JP3039975B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber having a carbon coating formed on its surface, and to improve hydrogen resistance and stress fatigue resistance by eliminating by-products during carbon coating formation. An excellent optical fiber can be continuously spun for a long time. [Prior Art] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to molecular vibration of hydrogen molecules diffused into the fiber increases, and further, P ₂ O ₅ and Ge contained as dopants are used.
O ₂ , B ₂ O _3, etc. react with hydrogen and are taken into the fiber glass as OH groups, so that there is a problem that transmission loss due to absorption of OH groups increases. In order to solve such problems, it was announced that a carbon coating was formed on the surface of an optical fiber by chemical vapor deposition (hereinafter abbreviated as CVD), thereby improving the hydrogen resistance of the optical fiber. Have been. As this method, for example, a bare optical fiber spun in a spinning furnace,
The carbon compound is supplied into the reaction furnace together with the raw material gas obtained by gasification and dilution with an inert gas or the like, and the raw material gas is thermally decomposed by the preheating of the bare optical fiber by spinning, thereby forming a carbon coating on the bare optical fiber surface. Methods of forming are known.
As an optical fiber manufacturing apparatus suitably used in such a method, there is, for example, one shown in FIG. In FIG. 4, reference numeral 1 denotes a bare optical fiber. The bare optical fiber 1 is obtained by melt-spinning an optical fiber preform 2 in an optical fiber spinning furnace 3. Immediately after spinning, the bare optical fiber 1 is supplied into a CVD reactor 4 provided below the optical fiber spinning furnace 3. The CVD reactor 4 is for forming a carbon coating on the surface of the bare optical fiber 1 by a CVD method to obtain an optical fiber. In the apparatus shown in FIG. 4, the thermal decomposition of the raw material gas proceeds by utilizing preheating when the bare optical fiber 1 is spun without using a separate heating device. The CVD reactor 4 is composed of a substantially cylindrical reaction tube 5 for advancing a CVD reaction inside, and a lower portion thereof has a source gas supply tube 6 for supplying a source gas, and an upper portion thereof has an unreacted gas. An exhaust pipe 7 for exhausting gas or the like is attached to each. Further, both ends of the reaction tube 5 are reduced in diameter so that the internal atmosphere of the reaction tube 5 can be kept constant. Gas seal mechanisms 8, 8 for sealing the inside of the reaction tube 5 are provided at both ends of the reduced diameter.
Are connected respectively. A resin coater 9 is provided in a lower stage of the CVD reactor 4. This resin coater 9 uses CV
D is for forming a resin coating layer on the surface of the optical fiber 10 obtained in the reactor 4. [Problems to be Solved by the Invention] By the way, 40 carbon compounds used as a raw material gas
When pyrolysis occurs at a relatively low temperature of about 0 to 500 ° C., a gaseous tar and pitch are generated as a by-product of the carbon coating by vaporization of an oily bituminous substance. (Hereinafter, these are referred to as by-products.) These by-products float in the reaction tube 5. On the other hand, in the above manufacturing method, the raw material gas is thermally decomposed by utilizing the pre-spinning of the bare optical fiber 1. Therefore, the bare optical fiber 1 must be supplied into the reaction tube 5 in a heated state. Must. Therefore, it is necessary to set the drawing speed of the bare optical fiber 1 high. However, if the drawing speed is increased, convection occurs in the reaction tube 5 along the drawing direction of the bare optical fiber 1. By this convection, by-products are entrained in the bare optical fiber 1 and the CVD reactor 4
Spill out of. The outflow by-product is gradually deposited on the nipple of the resin coater 9 provided at the lower stage of the CVD reactor 4,
The clogging of the nipple hole may cause clogging of the optical fiber 10
Disables resin coating. Therefore, in the above manufacturing method, although an optical fiber having excellent hydrogen resistance can be obtained, there is a problem that the optical fiber cannot be continuously spun for a long time. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a method of manufacturing an optical fiber capable of continuously spinning an optical fiber having excellent hydrogen resistance over a long period of time. [Means for Solving the Problems] The method of manufacturing an optical fiber according to claim 1 of the present invention is as follows.
After the carbon compound is pyrolyzed to form a carbon coating on the bare optical fiber surface to form an optical fiber, the optical fiber passes through a narrowing member that eliminates the pyrolysis by-product of the carbon compound. The solution is to cause the cleaning gas to flow through the constriction member.

