JPH0442841A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To improve the deposition speed of a carbon coating film and increase the density of the film formed on the surface of a bare optical fiber by specifying the temperatures of the surface of the bare optical fiber and the wall of a reaction tube. CONSTITUTION:A bare optical fiber 1 drawn from a heated preform 2 is passed through a CVD reaction furnace 4 to form a carbon coating film on the surface of the bare fiber 1. In the above process, the wall temperature of the reaction tube 5 is adjusted to <=400 deg.C with a temperature controller 6 and the surface temperature of the bare fiber in the reaction tube 5 is adjusted to <=700 deg.C and <1100 deg.C by setting the position of the furnace 4 and adjusting the drawing speed of the bare fiber 1. The thermal decomposition of the raw material gas can be accelerated by increasing the surface temperature of the bare fiber 1, however, the breakage of the bare fiber takes place at >=1100 deg.C. The thermal decomposition of the raw material gas is insufficient and the thickness of the film becomes thin at <700 deg.C. The size of carbon particle can be decreased by setting the wall temperature of the reaction tube 5 to <=40O deg.C to improve the deposition efficiency of the carbon particles on the surface of the bare fiber l. At the same time, the density of the carbon coating film can be improved since the carbon particles are deposited on the surface immediately after generation.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method of manufacturing an optical fiber having a carbon coating formed on its surface, and in forming a carbon coating on the surface of a bare optical fiber. By adjusting the temperature of the bare wire surface and the reaction tube wall to a predetermined temperature, an optical fiber having better hydrogen resistance can be obtained at a high drawing speed.

[Prior art and its problems] When a silica-based fiber comes into contact with hydrogen, absorption loss due to molecular vibration of hydrogen molecules diffused into the fiber increases. Furthermore, P2O5 and Q contained as dopants
Since e02, B, 03, 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, it is necessary to fill an optical cable with a liquid composition having hydrogen absorption ability (Japanese Patent Application No. 1983).
-251808), but the effect is not sufficient and the structure is complicated, which poses an economical problem.

In order to solve these problems, it has been announced that a carbon film can be formed on the surface of the fiber by chemical vapor deposition, thereby improving the hydrogen resistance of the optical fiber.

However, in the above manufacturing method, the deposition rate of the carbon film formed on the surface of the bare optical fiber is slow, and the quality of the film is not dense. It has to be kept at a high speed, and there is a problem with productivity.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a manufacturing method capable of drawing an optical fiber having excellent hydrogen resistance at high speed.

[Means for Solving the Problems] As a result of extensive research on improving the hydrogen resistance and spinning speed of optical fibers with carbon coatings formed on their surfaces, the present inventors have discovered that heated bare optical fibers When forming a carbon film by contacting the raw material gas in the reaction tube,
We have discovered that by adjusting the surface temperature of the bare optical fiber and the wall temperature of the reaction tube, the hydrogen resistance and drawing speed of the optical fiber can be significantly improved.

That is, in the manufacturing method of the present invention, a bare optical fiber heated to a surface temperature of 700° C. or more and less than 1100° C. and a raw material gas are brought into contact with each other in a reaction tube with a wall temperature of 400° C. or less, and the raw material gas is The solution was to form a carbon film on the surface of the bare optical fiber by thermal decomposition.

The present invention will be explained in detail below.

FIG. 1 shows an example of an optical fiber manufacturing apparatus suitably used in the optical fiber manufacturing method of the present invention.

In FIG. 1, reference numeral 1 indicates a bare optical fiber. The bare optical fiber 1 is obtained by heating and spinning an optical fiber preform 2 in an optical fiber spinning furnace 3. This bare optical fiber 1 is guided without being cooled to a CVD reactor 4 provided directly below the spinning furnace.

This CVD reactor 4 brings the heated bare optical fiber 1 into contact with the raw material gas, thermally decomposes the raw material gas by the surface temperature of the bare fiber 1, and forms a carbon coating on the surface of the bare optical fiber 1. It is intended to form a This CVD reactor 4 is generally composed of a generally cylindrical reaction tube 5 and a temperature control device 6 for adjusting the wall temperature of this reaction tube 5.

The temperature control device 6 is for keeping the wall temperature of the reaction tube 5 below 400° C., and is made of, for example, a winding cooling tube in which a refrigerant such as water or inert gas flows. It is connected to the reaction tube 5 via the section 7. This control section 7 is further connected to a temperature measurement section (not shown) consisting of a non-contact thermometer etc. that measures the wall temperature of the reaction tube 5, and the measurement results are used to determine the amount of refrigerant supplied to the temperature control device 6. etc. can be adjusted.

