JP3132866B2 - Recoating method of carbon coated optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recoating carbon on a portion of a carbon coated optical fiber where bare optical fibers are exposed.

[0002]

2. Description of the Related Art In general, an optical fiber in which a bare silica glass optical fiber is coated with an organic material such as a synthetic resin is used. The coating with this organic material causes dust in the external environment to be attached to the bare optical fiber made of glass,
This is intended to prevent the occurrence of scratches due to collision of dust or foreign matter, etc., thereby reducing the breaking strength of the optical fiber. However, this coating with an organic material cannot prevent water vapor in the external environment or hydrogen molecules having smaller molecules from diffusing into the bare optical fiber. If moisture adheres to the optical fiber while stress is applied, a fatigue phenomenon occurs,
The mechanical strength decreases over time. In addition, the diffusion of hydrogen into the glass of the bare optical fiber causes an increase in absorption loss due to molecular vibration of hydrogen molecules, and the P ₂ O ₅ and GeO ₂ contained as dopants in the optical fiber. , B ₂
There is a problem that an OH group is generated by reacting with O ₃ or the like, and absorption loss due to the OH group increases.

In order to solve such a problem, as shown in FIG. 3, a surface of a bare silica glass optical fiber 1 comprising a core 1a and a clad 1b is several hundreds to 1,000 degrees.
A carbon-coated optical fiber 4 in which a carbon-coated layer 2 having a thickness of 2 mm is formed and a resin coating layer 3 made of an organic material is further formed thereon has been proposed.

[0004] By the way, long-distance transmission of optical communication has been demanded, and a long optical fiber has been decided. However, the length of the optical fiber is finite. 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. In general, as a permanent connection, a fusion splicing method is used in which optical fibers are butted together in an arc discharge and fused and connected. .

[0005]

However, in order to apply the fusion splicing method to the carbon-coated optical fiber 4, the resin coating layer 3 at the end of the carbon-coated optical fiber 4 is removed, and the ends are joined together. The carbon coat layer 2 burns and disappears in the process of being heated by the arc discharge, and the bare optical fiber 1 is exposed at the connection portion. Also, an optical fiber core 1a
It is necessary to peel the carbon coat layer 2 to some extent in order to adjust the center. Since the bare optical fiber 1 exposed at the time of heat fusion is sufficiently heated, moisture in the external environment easily adheres. If moisture adheres to the bare optical fiber 1 or is exposed to a hydrogen atmosphere, there is a possibility that the breaking strength is reduced at the connection portion or the transmission loss is increased.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method of recoating carbon on a portion where an optical fiber bare wire is exposed by heat fusion or the like.

[0007]

According to a method of recoating a carbon-coated optical fiber according to the present invention, a heating element is arranged near a recoating portion, and the heating element is heated by a radiant heat source in a carbon-containing source gas atmosphere. Thus, the carbon-containing raw material gas is decomposed on the surface of the heating element, and carbon is deposited on a recoating portion near the heating element as a means for solving the above problem.

[0008]

According to the method of recoating a carbon-coated optical fiber of the present invention, a heating element is heated under a carbon-containing source gas atmosphere using a radiation type heat source, thereby thermally decomposing the source gas on the heating element, By disposing the recoated portion of the fiber near the high temperature portion of the heating element, pyrolytic carbon is deposited on the surface of the optical fiber at the recoated portion. As the radiation type heat source, an infrared lamp, a carbon dioxide laser, or the like can be used. When an infrared lamp is used, a large-scale device is not required and the operation can be performed relatively easily. When the heating element is heated by using an infrared lamp, the area of the focal point can be adjusted to a desired size depending on the size of the recoat portion.
When a laser beam or the like is used, a desired range can be heated by traversing the heating element and the recoating portion by an arbitrary method. Further, a heat-resistant ceramic plate, an aluminum oxide plate, or the like can be used as the heating element.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. FIG. 1 is a schematic configuration diagram of an apparatus suitably used for carrying out the recoating method of the present invention. This device is an infrared focusing furnace 6
And a reaction vessel 9. FIGS. 2A and 2B are perspective views of the reaction container 9, in which FIG. 2A shows the main body 9a and FIG. 2B shows the lid 9b.

