JPH0269339A - Coating device for optical fiber - Google Patents

Abstract

PURPOSE:To provide the title device which yields the optical fiber having high mechanical strength with high efficiency by providing heating elements into a reaction tube which thermally cracks gaseous raw materials and forms a carbon film on the surface of the bare optical fiber and forming the carbon film of a specified film thickness on the surface of the bare fiber. CONSTITUTION:The bare optical fiber 1 is inserted through an atmosphere adjusting chamber 4 connected to a gaseous raw material cracking and heating pipe 9 into the reaction tube 3 and is made to travel on the central axis of the tube 3; further, the fiber is made to travel at a prescribed line speed from the chamber 4 connected to one end of the tube 3 to the outside. The gaseous raw materials are supplied 6 at a prescribed flow rate into the pipe 9 and are heated by the heating elements 5. As a result, the gaseous raw materials heated in the pipe 9 are thermally cracked and are deposited as the carbon film on the surface of the bare fiber 1. As a result, the carbon film is deposited on the optical fiber surface with the high efficiency and, therefore, the drawing of the optical fiber at a high line speed is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical fiber coating device that is capable of forming a high-quality carbon coating on the surface of a bare optical fiber with high efficiency.

[Prior Art] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to the molecular vibration of hydrogen molecules diffused into the fiber increases, and furthermore, when a silica-based optical fiber comes into contact with hydrogen, the absorption loss due to the molecular vibration of hydrogen molecules diffused into the fiber increases.
Since eOx, B, 03, etc. react with hydrogen and are taken into the fiber glass as OH groups, there is a problem in that transmission loss due to absorption of OH groups also increases.

In order to cope with such problems, an optical fiber has been proposed in which a carbon coating having a hydrogen permeation blocking effect is formed on the surface of the optical fiber.

The method of forming a carbon film on the surface of a bare optical fiber is to apply a thermosetting resin such as furfuryl alcohol resin or phenol resin to the surface of the bare optical fiber, and then bake it in an inert gas atmosphere. The carbonization method is 198
In addition to being described in "New Carbon Industry" written by Toshiko Ishikawa et al., published by Kindai Editorial Co., Ltd. in 2010, a slurry compound is also produced by mixing a pitch-like compound obtained by incomplete thermal decomposition of an organic polymer with an aromatic solvent. Japanese Patent Publication No. 52-39684 discloses a method in which a carbon coating is formed by coating the surface of a bare optical fiber and then firing it in an inert atmosphere.

However, according to the above method, the raw material compound for the carbon coating undergoes large shrinkage during firing and carbonization, and the formed carbon coating tends to crack, so it is necessary to set the firing temperature high, and as a result, the transmission of optical fiber This has the disadvantage of increasing losses.

In order to solve these problems, it has recently been known to form a carbon film on the surface of the tip fiber by thermal CVD or plasma CVD, thereby improving the hydrogen resistance properties of the optical fiber.

Conventionally, an apparatus as shown in FIG. 5 has been used to form a carbon film on the surface of a bare optical fiber by the thermal CVD method.

In FIG. 5, reference numeral 1 indicates a bare optical fiber. This bare optical fiber l is spun from an optical fiber base material in an optical fiber spinning furnace (not shown), and its surface is coated with a hydrogen permeation blocking effect in a coating device 2 installed at the lower stage of the optical fiber spinning furnace. A carbon film is formed containing

This coating device 2 includes an atmosphere adjustment chamber 4 which supplies and discharges an inert gas or the like at a constant flow rate in order to maintain a constant internal atmosphere.
A roughly cylindrical reaction tube 3 with gases 4 connected to both ends, a heating element 5 provided on the outside of the reaction tube 3 and serving as a heat source when thermally decomposing the raw material gas, and a A raw material gas supply pipe 6 for supplying raw material gas such as hydrocarbons, and a cracked gas exhaust pipe 7 for exhausting cracked gas generated by thermal decomposition of the raw material gas from the reaction tube 3 together with unreacted raw material gas are respectively attached. It is something that is made possible.

