JPH03271140A - Producing apparatus of optical fiber - Google Patents

Abstract

PURPOSE:To make it possible to spin an optical fiber having carbon coating film with sufficient film thickness at a high speed by lengthening and providing an optical fiber bare wire-introducing tube from an optical fiber bare wire- introducing hole of a reaction tube to the vicinity of heating element. CONSTITUTION:An optical fiber bare wire 1 which is melt-spun in an optical fiber spinning furnace 2 is introduced into a cooling cylinder 3 to cool the optical fiber bare wire 1 and then passed through an optical fiber bare wire- introducing tube 12 which is lengthened until the vicinity of heating element 6 toward a reaction tube 5 and provided in one end to which a raw material gas feed tube 7 is connected to introduce the bare wire into a reaction tube 5 of CVD reaction furnace 4. A hydrocarbon compound fed from the feed tube 7 is thermally decomposed by a heating element 6 to form a carbon coating film on the surface of bare wire 1 and then the treated wire is introduced into a resin liquid coating device 10 to apply the resin liquid to the wire and the coated wire is cured in a curing device 11 to form a protective coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a manufacturing apparatus that is capable of spinning an optical fiber having a carbon coating formed on its surface at high speed.

[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.1. Furthermore, P, O,, which is contained as a dopant,
Since G e Ox, B t O3, etc. react with hydrogen and are incorporated into the fiber glass as OH groups, there is a problem in that transmission loss due to absorption of OH groups also increases.

In order to deal with such adverse effects, a method of filling an optical cable with a liquid composition having hydrogen absorption ability (Japanese Patent Application No. 1983) was proposed.
-251808), but the effect is not sufficient and the structure is complicated, resulting in economical problems.

In order to solve these problems, chemical vapor deposition method (
It has been announced that a carbon film can be formed on the surface of an optical fiber by a CVD method (hereinafter abbreviated as CVD method), thereby improving the hydrogen resistance properties of the optical fiber.

In this method, a bare optical fiber spun in a spinning furnace is inserted into a heating furnace, and a raw material gas such as a hydrocarbon compound is gasified and diluted with an inert gas, etc., and a raw material gas is supplied. This is a method of thermally decomposing raw material gas to form a carbon film on the surface of a bare optical fiber.

Conventionally, an apparatus as shown in FIG. 3 has been used to form a carbon film on the surface of a bare optical fiber by the above-mentioned CVD method.

In FIG. 3, reference numeral 1 indicates a bare optical fiber. The bare optical fiber 1 is obtained by melt-spinning an optical fiber preform (not shown) in an optical fiber spinning furnace 2. It is supplied into the CVD reactor 4 through the cooling cylinder 3. The cooling cylinder 3 has a generally cylindrical shape, and has a refrigerant supply port 3a such as an inert gas connected to one end and a refrigerant exhaust port connected to the other end. This cooling tube 3 cools the high-temperature bare optical fiber 1 melt-spun in the upper optical fiber spinning furnace 2 to an appropriate temperature, and also cools the reaction tube 5 to an appropriate temperature.
This is for sealing the top.

The CVD reactor 4 is for forming a carbon film on the surface of the bare optical fiber 1 spun in the upper optical fiber spinning furnace 2 by the CVD method.
It is comprised of a generally cylindrical reaction tube 5 that allows the reaction to proceed, and a heating element 6 that heats the reaction tube 5. A bare optical fiber introduction hole and a bare optical fiber outlet hole (not shown) are provided at the upper and lower parts of the reaction tube 5, respectively.
A bare optical fiber l spun in the optical fiber spinning furnace 2 can be inserted therethrough.

Further, a raw material gas supply pipe 7 for supplying raw material compounds into the reaction tube 5 is attached to the upper part of the reaction tube 5, and an exhaust pipe 8 for exhausting unreacted gas, by-products, etc. is attached to the lower part. There is. Furthermore, a gas seal mechanism 9 for sealing the reaction tube 5 is connected to the lower part of the reaction tube 5.