[Action]

In the manufacturing method according to the first aspect, by passing the optical fiber through the constriction member, the convection around the optical fiber is changed, and a by-product accompanies the optical fiber. Can be prevented. Hereinafter, the present invention will be described in more detail. FIG. 1 shows an example of an optical fiber manufacturing apparatus suitably used in the manufacturing method according to claim 1 of the present invention. The difference between the apparatus shown in FIG. 1 and the apparatus shown in FIG. 4 is that a constriction member 16 is provided between the CVD reactor 4 and the resin coater 9 and a cleaning gas flows through the constriction member 16. The cleaning gas supply pipe 19 is provided. The constriction member 16 causes by-products flowing out of the CVD reactor 4 together with the optical fiber 10 to precipitate so as not to reach the resin coater 9. The constricting member 16 is not particularly limited as long as it has a constricted portion having a diameter slightly larger than that of the optical fiber 10 so that convection around the optical fiber 10 can be changed to remove by-products. It is not something to be done. For example, in addition to a slit plate in which a hole for inserting the optical fiber 10 into the plate body is provided, a plurality of the plate members are provided inside a stenosis member outer tube 18 of a substantially cylindrical body as shown in FIG. And the like provided with the obstacles 17 can be suitably used. The obstacle 17 is an annular body having an outer diameter equal to the inner diameter of the stenosis member outer tube 18. The number of obstacles 17 can be arbitrarily selected as needed. Further, it is preferable that the diameter of the constriction formed by the obstacle 17 is smaller and the length of the constriction is longer. However, if the diameter of the constriction is too small or too long, the optical fiber
This is not preferable because 10 may come in contact with the obstacles 17. The diameter of the constricted portion is appropriately selected depending on the diameter of the optical fiber to be manufactured and the spinning speed, but usually the diameter is
About 1 mm to 4 mm is preferable. If it is less than 1 mm, the frequency of contact with the optical fiber increases, and if it exceeds 4 mm, by-products cannot be sufficiently eliminated. An inert gas is supplied into the lower portion of the outer tube 18 of the constriction member, and a cleaning gas supply tube 19 is in contact with the lower portion of the outer tube 18 so that by-products do not adhere to the surface of the optical fiber 10. The cleaning gas supply pipe 19 is for supplying an inert gas for cleaning the inside of the narrowing member 16 and the optical fiber 10. Further, in the example shown in FIG. 1, an adjusting pipe 20 connected to an exhaust pipe 21 is disposed on the outer circumference of the constriction member outer pipe 18 and is removed from the periphery of the optical fiber 10. By-products can be immediately exhausted. Adjustment tube like this
The provision of 20 can prevent the by-products removed from the optical fiber 10 from flowing back into the CVD reactor 4 and prevent the by-products from depositing on the outer wall of the narrowing member 16. Can be prevented. In order to manufacture an optical fiber using such an apparatus according to the manufacturing method described in claim 1 of the present invention, the following steps are performed. First, after spinning the bare optical fiber 1 from the optical fiber preform 2, a carbon coating is formed on the surface of the bare optical fiber 1 in the CVD reactor 4 to obtain the optical fiber 10. Next, the optical fiber 10 is inserted into a narrowing member 16 provided at the lower stage of the CVD reactor 4. At the same time, an inert gas is supplied from the cleaning gas supply pipe 19 into the stenosis member 16 to
The inside of 16 and the optical fiber 10 are cleaned. Further adjustment tube
By setting the exhaust pipe 21 connected to 20 to a reduced pressure state, the by-product desorbed from the optical fiber 10 is exhausted. When the optical fiber 10 passes through the narrowing member 16, the convection around the optical fiber 10 changes, and the flow accompanying the optical fiber 10 is blocked by the obstacles 17. As a result, by-products are removed from the optical fiber 10 and the obstacle 17
Precipitates on ... By-products not deposited on the obstacles 17 are discharged from the exhaust pipe 21 via the adjustment pipe 20. The optical fiber 10 from which by-products have been removed from its surroundings in this way
After the surface is cleaned by a cleaning gas supplied from a cleaning gas supply pipe 19 connected to the narrowing member 16, the resin is immediately inserted into the resin coater 9 to form a resin coating layer on the surface. According to the manufacturing method of the first aspect of the present invention, since the by-product does not reach the resin coater 9, the optical fiber can be continuously spun for a long time. In order to eliminate by-products, the optical fiber 10
Therefore, no special device and processing are required, so that the manufacturing cost of the conventional optical fiber can be maintained. In particular, if the apparatus shown in FIG. 1 is used, after removing by-products, the optical fiber 10 is cleaned with a cleaning gas, and then the resin coater 9 is cleaned.
Therefore, the resin coating layer can be formed uniformly. [Example] (Example 1) A CVD reactor and a constriction member are continuously provided at a lower stage of a spinning furnace for spinning an optical fiber bare wire from an optical fiber preform, and a resin coater is further provided at a lower stage thereof. An optical fiber manufacturing apparatus similar to that shown in FIG. 1 was prepared. Where the reaction tube,