When the bare optical fiber l passes through this coating device 2,
The raw material gas heated by the heating element 5 is thermally decomposed and becomes a bare optical fiber! A carbon film with a hydrogen permeation blocking effect is formed on the surface.

[Problem B to be Solved by the Invention] However, in the optical fiber coating apparatus as shown in FIG. There was a problem in that not only the thermal efficiency was low, but also the charcoal T was likely to be deposited on the inner wall of the reaction tube 3, and the efficiency of depositing the carbon film on the bare tip fiber 1 was low. Furthermore, if the diameter of the reaction tube 3 is set small for the purpose of improving the efficiency of depositing the carbon film on the surface of the bare optical fiber 1, the reaction tube 3 will be clogged by the carbon film deposited inside the reaction tube 3, and the cracked gas will not be exhausted. At this time, convection occurs within the reaction tube 3, causing wire wobbling of the optical fiber, making it impossible to maintain a constant carbon coating thickness and obtain a fiber end with high mechanical strength.

This invention has been made to solve the above problems, and is an optical fiber coating device that can efficiently manufacture optical fibers with high mechanical strength and having a carbon coating of a constant thickness formed on the surface thereof. is intended to provide.

[Means for Solving the Problems] In the optical fiber coating apparatus according to claim 1 of the present invention, the inside of a reaction tube that thermally decomposes a raw material gas to form a carbon film on the surface of a bare optical fiber is provided. In the optical fiber coating device according to claim 2, which is provided with a heating element,
The solution to each problem was to extend a line blur prevention tube from one end of the reaction tube connected to the cracked gas exhaust pipe toward the inside of the reaction tube.

[Function] In the optical fiber coating apparatus according to claim 1 of the present invention, since a heating element is provided in the reaction tube, the raw material gas can be heated efficiently, and a constant film can be formed on the surface of the optical fiber. A thick carbon film can be easily formed.

In addition, in the apparatus according to claim 2 of the present invention, since the line blur prevention tube is extended into the reaction tube, the optical fiber line is generated due to convection that occurs within the reaction tube when decomposed gas is exhausted from the reaction tube. Since wobbling can be prevented, a carbon coating having a more uniform thickness can be formed on the surface of the bare optical fiber, and the mechanical strength of the tip fiber can be further improved.

The present invention will be described in detail below.

FIG. 1 shows an example of a coating apparatus for an optical fiber according to claim I of the present invention. This optical fiber coating apparatus IO includes a gas decomposition heating tube 9 concentrically arranged in a reaction tube 3. This is the schematic structure that was inserted.

The reaction tube 3 has a cylindrical shape made of quartz glass or the like, and has a seal gas supply tube 8 in its upper part for supplying a seal gas to prevent a carbon film from adhering to the reaction tube 3, and a seal gas supply pipe 8 in its lower part for supplying a raw material gas. is connected to a cracked gas exhaust pipe 7 for discharging cracked gas generated by thermal decomposition from the reaction tube 3 along with seal gas and unreacted raw material gas. An atmosphere adjustment chamber 4 for keeping the atmosphere inside the reaction tube 3 constant is connected to the lower bottom. This atmosphere adjustment chamber 4 is an air chamber having an arbitrary shape, and piping pipes 4as, 4b, 4c are connected to each other at right angles in three directions. Two piping pipes 4a1 in series with
4b is connected to one end of the reaction tube 3 or the gas decomposition heating tube 9, and a bare optical fiber is placed on its central axis! It is designed to run. Seal gas such as inert gas can be supplied into the atmosphere adjustment chamber 4 from another pipe 4C that is perpendicular to the two pipes 4a and 4b connected in series on this straight line. By keeping the atmospheric pressure in the atmosphere adjustment chamber 4 constant, leakage of raw material gas, seal gas, etc. in the reaction tube 3 or gas decomposition heating tube 9 and intrusion of outside air into the reaction tube 3 can be prevented. It has become.

