JP2595364B2 - Optical fiber manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an optical fiber provided with a carbon coating, and more excellent resistance to resistance by forming a film while flowing a raw material gas at a predetermined flow rate. An optical fiber having hydrogen characteristics and mechanical strength can be produced.

[Prior Art and Problems to be Solved by the Invention] 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. P ₂ O ₅ and GeO further contained as dopants
₂ , B ₂ O _{3 and the} like react with hydrogen and are taken into fiber glass as OH groups, so that there is a problem that transmission loss due to absorption of OH groups increases.

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

In order to solve such problems, it has recently been announced that a carbon film can be formed on the surface of an optical fiber by a chemical vapor deposition method (hereinafter abbreviated as a CVD method), thereby improving the hydrogen resistance of the optical fiber. ing. This manufacturing method is a method in which a carbon coating is formed on the bare optical fiber surface by a CVD method, and then a protective coating layer is formed with an ultraviolet-curable resin or a thermosetting resin.

However, even in the case of an optical fiber manufactured in the same manner by such a manufacturing method, there may be a case where a great difference occurs in the hydrogen resistance characteristic and the fatigue characteristic.

The present invention has been made in view of the above circumstances, and has as its object to provide a manufacturing method capable of manufacturing an optical fiber having more excellent hydrogen resistance and mechanical strength.

[Means for solving the problem]

The present inventors have conducted intensive studies on the improvement of the hydrogen resistance characteristic and the mechanical strength of the carbon coated optical fiber, and as a result, the flow rate of the raw material gas at the time of forming the carbon coating was set to a range of 40 m / min to 80 m / min. By setting, it was found that the hydrogen resistance and the mechanical strength of the optical fiber can be remarkably improved.

When the flow rate of the raw material gas is less than 40 m / min, the carbon film formed has large clusters, as if a medium is deposited, and is inferior in permeation prevention performance of moisture and hydrogen molecules. Then, the manufactured optical fiber is inferior in hydrogen resistance and mechanical strength. On the other hand, if the flow rate exceeds 80 m / min, the film forming speed is reduced, which is uneconomical.

Here, the source gas is a gas supplied to a reaction tube for performing a chemical vapor deposition method, and is a mixture of at least a source compound and a carrier gas.

The raw material compound used in the production method of the present invention is not particularly limited as long as it is a compound that has volatility and generates carbon by thermal decomposition, but from the viewpoint of the properties of the formed carbon film and the deposition rate thereof, Up to 15 hydrocarbons or halogenated hydrocarbons are preferred. The halogen atom to be substituted is preferably a chlorine atom from the viewpoint of handleability and the like. Specific examples include methane, ethane, propane, benzene, toluene, and the like, as well as chloromethane and chlorobenzene in which hydrogen atoms of these compounds are substituted with chlorine atoms.

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

A diluent gas such as a chlorine gas may be mixed with the raw material gas.

When the carbon film is formed under the above conditions, the concentration of the raw material compound in the raw material gas is desirably set to about 1 to 6% by volume.

If the concentration of the raw material compound is less than the above range, the variation in cluster size of the obtained carbon coating increases.
Further, the film forming speed is reduced, which is uneconomical. On the other hand, if the concentration exceeds the above range, the tendency of the cluster size of the obtained carbon coating to increase becomes remarkable.

When forming a carbon film by this manufacturing method, it is desirable that the temperature in the CVD reactor be set to 600 ° C. or higher. If the temperature is lower than this, thermal decomposition of the starting compound does not proceed. It is desirable that the temperature (preheating temperature) of the bare optical fiber when introduced into the CVD reactor is set in the range of 1200 to 1500 ° C. If the preheating temperature exceeds 1500 ° C., the surface of the bare optical fiber made of quartz is undesirably melted. On the other hand, if the preheating temperature is lower than 1200 ° C., it is not preferable because the bare optical fiber may be cooled to less than 600 ° C. during which the thermal decomposition of the raw material compound does not proceed while passing through the CVD reactor.

[Operation] In the production method of the present invention, the source gas is flowed at a high speed, so that it is possible to prevent the radical species generated by the reaction of the source radicals in the gas phase from increasing. As a result, a carbon coating having a small cluster size and a small variation in size can be formed on the bare optical fiber. Since the carbon coating having a small cluster size is excellent in preventing moisture and hydrogen gas from permeating, the hydrogen resistance of the optical fiber can be improved. In addition, if a carbon coating having a small cluster size and a stable carbon coating is formed on the bare optical fiber, the mechanical strength of the optical fiber is also improved.