Both the outer tube of the stenosis member and the adjusting tube were quartz tubes, and a resistance heating furnace was used as a heating means. As shown in FIG. 3, the constriction member is a quartz tube having an inner diameter of 15 mm and a length of 50 mm and an inner diameter of 3 m.
An annular body having a thickness of 10 mm and a thickness of 10 mm was provided at a distance of 30 mm. An adjusting tube having an inner diameter of 30 mm and a length of 500 mm was provided on the outer periphery of the stenosis member. Then, a single-mode fiber preform having an outer diameter of 30 mm having a core portion impregnated with GeO ₂ as a dopant is installed in a spinning furnace, and the optical fiber preform is heated to 2000 ° C. and a spinning speed of 300 m / min. A single mode fiber having an outer diameter of 125 μm was spun. The bare optical fiber was inserted into a CVD reactor and a raw material gas was supplied into the reaction tube. As the source gas, benzene diluted with nitrogen was used, and the flow rate was benzene.
100 ml / min and 900 ml / min of nitrogen. Exhaust pipe is -4mmH ₂ O
The inside of the reaction tube was evacuated to a reduced pressure state, and nitrogen gas was introduced from a gas sealing mechanism to seal the inside of the CVD reactor. A non-contact type thermometer was installed at each of the connection part of the exhaust pipe of the reaction tube and the connection member of the raw material supply pipe, and the temperature of the bare optical fiber in the reaction tube was measured.
The temperature was 900 ° C and 750 ° C at the connection point of the raw material supply pipe. Thus, the bare optical fiber and the raw material gas were brought into contact with each other to form a carbon coating on the surface of the bare optical fiber to obtain an optical fiber. This optical fiber was inserted into a narrowing member provided at the lower stage of the CVD reactor. At this time, while supplying nitrogen gas as a cleaning gas to the constriction member at a flow rate of 2 / min,
The exhaust pipe of the regulating pipe was evacuated to −30 mmH ₂ O to exhaust by-products and the like. In this way, by-products flowing out of the reaction tube accompanying the optical fiber were removed in the narrowing member. Then insert the optical fiber into the resin coater,
An optical fiber having an outer diameter of 250 μm was obtained by forming a protective coating layer. (Examples 2 and 3) The type of raw material gas, the surface temperature of the optical fiber in the CVD reactor, the temperature of the heat treatment furnace, and the inner diameter of the obstruction of the narrowing member were changed as shown in Table 1. An optical fiber was manufactured under exactly the same conditions as in Example 1 except for the above. Comparative Example 1 An optical fiber was manufactured under exactly the same conditions as in Example 1 except that no obstruction was provided in the stenosis member and no air was exhausted from the adjusting tube. (Comparative Example 2) Although the air was exhausted from the adjusting member, an optical fiber was manufactured under the same conditions as in Example 1 except that no obstacle was provided in the narrowing member. (Test Example) After manufacturing the optical fibers of these Examples and Comparative Examples,
Tars and pitches deposited on the nipple in the dipping pot in the resin coater were dissolved in methyl alcohol, and the deposited amount was measured. The results are shown in Table 1. From the results in Table 1, it was confirmed that the by-products could be prevented from being deposited on the resin coater by applying a heat treatment furnace or passing through a narrowing member. That is, it was confirmed that continuous spinning was possible for a long time. [Effects of the Invention] As described above, according to the method for manufacturing an optical fiber according to the first aspect of the present invention, after forming a carbon fiber coating on the surface of the bare optical fiber to obtain an optical fiber, the inside of the narrowing member is removed. Since the cleaning gas is passed through the constriction member while passing the same, any by-products flowing out of the reaction tube along with the optical fiber are removed without damaging the optical fiber. Precipitation in the resin coater can be prevented. Therefore, an optical fiber having excellent hydrogen resistance can be continuously manufactured for a long time without reducing the spinning speed of the optical fiber.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus suitably used in the method of manufacturing an optical fiber according to claim 1 of the present invention;
FIG. 2 is an enlarged view of a main part of the apparatus shown in FIG. 1, FIG. 3 is a schematic structural view showing a narrowing member used in the first to third embodiments, and FIG. FIG. 2 is a schematic configuration diagram illustrating an example of a manufacturing apparatus suitably used in the method. DESCRIPTION OF SYMBOLS 1 ... bare optical fiber, 4 ... CVD reactor, 5 ... reaction tube, 10 ... optical fiber strand, 16 ... constriction member, 17 ... obstacle part, 19 ... cleaning gas supply pipe 20 ... ... adjustment tube.

Continuing from the front page (72) Inventor Shinji Araki 1440, Mukurosaki, Sakura-shi, Chiba Fujikura Electric Cable Co., Ltd.Sakura Plant (72) Inventor Hideo Suzuki 1440, Mukurosaki, Sakura-shi, Chiba Fujikura Electric Wire Co., Ltd. ) Inventor Yutaka Katsuyama 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-2-164745 (JP, A) JP-A-2-69339 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) C03C 25/02

Claims (1)

(57) [Claims] An optical fiber is obtained by thermally decomposing a carbon compound to form a carbon coating on the surface of an optical fiber bare wire, and removing the by-product of thermal decomposition of the carbon compound from the optical fiber. A method for manufacturing an optical fiber, comprising passing a cleaning gas through a narrowing member and flowing through the narrowing member.