JPH05246740A - Method for recoating exposed quartz fiber part of carbon-coated optical fiber with carbon film - Google Patents

Abstract

PURPOSE:To obtain a highly reliable carbon-coated optical fiber by eliminating the exposed part of an optical fiber causing the lowering of the mechanical strength of a carbon-coated optical fiber or an increase in transmission loss, previously removing the moisture adsorbed on the surface of an uncoated quartz fiber by gaseous chlorine and preventing the lowering of strength due to the silanol formed in the course of heating to remove moisture and a decrease in the fatigue characteristic by stress corrosion due to the moisture present on the surface of the uncoated quartz fiber. CONSTITUTION:The exposed part 10 of a quartz fiber at the welded junction of a carbon-coated optical fiber 4 having a carbon-film coating on the surface is recoated with a carbon film. In this case, the exposed part 10 is brought into contact with a chlorine-contg. gas and heated before being recoated with the carbon film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of recoating a carbon film on a portion of a carbon-coated optical fiber where a bare silica fiber is exposed. The present invention relates to a method of locally re-coating the exposed portion of the quartz fiber with a carbon film after removing water.

[0002]

2. Description of the Related Art Generally, as an optical fiber, a silica glass-based bare optical fiber coated with an organic material such as synthetic resin is used. The coating with the organic material is intended to prevent the breakage of the optical fiber from being lowered due to scratches caused by collision of dust, dust or foreign matter in the external environment with the above-mentioned bare silica fiber. However,
With this organic material coating, water vapor in the external environment,
Furthermore, it is not possible to prevent the diffusion of hydrogen molecules having small molecules into the bare silica fiber. When moisture adheres to the optical fiber under stress, a fatigue phenomenon occurs and mechanical strength decreases over time. Further, due to the diffusion of hydrogen into the glass of the bare silica fiber, the absorption loss due to the molecular vibration of hydrogen molecules increases, or P ₂ O ₅ and GeO ₂ contained as a dopant in the optical fiber. , B ₂
There is a problem that OH groups are generated by reacting with O ₃ etc., and absorption loss due to the OH groups increases.

In order to solve such a problem, as shown in FIG. 3, a carbon film 2 having a thickness of several 100 to 1000 angstroms is formed on the surface of a quartz fiber bare wire 1 composed of a core 1a and a clad 1b. Furthermore, a carbon-coated optical fiber 4 having a resin film 3 made of an organic material formed thereon has been proposed.

With the demand for long-distance transmission in optical communication, a long optical fiber is indispensable. However, the length of the optical fiber is finite, and when laying this, a finite length is required. Optical fiber must be connected and used. As such a connection method, there are various methods such as a connector method and a fusion splicing method. Generally, as a permanent connection, a fusion splicing method in which optical fibers are butted and melted in an arc discharge to be connected is used. ..

In order to apply the above fusion splicing method to the carbon-coated optical fiber 4, this carbon-coated optical fiber 4 is used.
The resin film 3 at the end of the is removed, and the ends are brought into contact with each other and fused by arc discharge, but the carbon film 2 burns and disappears in the process of being heated by this discharge, and the quartz is fused at the fused joint. The bare fiber 1 is exposed. Further, in order to align the core 1a of the optical fiber, it is necessary to remove the carbon film 2 to some extent.

As described above, the portion of the bare silica fiber 1 exposed during the heat fusion as described above increases the fatigue phenomenon associated with the diffusion of water vapor into the silica fiber and the absorption loss associated with the diffusion of hydrogen molecules. May occur. In addition, when the fusion splicing is performed, carbon dust is generated by burning carbon film, which may damage the bare silica fiber 1. Further, during heat fusion, the optical fiber is sufficiently heated, so that moisture in the external environment is likely to adhere. If moisture adheres to the bare silica fiber 1 or if it is exposed to a hydrogen atmosphere, there is a problem that the breaking strength at the connection portion is reduced, or the transmission loss is increased.

In order to solve the above-mentioned problems, a method has been proposed in which the exposed portion of the carbon-coated optical fiber quartz fiber is newly coated with a carbon film by thermal CVD in a heating furnace, plasma CVD, or a flame of a carbon-containing gas. (Japanese Patent Laid-Open No. 2-87106).

