JPH0337139A - Production of optical fiber and carbon coater - Google Patents

Abstract

PURPOSE:To enable stable production of optical fiber coated with carbon coating film by feeding an oxygen-containing gas from the bottom of the reaction tube to remove soot on the inner wall of the reactor by combustion, when carbon thin film is formed on the surface of a bare optical fiber by passing a bare optical fiber through the cylindrical reaction tube and feeding a starting gas forming carbon by decomposition to form a carbon thin film on the surface of the optical fiber. CONSTITUTION:A glass bare line for optical fiber 11 is passed through a cylindrical reaction tube 12 downward from the tube top to the bottom, while a hydrocarbon gas which forms carbon by pyrolysis is fed from the pipe 14. The hydrocarbon gas from the feeding pipe 14 is pyrolyzed in the reaction tube 12 with the heat from the heater 10 outside the tube and the generated carbon forms carbon coating film on the surface of the optical fiber 11. At this time, excess carbon deposits on the lower part of the reaction tube 12 in the form of soot and clogs the exhaustion pipe 15 and an oxygen-containing gas is fed from the inlet 19 to the lower inlet 20 to burn the soot deposited whereby the exhaustion pipe is prevented from being clogged to continue stable production of optical fibers which is coated with carbon coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing an optical fiber having a carbon coating formed on its surface, and a carbon coating device suitably used to carry out this manufacturing method.

[Prior Art] In general, silica-based optical fibers have the disadvantage that when they come into contact with hydrogen, hydrogen molecules diffuse into the fiber and cause molecular vibration, which increases absorption loss. In addition, P t containing diffused hydrogen molecules as a dopant
Os, Ge0t, B, 0. Since it reacts with the like and is incorporated into the fiber glass as OH groups, it also has the disadvantage that transmission loss increases due to absorption of the OH groups.

In order to eliminate these drawbacks, hydrocarbons or halogenated hydrocarbons, etc. are thermally decomposed to form a carbon film on the surface of the bare end fiber that acts to prevent hydrogen permeation, thereby improving the hydrogen resistance properties of the optical fiber. Improvements have already been proposed by the present inventors.

Figure 3 shows the heat C which is preferably used to carry out the above method.
An example of a VD device is shown below, and the frame number l in FIG.
2 is an optical fiber ridge line, and 2 is a coating device. The bare optical fiber 1 is spun from an optical fiber base material in an optical fiber spinning furnace (not shown), and is introduced into a coating device 2 provided below the optical fiber spinning furnace. The coating device 2 consists of a generally cylindrical reaction tube 3 and a heating element 4 provided on the outer periphery of the reaction tube 3 to thermally decompose the raw material gas. An inert gas or the like is supplied at a constant flow rate to both ends of the reaction tube 3 to keep the internal atmosphere constant.
Atmosphere adjustment chambers 5.5 for discharging are provided, and between these atmosphere adjustment chambers 5.5, a raw material gas supply pipe 6 for supplying a raw material gas consisting of a hydrocarbon compound into the reaction tube 3 and a raw material A cracked gas exhaust pipe 7 for discharging cracked gas generated by thermal decomposition of the gas from the reaction tube 3 together with unreacted raw material gas is connected to each of the pipes.

In order to form a carbon coating on the bare optical fiber l using such a coating device 2, the bare optical fiber l is introduced from the side of the reaction tube 3 where the raw material gas supply pipe 6 is provided, and the central axis of the reaction tube 3 is The raw material gas is transferred along the direction toward the side where the cracked gas exhaust pipe 7 is provided, and the raw material gas is supplied into the reaction tube 3. Next, the heating element 4 is made to generate heat above the decomposition temperature of the raw material gas to thermally decompose the raw material gas, thereby forming a carbon film on the surface of the bare optical fiber 1.

[Problems to be Solved by the Invention] By the way, the above carbon film forming method and coating apparatus have the following disadvantages.

