JPH07165444A - Method for producing carbon-coated optical fiber - Google Patents

Abstract

PURPOSE:To provide a method for producing a carbon-coated optical fiber, capable of producing the excellent carbon-coated fiber stabilized in the mechanical strength and the fatigue characteristics in the longitudinal direction. CONSTITUTION:A method for producing a carbon-coated optical fiber comprises forming a carbon coating film on the surface of an optical fiber by a thermal CVD method just after drawn, and subsequently exposing the surface of the carbon coating film to the atmosphere of oxygen within temperatures at which the carbon coating film surface of the optical fiber is oxidized and burned in an oxygen atmosphere, or comprises forming the carbon coating film on the surface of the optical fiber by the thermal CVD method and subsequently exposing the surface of the carbon coating film to the atmosphere of oxidative combustion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon-coated optical fiber, and more particularly to a method for forming a carbon film.

[0002]

2. Description of the Related Art When a silica-based optical fiber comes into contact with hydrogen, the transmission loss increases due to hydrogen molecules diffused in the optical fiber. Further, when the optical fiber is used in various environments for a long period of time, sufficient strength and fatigue characteristics are required. Therefore, a carbon-coated optical fiber coated with a carbon film has been proposed in order to prevent the intrusion of H ₂ O and H ₂ from the outside and improve the hydrogen resistance property and the strength and fatigue properties. , Are beginning to be used in fields such as optical components. A conventional carbon-coated optical fiber manufacturing method is
The thermochemical vapor deposition (CVD) method is used, and the raw material gas is thermally decomposed to 200 to 200 on the surface of the optical fiber immediately after drawing.
A 1000Å carbon film is formed.

[0003]

However, in the above-mentioned method for producing a carbon-coated optical fiber, the soot (carbon particles) produced in the vapor phase on the surface of the carbon film after it has been formed.
May be deposited or a carbon film surface partially formed by coarse crystallites may be formed. Then, the influence of the guide roller at the time of manufacturing the optical fiber cable, or the vibration after laying the optical fiber cable,
In addition, the soot and carbon film may be rubbed due to bending and ironing applied during mounting processing of the optical fiber used for parts,
Alternatively, the carbon film surface may be damaged due to coarse separation of the crystallites, which causes abnormal parts such as cracks and separation to form in the carbon film, resulting in strength and fatigue characteristics of the carbon-coated optical fiber. There was a problem that it decreased. The present invention, the unevenness of the carbon film surface due to the coarse crystallites, removing the effect of soot attached to the carbon film surface,
The purpose is to smooth the surface of the carbon film formed on the optical fiber to enhance the mechanical reliability of the carbon-coated optical fiber.

[0004]

The present invention provides a method for producing a carbon-coated optical fiber which solves the above-mentioned problems. After forming a carbon film on the surface of an optical fiber immediately after drawing by a thermal CVD method, The first invention is to expose the carbon film surface to the oxygen atmosphere while the carbon film surface temperature of the optical fiber is a temperature at which carbon oxidizes and burns in a predetermined oxygen atmosphere.
A second invention is to form a carbon film by the VD method and then expose the surface of the carbon film to an atmosphere in which carbon oxidizes and burns.

[0005]

As described above, when the carbon film formed on the surface of the optical fiber is treated by the methods of the first and second inventions, the surface of the carbon film is oxidatively burned by a slight thickness. Then, the soot adhering to the surface of the carbon film, or the convex portion of the surface due to the coarse crystallites that compose the carbon film itself burns, and the surface of the carbon film is clean with no deposits and the surface irregularities are improved. can get.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. Example 1 FIG. 1A is an explanatory diagram of an apparatus used in an example of a method for producing a carbon-coated optical fiber according to the present invention. In the figure, 1 is a drawing furnace, 2 is a thermal CVD reaction furnace, 3 is a gas nozzle part, 4 is an optical fiber base material, 5 is a heater of the drawing furnace 1, 6 is acetylene gas for forming a carbon film such as acetylene gas, An inlet for introducing a raw material gas such as propane gas, 7 an outlet for the raw material gas, 8 an outer diameter measuring device of an optical fiber, 9 a coating die portion for coating the outer circumference of the optical fiber with a resin, 10 a resin A curing furnace for curing the coating material, 11 a coating outer diameter measuring instrument, 12a, 12b and 12c optical fibers,
13 is a capstan. 1b and 1c show a plan view and a side view of the gas nozzle unit 3. Reference numeral 3a is an oxidative combustion gas inlet.