In addition, a resin liquid coating device l is installed at the lower stage of this CVD reactor 4.
O and the curing device 11 are provided in succession, and the above C
A protective coating layer is formed on the carbon coating formed on the bare optical fiber I in the VD reactor 4.

[Problems to be Solved by the Invention] However, in the manufacturing apparatus shown in FIG.
Since the raw material gas and the bare optical fiber 1 are supplied together within the chamber, the bare optical fiber 1 comes into contact with the raw material gas before being thermally decomposed. This undecomposed source gas adheres to the surface of the bare optical fiber 1, and the rate of deposition of the carbon film on the surface of the bare optical fiber 1 is reduced. Therefore, in order to form a carbon film with a sufficient thickness, there is a problem in that the spinning speed of the optical fiber must be slowed down.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical fiber manufacturing apparatus that can spin a tip fiber having a carbon coating of sufficient thickness at high speed.

[Means for Solving the Problems] The optical fiber manufacturing apparatus of the present invention includes a reaction tube having a bare optical fiber introduction hole at one end and a bare optical fiber outlet hole at the other end, and a reaction tube having a bare optical fiber introduction hole at the other end. It is equipped with a raw material gas supply pipe installed at one end, an exhaust pipe installed at the other end of the reaction tube, and a heating element installed around the outer periphery of the reaction tube, and the raw material gas is thermally decomposed inside the tube. In an optical fiber manufacturing apparatus in which a carbon film is formed on the surface of a bare optical fiber, a bare optical fiber introduction tube is extended from the bare optical fiber introduction hole to the vicinity of the heating element.

[Function] Since the bare optical fiber introduction tube is extended from the bare optical fiber introduction hole to the vicinity of the heating element, the bare optical fiber and the raw material gas are transferred into the reaction tube heated to the thermal decomposition temperature of the raw material gas. Contact with. Since the tip bare fiber does not come into contact with the undecomposed source gas, it is possible to reduce the adhesion of the undecomposed source gas to the surface of the bare optical fiber and improve the deposition rate of the carbon film. . Therefore, high-speed spinning of optical fiber becomes possible.

The present invention will be explained in detail below.

FIG. 1 shows an example of an optical fiber manufacturing apparatus according to the present invention. The difference between the apparatus shown in FIG. 1 and the apparatus shown in FIG. The bare optical fiber introduction tube 12 has been extended to reach the point shown in FIG. Other identical parts are given the same reference numerals and explanations will be omitted.

The bare optical fiber introduction tube 12 extends from the cooling tube 3 connecting the reaction tube 5 and the optical fiber spinning furnace 2 into the reaction tube 5.
It is a tube that extends to reach the vicinity of the heating element 6, and a bare optical fiber 1 is inserted on its central axis. The open end of the bare optical fiber introducing tube 12 is located below the position where the raw material gas supply lower is attached and on the inside near the heating element 6.

When such a bare optical fiber introducing pipe 12 is extended, the raw material gas and the bare optical fiber 1 come into contact inside the heating element 6. Therefore, the bare optical fiber 1 does not come into contact with undecomposed raw material gas that has not yet been sufficiently heated, so that the carbon coating can be efficiently deposited on the surface of the bare optical fiber 1. As a result, the spinning speed of the optical fiber can be improved.

Furthermore, since undecomposed raw material gas is not contained in the carbon coating formed on the surface of the bare optical fiber 1, the optical fiber obtained by the manufacturing apparatus of the present invention has good hydrogen resistance properties. becomes.

To form a carbon film on the surface of the bare optical fiber 1 using such a manufacturing apparatus, the following steps are performed.

The optical fiber preform is melt-spun in the optical fiber spinning furnace 2, and a cooling tube 3, a CVD reactor 4, a resin liquid coating device 1O1 and a curing device 1 are provided at the lower stage of the optical fiber spinning furnace 2.
1 and are fed so as to run on these central axes at a predetermined linear speed.

