JPH0664944A - Hermetic coating of optical fiber with carbon - Google Patents

Abstract

PURPOSE:To prevent the damage to the surface of an optical fiber and the lowering of the optical fiber strength by locally coating an optical fiber with a carbon hermetic coating. CONSTITUTION:A plasma 3 is generated around an optical fiber 2 by applying a high-frequency electric power to an electrode 1 and a raw material for hermetic coating is supplied to the plasma 3 to form a hermetic coating film on a part of the optical fiber 2. The high-frequency energy applied to the electrode 1 is varied continuously or stepwise during the formation of the hermetic coating film.

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 Since a connector connecting portion and a fusion splicing portion of an optical fiber are formed by removing a coating resin, the surface is easily scratched by contact with various jigs used for the connection. If there is a flaw on the surface of the fiber, moisture in the environment penetrates into the flaw to spread the flaw, resulting in a remarkable deterioration of the fiber strength (fatigue phenomenon). Therefore, it is effective to form a hermetic coating film that does not allow water to permeate on the surface of the damaged fiber in order to improve the long-term reliability of the strength of the fiber.

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. The present invention relates to the latter of the above two methods.

[0004]

In the past, since the high frequency power applied to the electrodes during film formation was kept constant, the energy of the plasma was also kept constant over time. However, in order to form a carbon film having an amorphous structure containing graphite having an excellent hermetic function,
It is necessary to generate a plasma of considerably high energy. For this reason, there is a tendency that high-energy particles in plasma impact the surface of the optical fiber before the carbon film is formed, and the surface of the optical fiber is damaged by a large number and the fiber strength is significantly reduced. Was given.

An object of the present invention is to provide a method for locally applying a carbon hermetic coating to an optical fiber so that the surface of the optical fiber is not scratched and the strength of the optical fiber is not lowered.

[0006]

In the carbon hermetic coating method for an optical fiber of the present invention, a high frequency power is applied to an electrode 1 to generate a plasma 3 around the optical fiber 2 as shown in FIG. In the method for forming a hermetic coating film on the local surface of the optical fiber 2 by supplying the hermetic raw material into the electrode 3, the high frequency energy supplied to the electrode 1 during the formation of the hermetic coating film is continuously or stepwise. A carbon hermetic coating method for an optical fiber characterized by varying.

[0007]

The carbon hermetic coating method for an optical fiber according to the present invention continuously or stepwise changes the high frequency energy supplied to the electrode 1 during the formation of the hermetic coating film, so that plasma is applied to the surface of the optical fiber. If the plasma energy is lowered at the initial stage of film formation where the film is directly touched, the surface of the optical fiber 2 is impacted by the energetic particles in the plasma even when a carbon film having an amorphous structure containing graphite having an excellent hermetic function is formed. It becomes difficult to scratch the surface of the optical fiber 2. If the energy of plasma is increased after the carbon film is formed to a certain thickness, the carbon film already formed prevents the energy particles in the plasma from impacting the optical fiber 2. A carbon film excellent in hermetic function is formed without lowering the strength of the carbon.

[0008]

FIG. 1 shows the structure of a hermetic coating apparatus using a plasma CVD method as an example of a carbon hermetic coating method for optical fibers according to the present invention. The inside of the chamber 5 is evacuated by a vacuum pump so that the degree of vacuum inside the chamber 5 can be set to about 0.01 to 5 Torr. A hollow cylindrical electrode 1 is arranged in the chamber 5, and a fiber 2 is arranged so as to vertically penetrate the electrode 1.

Benzene, toluene and xylene were used as hermetic raw materials. Although there is a difference in film forming rate, any hydrocarbon-based raw material can be used. In addition, before supplying the raw material, A at 20 W, 0.8 Torr for about 1 minute
The surface of the optical fiber 2 was treated with r plasma.

A study was conducted using a carbon-coated optical fiber for communication (fiber diameter 125 μm, carbon film thickness 400 Å, UV resin coating diameter 250 μm). The fiber end surface from which the UV resin was removed was cut, and two fibers were fusion-spliced by arc discharge. Carbon was peeled off from the fusion-bonded portion by about 10 mm due to arc discharge. Figure 1
It is set in the chamber 5 of, and the inner diameter is about 10 mm and the height is about 1
Plasma CVD using 5 mm hollow cylindrical electrode 1
A carbon hermetic film was recoated on the fusion-bonded portion by a method.

In this case, the film formation time was set to 20 seconds, and a high frequency voltage was applied to the electrode 1 through a high frequency oscillator empty matching circuit. In this case, the applied voltage was set to 20 W for about 3 seconds after the start of application, and 120 W for 17 seconds thereafter. When the sample manufactured in this manner was observed with an electron microscope, the thickness of the carbon layer was 300 to 5 for both the first layer and the second layer.
It was 00Å.

The outer periphery of the sample produced as described above was coated again with UV resin to obtain strain rates of 0.5, 2, 5, and 2.
As a result of examining the tensile breaking strength at 0,50% / min and n = 9, the 50% value of the strength at 0.5% / min was 2.9 kg.
The fatigue coefficient n value was 150.

By changing the power variation pattern, 20 W
Change continuously up to ~ 120W, then 1 at 120W
20W → 40W → 60W → 100W even after holding for 5 seconds
Even if the value was changed to 120 W in 3 second increments, although there was a difference in the film thickness, a recoat film excellent in fatigue characteristics could be formed while suppressing the decrease in strength.

As Comparative Example 1, the voltage applied to the electrode 1 was 1
The film was formed for 20 seconds with a constant power of 20W. As a result of conducting a tensile test on this optical fiber in the same manner as described above and examining the breaking strength, the breaking strength was about 1.2 kg, and a clear strength deterioration was observed. However, the fatigue coefficient n
The value is 140, which is a good value.

As Comparative Example 2, the voltage applied to the electrode 1 was 20 W from the beginning to the end. The breaking strength at this time was 2.3 kg, but since the film was formed with low power, the fatigue coefficient n value was 20 and it was found that it did not have a sufficient hermetic function.

[0016]

As described above, according to the present invention, the electrode 1
Since the high-frequency power applied to the film is changed during film formation, the surface of the optical fiber 2 is not damaged by the high-energy particles in the plasma during film formation, and the strength of the carbon coated portion does not decrease.

[Brief description of drawings]

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

[Explanation of symbols]

 1 electrode 2 optical fiber 3 plasma

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunio Ogura Kunio Ogura 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Nobuyuki Yoshizawa 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A hermetic coating film on a local surface of an optical fiber 2 by applying a high frequency power to an electrode 1 to generate a plasma 3 around the optical fiber 2 and supplying a hermetic raw material into the plasma 3. A carbon hermetic coating method for an optical fiber, wherein the high frequency energy supplied to the electrode 1 is continuously or stepwise changed during the formation of the hermetic coating film.