JPH05297239A - Method for covering optical fiber with carbon - Google Patents

Abstract

(57) [Abstract] [Purpose] To make it possible to form a carbon hermetic coating film having a very low hydrogen content on the surface of an optical fiber and having a water resistance and a water permeation preventing function. A gas pressure in a container 2 in which the optical fiber 1 is set is set to 1.5 Torr or less, high frequency power is supplied to a hollow electrode 3 of the container 2 to generate a plasma 4 around the optical fiber 1, and the plasma is generated. The mole fraction of the hydrocarbon gas in the mixed gas of hydrocarbon gas and argon in 4 was set to 20% or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for locally forming a carbon hermetic coating film on a fusion splicing portion or an end of an optical fiber.

[0002]

2. Description of the Related Art Optical fiber connector splicing parts and fusion splicing parts are made by removing the coating resin on the outer circumference of the fiber core wire, so that the surface of the fiber core wire can be contacted with various jigs used for connection. Is easily scratched. If there is a flaw on the surface of the fiber core, moisture in the environment penetrates into the flaw and the flaw spreads, resulting in remarkable deterioration of the fiber strength (fatigue phenomenon).
Therefore, it is effective to form a hermetic coating film that does not allow moisture to permeate the surface of the damaged fiber in order to improve the long-term reliability of the fiber strength.

Currently, as a method for forming a hermetic coating film, a method of heating an optical fiber by a carbon dioxide gas laser to form a film by a thermal CVD method and a plasma containing a hermetic raw material around the optical fiber are used. A method of generating and forming a film (plasma CVD method) has been proposed.
In the plasma CVD method, the inside of the container in which the fiber is set is kept in a depressurized state, and high-frequency power is supplied to a hollow cylindrical electrode provided inside the container to generate plasma around the fiber vertically passing through the electrode. Then, a carbon hermetic coating film is formed on the surface of the optical fiber.
As a raw material, a method in which a liquid raw material such as a hydrocarbon-based organic solvent is bubbled with an inert gas such as argon and introduced, or a method in which a hydrocarbon-based gas is diluted with argon and supplied is generally used.

[0004]

In the plasma CVD method, since a film is formed by plasma of a mixed gas of two or more kinds, naturally the film forming state largely changes depending on the mixing ratio of the gases. In terms of the structure of the film, film quality appears in a very wide range from organic polymer film similar to polyethylene to graphite-like carbon film, and macroscopically from powder to oil film. It is considered that this is largely related to the hydrogen content in the film.

In order to have a water resistance and a water permeation preventing function required as a carbon hermetic coating film,
It is desirable that the coating film contains almost no hydrogen,
In that case, hydrogen ions desorbed by electron impact in plasma are recombined, so that it is difficult to form a carbon hermetic coating film having a desired structure. In addition to this, there is a method to prevent recombination of hydrogen by increasing the applied power, but with this method, if the power is too high, the fiber may be overheated and melted down, resulting in a satisfactory effect. Absent.

An object of the present invention is to provide a carbon coating method capable of forming a carbon hermetic coating film having a very low hydrogen content on the surface of an optical fiber and having a water resistance and a water permeation preventing function.

[0007]

The method for coating an optical fiber with carbon according to the present invention keeps the inside of the container 2 in which the optical fiber 1 is set in a depressurized state as shown in FIG.
Is supplied with high frequency power to generate plasma 4 around the optical fiber 1, and a hermetic raw material is supplied into the plasma 4 to form a carbon hermetic coating film on the local surface of the optical fiber 1. In the carbon coating method, the gas pressure in the container 2 is set to 1.5 To.
The mole fraction of the hydrocarbon gas in the mixed gas of the hydrocarbon gas and the argon in the plasma 4 to be generated is 20% or less.

[0008]

In the present invention, the mole fraction of the hydrocarbon gas in the mixed gas of hydrocarbon gas and argon in the generated plasma is set to 20% or less (the ratio of the hydrocarbon-based raw material in the mixed gas is reduced). A carbon coating with a very low hydrogen content can be applied to the optical fiber. Moreover, since the gas pressure in the container 2 is set to 1.5 Torr or less (the gas pressure is lowered), a carbon hermetic coating film having good adhesion is formed on the surface of the optical fiber 1.

