JPH05270867A - Recoating method for optical fiber coated with carbon - Google Patents

Abstract

PURPOSE:To subject the part of the optical fiber coated with carbon where the bare fiber is exposed by heating and fusing of the fiber to recoating with the carbon. CONSTITUTION:Carbon-contg. gaseous raw materials are injected to the recoating section of the optical fiber 4 coated with carbon. The recoating part is heated by irradiating the part plural times with a CO2 laser beam 6. As a result, the exposed part of the optical fiber to be the cause for decreasing the mechanical strength of the optical fiber coated carbon and increasing the transmission loss and the strain in the juncture generated after fusion splicing by an arc discharge are decreased and the optical fiber coated with carbon having high reliability is obtd.

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 a bare optical fiber is exposed.

[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 of this organic material is applied to the bare optical fiber made of glass, dust in the external environment,
The purpose is to prevent dust or foreign matter from colliding with each other and causing scratches to reduce the breaking strength of the optical fiber. However, the coating with the organic material cannot prevent diffusion of water vapor in the external environment and hydrogen molecules having smaller molecules into the bare optical fiber. And if water adheres to the optical fiber under stress, a fatigue phenomenon occurs,
Mechanical strength decreases over time. Further, due to the diffusion of hydrogen into the glass of the bare optical 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, several 100 to 1000 Å is formed on the surface of the bare silica glass optical fiber 1 comprising a core 1a and a clad 1b.
There has been proposed a carbon-coated optical fiber 4 in which a carbon-coated layer 2 having a thickness of 1 is formed and a resin-coated layer 3 made of an organic material is further formed thereon.

By the way, with the demand for long distance transmission in optical communication, a long optical fiber is indecisable, but 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. ..

[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 thereof are joined together. Although they are abutted and fused by arc discharge, the carbon coat layer 2 burns and disappears in the process of being heated by this discharge, and the bare optical fiber 1 is exposed at the connection portion. Also, the optical fiber core 1a
It is necessary to remove the carbon coat layer 2 to some extent in order to align it. Since the bare optical fiber 1 exposed during the heat fusion is sufficiently heated in this manner, moisture in the external environment is likely to adhere to it. If moisture adheres to the bare optical fiber 1 or if it is exposed to a hydrogen atmosphere, there is a risk that the breaking strength at the connection portion will decrease, or the transmission loss will increase.

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 for recoating carbon on a portion where a bare optical fiber is exposed by heat fusion or the like.

[0007]

The method for recoating a carbon-coated optical fiber according to the present invention comprises the steps of injecting a carbon-containing raw material gas onto a recoat portion and irradiating the recoat portion with laser light a plurality of times to heat the recoated portion. It was used as a solution to the problem.

[0008]

In the method for recoating a carbon-coated optical fiber according to the present invention, the carbon-containing raw material gas is jetted to the recoat portion, and the laser beam is irradiated a plurality of times to heat the recoated portion to cover the entire surface and inside of the recoated portion. Since almost uniform heat is applied to the surface of the optical fiber at the recoating site, carbon is recoated on the surface of the optical fiber by thermal CVD, and at the same time, the splicing due to the arc discharge anneals the carbon coated optical fiber splicing part inside It is a thing. By directly injecting the carbon-containing raw material gas to the recoat portion, the periphery of the recoat portion can be locally made oxygen-free, and the required raw material gas concentration can be easily obtained. Further, as the laser light, carbon dioxide gas laser light which is an infrared ray can be preferably used.

[0009]

The present invention will be described in detail below. FIG. 1 is a schematic configuration diagram 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 9. FIG. 2 is a perspective view of the reaction container 9, in which (a) is a main body 9a and (b) is a lid 9b.

The carbon dioxide laser beam 6 emitted from the carbon dioxide laser oscillator 5 is incident on the reflecting mirror 7 and the direction thereof is changed. Then, the carbon dioxide laser beam 6 is condensed by the condenser lens 8 to be a beam, which is applied to the reaction vessel 9. To be done. The reaction container 9 is a main body 9a,
It is composed of a lid portion 9b, and a window 9c for transmitting a laser beam is provided at the center of the lid portion 9b. The carbon-coated optical fiber 4 is arranged so as to penetrate the reaction container 9 so that the recoat portion 12 is located below the window 9c, and is fixed in the groove 9d formed in the portion penetrating the reaction container 9. .. Further, the reaction vessel 9 is provided with a gas supply pipe 10 for supplying an inert gas and a carbon-containing raw material gas to the recoat portion 12, and an exhaust pipe 11. The gas supply pipe 10 is provided so that the nozzle at the tip thereof is located in the vicinity of the recoat portion 12 of the carbon-coated optical fiber 4 fixed to the reaction container 9. Further, in this device, a condenser lens 8 and a window 9 for transmitting a laser beam are provided.
c is preferably made of ZnSe.

In order to recoat carbon on the exposed portion 12 of the optical fiber bare wire 1 of the connection portion by fusion splicing using such an apparatus, first, the carbon coated optical fiber 4 is fixed in the groove 9d of the reaction vessel 9. To do. At this time, the recoat portion 12 is arranged below the window 9c of the reaction container 9 and in front of the nozzle of the gas supply pipe 10. Next, while supplying the inert gas from the gas supply pipe 10, the gas is exhausted from the exhaust pipe 11 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 9 is set to 2000 pp.
It is preferably m or less. Further, as the inert gas used here, N ₂ , Ar, He or the like can be used.

