JP2683070B2 - Optical fiber manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an optical fiber having a carbon coating on its surface, which is a raw material of a hydrocarbon containing at least one chlorine atom in its molecule. By using it as a compound, an optical fiber having excellent hydrogen resistance and mechanical strength can be obtained.

[Prior Art] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to molecular vibration of hydrogen molecules diffused in the fiber increases, and further, P ₂ O ₅ , Ge contained as a dopant is added.
Since O ₂ , B ₂ O _3, etc. react with hydrogen and are taken into the fiber glass as OH groups, there is a problem that transmission loss due to absorption of OH groups increases.

To cope with such adverse effects, a method of filling a liquid composition having a hydrogen absorbing ability into an optical cable (Japanese Patent Application No.
No. 251808) is considered, but the effect is insufficient, and the structure becomes complicated, which is economically problematic.

In order to solve such a problem, it was recently announced that a chemical vapor deposition method (hereinafter abbreviated as CVD method) may be used to form a carbon coating on the optical fiber surface, thereby improving the hydrogen resistance of the optical fiber. Has been done. In this manufacturing method, a bare optical fiber spun in a spinning furnace is inserted into a thermal CVD furnace, and a hydrocarbon compound is supplied to thermally decompose the hydrocarbon to form a carbon coating on the bare optical fiber surface. Is the way.

[Problems to be Solved by the Invention] However, in the optical fiber manufacturing method as described above, water molecules adsorbed on the surface of the bare optical fiber are diffused into the core of the optical fiber during thermal CVD and There is a disadvantage that it reacts with the dopant diffused in advance and significantly increases the transmission loss at the wavelength of 1.39 μm due to the absorption of OH groups.

Furthermore, when heated at a high temperature to form a carbon film, water molecules adsorbed on the surface of the optical fiber react with the optical fiber to form silanol groups, and the silanol groups erode the surface of the optical fiber. There was also the inconvenience that the physical strength was lowered.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a manufacturing method capable of obtaining a high-strength optical fiber having excellent hydrogen resistance.

[Means for Solving the Problems] The method for producing an optical fiber according to the present invention is a high fiber bare wire spun by pyrolyzing a hydrocarbon containing at least one chlorine atom and at least one double bond in the molecule. Forming a carbon coating on the surface was the solution.

[Action] As a raw material compound, at least one chlorine atom is included in the molecule.
When hydrocarbons containing more than one of them are used, chlorine radicals are generated during thermal decomposition, and these react with hydrogen atoms in water molecules adsorbed on the bare surface of the optical fiber. As a result, water molecules adsorbed on the surface of the bare optical fiber can be removed. Further, the presence of the double bond allows the hydrocarbon to be easily pyrolyzed and a carbon film having good crystallinity can be formed.

 Hereinafter, the present invention will be described in detail.

FIG. 1 shows an example of an optical fiber manufacturing apparatus suitably used for the optical fiber manufacturing method of the present invention. In FIG. 1, reference numeral 1 denotes a bare optical fiber. The bare optical fiber 1 is obtained by heating and spinning an optical fiber preform (not shown) in an optical fiber spinning furnace 2.
Is spun and supplied into a heating furnace 3 provided in the lower stage of the optical fiber spinning furnace 2. The heating furnace 3 is for forming a carbon coating on the surface of the bare optical fiber 1 spun in the upper optical fiber spinning furnace 2 by the CVD method, and is a schematic for promoting a CVD reaction inside the carbon coating. It is composed of a cylindrical reaction tube 4 and a heating element 5 for heating the reaction tube 4. A raw material compound supply pipe 4a for supplying a raw material compound into the reaction pipe 4 is attached to the upper portion of the reaction pipe 4, and an exhaust pipe 4b for exhausting unreacted gas or the like is attached to the lower portion thereof. The reaction tube 4 and the heating element 5 for heating the reaction tube 4 can be appropriately selected depending on the heating temperature and the like, and a resistance heating furnace, an induction heating furnace, an infrared heating furnace or the like can be used. It is also possible to use a device in which plasma is generated by using high frequency or microwave to ion-decompose the raw material compound. A resin liquid coating device 6 and a curing device 7 are continuously provided in the lower stage of the heating furnace 3 and
A protective coating layer can be formed on the carbon coating formed inside.

