JPH0442839A - Production of optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 thereon, and in which a raw material gas is supplied at a predetermined flow rate when forming the carbon coating, This makes it possible to obtain an optical fiber having better hydrogen resistance and mechanical strength.

[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, P, 05, and G contained as dopants
Since eO2, B, 03, etc. react with hydrogen and are incorporated into the fiber glass as OH groups, there is a problem that transmission loss due to absorption of OH groups also increases.

In order to deal with such adverse effects, it is necessary to fill the optical cable with a liquid composition having hydrogen absorption ability (Japanese Patent Application No. 1983).
-251808), but its effectiveness is insufficient and the structure is complicated, which poses economical problems.

In order to solve these problems, it has been announced that a carbon film can be formed on the surface of an optical fiber using chemical vapor deposition, thereby improving the hydrogen resistance properties of the optical fiber. There were problems in that the fiber strength was inferior to that of conventional optical fibers, and the fatigue characteristics were different.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a manufacturing method capable of obtaining an optical fiber having superior hydrogen resistance and mechanical strength.

[Means for Solving the Problems] As a result of extensive research into improving the hydrogen resistance and mechanical strength of optical fibers coated with carbon, the present inventors have found that the raw material gas is supplied to the reaction tube in a specified manner. It has been found that by supplying at a flow rate, the hydrogen resistance and mechanical strength of the optical fiber can be significantly improved.

That is, the manufacturing method of the present invention is a method for manufacturing an optical fiber in which a raw material gas is thermally decomposed in a reaction tube to form a carbon film on the surface of the bare optical fiber, and the flow rate A of the raw material gas in the reaction tube and the wire of the optical fiber are Ratio A/ to pulling speed B
The solution is that B is 5 or more.

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 optical fiber bare wire 1 is obtained by heating and spinning an optical fiber base material in an optical fiber spinning furnace 2, and the spun optical fiber bare wire 1 is passed through a cooling pipe 11 through which cooling helium flows to a CVD reactor 3. It is designed to lead you to. This CVD reaction P3 is for forming a carbon film on the surface of the bare optical fiber 1 by allowing the CVD reaction to proceed therein. CVD
The reactor 3 is generally composed of a generally cylindrical reaction tube 4 and a heating element 5 that heats the reaction tube 4. The reaction tube 4 and the heating element 5 that heats it can be appropriately selected depending on the heating temperature, etc., and a resistance CVD reactor, an induction CVD reactor, an infrared CVD reactor, etc. can be used. It is also possible to use a method that generates plasma using high frequency waves or microwaves to decompose raw material gas into ions.

A raw material gas supply pipe 6 for supplying raw material gas within the reaction tube 4 is attached to the upper part of the reaction tube 4, and an exhaust pipe 7 for exhausting unreacted gas and the like is attached to the lower part. A gas nol mechanism 8 for nodding the reaction tube 4 and the optical fiber spinning furnace 2 is provided at the bottom of the reaction tube 4 .

In addition, a resin liquid coating device 9 is provided at the lower stage of this CVD reactor 3.
A curing device 10 is provided so that a protective film can be formed on the carbon film formed in the CVD reactor 3.

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 is heated and spun in the optical fiber spinning furnace 2, and a cooling pipe 11 provided at the lower stage of the optical fiber spinning furnace 2. CVD reactor 3, resin liquid coating device 9, curing device 1
They are sequentially inserted into O and are fed so as to run on these central axes at a predetermined linear speed. In the apparatus shown in FIG. 1, the spinning speed of the tip fiber and the drawing speed of the bare optical fiber l coincide with each other.

Next, the heating element 5 generates heat to heat the inside of the reaction tube 4 to a predetermined temperature, and the raw material gas is supplied into the reaction tube 4 from the raw material gas supply pipe 6 at a predetermined flow rate. The temperature inside the reaction tube 4 is appropriately selected depending on the type of raw material gas, the drawing speed of the optical fiber, etc., but it is sufficient as long as it is sufficient for thermal decomposition of the raw material gas, and approximately 500 to 1400°C is preferable. . Heating temperature 5
If the temperature is lower than 00°C, the thermal decomposition of the raw material residue will not proceed, and 1
If the temperature is higher than 400°C, a large amount of soot will be generated and the hydrogen resistance of the carbon film formed on the surface of the bare optical fiber 1 will deteriorate, both of which are not preferred.

Further, in order to suppress the generation of soot, it is preferable to set the temperature to be slightly lower than the thermal decomposition temperature of the raw material residue.

Note that the raw material gas here refers to the waste supplied to the reaction tube 4 in which the CVD reaction proceeds, and is a mixture of at least a raw material compound and a carrier gas. Specific examples include methane, ethane, propane, hensen, toluene, and the like, as well as chloromethane, chloromenzene, and the like, which are obtained by replacing the hydrogen atoms of these compounds with chlorine atoms.

Further, various known carrier gases such as helium gas, argon gas, and hydrogen gas can be used as the carrier gas.

The flow rate of this raw material gas is appropriately selected depending on the type of raw material compound, heating temperature, etc., but is usually 0°2 to 1.0ρ/
It takes about a minute. and the ratio A/B of the flow rate A of the raw material gas in the reaction tube 4 and the drawing speed B of the optical fiber is 5 or more,
Preferably, it is set in a range of 5 to 10.

