyroscope, the inner layer 2
The silicone / outer layer 3 has a structure of epoxy acrylate.

[0005]

However, even in the polarization-maintaining optical fiber core wire using the coating material of this combination, the polarization-maintaining characteristics are slightly deteriorated on the low temperature side. In addition, since the adhesion between the silicone of the inner layer 2 and the epoxy acrylate of the outer layer 3 is poor, when the proof test level is raised for an optical fiber gyroscope that requires high reliability, the silicone layer and the epoxy acrylate layer peel off and conversely The polarization-maintaining characteristics of the polarization-maintaining optical fiber were deteriorated. Such a polarization-maintaining optical fiber core wire has a problem that the temperature characteristics are deteriorated and the polarization-maintaining characteristics at low temperatures are deteriorated.

The present invention has been made in view of the above circumstances, and provides a polarization-maintaining optical fiber which has good polarization-maintaining characteristics at low temperatures without peeling of the coating layer.

[0007]

In the polarization-maintaining optical fiber core wire of the present invention, a bare optical fiber is coated with a cushion layer, an adhesive layer, and a protective layer in this order to solve the above problems.

[0008]

The present invention will be described in detail below. FIG. 1 shows an example of the polarization-maintaining optical fiber core wire of the present invention. In the figure, reference numeral 1 is a known polarization-maintaining optical fiber bare wire such as a so-called panda type polarization-maintaining optical fiber. A cushion layer 4 is first coated on the polarization maintaining optical fiber bare wire 1. The cushion layer 4 has a low elasticity (Young's modulus), preferably in the range of 0.01 to 0.4 kg / mm ^{2, and} a small coefficient of thermal expansion, preferably in the range of 0.1 to 5.0 × 10 ⁻⁴ , It is a coating layer of synthetic resin having a hardness (Shore A hardness) of about 20 and having a thickness of 10 to 25 μm.

As the synthetic resin satisfying the above conditions, modified silicone, UV curable silicone and the like are preferable. U
The use of V-curable silicone has the advantage that the base material drawing process can be speeded up. The cushion layer 4 is for suppressing the contraction of the coating of the polarization-maintaining optical fiber core wire at a low temperature and preventing microbending. This effect can be further enhanced by increasing the cross-sectional area of the cushion layer 4.

An adhesive layer 5 is coated on the cushion layer 4. The adhesive layer 5 has elasticity (Young's modulus) which is an intermediate value between that of the cushion layer 4 and the protective layer 6 described later, and is preferably 0.
In the range of 1 to 0.6 kg / mm ^2, the coefficient of thermal expansion is an intermediate value between the cushion layer 4 and the protective layer 6, preferably 0.1 to 10.0 ×
In the range of 10 ⁻⁴ , the hardness (Shore A hardness) is about 30, and the cushion layer 4 and the protective layer 6 are 10 to 35 μm thick and made of a synthetic resin having good adhesion to the cushion layer 4 and the protective layer 6. Is to bond them to make them constant. As the synthetic resin satisfying the above conditions, an acrylate silicone, that is, a silicone oil in which an acrylate material and a photopolymerization initiator are mixed and cured by UV irradiation is preferable. The acrylate-based silicone has a moderate adhesive strength to both the silicone preferably used as the cushion layer 4 and the epoxy acrylate preferably used as the protective layer 6.

A protective layer 6 is coated on the adhesive layer 5. This protective layer 6 has high elasticity (Young's modulus), preferably in the range of 50 to 200 kg / mm ² , and has a thermal expansion coefficient of 0.5.
~ 10.0 × 10 ^-4 range, hardness (Shore D hardness) is 4
A coating layer having a thickness of 10 to 55 μm and made of a synthetic resin of about 0 is provided to improve the lateral pressure characteristic of the polarization maintaining optical fiber core and protect the polarization maintaining optical fiber core. As the synthetic resin satisfying the above conditions, UV-curable epoxy acrylate which has been conventionally used is preferable.
Since the UV-curable epoxy acrylate rarely shows tack on the surface, the coiling work is easy. If the cross-sectional area of the protective layer 6 is increased, the proof resistance of the polarization-maintaining optical fiber core wire can be improved.