When the reaction tube is made thinner in order to increase the efficiency of carbon deposition onto the bare optical fiber, the soot formed as particles without being deposited on the optical fiber ridge adheres to the inner wall of the reaction tube and accumulates, resulting in a short period of time. This causes the reaction tube to become clogged, making continuous production of carbon-coated optical fibers impossible.

In addition, if the diameter of the reaction tube is increased to prevent blockage of the reaction tube due to soot accumulation, the inner wall of the reaction tube is at a higher temperature and the raw material gas is preferentially decomposed on the inner wall of the reaction tube. The efficiency of carbon deposition on the bare optical fiber passing along the central axis of the tube becomes low. For this reason, in order to generate a film with a specified thickness or more on the surface of a bare optical fiber, it is necessary to increase the concentration of the raw material gas, but this results in a large amount of soot being deposited on the inner wall of the reaction tube, which also increases the diameter of the reaction tube. The reaction tube will become clogged in the same way as when it is small.

Due to such clogging of the reaction tube, it becomes difficult to manufacture a long optical fiber having a uniform carbon coating.

[Means for Solving the Problems] Therefore, in the method for manufacturing an optical fiber according to claim 1 of the present invention, a supply pipe for supplying a raw material gas made of a hydrocarbon compound to one side is connected to a supply pipe for supplying a raw material gas made of a hydrocarbon compound to the other side. A reaction system in which an exhaust pipe for exhausting gas is provided, and a reaction section is formed along the length of the supply pipe and the exhaust pipe to thermally decompose the raw material gas and form a carbon coating. An optical fiber is introduced into the tube from the side where the supply pipe is provided and is transferred toward the side where the exhaust pipe is provided, and the raw material gas is supplied from the supply pipe, and then the raw material gas is thermally decomposed in the reaction section. The above problem was solved by forming a carbon film on the surface of the optical fiber and supplying oxygen-containing gas along the inner wall of the reaction tube on the exhaust pipe side of the reaction section.

The carbon coating device according to claim 2 further includes a reaction tube that forms a carbon coating on the surface of the optical fiber while passing the optical fiber therethrough;
A heating section for heating the inside of the reaction tube, a supply pipe for supplying a raw material gas made of hydrocarbon compounds to one side of the reaction tube, and a supply pipe for exhausting decomposed raw material gas to the other side. A reaction section for thermally decomposing the raw material gas and coating it with carbon is formed along the length direction between the supply pipe and the exhaust pipe, and an exhaust pipe of the reaction section is provided. The solution to the above problem was to provide an oxygen gas supply port on the side of the reactor tube for supplying oxygen-containing gas along the inner wall of the reaction tube.

"Function" The method for manufacturing an optical fiber according to claim 1 of the present invention (according to this, since the gas containing oxygen is supplied along the inner wall of the reaction tube on the exhaust pipe side of the reaction section, the position where oxygen is introduced is The soot that has accumulated on the inner wall of the reaction tube toward the exhaust pipe is burned and exhausted as carbon dioxide.

Furthermore, in the carbon coating apparatus according to claim 2, since an oxygen gas supply port is provided on the exhaust pipe side of the reaction section to supply oxygen-containing gas along the inner wall of the reaction tube, it is possible to supply oxygen. As in the case of claim 1, soot deposited on the inner wall of the reaction tube from the point where oxygen is supplied to the exhaust pipe is burned and exhausted.

[Example] Hereinafter, the present invention will be explained based on the carbon coating apparatus according to claim 2.

FIG. 1 is a diagram showing an embodiment of the carbon coating device of the invention described in claim 2, and frame number 10 in FIG. is a bare optical fiber.

The coating device 11 consists of a generally cylindrical reaction tube 12 and a heat generating source 13 provided on the outer periphery of the reaction tube 12. The reaction tube 12 is provided with an atmosphere adjustment chamber (as shown) on the side into which the bare optical fiber 11 is introduced, for supplying an inert gas at a constant flow rate in order to keep the internal atmosphere of the reaction tube 12 constant. Furthermore, below this atmosphere adjustment chamber, there is a raw material gas supply pipe 14 that supplies raw material gas to the side where the bare optical fiber 11 is introduced, and to the opposite side, a raw material gas supply pipe 14 that supplies decomposed gas of the raw material gas. A cracked gas exhaust pipe 15 for exhausting unreacted raw material gas and the like is connected to each of them.