[0009]

EXAMPLE As a carbon hermetic coating method for an optical fiber according to the present invention, a carbon hermetic coating film is formed by plasma 4 using a mixed gas of ethylene and argon, using the hermetic coating apparatus shown in FIG. I went. The hermetic coating apparatus shown in FIG. 1 has a chamber 2
The inside of the container 2 is evacuated by a vacuum pump to adjust the degree of vacuum in the container 2 to about 0.0.
The container 2 has a hollow cylindrical electrode 3 arranged therein, and the hollow electrode 3 has an optical fiber 1 vertically extending therethrough.

Then, the high frequency output of the high frequency oscillator 5 in FIG. 1 is set to about 60 W and the frequency is set to 13.56 MHz, and the container 2
The interior is evacuated with a vacuum pump, and the vacuum density of the mixed gas is adjusted to about 0.
It was set to 3 Torr. Ethylene was used as a hermetic raw material. The hermetic raw material may be methane, acetylene or the like as long as it is a hydrocarbon-based raw material although the film forming rate is different. The gas pressure (vacuum degree) is 1.5 Torr.
Is the upper limit, and above this range, a carbon hermetic coating film having good adhesion is not formed even if the gas mixing ratio is changed.

As a sample, a carbon-coated optical fiber for communication (fiber diameter 125 μm, carbon film thickness 1000)
Å, the resin coating diameter is 250 μm), the resin coating layer of the optical fiber 1 is removed, the removed portion is cut, and the cut end faces of the two cut fibers are abutted and fused by arc discharge. Connected Carbon is peeled off from the fusion spliced part by arc discharge for about 3 mm. The fiber 1 is pierced (set) so as to be located in the center of the cylindrical electrode 3 having an inner diameter of about 10 mm and a height of about 10 mm, the film formation time is set to about 60 seconds, and the high frequency oscillator 5 to the matching circuit 6 are set.
A high frequency voltage is applied to the hollow electrode 3 through the plasma to generate plasma 4 around the optical fiber 1, and a hermetic raw material is supplied into the plasma 4. Recoated.

When the prepared sample was observed with an electron microscope, the thickness of the carbon hermetic coating film recoated on the fusion spliced portion was 500 to 800 Å. The surface of the coating film was smooth with almost no irregularities.

The sample prepared in this way is heated to 80 ° C.
It was immersed in warm water for 100 hours and the breaking strength was examined at 5 levels of tensile speed, and the dynamic fatigue characteristics were examined. As a result, the fatigue coefficient n was 100 or more, and It was found that almost completely prevented the permeation of water.

[0014]

[Comparative Example] As a comparative example, eight samples were prepared and examined in a mole fraction of the hydrocarbon raw material in the range of 10% to 80%. The tensile test was not carried out on the sample having a raw material ratio of 80% because the carbon hermetic coating film was peeled off during immersion in warm water. The results of this experiment are shown in Table 1.

In a sample having a mole fraction of 40% or less, the fatigue coefficient n value is about 100 or more, and it can be seen that the carbon hermetic coating film recoated on the connection portion almost completely prevents moisture permeation.

Further, the sample having a mole fraction of 45% or more has a fatigue coefficient n value of about 20 to 50, which cannot prevent the permeation of water and is considered to have caused fatigue.

[0017]

[Table 1]

[0018]

The carbon fiber coating method of the present invention has the following effects. A carbon hermetic coating film having an extremely low hydrogen content can be applied to the surface of the optical fiber 1, and it has a water resistance and a water permeation preventing function required for the carbon hermetic coating film. A carbon hermetic coating film having good adhesion can be formed on the surface of the optical fiber 1.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a carbon coating method for an optical fiber according to the present invention.

[Explanation of symbols]

 1 Optical fiber 2 Container 3 Hollow electrode 4 Plasma

Claims (1)

[Claims] 1. A container 2 in which an optical fiber 1 is set is kept in a depressurized state, and high frequency power is supplied to a hollow electrode 3 in the container 2 to generate plasma 4 around the optical fiber 1.
In the carbon fiber coating method for forming a carbon hermetic coating film on the local surface of the optical fiber 1 by supplying the hermetic raw material into the plasma 4, the gas pressure in the container 2 is set to 1. Less than 5 Torr,
A carbon coating method for an optical fiber, characterized in that the mole fraction of the hydrocarbon gas in the mixed gas of the hydrocarbon gas and the argon in the plasma 4 to be generated is 20% or less.