Further, an inert gas or the like serving as a refrigerant is supplied into the cooling cylinder 3 at a predetermined flow rate from the refrigerant supply port 3a to cool the bare optical fiber 1 to a desired temperature and seal the reaction tube 5. The bottom of the reaction tube 5 is sealed by supplying an inert gas or the like to the gas seal mechanism 9 at a predetermined flow rate.

Next, the heating element 6 is made to generate heat to heat the inside of the reaction tube 5 to a predetermined temperature, and the raw material gas is supplied into the reaction tube 5 from the raw material gas supply pipe 7.

The hydrocarbon compound used for this raw material gas is not particularly limited as long as it forms a carbon film by thermal decomposition, and examples include aliphatic carbon compounds such as methane, ethane, propane, ethylene, acetylene, pentane, and hexane. In addition to hydrogen, aromatic hydrocarbons such as benzene and naphthalene can be used. When these raw material compounds are liquid or solid, they can be made into a raw material gas by gasifying with an inert gas or the like.

The feed rate and temperature of the raw material gas are appropriately selected depending on the type thereof, their mixing ratio, the heating temperature of the CVD reactor 4, etc., but usually about 0.2 to 1.1/min is suitable.

The temperature in the reaction tube 5 can be appropriately selected depending on the type of raw material gas, the spinning speed, etc., but it may be any temperature sufficient for thermal decomposition of the hydrocarbon compound, and is preferably about 500 to 1300°C. If the heating temperature is lower than 500°C, the thermal decomposition of the hydrocarbon compound will not proceed, and if the heating temperature is higher than 13,000°C, a large amount of by-product soot will be generated and the structure of the carbon film formed on the surface of the bare optical fiber 1 will deteriorate. becomes close to a graphite structure,
This is not preferable because sufficient hydrogen resistance properties cannot be obtained.

Further, in order to prevent the generation of soot as a by-product, it is desirable that the heating temperature be set to a temperature slightly lower than the thermal decomposition temperature of the raw material compound.

Bare optical fiber l with carbon coating formed in this way
is introduced into the resin liquid coating device 10 provided in the lower stage,
Then, it is inserted into a curing device ll for curing the resin liquid.

The bare optical fiber l inserted into the resin liquid coating device lO is coated with an ultraviolet curing resin liquid or a thermosetting resin liquid to form a protective coating layer, and then subjected to a suitable curing process for the applied resin liquid. A protective coating layer is formed by curing in a curing apparatus II having conditions.

As described above, by extending the bare optical fiber introducing tube 12 from the cooling cylinder 3 toward the inside of the reaction tube 5, the bare optical fiber 1 is brought into contact only with the sufficiently heated and pyrolyzed raw material gas. Therefore, the deposition rate of the carbon film can be improved. Therefore, even if the optical fiber is spun at high speed, a carbon coating of sufficient thickness can be formed. Further, since the carbon coating does not contain undecomposed source gas and the purity of the carbon coating improves, the resulting optical fiber has excellent hydrogen resistance.

In this example, a single carbon coating was formed on the surface of the bare optical fiber 1, but the number of carbon coatings formed on the surface of the bare optical fiber 1 is not limited to this, and two or more layers of carbon coatings may be formed. may be formed continuously.

Further, in this example, a single protective coating layer is formed on the carbon film, but the number of protective coating layers is not limited to this, and a plurality of protective coating layers may be formed.

[Example] (Example) A resistance CVD reactor having a reaction tube also made of quartz tube was connected to the lower stage of a spinning furnace for spinning bare optical fiber from an optical fiber base material through a quartz tube serving as a cooling tube. Installed it.

Furthermore, an optical fiber bare wire introducing tube made of a quartz tube was extended from the cooling tube toward the inside of the reaction tube to obtain an optical fiber manufacturing apparatus similar to that shown in FIG.

