JP3039961B2 - Optical fiber manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber having a carbon coating formed on the surface thereof, and relates to a method for forming a carbon coating on a bare optical fiber surface. By adjusting the bare wire surface and the reaction tube wall to a predetermined temperature, an optical fiber having more excellent hydrogen resistance can be obtained at a high drawing speed.

[Prior art and its problems] When a silica 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 Ge further contained as dopants
Since O ₂ , B ₂ O _{3 and the} like 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 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 a problem, it has been disclosed that a carbon coating is formed on the surface of an optical fiber by a chemical vapor deposition method, whereby the hydrogen resistance of the optical fiber can be improved.

However, in the above structure method, the deposition rate of the carbon coating formed on the bare optical fiber surface is low, and the quality of the coating is not dense. Speed had to be kept and there was a problem in its 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 excellent in hydrogen resistance characteristics at high speed.

Means for Solving the Problems The present inventors have conducted intensive studies on the improvement of the hydrogen resistance and the spinning speed of an optical fiber having a carbon coating formed on the surface thereof. When the raw material gas is contacted in the reaction tube to form a carbon coating, the surface temperature of the bare optical fiber and the wall temperature of the reaction tube are adjusted to significantly improve the hydrogen resistance of the optical fiber and the drawing speed. I found what I could do.

That is, in the production method of the present invention, the surface temperature of the bare optical fiber into the reaction tube is 850 to 1100 ° C., the surface temperature at the time of exit is 700 to 850 ° C., and the wall temperature of the reaction tube is 40 ° C.
The solution was set to 0 ° C. or lower.

 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. An optical fiber bare wire 1 is made of an optical fiber preform 2 and an optical fiber spinning furnace 3.
Heat-spun inside. This bare optical fiber 1
Is led to the CVD reactor 4 provided immediately below the spinning furnace without being cooled.

The CVD reactor 4 brings the heated optical fiber bare wire 1 into contact with the raw material gas, and thermally decomposes the raw material gas according to the surface temperature of the optical fiber bare wire 1 to form a carbon coating on the surface of the optical fiber bare wire 1. Is formed. The CVD reactor 4 is roughly composed of a substantially cylindrical reaction tube 5 and a temperature control device 6 for adjusting the wall temperature of the reaction tube 5.

The temperature control device 6 is for maintaining the wall temperature of the reaction tube 5 at 400 ° C. or lower, and is, for example, a device in which a cooling tube in which a coolant such as water or an inert gas is flown is wound. It is connected to the reaction tube 5 via the section 7. The control section 7 is further connected to a temperature measuring section (not shown) including a non-contact thermometer or the like for measuring the wall temperature of the reaction tube 5, and based on the measurement result, the refrigerant supply amount of the temperature control device 6 and the like. Can be adjusted.

Adjustment of the surface temperature when the bare optical fiber 1 enters the reaction tube 5 and the surface temperature when exiting the reaction tube 5 is performed by adjusting the distance between the optical fiber spinning furnace 3 and the CVD reaction furnace 4, in other words, the CVD. This is performed according to the installation position of the reaction furnace 4 and the spinning speed of the bare optical fiber 1. For example, when the bare optical fiber 1 is spun at a speed of 300 m / min, the distance between the CVD reactor 4 and the neck down portion of the optical fiber preform 2 is about 30 mm.

A source gas supply pipe 8 for supplying a source gas is attached to an upper portion of the reaction tube 5, and an exhaust pipe 9 for exhausting unreacted gas and surplus carbon fine particles is attached to a lower portion of the reaction tube 5. Further, the upper and lower stages of the reaction tube 5
A gas seal mechanism 10 for sealing the inside is continuously provided.

Furthermore, a resin liquid coating device 1
1 and a curing device 12 are provided so that a protective coating made of resin can be formed on the carbon coating.

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

The optical fiber preform 2 is heated and spun in an optical fiber spinning furnace 3 and a CV provided in a lower stage of the optical fiber spinning furnace 3.
D The reactor is sequentially inserted into the reaction furnace 4, the resin liquid application device 11, and the curing device 12, and supplied so as to travel on the central axis. At this time, the surface temperature when the bare optical fiber 1 enters the reaction tube 5, that is, the surface temperature near the raw material gas supply tube 8 becomes 850 to 1100 ° C. The position of the CVD reactor 4 is set so that the temperature, that is, the surface temperature near the exhaust pipe 9 is 700 to 850 ° C.
The spinning speed of the bare optical fiber 1, that is, the drawing speed is set. By maintaining the surface temperature of the bare optical fiber 1 in this manner, a carbon coating having good characteristics is formed as will be described in Examples below.

Next, a source gas is supplied into the reaction tube 5 from the source gas supply pipe 8. The raw material gas is not particularly limited as long as it is a carbon compound capable of forming a carbon film by thermal decomposition, and is obtained by mixing at least the raw material compound and a carrier gas for diluting and transferring the raw material compound. Specific examples of the raw material compounds include methane, ethane, propane, benzene, toluene, and the like, and chloromethane and chlorobenzene in which a hydrogen atom of these compounds is replaced with a chlorine atom. Among these compounds, benzene is preferred because it has good thermal decomposability and gives a carbon film having good characteristics. As the carrier gas, various known gases such as helium gas, argon gas, hydrogen gas, and nitrogen gas can be used.