To adjust the surface temperature of the bare optical fiber 1, spinning preheating can be used. That is, the CVD reactor 4 is installed at a position where the surface temperature of the spun bare optical fiber 1 is 700°C or more and less than 1100°C. This is appropriately selected depending on the spinning speed of the bare optical fiber l, etc.
For example, when spinning a bare optical fiber l at a speed of 300 m/min, the position is approximately 30 mm from the neck-down portion of the optical fiber preform 2.

Further, a raw material gas supply pipe 8 for supplying raw material gas is attached to the upper part of the reaction tube 5, and an exhaust pipe 9 for exhausting unreacted gas, excess carbon particles, etc. is attached to the lower part. Further, gas seal mechanisms 10 for sealing the inside of the reaction tube 5 are connected to the upper and lower portions of the reaction tube 5.

Furthermore, a resin liquid coating device 11 and a curing device 12 are provided at the lower stage of the CVD reactor 4, so that a resin protective film can be formed on the carbon film.

To manufacture an optical fiber according to the manufacturing method of the present invention using the above manufacturing apparatus, the following steps are performed.

The optical fiber preform 2 is heated and spun in the optical fiber spinning furnace 3, and a
It is sequentially inserted into the VD reactor 4, the resin liquid coating device 11, and the curing device 12, and is fed so as to run on the central axes thereof. At this time, the position of the CVD reactor 4 is set so that the surface temperature of the bare optical fiber l is 700°C or more and less than 1100°C in the reaction tube 5, and the spinning speed of the bare optical fiber l, i.e. Set the drawing speed.

It is preferable for the surface temperature of the bare optical fiber l to be high because it promotes thermal decomposition of the raw material gas, but if it is higher than 100°C, it will be close to the softening point of quartz and breakage of the bare optical fiber l will occur. Undesirable. Also, optical fiber bare wire 1
If the surface temperature is less than 700° C., the raw material gas cannot be thermally decomposed sufficiently, the thickness of the carbon film becomes thin, and the hydrogen resistance properties deteriorate.

Then, the raw material gas is supplied into the reaction tube 5 from the raw material gas supply pipe 8 . This raw material gas is not particularly limited as long as it is a carbon compound that can form a carbon film by thermal decomposition, and is a mixture of at least the raw material compound and a carrier gas that dilutes and transports it. Specific examples of the raw material compounds include methane, ethane, propane, benzene, toluene, and the like, as well as chloromethane and chlorobenzene obtained by replacing the hydrogen atoms of these compounds with chlorine atoms. Further, various known carrier gases such as helium gas, argon gas, hydrogen gas, and nitrogen gas can be used as the carrier gas.

At this time, the 8-temperature device 6 is driven so as to keep the wall temperature of the reaction tube 5 below 400°C. The lower the wall temperature of the reaction tube 5, the better the hydrogen resistance and spinning speed, so it is particularly preferably 50°C or lower, and the upper limit is 400°C. When the wall temperature of the reaction tube 5 exceeds 400° C., carbon particles generated by thermal decomposition of the raw material gas adhere to the inside of the reaction tube 5, reducing the rate of precipitation of the carbon film on the surface of the bare optical fiber 1. It's for a reason. This is also because coarse carbon particles grown in the gas phase region tend to adhere to the surface of the bare optical fiber 1, reducing the hydrogen resistance of the resulting optical fiber.

The bare fiber l on which the carbon coating was formed in this way
is introduced into the resin liquid coating device ll provided in the lower stage. Bare optical fiber l inserted into the resin liquid coating device 11
The material is coated with an ultraviolet curable resin liquid or a thermosetting resin liquid for forming a protective film, and then cured in a curing device 12 having curing conditions suitable for the applied resin liquid to form a protective film. It is considered as an optical fiber.

In this way, when bringing the heated bare optical fiber into contact with the raw material gas in the reaction tube to form a carbon film on the surface of the bare optical fiber, the surface temperature of the bare optical fiber is kept at 700°C.
By setting the above temperature to less than 1100°C and the wall temperature of the reaction tube to 400°C or less, particularly preferably 50°C or less, the carbon particles are made finer and the precipitation efficiency of the carbon fine particles on the surface of the bare optical fiber is improved. Therefore, even if the drawing speed is increased, a carbon film of sufficient thickness can be formed. Furthermore, since the carbon fine particles are deposited on the surface of the bare optical fiber immediately after being generated, the carbon film formed is dense and has excellent hydrogen resistance.