Further, a gas decomposition heating tube 9 through which a bare optical fiber 1 is inserted is concentrically inserted from the neck of the reaction tube 3 on its central axis. This gas decomposition heating tube 9 is connected to a raw material gas supply pipe 6 for supplying raw material gas such as hydrocarbons or halogenated hydrocarbons, which are raw materials to be thermally decomposed to form a carbon film, into the gas decomposition heating tube 9 and the above-mentioned atmosphere. One end is connected to the control chamber 4, and the other end is provided with a heating element 5 that heats the raw material gas to form a carbon film on the surface of the bare optical fiber 1. This gas decomposition heating tube 9 generates heat. It is inserted so that one end to which the body 5 is attached faces the one end of the reaction tube 3 to which the atmosphere control chamber 4 is connected, and their central axes coincide.

Using such a coating device tIO, the surface of the bare optical fiber 1 is coated with carbon having a hydrogen permeation blocking effect. The following steps are used to form the It pattern.

The bare optical fiber l spun from the pre-fiber base material is inserted into the reaction tube 3 through the atmosphere adjustment chamber 4 connected to the raw material gas decomposition heating tube 9, run on the central axis of the reaction tube 3, and then The reaction tube 3 is caused to travel from the atmosphere adjustment chamber 4 connected to one end of the reaction tube 3 to the outside at a predetermined linear speed. Next, raw material gas supply pipe 6
The raw material gas is supplied into the gas decomposition heating tube 9 at a predetermined flow rate, and the raw material gas is heated by the heating element 5.

The raw material gas heated in the gas decomposition heating tube 9 undergoes thermal decomposition and is deposited on the surface of the bare optical fiber 1 as a carbon film. The bare optical fiber I, on which the carbon coating has been formed in the reaction tube 3 in this way, is sent to another coating device (not shown) installed at the lower stage of this coating device, and the carbon coating is coated with an ultraviolet curing resin. A resin layer is formed and used as a cored optical fiber. On the other hand, since a part of the raw material gas generates cracked gas consisting of hydrocarbons, hydrogen, etc., this cracked gas is sucked through the cracked gas exhaust pipe 7 connected to one end of the reaction tube 3. Furthermore, in order to prevent a carbon film from depositing in the reaction tube 3, a seal gas that is inert to the raw material gas is supplied from the seal gas supply tube 8, and the raw material gas, decomposed gas, and seal gas are fed into the reaction tube 3. The airflow of the mixed gas becomes laminar.

The heating element attached to the outer wall of one end of the gas decomposition heating tube 9 may be of any type as long as it can generate a temperature at which the raw material gas can be thermally decomposed; From this point of view, an infrared condensing furnace or the like can be used.

The raw material gas supplied from the raw material gas supply pipe 6 into the gas decomposition heating tube 9 is a carbon compound that forms a carbon film on the surface of the bare optical fiber 1 by thermal decomposition, such as hydrocarbons or halogenated gases. Hydrocarbons and the like are preferred.

The seal gas supplied into the reaction tube 3 from the seal gas supply pipe 8 may be any gas that is inert to the thermal decomposition reaction of the raw material gas, such as inert gases such as helium, argon, etc. Chemically inert nitrogen or the like can be used.

The raw material gas supply rate at this time is appropriately selected depending on the type of raw material gas and the heating temperature, but is usually 0.2 to 1.
The heating temperature of the heating element 5 is selected as appropriate depending on the type of raw material gas, etc., but is usually 400 to 1200.
It is about ℃. The supply rate of the sealing gas is appropriately selected depending on the supply rate of the raw material gas, the heating temperature, the generation rate of the cracked gas, etc., but it is usually 09.5 to 1000 to form a laminar flow together with the cracked gas in the reaction tube 3. It is about 1012/min.