The following steps are used to manufacture an optical fiber according to the manufacturing method of the present invention using the above manufacturing apparatus.

The optical fiber preform is heated and spun in the optical fiber spinning furnace 2, and is inserted into the heating furnace 3, the resin liquid coating device 6, and the curing device 7 provided in the lower stage of the optical fiber spinning furnace 2, and their central axes It is supplied so that it travels at a predetermined linear speed.
Then, the heating element 5 is caused to generate heat to heat the inside of the reaction tube 4 to a predetermined temperature, and at the same time, the raw material compound is supplied into the reaction tube 4 from the raw material compound supply pipe 4a. As this raw material compound, a hydrocarbon containing at least one chlorine atom and at least one double bond in its molecule, which forms a carbon film by thermal decomposition, is used, and the properties of the carbon film formed and its deposition rate are used. From the viewpoint of the above, those having 15 or less carbon atoms are particularly preferable.
Specific examples of such hydrocarbons include monochlorobenzene, 1,2 dichloroethylene and the like. The hydrocarbon as the raw material compound can be supplied to the reaction tube 4 in a gas state, or the one diluted with an inert gas can be used, and the supply rate is appropriately selected depending on the kind of the raw material compound and the heating temperature. However, usually 0.2 to 1.0 / min is suitable. The temperature in the reaction tube 4 can be appropriately selected depending on the type of raw material compound, the spinning speed, etc., but may be a temperature sufficient for the thermal decomposition of hydrocarbons of the raw material compound.
About 0 to 1200 ° C is suitable. If the heating temperature is 500 ° C or lower, the thermal decomposition of the raw material compound does not proceed, and if it is 1200 ° C or higher, a large amount of soot as a by-product is generated and the structure of the carbon coating formed on the surface of the bare optical fiber 1 It is not preferable because it becomes close to a graphite structure and sufficient hydrogen resistance cannot be obtained. For the purpose of preventing the generation of soot as a by-product,
It is desirable that the heating temperature is set to be slightly lower than the thermal decomposition temperature of the raw material compound. The bare optical fiber 1 having the carbon coating thus formed is introduced into the resin liquid coating device 6 provided in the lower stage, and then inserted into the curing device 7 for curing the resin liquid. The optical fiber bare wire 1 inserted into the resin liquid coating device 6 is coated with an ultraviolet curable resin liquid or a thermosetting resin liquid for forming a protective coating layer, and then a suitable curing of the applied resin liquid is performed. The protective coating layer is formed by being cured in the curing device 7 having the conditions.

As mentioned above, at least one chlorine atom is included in the molecule.
When using a hydrocarbon containing more than one as a raw material compound,
Chlorine radicals are generated during thermal decomposition. The chlorine radicals react with hydrogen atoms in water molecules adsorbed on the surface of the bare optical fiber 1 to form hydrogen chloride, so that the surface of the bare optical fiber 1 can be dehydrated. As a result, it is possible to prevent the water molecules adsorbed on the surface of the bare optical fiber 1 from diffusing into the core of the optical fiber, and also to prevent the generation of OH groups due to the reaction between the water molecules and the dopant. It is possible to reduce the transmission loss of the optical fiber due to the absorption of the OH group. Furthermore, by removing water molecules from the surface of the bare optical fiber 1, it is possible to prevent the production of silanol groups, which causes a decrease in the mechanical strength of the optical fiber, so that a high-strength optical fiber can be obtained. . Further, since the raw material compound has a double bond, it is easily thermally decomposed, and the obtained carbon coating has a dense structure, so that it also 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. The coating may be formed continuously. Further, in this example, a single protective coating layer was formed on the carbon coating, but the number of protective coating layers is not limited to this, and a plurality of protective coating layers may be formed.