At this time, the temperature controller 6 is driven so that the wall temperature of the reaction tube 5 is kept at 400 ° C. or lower. The lower the wall temperature of the reaction tube 5 is, the more the hydrogen resistance and the spinning speed can be improved. Therefore, the temperature 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 fine particles generated by the thermal decomposition of the raw material gas adhere to the inside of the reaction tube 5 and the deposition rate of the carbon film on the surface of the bare optical fiber 1 decreases. That's why. In addition, coarse particles of carbon grown in the gas phase region are more likely to adhere to the surface of the bare optical fiber 1, thereby lowering the hydrogen resistance of the obtained optical fiber.

The bare optical fiber 1 on which the carbon coating is formed in this manner is introduced into a resin liquid coating device 11 provided at the lower stage. Optical fiber bare wire 1 inserted into resin liquid coating device 11
A UV-curable resin liquid or a thermosetting resin liquid for forming a protective film is applied, and then the applied resin liquid is cured in a curing device 12 having suitable curing conditions to form a protective film. Optical fiber.

As described above, when the heated bare optical fiber and the raw material gas are brought into contact with each other in the reaction tube to form a carbon coating on the bare optical fiber surface, the surface of the bare bare optical fiber when entering the reaction tube is exposed. The temperature is 850-1100 ° C, the surface temperature at the time of outgoing from the reaction tube is 700-850 ° C, and the wall temperature of the reaction tube is 400
By setting the temperature to not more than ℃, the carbon particles can be refined, and the deposition efficiency of the carbon particles on the bare optical fiber surface can be improved. Therefore, even if the drawing speed is increased, a carbon film having a sufficient thickness is formed. be able to. Further, the carbon fine particles are deposited on the bare optical fiber surface immediately after the generation, so that the formed carbon film becomes dense and has excellent hydrogen resistance.

[Example] (Example) While installing a reaction tube in the lower stage of the optical fiber spinning furnace,
A cooling tube using water as a refrigerant was wound around the reaction tube to obtain a device similar to that shown in FIG. The reaction tube was set at a position 30 mm from the neck down position of the optical fiber preform.

A single-mode optical fiber preform having an outer diameter of 30 mm and a core portion impregnated with GeO ₂ as a dopant was installed in an optical fiber spinning furnace. This optical fiber preform was 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 0 m / min.

Next, the raw optical fiber is inserted into the reaction tube, and benzene is used as a raw material compound, a raw material gas is supplied using nitrogen gas as a carrier gas, and the raw material gas is thermally decomposed by contacting the raw optical fiber with the raw optical fiber. A carbon coating was formed on the bare optical fiber surface. The flow rate of the raw material gas was benzene gas 0.2 / min and nitrogen gas 0.8 / min. The inside of the reaction tube was evacuated with an exhaust pressure of −4 mmH ₂ O from the exhaust tube. Then, the surface temperature of the bare optical fiber inserted into the reaction tube is
It was 900 ° C and 750 ° C when measured using a non-contact thermometer at two points near the source gas supply port and the exhaust pipe. The wall temperature of the reaction tube was 300 ° C.

The optical fiber thus formed with the carbon coating is coated with a urethane acrylate resin solution (Young's modulus 70 kg / mm ² , elongation 60
%) Into the die spot for resin coating in which
Next, the applied resin is cured by a curing device equipped with an ultraviolet irradiation lamp to form a protective film, and the outer diameter is 250 μm.
Optical fiber.

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

(Test Example 1) Each of the optical fibers obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was sampled for 1 km, and the transmission loss at a wavelength of 1.24 μm was measured. After this, these are 150mm in diameter
And left in a pressurized hydrogen evaluation container at a temperature of 80 ° C. and a hydrogen partial pressure of 1 atm for 96 hours. After this, the wavelength is again 1.24μ
The transmission loss at m was measured to determine the increase in absorption loss due to hydrogen. The results are 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 with a solvent, and the electrical resistance of the carbon coating formed on the bare optical fiber surface was measured. The values were measured with a digital multimeter. A method of measuring the degree of adhesion of the carbon film using the electric resistance value was adopted.
The results are shown in Table 1.

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, the surface temperature of the bare optical fiber into and out of the reaction tube and the wall temperature of the reaction tube are appropriately adjusted to the temperature. Since the adjustment is performed, the carbon particles generated by the thermal decomposition of the raw material gas can be miniaturized, and the efficiency and speed of the deposition of the carbon particles on the bare optical fiber surface can be remarkably improved.

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

[Brief description of the 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, 5 ... reaction tube, 6 ... temperature control device.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shinji Araki 1440, Mukurosaki, Sakura City, Chiba Prefecture Inside the Sakura Plant of Fujikura Electric Wire Co., Ltd. (72) Inventor Yutaka Katsuyama 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-2-24439 (JP, A) JP-A-3-126645 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C03C 25/02

Claims (2)

(57) [Claims] An optical fiber bare wire is fed into a reaction tube to which a raw material gas is supplied, and when the raw material gas is thermally decomposed to form a carbon coating on the surface of the optical fiber bare wire, the optical fiber bare wire is supplied to the reaction tube. 850-1
100 ° C, and the surface temperature when outgoing from the reaction tube is 700-850
° C and the wall temperature of the reaction tube is 400 ° C or lower. 2. The method for manufacturing an optical fiber according to claim 1, wherein said source gas contains benzene.