In the production of such a polarization-maintaining optical fiber core wire, the cushion layer, the adhesive layer, and the protective layer can be coated at the same time when the polarization-maintaining optical fiber bare wire is drawn. Further, the cushion layer and the adhesive layer may be coated simultaneously with the drawing of the bare polarization-maintaining optical fiber, and then the protective layer may be coated in another step. Young's modulus of each layer, thermal expansion coefficient,
Since the optimum polarization-maintaining optical fiber core wire can be obtained by appropriately selecting the hardness and the hardness, the degree of freedom in coating design increases.

Example 1 A panda-type polarization-maintaining optical fiber core wire was prepared according to the specifications shown in Table 1. Using this polarization-maintaining optical fiber core wire, a fiber coil of 500 m was prepared, and the temperature dependence of crosstalk was investigated. The results are shown by black circles in FIG.

[Table 1] (Comparative Example 1) A panda-type polarization-maintaining optical fiber was prepared according to the specifications shown in Table 2. Using this polarization-maintaining optical fiber core wire, a fiber coil of 500 m was prepared, and the temperature dependence of crosstalk was investigated. The results are shown by white squares in FIG.

[Table 2] From the results of FIG. 3, it is confirmed that the polarization-maintaining optical fiber core wire obtained in Example 1 has improved temperature characteristics as compared with the polarization-maintaining optical fiber core wire obtained in Comparative Example 1. Was given.

Example 2 A panda-type polarization-maintaining optical fiber was prepared according to the specifications shown in Table 3. This polarization-maintaining optical fiber core is proofed with 1.5%, and then 500
A fiber coil of m was prepared and the temperature dependence of crosstalk was investigated. The results are shown by black circles in FIG.

[Table 3] (Comparative Example 2) A panda-type polarization-maintaining optical fiber was prepared according to the specifications shown in Table 4. A proof of 1.5% was applied to this polarization-maintaining optical fiber core wire, and then a fiber coil of 500 m was prepared, and the temperature dependence of crosstalk was investigated.
The results are shown by white circles in FIG.

[Table 4] From the results of FIG. 4, the polarization-maintaining optical fiber core wire obtained in Example 2 does not deteriorate in temperature characteristics after the proof test as compared with the polarization-maintaining optical fiber core wire obtained in Comparative Example 2. It was confirmed.

[0015]

As described above, the polarization-maintaining optical fiber core wire of the present invention is obtained by coating the bare polarization-maintaining optical fiber with the cushion layer, the adhesive layer, and the protective layer in this order. Since the cushion layer is made of a material having a small coefficient of thermal expansion and a high Young's modulus even at low temperatures, the effect of suppressing the occurrence of microbending caused by the contraction of the coating of the polarization-maintaining optical fiber core wire at low temperatures can be obtained. is there. Further, since the protective layer is made of a material having a high Young's modulus, it has the effect of improving the lateral pressure characteristic of the polarization-maintaining optical fiber core and protecting the polarization-maintaining optical fiber core. Since the adhesive layer is made of a material that has a high adhesive strength to the cushion layer and the protective layer, the adhesiveness of both layers is increased, and the polarization-maintaining optical fiber core wire is subjected to a high load such as a proof test. Also, there is an effect of preventing both layers from peeling and degrading the temperature characteristics of the polarization-maintaining optical fiber core wire at a low temperature.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a coating structure for a polarization-maintaining optical fiber according to the present invention.

FIG. 2 is a cross-sectional view showing an example of a conventional polarization-maintaining optical fiber core wire coating structure.

FIG. 3 is a graph showing the temperature dependence of the polarization characteristics of the fiber coil produced using the polarization-maintaining optical fiber core wires obtained in Example 1 and Comparative Example 1.

FIG. 4 shows the polarization-maintaining optical fiber core wires obtained in Example 2 and Comparative Example 2 after undergoing a proof test, and then examined the temperature dependence of the polarization characteristics of the fiber coil produced using them. It is a graph.

[Explanation of symbols]

1 ... Bare optical fiber, 4 ... Cushion layer, 5 ... Adhesive layer,
6 ... Protective layer

Claims (1)

[Claims] 1. A polarization-maintaining optical fiber core wire comprising a bare polarization-maintaining optical fiber, a cushion layer, an adhesive layer, and a protective layer, which are sequentially coated.