Further, a heating element 16 is provided on the outer peripheral surface of the reaction tube 12 so as to cover it, and an oxygen gas supply pipe 17 is further inserted into the outer peripheral part of the heating element 16.

The heating element 1G generates heat by the heat generating source 13, and heats the inside of the reaction tube 12 to thermally decompose the raw material gas. In addition, the inside of the reaction tube 12 covered with this heating element 16 decomposes the raw material gas and produces a bare optical fiber.
This serves as a reaction section 18 for forming a carbon film on the surface.

The oxygen gas supply pipe 17 has an introduction pipe 19 for supplying oxygen gas on the side of the raw material gas supply pipe 13 and is closed on the opposite side, and the end 17a on the closed side is connected to the reaction tube. 12 and the heating element 16 to communicate with the inside of the reaction tube 12 via an oxygen gas supply port 20 formed through the heating element 16 . Here, the oxygen gas supply port 20 is arranged below the center position of the heating element t6 (on the cracked gas exhaust pipe i5 side), and preferably at the lower end of the heating element 16 with respect to the length Q of the heating element 16. The distance Q from to the oxygen gas supply port 20 is,
It is arranged so that it becomes 1/3 to 115. In this example, Q is 12. It is said to be about 1/4 of the Further, when the oxygen gas flowing through the oxygen gas supply pipe 17 passes through the oxygen gas supply port 20 and flows into the reaction tube 12, the closed end 17a of the oxygen gas supply pipe 17 The lower side is narrowed so that it flows along the inner wall surface of 12.

The heat source 13 is composed of, for example, an infrared concentrator,
The heating element 16 generates heat, thereby heating the inside of the reaction tube 12 to a temperature higher than the decomposition temperature of the raw material gas. Note that when an infrared condensing furnace is used as the heat generating source 13, a material that does not transmit infrared rays is used as the heating element 16.

The optical fiber ridge line ll is spun from an optical fiber base material by the optical fiber spinning furnace shown in the figure, similar to the optical fiber bare line 1 shown in FIG. 3, and is provided below the optical fiber spinning furnace. It is introduced into the coating apparatus 10 described above.

Next, the formation of a carbon coating on the bare optical fiber 11 using the coating device having such a configuration will be explained based on the method for manufacturing an optical fiber according to claim 1 of the present invention.

First, the bare optical fiber 11 is introduced from the side of the reaction tube 12 where the raw material gas supply pipe 13 is installed, and is transferred along the central axis of the reaction tube 12 toward the side where the cracked gas exhaust pipe 14 is installed. An inert gas is passed through the atmosphere adjustment chamber along the traveling direction of the bare optical fiber 11 to keep the atmosphere inside the reaction tube 12 constant. At the same time, the raw material gas is transferred to the reaction tube 3.
Oxygen gas is supplied to the inlet pipe 19 at a flow rate sufficiently lower than the total flow rate of the inert gas and raw material gas flowing from the atmosphere adjustment chamber. Then, the raw material gas flows in the traveling direction of the bare optical fiber 11 along with the inert gas flowing from the atmosphere adjustment chamber. On the other hand, oxygen gas A travels along the oxygen gas supply pipe 17 to reach its end 17a, changes course, passes through the oxygen gas supply port 20, and flows into the reaction tube 12. In this case, the reaction tube 12
Since the supply amount of the oxygen gas A that has flowed into the reaction tube 12 is set in advance so that it flows into the reaction tube 12 at a flow rate that is sufficiently lower than the total flow rate of the inert gas and the raw material gas, the oxygen gas A that has flowed into the reaction tube 12 is Bare optical fiber 1 moving on the central axis of
1, but flows along the inner wall of the reaction tube 12 toward the cracked gas exhaust pipe 15, as shown by the arrow in FIG.