Using the above apparatus, the single mode optical fiber preform 4 having GeO ₂ added as a dopant in the core is spun in the drawing furnace 1 to have a fiber diameter of 125 μm to form an optical fiber 12a. Next, the optical fiber 12a is introduced into the thermal CVD reaction furnace 2 installed immediately below the drawing furnace 1, and, for example, acetylene gas introduced from the raw material gas introduction port 6 is thermally decomposed to form a carbon film on the surface of the optical fiber 12a. To form an optical fiber 12b. An optical fiber 12b with a carbon film in a state where the temperature of the surface of the carbon film for oxidative combustion in air is maintained is passed through the gas nozzle section 3, and a predetermined amount of oxidative combustion gas is blown. Next, the optical fiber 12b is coated with a resin die made of, for example, an ultraviolet curable resin at the coating die portion 9, and the resin is coated in the curing furnace 1
Optical fiber 12c with an outer diameter of 250 μm after curing with 0
Then, the optical fiber 12c thus obtained is wound via the capstan 13. The drawing furnace temperature is about 2000 ° C., and the spinning speed is 6 m / sec. Further, the gas nozzle portion 3 was moved in the vertical direction to oxidize and burn the carbon film to some extent at various carbon film surface temperatures. In addition, 5 from the gas nozzle part 3 in the drawing furnace direction.
The surface temperature of the carbon film was measured with a traveling type radiation thermometer at a position separated by 0 mm.

The carbon-coated optical fiber thus obtained was repeatedly subjected to bending and ironing, and then subjected to a tensile test, a dynamic fatigue test and a high temperature hydrogen test to compare the characteristics before and after the repeated bending and ironing. . Figure 3 shows how to repeatedly bend and iron the carbon-coated optical fiber.
Will be described. In this method, first, the optical fiber 12c
A weight 32 is applied to the dancer portion 36 so that a tensile strain of about 1% is applied to the dancer portion 36. Further, 100 turns are wound around the mandrel 33 having an outer diameter of 25 mm, two mandrels 33 are set as one set, and four sets of the mandrels 33 are set in such a positional relationship that they are twisted by 45 degrees with respect to the cross section of the optical fiber. In this way, four sets of mandrels 33 repeatedly bend and squeeze from eight directions in accordance with the cross section of the optical fiber. In addition, the optical fiber 12c is connected to the bobbin 3
Then, the bobbin 35 is unwound from the bobbin 35 and wound on the bobbin 35, and then the bobbin 35 is unwound and wound on the bobbin 34. The optical fiber 12c was unwound from the bobbin 34 and wound up to form one cycle. After 500 cycles, a tensile test, a dynamic fatigue test and a high temperature hydrogen test were performed. The mandrel 33 is engraved with a spiral groove, and the mandrel 33 is provided with the optical fiber 12 from the bobbin 34.
Rotate around the axis in synchronization with the feeding and winding of c,
The two mandrels 33 of each set are also configured to move relatively in the axial direction.

Carbon film surface temperature is 500 to 1200 ° C.
Table 1 shows the test results for the case. In addition, as a comparative example, the results of the test conducted on the carbon-coated optical fiber manufactured without blowing the air from the gas nozzle portion 3 are also shown. As can be seen from Table 1, this example shows less decrease in tensile strength and dynamic fatigue coefficient than the comparative example in the characteristics after repeated bending and ironing. Even if the gas blown from the gas nozzle unit 3 is a gas other than air, the same effect can be obtained as long as the oxygen content is 10% or more. Further, if the carbon film surface temperature is 150 ° C., the same effect can be obtained. Furthermore, the flow rate of the gas blown from the gas nozzle unit 3 is 0.1.
If it is 1 / min or more, the effect of the present invention can be obtained,
If it is 50 l / min or more, problems such as vibration of the optical fiber may occur, which is not preferable. 0.5-5 l / min
The gas flow rate in the range is preferable, and when the flow rate is low, it is better to increase the oxygen content rate.

[0010]

[Table 1] Note) Measurement conditions Tensile rupture strength: 10 m long, tensile elongation rate 5% / min, number of samples 50. Dynamic fatigue coefficient: 40 cm long elongation, 0.5, 1.0 tensile elongation rate,
5.0, 10,50% / min, sample number 20. proof _{characteristic: H 2 1atm, 80 ℃,} 1.24 after 144 hours
Transmission loss increase in μm.