[Example] (Example) A reaction tube was installed in the lower stage of an optical fiber spinning furnace, and a cooling tube using water as a coolant was wound around the reaction tube.
The device was similar to that shown in the figure.

Note that the reaction tube was installed 30 mm from the neck-down position of the optical fiber preform.

A single mode optical fiber preform having an outer diameter of 30+ am and having a core impregnated with GeOz as a dopant was placed in an optical fiber spinning furnace. This optical fiber base material was heated to 2000°C.
The fiber was heated to 300 m/min and spun into a single mode fiber with an outer diameter of 125 μm at a spinning speed of 300 m/min.

Next, this bare optical fiber is inserted into the reaction tube, and a raw material gas containing benzene as a raw material compound and nitrogen gas as a carrier gas is supplied, and this raw material gas is thermally decomposed by contacting with the bare fiber at the end. A carbon film was formed on the surface of a bare optical fiber. Note that the meteor gases used as raw material gases were benzene gas 02Q/min and nitrogen gas 08Q/min. The inside of the reaction tube was evacuated from the exhaust pipe at an exhaust pressure of -4 mmHtO.

The surface temperature of the bare optical fiber inserted into the reaction tube was measured using a non-contact thermometer at two points near the raw material gas supply port and the exhaust pipe, and found to be 900'C and 750C. The wall temperature of the reaction tube was 3°0°C.

The optical fiber with the carbon film formed in this way was inserted into a resin coating die spot filled with urethane acrylate resin liquid (Young's modulus 70 kg/mm', elongation 60%), and then equipped with an ultraviolet irradiation lamp. The resin applied by the curing device is cured to form a protective film, and the outer diameter is 2.
A 50 μm optical fiber was used.

(Examples 2 to 4 and Comparative Examples 1 to 4) Example 1 above except that the type of raw material gas, the spinning speed of the bare optical fiber, and the wall temperature of the reaction tube were changed as shown in Table 1. An optical fiber was manufactured in exactly the same manner.

(Test Example 1) Each optical fiber obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was sampled at a length of 1 km, and the wavelength was 1.24 μm.
The transmission loss was measured. After this, make these with a diameter of 1
Wrap it into a bundle of 50 m + n, and store it at a temperature of 80°C and a hydrogen partial pressure of 1.
It was left in an ATM hydrogen evaluation pressurized container for 96 hours. Thereafter, the transmission loss at the wavelength mark of 1.24 μm was measured again to examine the increase in absorption loss due to hydrogen. The results are also shown in Table 1.

(Test Example 2) The urethane acrylate resin coating layer of each optical fiber obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was removed using a solvent, and the electrical resistance of the carbon coating formed on the surface of the bare optical fiber was The values were measured using a digital multimeter. This electrical resistance value was used as a method of measuring the degree of adhesion of the carbon film. The results are also shown in Table 1.

(Hereinafter, blank space) [Effects of the Invention] As explained above, the manufacturing method of the present invention adjusts the surface temperature of the bare optical fiber and the wall temperature of the reaction tube to appropriate temperatures, so that the raw material gas The carbon particles generated by the thermal decomposition of carbon particles can be made finer, and the efficiency and rate of precipitation of these fine carbon particles onto the surface of the bare optical fiber can be significantly improved.

Therefore, even if the drawing speed of the optical fiber is increased, a dense carbon film can be deposited with sufficient thickness.
Optical fibers with excellent hydrogen resistance can be obtained at high speed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an optical fiber manufacturing apparatus suitably used in the manufacturing method of the present invention. l... Bare optical fiber, 5... Reaction tube, 6...
・Temperature control device.

Claims (2)

[Claims] (1) A bare optical fiber heated to a surface temperature of 700°C or more and less than 1100°C and a raw material gas are placed in a reaction tube,
A method for manufacturing an optical fiber, characterized by forming a carbon film on the surface of the bare optical fiber by thermally decomposing the raw material gas by contacting the reaction tube at a wall temperature of 400° C. or less. (2) The method for manufacturing an optical fiber according to claim 1, characterized in that the wall temperature of the reaction tube is 50° C. or less.