[0008]

However, with the above-mentioned carbon film recoating method, it is difficult to recoat the carbon film only on the exposed portion of the quartz fiber having a width of only about 5 mm. In addition, the heat of recoating damages the optical fiber, resulting in new problems such as a decrease in optical fiber strength and a decrease in fatigue characteristics.

It is considered that such a decrease in the strength and the fatigue property of the optical fiber is due to the water adsorbed on the exposed surface of the bare silica fiber before the exposed portion of the silica fiber is recoated with the carbon film. That is, it is considered that the decrease in the strength of the optical fiber is caused by the formation of silanol when the surface of the bare silica fiber that is adsorbed with water is reheated, and the silanol grows a small scratch on the surface of the bare silica fiber. In addition, the deterioration of the fatigue characteristics of the optical fiber is due to the fact that the water adsorbed on the fiber surface before re-coating the carbon film is inherent even after the carbon film re-coating.
It is considered that this intrinsic moisture promotes stress corrosion. From the above, in order to improve the strength and fatigue characteristics of the fusion spliced portion, it is necessary to sufficiently remove the moisture adsorbed on the surface of the quartz fiber before recoating the carbon film.

The present invention has been made in view of the above circumstances, and after performing a pretreatment for removing adsorbed moisture on the surface of the exposed portion of the quartz fiber of the carbon-coated optical fiber, the carbon film is locally applied to the exposed portion of the quartz fiber. The present invention provides a method for recoating the same.

[0011]

According to the method of recoating a carbon film of the present invention, the exposed portion of the quartz fiber, which is the recoated portion, is subjected to a pretreatment of heating while contacting a chlorine-containing gas, and then the quartz fiber Recoating the exposed portion with the carbon film was taken as a means for solving the above problems.

[0012]

According to the present invention, prior to the re-coating treatment, the chlorine-containing gas is brought into contact with the exposed portion of the quartz fiber, which is the re-coated portion, to heat it, thereby removing the moisture adhering to the surface of the quartz fiber. it can.

[0013]

The present invention will be described in detail below. FIG. 1 is a schematic configuration diagram showing an example of an apparatus preferably used for carrying out the recoating method of the present invention. This apparatus is roughly composed of a carbon dioxide laser oscillator 5 and a reaction vessel 6.
2A and 2B are perspective views of the reaction container 6, wherein FIG. 2A is a reaction container body 6a and FIG. 2B is a reaction container lid portion 6b.

The carbon dioxide laser light 7 emitted from the carbon dioxide laser oscillator 5 impinges on the reflecting mirror 8 to change its direction, and then is condensed by the condenser lens 9 to be a beam, which is applied to the reaction vessel 6. The reaction container 6 includes a main body 6a and a lid 6
A window 6c for transmitting a laser beam is provided at the center of the lid 6b. Carbon coated optical fiber 4
Is disposed so as to penetrate the reaction vessel 6 so that the recoating portion 10 is located below the window 6c, and is fixed in a groove 6d formed in a portion penetrating the reaction vessel 6. Further, the reaction vessel 6 is provided with a raw material supply pipe 11 for supplying a carbon-containing raw material gas to the recoating portion 10, a chlorine gas supply pipe 12 for supplying chlorine gas, and an exhaust pipe 13. The raw material supply pipe 11 is provided so that the nozzle at the tip thereof is located in the vicinity of the recoating portion 10 of the carbon-coated optical fiber 4 fixed to the reaction vessel 6.
Further, in this apparatus, the condenser lens 9 and the window 6c for transmitting the laser beam are preferably made of ZnSe. Although an example of an apparatus using carbon dioxide gas laser light as a radiation type heat source has been described above, the heat source in the present invention is not limited to carbon dioxide gas laser, and arc discharge, micro heater, laser heating, etc. can be widely used.

To recoat the carbon film on the exposed portion 10 of the bare quartz fiber using this apparatus, first, the carbon-coated optical fiber 4 is fixed in the groove 6d of the reaction vessel 6. At this time, the recoating portion 10 is arranged below the window 6c of the reaction vessel 6 and in front of the nozzle of the chlorine gas supply pipe 12.