If the ratio A/B between the flow rate A of the raw material gas in the reaction tube 4 and the drawing speed B of the optical fiber is less than 5, the strength of the optical fiber will be significantly reduced. This is because the optical fiber comes into contact with a region where hydrogen radicals generated by decomposition of the source gas exist before the carbon film is formed to a sufficient thickness on the surface of the optical fiber. This is because when an optical fiber comes into contact with hydrogen radicals, SiO bonds are decomposed by the hydrogen radicals, forming silanol (Si-OH) groups that cause a decrease in the strength of the optical fiber and an increase in transmission loss. Moreover, if the above-mentioned A/B exceeds 15, only a small amount of carbon film will be deposited, so it is usually set to less than this.

Bare optical fiber l with carbon coating formed in this way
is introduced into the resin liquid coating device 9 provided at the lower stage.

The bare optical fiber l inserted into the resin liquid coating device 9 is
An ultraviolet curable resin liquid or a thermosetting resin liquid for forming a protective film is applied, and then cured in a curing device 10 having curing conditions suitable for the applied resin liquid to form a protective film and exposed to light. Considered to be fiber.

As mentioned above, the feed rate of the raw material gas and the spinning speed are set so that the ratio A/B between the flow rate A of the raw material gas in the reaction tube 4 and the drawing speed B of the bare optical fiber 1 is 5 or more. This prevents the optical fiber, which does not have a sufficient carbon coating, from coming into contact with the hydrogen radicals generated by thermal decomposition of the raw material gas, which causes a decrease in the hydrogen resistance of the optical fiber and an increase in transmission loss. The formation of ranol groups can be suppressed.

[Example] (Example 1) A resistance CVD reactor having a quartz tube reaction tube was attached to the lower stage of an optical fiber spinning furnace to prepare an apparatus similar to that shown in FIG. 1.

A single mode optical fiber preform having an outer diameter of 30 mm and having a core impregnated with GeO7 as a dopant was placed in an optical fiber spinning furnace. This optical fiber base material was heated to 2000°C.
The fibers were heated to 15 m/min and spun into a single moat fiber with an outer diameter of 125 μm at a spinning speed of 15 m/min. After cooling this bare optical fiber to 50° C. in a cooling tube, it was introduced into a CVD reactor to form a carbon film. Note that since the drawing speed of the bare optical fiber matches the spinning speed of the optical fiber, the drawing speed B is 15 m/min.

The heating element was heated so that the temperature inside the CVD reactor was 1200° C., and the raw material gas was supplied at a flow rate of 15 ρ/min, so that the flow rate A of the raw material gas in the reaction tube was 80 m/min. The raw material gas used was a benzene/helium mixed gas generated by introducing helium into Hensen. The benzene concentration of this mixed gas is 0,5 vo
The concentration was 1%. Also, the exhaust pressure of the CVD reactor is -7
It was set as mmHg. The ratio A/B between the flow rate A of the raw material gas in the reaction tube and the drawing rate B of the bare optical fiber was 5.3.

The optical fiber with the carbon coating formed in this manner is treated with a urethane acrylate resin solution (Young's modulus: 70 kg/mm2,
The optical fiber was inserted into a die spot for resin coating sealed with an elongation of 60%, and then the applied resin was cured using a curing device equipped with an ultraviolet irradiation lamp to form a protective coating, and an optical fiber with an outer diameter of 250 μm was obtained.

(Examples 2 to 3 and Comparative Examples 1 to 4) Except that the drawing speed B of the bare optical fiber and the flow rate A of the raw material gas in the reaction tube were changed as shown in Table 1, respectively. An optical fiber was manufactured in exactly the same manner as in Example 1 above.

(Hereinafter, blank space) (Test Example 1) The optical fibers obtained in the above Examples and Comparative Examples were each taken at a length of I km, and the transmission loss at a wavelength of 1.24 μm was measured. Thereafter, these were wound into a bundle with a diameter of 150 mm, and left in a hydrogen evaluation pressurized container at a temperature of 80° C. and a hydrogen partial pressure of 1 atm for 48 hours.

After this, the transmission loss at a wavelength 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) To measure the tensile strength of each optical fiber obtained in the above Examples and Comparative Examples. The conditions for the tensile strength test were as follows: the number of specimens tested was 25, the gauge length was 3 m, the strain rate was 10%/min, the temperature was 23° C., and the relative humidity was 50%, and the tensile strength was evaluated based on the probability of breakage. The results are also shown in Table 1.

[Effects of the Invention] As explained above, in forming a carbon film on the surface of the bare optical fiber 1, the ratio A/B of the flow rate A of the raw material gas in the reaction tube and the drawing speed B of the optical fiber is 5 or more. If the feed rate of the raw material gas and the drawing rate of the bare optical fiber are respectively set so that Due to the contact with the silanol group, no silanol groups are formed. Therefore, it is possible to suppress the production of silanol groups, which cause a decrease in hydrogen resistance and mechanical strength, due to hydrogen radicals, so it is possible to obtain an optical fiber having better hydrogen resistance and mechanical strength. .

[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. 1. Bare optical fiber, 3. CVD reactor, 4. Reaction tube.

Claims (1)

[Scope of Claims] A method for manufacturing an optical fiber in which a raw material gas is thermally decomposed in a reaction tube to form a carbon film on the surface of a bare optical fiber, the flow rate A of the raw material gas in the reaction tube and the drawing speed of the optical fiber. A method for manufacturing an optical fiber, characterized in that the ratio A/B to B is 5 or more.