Then, a carbon-containing raw material gas is supplied from the gas supply pipe 10 by a bubbling method and injected into the recoat portion 12. Here, as the carbon-containing raw material gas, for example, a hydrocarbon compound such as acetylene, ethylene, benzene, propane, or a hydrocarbon compound containing chlorine such as dichloroethane or trichloroethane, and a carbon-containing compound gas such as a mixture thereof are used. .. Moreover, as the bubbling gas, for example, N ₂ gas or the like can be used. The conditions for supplying the carbon-containing raw material gas are preferably 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 / min.

In this state, the carbon dioxide gas laser beam 6 is used to heat the recoat portion 12. A carbon dioxide gas laser beam 6 is generated from an oscillator 5, and a reflecting mirror 7 and a condenser lens 8 are arranged so that the laser beam 6 is focused on the recoat portion 12 in the reaction container 9. Here, recoat part 1
It is preferable that the heating temperature of 2 is appropriately selected according to the thermal decomposition temperature of the carbon-containing raw material gas. Then, laser light 6
The reaction container 9 is traversed a plurality of times in the longitudinal direction of the carbon-coated optical fiber 4 so that the heat generated by the irradiation of (2) is spread over the entire surface and inside of the recoating portion 12. The traverse speed is preferably 5 mm / min or less, the number of traverses is preferably about 2 to 8 and the interval between traverses is preferably about 10 seconds.

In this way, the carbon dioxide laser beam 6 is gradually irradiated from one end to the other end of the recoat portion 12, and this is repeated a plurality of times, whereby the recoat portion 12 is regenerated.
Almost uniform heat is applied to the entire surface and inside of the carbonaceous material, and thermal CVD is performed on the surface of the recoating portion 12 so that carbon can be recoated on the surface of the recoating portion 12 and, at the same time, the internal connection of the distortion due to the fusion splicing by the arc discharge. The resulting recoat site 12 can be annealed. Further, the optical fiber to be recoated with carbon by this method can be applied not only to the fusion spliced portion of the carbon coated optical fiber, but also to an optical fiber having a portion where carbon is not locally coated.

(Example) Using the above apparatus, carbon was recoated on the carbon-coated optical fiber 4 in which the bare optical fiber 1 at the connection portion was exposed by fusion splicing. Waveguide CO with built-in RF power source as heat source
₂ lasers 5 (Kinmon 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 9. At this time, the recoating portion 12 was fixed so as to be located below the window 9c and in front of the gas supply pipe 10. Next, N ₂ gas was supplied from the gas supply pipe 10 and exhaust was performed from the exhaust pipe 11 to reduce the oxygen concentration in the reaction vessel 9 to 2000 ppm or less. Then, the gas supply pipe 1
Dichloroethane was sprayed onto the recoat site 12 from 0 by a bubbling method. N ₂ gas was used as the bubbling gas, and the flow rate was 1.0 l / min.

In this state, the carbon dioxide laser oscillator 5 was activated to generate the carbon dioxide laser light 6. The laser beam 6 was reflected by a reflecting mirror 7 and focused by a ZnSe condenser lens 8 on a recoat portion 12 in a reaction vessel 9 so as to be focused. Then, the traverse with the reaction vessel 9 at a speed of 3 mm / min in the longitudinal direction of the carbon-coated optical fiber 4 and at intervals of about 10 seconds for each traverse is performed about 4 times, and the laser beam 6 is applied over the entire area of the recoat portion 12. Irradiation was performed and the temperature of the surface and inside of this area was about 9
It heated so that it might be set to 00 degreeC.

In this way, the surface of the recoated portion 12 was recoated with carbon, and the recoated portion 12 having internal strain due to fusion splicing by arc discharge could be annealed. With respect to the obtained carbon-coated optical fiber 4, when the static fatigue coefficient of the recoated and annealed recoated portion 12 and the static fatigue coefficient of the portion other than the recoated portion 12 were measured, no difference was observed between the two. It was confirmed that the recoated portion 12 was reinforced to the same strength as other carbon coated portions.

[0018]

As described above, the method for recoating a carbon-coated optical fiber of the present invention is to inject a carbon-containing raw material gas to the recoating site and irradiate the recoating site with laser light a plurality of times to heat the recoating site. is there.

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. Then, at the time of connection, reinforcing the splicing portion of the carbon-coated optical fiber where the bare optical fiber is exposed by fusion splicing, and annealing the splicing portion internally generated by fusion splicing by arc discharge to distort the strain. By reducing the amount, it is possible to prevent the mechanical strength from decreasing and the transmission loss from increasing. Further, since the radiation type heat source can locally heat the recoated portion of the optical fiber, the carbon coated layer and the optical fiber other than this portion can be recoated without damage. Further, by injecting the carbon-containing raw material gas to the recoat site, the periphery of the recoat site is locally anoxic,
The required source gas concentration can be easily adjusted, and recoating can be performed efficiently.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus preferably used in a 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]

1 ... Bare optical fiber, 4 ... Carbon coated optical fiber,
5 ... Laser light oscillator (carbon dioxide laser oscillator), 10 ...
Gas supply pipe, 12 ... Recoat part

Front page continuation (72) Inventor Shinji Araki 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Electric Wire Co., Ltd. Sakura Factory

Claims (1)

[Claims] 1. A method for recoating carbon on a portion of a carbon-coated optical fiber where an bare optical fiber is exposed, which comprises injecting a carbon-containing source gas onto the recoated portion and irradiating the recoated portion with laser light a plurality of times. And a method of recoating a carbon-coated optical fiber, which comprises heating.