In this case, hydrocarbons are used as the raw material gas, and specific examples of hydrocarbons include hydrocarbons such as benzene,
Halogenated hydrocarbons such as dichloromethane, and further halogenated carbons in which all hydrogen groups are replaced with halogen groups, are used. Further, the oxygen gas is not limited to pure oxygen, and a mixed gas of oxygen and an inert gas can also be used.

Furthermore, prior to introducing the bare optical fiber 11 and supplying each gas, the heat generating source 13 is activated to cause the heating element 16 to generate heat, and the reaction section 18 in the reaction tube 12 is heated to a temperature higher than the decomposition temperature of the raw material gas. put. Then, carbon generated by the decomposition of the raw material gas in the reaction section 18 gradually adheres and accumulates on the surface of the first bare fiber 1i as the bare optical fiber 11 advances. In this case, even in the reaction section 18 after (below) the oxygen gas supply port 20 into which oxygen gas flows, the oxygen gas does not reach the R side of the bare optical fiber 11 on which carbon is deposited. Since the carbon flows along the inner wall of the reaction tube 12, the above-mentioned carbon deposition on the bare optical fiber 11 continues, and
The reaction between the deposited carbon and oxygen gas is prevented.

As carbon is gradually deposited on the surface of the bare optical fiber 11 in the reaction section 17, the optical fiber led out from the reaction tube 12 has a carbon coating formed on its surface. Thereafter, the carbon coating is further coated with an organic polymer such as an ultraviolet curable resin or nylon, thereby forming a cored optical fiber.

Furthermore, unreacted portions of the cracked gas and raw material gas are discharged from the cracked gas exhaust pipe 15. On the other hand, the oxygen gas flowing along the inner wall of the reaction tube 12 reacts with the soot that has adhered and accumulated on the inner wall of the reaction tube 12 and becomes carbon dioxide.
More exhaust. As a result, on the inner wall of the reaction tube 12 on the side of the cracked gas exhaust pipe 15 from the oxygen gas supply port 20, the accumulated soot reacts with oxygen gas, burns, and is exhausted, so that the accumulation of soot is suppressed.

By the way, soot buildup on the inner surface of the reaction tube 12 occurs in the reaction section 1.
The inventors of the present invention have confirmed that this phenomenon is most frequently observed between the lower end of the cracked gas exhaust pipe 15 and the cracked gas exhaust pipe 15. That is, some of the carbon radicals generated by thermal decomposition of the raw material gas pass through the reaction section 18 and are cooled as the ambient temperature decreases, thereby turning into soot and flowing into the reaction tube 1.
This is because, in addition to being deposited on the inner surface of No. 2, it also causes the growth of carbon dendrites. However, as described above, according to the present invention, such soot accumulation can be suppressed and the reaction tube 12 can be prevented from being clogged due to soot accumulation.

(Experimental Example) Using the coating apparatus shown in FIG. 1, a carbon coating was formed on the surface of a bare optical fiber under the following conditions.

A reaction tube with an inner diameter of 30 x yt was used, 1,2-dichloroethylene was used as the raw material gas, and 1,2-dichloroethylene was supplied at a flow rate of 5 U, and the temperature of the heating element was 1300°C. It was introduced at a flow rate of 0.5 Q/min.

The relationship between the spinning length and the carbon film resistance of the optical fiber that is spun with the carbon film obtained in this way was investigated, and the results were used in the second
Shown in the figure.

For comparison, an optical fiber with a carbon film was formed using the apparatus shown in Figure 1 without introducing oxygen and under the same conditions as above, and the relationship between the spinning length and the carbon film resistance was calculated. The relationship was investigated and the results are also shown in Figure 2.