Next, a pretreatment for removing the moisture adsorbed on the exposed surface of the bare silica fiber is performed as follows. A chlorine-containing gas typified by chlorine gas is supplied from the chlorine gas supply pipe 12 at a flow rate of 50 to 200 cc / min so that the oxygen concentration in the reaction vessel 5 is 0.5% by volume or less. In such a state, the recoating site 10 is heated using the carbon dioxide laser beam 7. Carbon dioxide gas laser light 7 is generated from the oscillator 5, and this laser light 7 is applied to the recoating site 1 in the reaction vessel 6.
The reflecting mirror 8 and the condenser lens 9 are arranged so as to focus on 0. Here, the laser power and the focus are determined by the recoating portion 10
Adjust the surface temperature of the so that it becomes 500-1000 ℃,
Try to prevent thermal strain on the fiber surface.
Further, the reaction vessel 6 is traversed in the longitudinal direction of the carbon-coated optical fiber 4 so that the irradiation of the laser beam 7 will be applied to the entire area of the recoating portion 10 during heating. The traverse speed is preferably 3 to 9 mm / min.

Subsequently, a carbon film recoating process is performed as follows. After the introduction of chlorine gas is stopped and chlorine gas is discarded from the reaction vessel 6, the carbon-containing compound gas is supplied from the raw material supply pipe 11 to 50 to 200 cc / min, and the nitrogen gas is 40
Supply at a flow rate of 0-1800cc / min. Examples of the carbon-containing compound gas as a raw material here include hydrocarbon compounds such as acetylene, ethylene, benzene, and propane, or chlorine-containing hydrocarbon compounds such as dichloroethane, trichloroethane, and dichloromethane, and mixtures thereof, particularly N ₂ , A mixture with an inert gas such as Ar or He is used, and any of them is preferably a compound having a low decomposition temperature.

After the inside of the reaction vessel 6 is filled with the raw material gas atmosphere, the carbon dioxide laser beam 7 is used to heat the recoating portion 10. A carbon dioxide laser beam 7 is generated from an oscillator 5, and a reflecting mirror 8 and a condenser lens 9 are arranged so that the laser beam 7 is focused on a recoating site 10 in the reaction vessel 6. The heating temperature at this time is preferably appropriately selected according to the thermal decomposition temperature of the carbon-containing raw material gas. Then, at this time, the reaction vessel 6 is traversed in the longitudinal direction of the carbon-coated optical fiber 4 so that the irradiation of the laser beam 7 is spread over the entire area of the recoating portion 10. The speed of this traverse is 3-9 mm / m
It is preferably in. In this way, thermal CVD is carried out at the heated portion, and the carbon film can be recoated there. Further, as the optical fiber whose carbon film is re-coated by this method, not only the quartz fiber exposed part of the fusion splicing part of the carbon-coated optical fiber but also an optical fiber having a part where the carbon film is not locally coated Can also be applied to. The carbon film re-coating method described above is a method of re-coating the carbon film on the surface of the optical fiber at this portion by thermal CVD by injecting the carbon-containing raw material gas and heating it using a radiation type heat source. Is. By directly injecting the carbon-containing raw material gas to the recoating portion, the periphery of the recoating portion can be locally made oxygen-free, and the required raw material gas concentration can be easily obtained.

(Example 1) Using the above-mentioned apparatus, the carbon film was recoated on the carbon-coated optical fiber in which the bare silica fiber of the connection portion was exposed by fusion splicing. Waveguide CO with built-in RF power source as heat source
₂ Laser 5 (Kinmen Denki LM-4 type; maximum output 5W,
A rated output of 4 W and a pulse modulation signal of DC12V) were used.
First, the carbon-coated optical fiber 4 was fixed to the reaction vessel 6. At this time, the recoating portion 10 was fixed so as to be located below the window 6c and in front of the chlorine gas supply pipe 12.

Then, the reaction vessel 6 was closed and chlorine gas was introduced through the chlorine gas supply pipe 12 at a flow rate of 100 ml / min. When the oxygen concentration in the reaction vessel 6 is 2000 ppm or less, start the carbon dioxide laser oscillator 5 and set the output to 1
The carbon dioxide gas laser light 7 was generated by setting to w. The laser light 7 was reflected by a reflecting mirror 8 and condensed by a ZnSe condensing lens 9 so as to be focused on the recoating site 10 in the reaction vessel 6, and the recoating site 10 was heated. Then, the reaction vessel 6 is placed 6 mm / in the longitudinal direction of the carbon-coated optical fiber 4.
It was traversed at a speed of min so that the entire recoating site 10 of about 5 mm width was heated.