The infrared ray condensing furnace 6 has a hollow shape with a bottom and is provided with an infrared lamp 5 at the center of the bottom, and its inner wall is formed of an infrared reflecting material. The infrared condensing furnace 6 is arranged so as to open toward the reaction vessel 9. The infrared rays 7 emitted from the infrared lamp 5 are reflected and condensed on the inner wall of the condensing furnace 6 and irradiated on the reaction vessel 9.
The peripheral wall of the infrared ray condensing furnace 6 has a double structure, and is provided with two cooling pipes 8, 8 communicating with the hollow layers of the inner and outer walls and the outside. The cooling pipes 8, 8 are suitably provided at substantially opposite positions on the outer wall. By passing water from one cooling pipe 8 through the hollow layer of the peripheral wall to the other cooling pipe 8, the infrared condensing furnace 6 The surrounding wall can be cooled.

The reaction vessel 9 comprises a hollow main body 9a having an open top and a lid 9b fitted into the opening of the main body 9a. A window 9c for transmitting infrared rays is provided at the center of the lid 9b. ing. A heating element 10 is provided below the window 9c. Infrared ray 7 collected by infrared ray condensing furnace 6
Is irradiated on the heating element 10 through the window 9c. Here, the window 9c for infrared transmission is preferably made of quartz. The carbon-coated optical fiber 4 is disposed through the reaction vessel 9 such that the recoating portion 13 is located between the window 9 c and the heating element 10 and near the heating element 10. 9a and lid 9b
Is fixed in a groove 9d formed in the peripheral portion of the.

The reaction vessel 9 is provided with a gas supply pipe 11 for supplying an inert gas and a carbon-containing raw material gas, and an exhaust pipe 12. The gas supply pipe 11 has a nozzle at the tip thereof, which is a heating element 10 and a recoating portion 13.
Is provided in the vicinity of. Here, as a method of setting the periphery of the heating element 10 to a raw material gas atmosphere, the reaction vessel 9 may be airtight and the inside of the reaction vessel 9 may be replaced with the raw material gas. By doing so, it is possible to easily and efficiently obtain the required source gas concentration by making the periphery of the recoating portion 13 locally in an oxygen-free state. Also, the recoat part 13
By injecting the source gas into the recoat portion 13
And its surroundings are air-cooled and reheated during the heating process.
It is possible to prevent the carbon coat layer 2 other than 3 from burning. Alternatively, at any position, the recoating site 13
An air cooling pipe for injecting a cooling gas to cool the air by cooling air may be provided in the vicinity of the cooling gas.

In order to recoat carbon on the portion 13 where the bare optical fiber 1 is exposed by using this apparatus, first, the carbon coated optical fiber 4 is fixed to the groove 9 d of the reaction vessel 9. At this time, the recoat portion 13 is located at the window 9c of the reaction vessel 9.
And the heating element 10 and in the vicinity of the nozzle of the gas supply pipe 11. Next, the inert gas is supplied from the gas supply pipe 11 and the exhaust gas is exhausted from the exhaust pipe 12 to expel the air in the reaction vessel 9. At this time, in order to prevent the carbon-containing raw material gas from burning in the subsequent heating process, the oxygen concentration in the reaction vessel is preferably set to 2000 ppm or less. The inert gas used here is N 2
₂ , Ar, He or the like can be used.

Subsequently, a carbon-containing raw material gas is supplied from a gas supply pipe 11 in a bubbling manner and injected to the heating element 10 and the recoating portion 13. Here, as the carbon-containing source gas, for example, hydrocarbon compounds such as acetylene, ethylene, benzene, and propane, or hydrocarbon compounds containing chlorine such as dichloroethane and trichloroethane, and carbon-containing compound gases such as a mixture thereof are used. . As the bubbling gas, for example, N ₂ gas or the like can be used. The supply conditions of the carbon-containing raw material gas are such that the bubble temperature is kept at room temperature (around 25 ° C.) and the flow rate of the bubbling gas is 0.5 to 2 l / l.
min is preferable.