Example 2 FIG. 2A is an explanatory view of an apparatus used in another example of the method for producing a carbon-coated optical fiber according to the present invention.
The single mode optical fiber preform 4 having GeO ₂ added as a dopant in the core is spun in the drawing furnace 1 to have a fiber diameter of 125 μm to form an optical fiber 12a. Then, the optical fiber 12a is introduced into the thermal CVD reaction furnace 2 installed immediately below the drawing furnace 1, and acetylene gas is introduced through the gas introduction port 6 to form a carbon film on the surface of the optical fiber 12a. 12b. Up to this point, the procedure is the same as in the first embodiment. Next, the optical fiber 12b having residual heat of reaction was passed through the oxidation combustion chamber portion 23 in which the oxidation combustion gas having a predetermined oxygen content rate was flowed at a predetermined flow rate to make the surface of the carbon film smooth. Thereafter, the optical fiber 12b is coated with a resin at the coating die portion 9 to form an optical fiber 12c having an outer diameter of 250 μm.
Winding 2c through the capstan 13 is also the same as in the first embodiment. The drawing furnace temperature is about 2000.
C. and the spinning speed is 6 m / sec. As shown in FIG. 2 (b), the oxidation combustion chamber section 23 has a cylindrical shape with a length of 450 mm, and the oxygen-containing gas is introduced from the gas introduction port 23 a provided in the lower part, and the gas exhaust gas provided in the upper part. Exit 23
Discharge from b.

The carbon-coated optical fiber thus obtained was repeatedly bent and ironed as in Example 1, and then subjected to a tensile test, a dynamic fatigue test and a high temperature hydrogen test.
The characteristics before and after repeated bending and ironing were compared. Table 2 shows the test results when the oxygen content of the oxidizing combustion gas was changed in the range of 20 to 50%. As a comparative example, the results of the tests conducted on the carbon-coated optical fiber manufactured by flowing He gas into the oxidizing combustion chamber are also shown. As can be seen from Table 2, in the present example, when the characteristics after repeated bending and ironing are compared with those in the case where bending and ironing are not performed, the tensile strength and the dynamic fatigue coefficient are less decreased than in the comparative example. Note that the present invention is not limited to the above Examples 2a, 2b, and 2c, and in order to oxidize and burn the carbon film surface to a slight thickness, the gas flow rate of the gas flowing into the oxidative combustion chamber, the oxygen content rate,
It goes without saying that the reaction time is appropriately set depending on the surface temperature of the carbon film. If the carbon film surface temperature is low, it is necessary to increase the oxygen content rate.If the carbon film surface temperature is high, flowing a gas with a high oxygen content rate causes a considerable amount of the carbon film to oxidize and burn. Therefore, do not set the oxygen content too high. Further, in the above embodiment, after forming a carbon film on the surface of the optical fiber,
Although this optical fiber is continuously exposed to the oxidizing combustion atmosphere, the same effect can be obtained even if the optical fiber with the carbon film is wound up without resin coating and exposed to the oxidizing combustion atmosphere in another process. it can.

[0012]

[Table 2] Note) The measurement conditions are the same as in Table 1.

[0013]

As described above, according to the present invention, after the carbon film is formed on the surface of the optical fiber immediately after drawing by the thermal CVD method, the surface temperature of the carbon film of the optical fiber is kept in a predetermined oxygen atmosphere. The carbon film surface is exposed to the oxygen atmosphere while the carbon is at a temperature for oxidative combustion, or after the carbon film is formed on the optical fiber surface by the thermal CVD method, the carbon film surface is oxidatively burned. Since it is exposed to the atmosphere, it is possible to obtain a carbon film that is clean and has a smooth surface with no deposits.
There is a remarkable effect that the mechanical strength and fatigue characteristics are stable in the longitudinal direction for a long period of time and an excellent carbon-coated optical fiber can be manufactured.

[Brief description of drawings]

1 (a), (b), and (c) are explanatory views of one embodiment of a method for producing a carbon-coated optical fiber according to the present invention, a plan view and a side view of a gas nozzle portion used in this embodiment, respectively. It is a figure.

2 (a) and 2 (b) are an explanatory view of another embodiment and a sectional view of an oxidation combustion chamber portion, respectively.

FIG. 3 is an explanatory diagram of a method of repeatedly bending and ironing an optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drawing furnace 2 Thermal CVD reaction furnace 3 Gas nozzle part 3a, 23a Gas inlet port 4 Optical fiber preform 5 Heater 6 Introducing port 7 Exhaust port 8 Outer diameter measuring instrument 9 Coating die part 10 Curing furnace 11 Coating outer diameter measuring instrument 12a, 12b, 12c Optical fiber 13 Capstan 23 Oxidizing combustion chamber part 23b Gas discharge port 32 Weight 33 Mandrel 34, 35 Bobbin 36 Dancer part

Claims (2)

[Claims] 1. Thermal CVD on the surface of an optical fiber immediately after drawing
After forming a carbon film by a method, the carbon film surface is exposed to the oxygen atmosphere while the carbon film surface temperature of the optical fiber is a temperature at which carbon oxidizes and burns in a predetermined oxygen atmosphere. Method for producing carbon-coated optical fiber. 2. A method for producing a carbon-coated optical fiber, which comprises forming a carbon film on a surface of an optical fiber by a thermal CVD method and then exposing the surface of the carbon film to an atmosphere in which carbon is oxidized and burned.