After that, the introduction of chlorine gas was stopped, and nitrogen gas containing 10% by volume of dichloroethane was introduced from the raw material supply pipe 11 at a flow rate of 1 liter per minute. At this time, the valve of the exhaust pipe 13 is adjusted so that the inside of the reaction vessel 6 is 1.5 mmH ₂
The pressure of O was adjusted. After the pressure in the reaction vessel 6 became stable, the laser beam 7 was irradiated again with an output of 1 w to move the reaction vessel 6 at a speed of 6 mm / min, and the quartz fiber exposed portion 10 was recoated with the carbon film. Furthermore, a hard material was recoated to a coating diameter of 250 μm on the recoated portion of the carbon film recoated fiber by using a UV resin recoating device,
A carbon-coated optical fiber 4 was obtained. Tensile tests were carried out on each of the obtained fibers at a span length of 100 mm and a strain rate of 100, 10, 1 mm / min. Table 1 shows the fracture strength F ₅₀ and the dynamic fatigue index n at the 50% fracture probability.

Example 2 The same procedure as in Example 1 was carried out except that the carbon compound as the raw material was changed to benzene instead of dichloroethane. (Example 3) The same procedure as in Example 1 was carried out except that the fiber moving speed during the carbon film recoating treatment was changed to 10 mm / min. (Comparative Example 1) The same procedure as in Example 1 was performed, except that chlorine gas was not introduced and heating was not performed before the carbon film recoating treatment. (Comparative Example 2) After fusion splicing of carbon-coated optical fibers,
An optical fiber was prepared by directly re-coating the exposed portion of the quartz fiber with UV resin without introducing chlorine gas, heating, or re-coating the carbon film, and the same tensile test as in Example 1 was performed.

[Table 1] As shown in Table 1, in the optical fibers re-coated with a carbon film after the pretreatment for removing the adsorbed moisture on the surface of the exposed portion of the quartz fiber obtained in Examples 1, 2, and 3, the above pretreatment Comparative Example 1 in which the carbon film was recoated without performing
In comparison with the optical fiber of Comparative Example 2 and the optical fiber of Comparative Example 2 in which the resin film was directly coated without performing both the pretreatment and the carbon film recoating treatment described above, the breaking strength and the dynamic fatigue index were significantly improved. Was given.

[0023]

As described above, according to the carbon film recoating method of the present invention, after the chlorine-containing gas is heated while contacting the exposed portion of the quartz fiber, which is the recoating portion, in advance,
The exposed portion of the quartz fiber is newly coated with a carbon film.

Therefore, it is possible to obtain a carbon-coated optical fiber having high reliability by eliminating the exposed portion of the optical fiber which causes a decrease in the mechanical strength of the carbon-coated optical fiber. At the time of connection, the splicing connection reinforces the spliced portion of the carbon-coated optical fiber where the bare silica fiber is exposed to prevent the fusion splicing from lowering the mechanical strength and increasing the transmission loss. be able to.

Further, a pretreatment of introducing chlorine gas and heating is performed before recoating the carbon film to remove the adsorbed moisture on the exposed surface of the bare quartz fiber, so that the heating process under moisture adsorption is performed. It is possible to prevent the strength from being reduced by the silanol formed in step (4) and the fatigue property from being deteriorated due to the promotion of stress corrosion of the moisture existing on the surface of the bare silica fiber.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus preferably used in a carbon film recoating method of the present invention.

FIG. 2 is a perspective view of a (a) main body and a (b) lid part of a reaction container.

FIG. 3 is a perspective view of a carbon-coated optical fiber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Bare silica fiber, 2 ... Carbon film, 4 ... Carbon coated optical fiber 5 ... Laser oscillator, 7 ... Laser light, 10 ... Recoating site (exposed quartz fiber) 11 ... Raw material supply pipe, 12 ... Chlorine gas supply tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Shimichi 1440 Rokuzaki, Sakura City, Chiba Prefecture, Sakura Factory, Fujikura Cable Co., Ltd. (72) Shinji Araki 1440, Rokuzaki, Sakura City, Chiba Prefecture, Fujikura Cable, Ltd. (72) Inventor Nobuyuki Yoshizawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A quartz fiber exposed portion of a carbon-coated optical fiber having a carbon film coating on the surface of the optical fiber,
In the method of re-coating the carbon film, the exposed portion of the quartz fiber is heated while contacting chlorine-containing gas in advance, and then the exposed portion of the quartz fiber is coated with a new carbon film. Carbon film recoating method.