Regarding the relationship between the spinning length and the carbon film resistance, when the spinning conditions are the same, the lower the electrical resistance value of the carbon film, the better the carbon deposition efficiency on the bare optical fiber. If the temperature is high, carbon adhesion on the bare optical fiber (
It is known that the amount of sedimentation is extremely small. Therefore, from the results shown in Fig. 2, the optical fiber obtained by the manufacturing method of the present invention always has a low resistance value regardless of the spinning length. It was confirmed that a good and constant amount had been deposited.

In addition, in a comparative example in which a carbon film was formed without flowing oxygen, the resistance value suddenly increased midway through the process, indicating that the efficiency with which carbon was deposited onto the bare optical fiber decreased significantly during the manufacturing process.

[Effects of the Invention] As explained above, the method for producing a tip fiber according to claim 1 according to the present invention provides
Since the gas containing oxygen is supplied along the inner wall of the reaction tube at the point where the oxygen is introduced, the soot that has accumulated on the inner wall of the reaction tube from the point where oxygen is introduced to the exhaust pipe can be burned and exhausted. It is possible to prevent clogging of the reaction tube caused by soot accumulation, and to enable continuous production of optical fibers with a carbon coating.Therefore, long optical fibers with a uniform carbon coating can be produced. can be manufactured.

Further, the carbon coating device according to claim 2 is provided with an oxygen gas supply port on the exhaust pipe side of the reaction section for supplying oxygen-containing gas along the inner wall of the reaction tube. Similarly, by supplying oxygen, it is possible to burn and exhaust soot that has accumulated in the exhaust pipe or on the inner wall of the reaction tube at IJ from the point where oxygen is supplied. It is possible to prevent this and enable continuous production of optical fibers having a carbon coating. therefore,
By reducing the inner diameter of the reaction tube, the efficiency of carbon deposition onto the tip fiber can be increased, thereby making it easier to manufacture an optical fiber with a carbon coating formed thereon.

[Brief explanation of drawings]

Fig. 1 and Fig. 2 (views according to the present invention; Fig. 1 is a schematic diagram showing an embodiment of carbon coating production according to claim 2; Fig. 2 is a diagram showing a carbon coating according to an embodiment of the present invention; A graph showing the relationship between the spinning length of an optical fiber and the carbon film resistance, and FIG. 3 is a schematic diagram showing an example of a conventional carbon coating device. 10...Carbon coating device, it... Bare optical fiber, 12... Reaction tube, 13... Heat generation source, 14... Raw material gas supply pipe, 15...
・Cracked gas exhaust pipe, 16... Heating element, 18...
... Reaction section, 20 ... Oxygen gas supply port, A.
...Oxygen gas.

Claims (2)

[Claims] (1) A supply pipe for supplying raw material gas consisting of hydrocarbon compounds is provided on one side, and an exhaust pipe for exhausting decomposed raw material gas is provided on the other side, and these supply pipes and exhaust pipes are connected to each other. An optical fiber was introduced from the side where the supply pipe was provided, and an exhaust pipe was provided in the reaction tube, in which a reaction section for thermally decomposing the raw material gas and coating with carbon was formed along its length. At the same time, the raw material gas is supplied from the supply pipe, and then the raw material gas is thermally decomposed in the reaction section to form a carbon film on the surface of the optical fiber, and oxygen is removed from the exhaust pipe side of the reaction section. A method for producing an optical fiber, characterized in that a gas containing gas is supplied along the inner wall of a reaction tube. (2) It is equipped with a reaction tube that forms a carbon film on the surface of the optical fiber while passing through it, and a heating section that heats the inside of the reaction tube, and one side of the reaction tube is made of a hydrocarbon compound. A supply pipe for supplying the raw material gas is provided with an exhaust pipe for exhausting the decomposed raw material gas on the other side, and the raw material gas is disposed between the supply pipe and the exhaust pipe along the length thereof. A carbon coating apparatus having a reaction section that performs carbon coating by thermal decomposition, characterized in that an oxygen gas supply port is provided on the exhaust pipe side of the reaction section to supply a gas containing oxygen along the inner wall of the reaction tube. carbon coating equipment.