[Example] (Example 1) A resistance heating furnace having a reaction tube of a quartz tube having an inner diameter of 40 mm was attached to the lower stage of a spinning furnace for spinning a bare optical fiber from an optical fiber preform. Next, in this spinning furnace, a single mode optical fiber preform having an outer diameter of 30 mm and having a core portion impregnated with GeO ₂ as a doping agent was installed. This optical fiber preform is 2000
The fiber was heated to 0 ° C. and spun into an optical fiber having an outer diameter of 125 μm at a spinning speed of 20 m / min. Further, while heating the inside of the resistance heating furnace to 1000 ° C., monochlorobenzene vapor diluted with argon gas to about 5 vol% was supplied into the reaction tube at a flow rate of about 3 / min to form a carbon coating on the surface of the bare optical fiber spun. Formed. Furthermore, a urethane acrylate resin liquid (Young's modulus 50 kg / mm ² , elongation 60%) is enclosed in the resin coating die spot, and an optical fiber with a carbon coating is inserted through this, and the surface is UV cured. After applying the resin solution, the resin solution is irradiated with an ultraviolet lamp to cure the resin solution and the outer diameter is about 250 μm.
Manufactured optical fiber.

(Example 2) An optical fiber was manufactured in exactly the same manner as in Example 1 except that the raw material compound to be fed into the reaction tube was 1,2 dichloroethylene diluted with argon gas to 5 vol%.

(Comparative Example 1) An optical fiber was manufactured in exactly the same manner as in Example 1 except that the starting compound supplied to the reaction tube was methane diluted with argon gas to 5 vol% and the heating temperature was 1400 ° C.

(Comparative Example 2) An optical fiber was manufactured in exactly the same manner as in Example 1 except that the starting compound supplied into the reaction tube was benzene diluted with argon gas to 5 vol%.

(Comparative Example 3) An optical fiber was produced in exactly the same manner as in Example 1 except that the raw material compound supplied into the reaction tube was ethylene diluted to 5 vol% with argon gas.

(Test Example 1) 20 optical fibers obtained in each of Examples 1 and 2 and Comparative Examples 1 to 3 were prepared, and the gauge length was 3 m.
Tensile at a strain rate of 10% / min., A Weibull plot of fracture probability and tensile strength was performed, and the tensile strength at 50% fracture probability was measured. The results are shown in Table 1.

(Test Example 2) 500 m of each optical fiber obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was prepared, and the absorption loss at each wavelength was measured by an optical loss wavelength characteristic measuring device. First, the loss amount at the wavelength of 1.30 μm where the absorption loss due to the absorption of OH groups appears
It is also shown in the table.

From the above results, Example 1 according to the manufacturing method of the present invention
Each of the optical fibers of 2 and 2 has high mechanical strength,
It was confirmed that the amount of absorption loss was low.

[Effects of the Invention] As described above, the optical fiber manufacturing method of the present invention has at least one chlorine atom and at least one double bond in the molecule.
Pyrolysis of the hydrocarbons contained in more than one, to form a carbon coating on the surface of the bare optical fiber spun,
Since the water molecules adsorbed on the surface of the bare optical fiber at the time of forming the carbon film can be removed, the water molecules can be prevented from diffusing into the core portion of the optical fiber. Therefore, the amount of absorption loss due to the absorption of the OH group decreases, so that an optical fiber with low transmission loss can be obtained. Furthermore, the removal of water molecules during the formation of the carbon coating prevents the production of silanol groups that erode the fiber surface, so that the obtained optical fiber has high mechanical strength.

In addition, since the hydrocarbon has a double bond, it is easily pyrolyzed, and the resulting carbon film has good crystallinity and high hydrogen permeation blocking ability, so it has excellent hydrogen resistance. Fibers can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber manufacturing apparatus preferably used in the optical fiber manufacturing method of the present invention. 1 ... Optical fiber bare wire.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Shimichi 1440 Rokuzaki, Sakura City, Chiba Prefecture, Fujikura Electric Cable Co., Ltd., Sakura Factory (56) Reference JP-A-2-35404 (JP, A) JP-A-2 -73315 (JP, A) JP-A-2-83240 (JP, A)

Claims (1)

(57) [Claims] 1. An optical fiber characterized in that a hydrocarbon containing at least one chlorine atom and at least one double bond in the molecule is pyrolyzed to form a carbon coating on the surface of a bare bare optical fiber. Manufacturing method.