〔Example〕

Embodiment 1 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 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, and the spun optical fiber 1 passes through a cooling pipe 12 through which helium for cooling flows. It is led into the CVD reactor 3. This CVD
The reaction furnace 3 forms a carbon coating on the surface of the bare optical fiber 1 by advancing a CVD reaction in the inside thereof, and is roughly constituted by a reaction tube 4 and a heating element 5. Reaction tube 4 has an inner diameter of 50
mm, 900 mm long, almost cylindrical. A supply pipe 6 for supplying a raw material gas is provided at an upper portion of the reaction tube 4, and an exhaust pipe 7 for exhausting unreacted gas and the like is provided at a lower portion. As the heating element 5, a heating resistor that emits infrared rays is used. Reaction tube 4 of CVD reactor 3
A gas seal mechanism 8 for keeping the airtight inside the reactor 3
Are connected. A resin coating die spot 9 and a curing device 10 are continuously provided below the CVD reactor 3 so that a protective coating layer can be formed on the carbon coating formed in the CVD reactor 3. It has become.

An optical fiber was manufactured using this optical fiber manufacturing apparatus as follows.

First, a single mode fiber preform having an outer diameter of 30 mm and a core portion impregnated with GeO ₂ as a doping material was installed in the optical fiber spinning furnace 2. This optical fiber preform is heated to 2000 ° C.
The fiber was spun into a single mode fiber having an outer diameter of 125 μm at a spinning speed of 15 m / min. And this spun fiber bare wire 1 is
After cooling to 50 ° C. in the cooling cylinder 12, it was introduced into the CVD reactor 3 to form a carbon coating.

 The film forming conditions are as follows.

As a source gas, a benzene / helium mixed gas generated by introducing a helium gas as a carrier gas into a benzene compound was used.

The bare optical fiber 1 passed through the reaction furnace 3 and coated with a carbon coating was coated with a urethane acrylate resin solution (Young's modulus 70
(kg / mm ² , elongation 60%) is inserted into the resin coating die spot 9 in which the resin is applied, and the applied resin is cured by a curing device 10 equipped with a UV lamp to form a protective coating layer.
An optical fiber of 250 μm was used.

(Other Examples and Comparative Examples) An optical fiber was produced by changing the flow rate of the raw material gas.
Other conditions are the same as in the first embodiment. Table 1 shows the flow rate of the raw material gas when each optical fiber was manufactured.

(Test 1) Each of the optical fibers manufactured under the conditions described above was 1 k
The transmission loss at a wavelength of 1.24 μm was measured. After that, they are wound into a bundle by winding them to a diameter of 150 mm,
It was left for 48 hours in a pressure vessel for hydrogen evaluation at 1 ° C. and a hydrogen partial pressure of 1 atm. Thereafter, 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 shown in Table 1.

(Test 2) The tensile strength of each manufactured optical fiber was measured. The conditions for the tensile test were 25 test pieces, a gauge length of 3 m, a strain rate of 10% / min, a temperature of 23 ° C, and a relative humidity of 50%. Weibull plotting of the probability of breakage and tensile strength was performed, and the tensile strength of 50% breakage probability was determined. Was evaluated. The results are shown in Table 1.

(Test 3) The carbon size of the manufactured optical fiber was observed with a scanning electron microscope to measure the cluster size. The results are shown in Table 1.

From the results in Table 1, when the flow rate of the raw material gas is set to less than 40 m / min (Comparative Examples 1 and 2), the cluster size of the formed carbon coating increases, and the obtained optical fiber has poor hydrogen resistance. It turned out to be.

When the source gas is flowed at a flow rate exceeding 80 m / min (Comparative Example
3,4), it was found that the film formation speed of the carbon film was extremely slow, and it was found that the carbon film of the required thickness could not be formed within the normal spinning speed range. When set within the range of minutes (Examples 1 to 3), a carbon film having a small cluster size and a stable size could be formed. It was found that the obtained optical fiber had good hydrogen resistance and tensile properties.

〔The invention's effect〕

As described above, in the method of manufacturing an optical fiber according to the present invention, the flow rate of the raw material gas is set to 40 to 80 m / min, so that the radical species generated by the reaction of the raw material radicals in the gas phase can be prevented from increasing. As a result, it is possible to form a carbon coating on the bare optical fiber having a small cluster size, excellent moisture and hydrogen gas permeation prevention performance, and excellent mechanical strength. Therefore, according to the method of manufacturing an optical fiber of the present invention, an optical fiber having more excellent hydrogen resistance and mechanical strength can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical fiber manufacturing apparatus used in an embodiment.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Tsuruzaki 1440, Mukurosaki, Sakura-shi, Chiba Fujikura Electric Cable Co., Ltd.Sakura Plant (72) Inventor Shinji Araki 1440, Mukurosaki, Sakura-shi, Chiba Fujikura Electric Wire Co., Ltd.Sakura Plant (72) Inventor Hideo Suzuki 1440, Murosaki, Sakura-shi, Chiba Prefecture Fujikura Electric Wire & Cable Co., Ltd.Sakura Plant (72) Inventor Nobuyuki Yoshizawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Yutaka Katsuyama Nippon Telegraph and Telephone Corporation

Claims (1)

(57) [Claims] 1. A method of forming a carbon coating on a bare optical fiber spun by a thermal chemical vapor deposition method, wherein a flow rate of a raw material gas in a reaction tube is set to 40 m / min to 80 m / min. Optical fiber manufacturing method.