A single mode optical fiber preform having an outer diameter of 30 mm and having a core impregnated with G e Ot as a dopant was placed in a spinning furnace. This optical fiber preform was heated to 2000°C, and the spinning speed was sequentially set to 10 m/min, 50 ffl/min, 100 m/min,
The fiber was spun into a single mode optical fiber with an outer diameter of 125 μm. Furthermore, the inside of the resistance CVD reactor was
heated to ℃. Benzene gasified to about 10 vol % with helium gas was supplied into the reaction tube from the raw material gas supply port at a flow rate of 5J/min to form a carbon film on the surface of the bare optical fiber. By-product acids and unreacted products are located 16 meters from the exhaust pipe.
It was removed with an evacuation pressure of mHg.

Furthermore, urethane acrylate resin liquid (Young's modulus 70 kg/mm1, elongation 60
%), the optical fiber on which the carbon film was formed in the above process is inserted into the optical fiber, and the surface of the optical fiber is coated with an ultraviolet curable resin liquid, and then an ultraviolet lamp is irradiated to cure the above-mentioned tree HF.
km was cured to produce an optical fiber with an outer diameter of about 250 μm.

(Comparative Example) Optical fibers were manufactured in exactly the same manner as in the example except that the same optical fiber manufacturing apparatus as shown in FIG. was manufactured.

(Test Example) As a guideline for determining the amount of carbon coating formed on the surface of each optical fiber obtained in the above examples and comparative examples, the electrical resistance value (kΩ/cm) of the surface of each optical fiber was measured.

The electrical resistance value was measured using a two-terminal method using a digital multimeter. The results are shown in FIG. In FIG. 2, the solid line shows the measurement results of the optical fiber of the example, and the broken line shows the measurement results of the optical fiber of the comparative example. Note that since the carbon film is electrically conductive, the smaller the electrical resistance value of the carbon film, the more the carbon film is attached.

From the results shown in FIG. 2, it was confirmed that by using the manufacturing apparatus of the present invention, a carbon film of sufficient thickness could be formed on the surface of the bare optical fiber even at high spinning speeds.

[Effects of the Invention] As explained above, the optical fiber manufacturing apparatus of the present invention has a bare optical fiber introduction tube extending from the bare optical fiber introduction hole to the vicinity of the heating element, so it cannot be disassembled. This prevents the source gas from coming into contact with the bare optical fiber.

Therefore, even if the optical fiber is spun at high speed, it is possible to form a carbon film with a thickness sufficient to exhibit hydrogen resistance.

Further, since the optical fiber obtained by the manufacturing apparatus of the present invention has a carbon coating having hydrogen permeation blocking ability formed on its surface, an optical fiber having excellent hydrogen resistance properties can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an example of the optical fiber manufacturing apparatus of the present invention, Fig. 2 is a graph showing the relationship between the spinning speed of the optical fiber and the electric resistance value, and Fig. 3 is a graph showing the relationship between the spinning speed of the optical fiber and the electrical resistance value. 1 is a schematic configuration diagram showing a manufacturing apparatus. Bare optical fiber, 3... Cooling tube,... CVD reactor, 5... Reaction tube, 6... Heating element, 7... Raw material gas supply pipe, - Exhaust pipe, 2... Bare optical fiber Line introduction tube.

Claims (1)

[Claims] A reaction tube having an optical fiber bare wire introduction hole at one end and an optical fiber/bare wire outlet hole at the other end, a raw material gas supply pipe provided at one end of the reaction tube, and a raw material gas supply pipe provided at the other end of the reaction tube. An optical fiber manufacturing device, which is equipped with a heated exhaust pipe and a heating element provided on the outer periphery of a reaction tube, and thermally decomposes a raw material gas inside the heating element to form a carbon film on the surface of a bare optical fiber. An optical fiber manufacturing apparatus characterized in that a bare optical fiber introduction tube is extended from the bare optical fiber introduction hole to the vicinity of the heating element.