In such a state, the infrared ray 7 is generated from the infrared ray lamp 5, thereby heating the heating element 10. The infrared rays 7 are focused by the infrared ray focusing furnace 6 so as to be focused on the heating element 10 in the reaction vessel 9. At this time,
It is preferable that the focal point of the infrared ray 7 be a circle having at least the same diameter as the width of the recoat portion 13. It is preferable that the surface temperature of the heating element 10 is appropriately selected according to the thermal decomposition temperature of the carbon-containing source gas. The raw material gas is thermally decomposed on the heating element 10 heated to a high temperature in this way, and carbon is deposited on the bare optical fiber 1 at the recoating portion 13 disposed near the high temperature portion. Thus, the carbon coated optical fiber 4 can be recoated with carbon. In addition, by using infrared rays as a heat source, a large-scale apparatus is not required as compared with the case of using a carbon dioxide gas laser. Can be recoated. Further, as the optical fiber to be recoated with carbon by this method, the present invention can be applied not only to a fusion spliced portion of a carbon coated optical fiber, but also to an optical fiber having a locally uncoated portion of carbon.

(Embodiment) Using the above-mentioned apparatus, carbon was recoated on the carbon-coated optical fiber 4 in which the bare optical fiber 1 of the connecting portion was exposed over 10 mm by fusion splicing. Infrared lamp 5 as heat source
(Thermo Riko Co., Ltd. IR-2000) was used, and the heating element 10 was an alumina plate. First, the carbon coated optical fiber 4 was fixed to the reaction vessel 9. At this time, the recoating portion 13 was fixed so as to be located between the window 9c and the heating element 10 and in front of the gas supply pipe 11. Next, N ₂ gas was supplied from the gas supply pipe 11, and the inside of the reaction vessel 9 was purged until the oxygen concentration became 2000 ppm or less. Subsequently, 1,1,1-trichloroethane was supplied from the gas supply pipe 11 by a bubbling method. N ₂ gas was used as the bubbling gas, and the flow rate was 1.0 l / m.
in.

In this state, the infrared lamp 5 is activated to generate the infrared ray 7, and the
The light was focused so as to focus on the alumina plate 10 inside. At this time, the focal point of the infrared ray 7 was a circle with a diameter of about 10 mm, and the surface temperature of the alumina plate 10 was 900 ° C. In this way, carbon could be vapor-deposited on the recoat portion 13. When the static fatigue coefficient of the recoated connection part and the static fatigue coefficient of the part other than the connection part were measured for the obtained carbon-coated optical fiber 4, no difference was observed between the two parts. It was confirmed that the reinforcement was made to have the same strength as that of the carbon-coated part.

[0018]

As described above, in the method for recoating a carbon-coated optical fiber according to the present invention, a heating element is disposed near a recoated portion, and the heating element is heated by a radiant heat source in a carbon-containing source gas atmosphere. By
The carbon-containing raw material gas is decomposed on the surface of the heating element, and carbon is deposited on a recoat portion near the heating element.

Therefore, the exposed portion of the optical fiber, which causes a reduction in the mechanical strength of the carbon coated optical fiber, is eliminated, and a highly reliable carbon coated optical fiber can be obtained. At the time of connection, the joint portion of the carbon coated optical fiber where the bare optical fiber is exposed by heat fusion is reinforced to prevent the mechanical enemy strength from being reduced by fusion splicing and the transmission loss from increasing. be able to.

[Brief description of the drawings]

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

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

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

[Explanation of Signs] 1 ... bare optical fiber, 4 ... carbon coated optical fiber,
5: radiation heat source (infrared lamp), 10: heating element, 11
... gas supply pipe, 13 ... recoat part

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Araki 1440, Mukurosaki, Sakura-shi, Chiba Fujikura Electric Wire Co., Ltd. Inside the Sakura Plant In-plant (72) Inventor Nobuyuki Yoshizawa 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-4-202029 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C03C 25/42 G02B 6/44 301

Claims (1)

(57) [Claims] 1. A method for recoating carbon on a recoated portion of a carbon-coated optical fiber where bare optical fibers are exposed, wherein a heating element is disposed in the vicinity of the recoated portion, and the heating element is placed in a carbon-containing source gas atmosphere. A method for recoating a carbon-coated optical fiber, comprising decomposing a carbon-containing raw material gas on the surface of a heating element by heating with a radiant heat source and depositing carbon on a recoating portion near the heating element.