Under such conditions, the raw material gas can be decomposed to efficiently form a carbon film with a thickness of about 0.1 to 0.6 μm on the surface of the optical fiber probe 1. If the thickness of the carbon film formed on the surface of the bare optical fiber I is less than 0.1 μm, locally thin parts or pinholes are likely to be formed, and hydrogen will permeate through these parts, increasing the transmission loss of the optical fiber. Therefore, it is not preferable, and if the film thickness is 0.6 μm or more, cracks are likely to occur in the carbon wave film, which is not preferable.

In this way, when inert gas is supplied into the reaction tube 3 from the seal gas supply pipe 8 and sucked through the cracked gas exhaust pipe 7 so as to form a laminar flow in the reaction tube 3 along with the cracked gas, the gas is thermally decomposed by the raw material gas. It is possible to prevent the obtained carbon wave film from being deposited in areas other than the optical fiber section gAI, and it is possible to prevent the reaction tube 3 from getting stuck.

In such an optical fiber coating apparatus 10, since the gas decomposition heating tube 9 to which the heating element 5 is attached is provided inside the reaction tube 3, the raw material gas can be heated efficiently.
Gas pyrolysis efficiency and charcoal T on the surface of bare optical fiber 1
: The deposition efficiency of the film can be improved.

In addition, a seal gas supply pipe 8 is provided in the reaction tube 3, and the seal gas is supplied so as to form a laminar flow in the reaction tube 3 together with the cracked gas generated by thermal decomposition of the raw material gas, and is exhausted from the cracked gas exhaust pipe 9. It is possible to prevent the soot generated together with the carbon coating during the thermal decomposition of the raw material gas from adhering to the inside of the reaction tube 3 and the gas decomposition heating tube 9, so that the coating device +o does not get stuck, and the optical fiber is not coated. ! Since the carbon film is uniformly formed on the surface of the Li wire 1, an optical fiber with high mechanical strength can be obtained.

FIG. 2 shows another example of the optical fiber coating apparatus according to claim 2 of the present invention. The difference between the coating device 11 for the fiber and the one shown in FIG. The preheating heating element 5a has been attached to the outer wall of the housing. When the preheating heating element 5a is attached, the raw material gas can be sufficiently heated, so that the deposition efficiency of the carbon wave film can be further improved, and the drawing speed of the bare optical fiber I can be increased.

Next, an optical fiber coating apparatus according to claim 2 of the present invention will be explained. 3 and 4 both show an example of an optical fiber coating apparatus according to claim 2 of the present invention. The apparatus shown in FIG. 3 is used as the optical fiber coating apparatus shown in FIG. 1, and the apparatus shown in FIG.
Each of the wires shown in the figure is provided with a line blur prevention tube 14.

The line blur prevention tube 14 is a cylindrical tube extending into the reaction tube 3 from a piping pipe 4a connecting the reaction tube 3 and the atmosphere adjustment chamber 4, and has a carbon coating on its central axis. The bare optical fiber 1 formed with the above is run, and the position of the open end of the shaky spinning tube 14 is closer to the heating element 5 than the position where the cracked gas exhaust pipe 7 is attached to the reaction tube 3. It is set at the upper side. When such a line blur prevention tube I4 is installed, the decomposition gas exhaust pipe 7 installed at the bottom of the reaction tube 3 can prevent airflow turbulence from acting on the bare optical fiber 1, and the gas decomposition Since the wire wobbling of the bare optical fiber 1 can be more effectively prevented within the heating tube 9, the bare optical fiber can be coated with a carbon coating having a uniform thickness! It can be formed on the surface, and the mechanical strength of the pre-coated fiber can be further improved.

[Example] (Example 1) A gas decomposition heating tube with a diameter of 3611 and a length of 800 a + m was provided in a reaction tube with a diameter of 60 mm and a length of 1100 nm, and an infrared concentrating furnace was attached to the tip of this gas decomposition heating tube. An optical fiber coating device similar to that shown in the figure was manufactured. A bare optical fiber with a diameter of 125 μm is supplied into this optical fiber coating device at a linear velocity of 20 Il/min, and dichloroethylene diluted to lovol% with argon gas is supplied as a raw material gas at a flow rate of 200 cm3/min. Argon gas was supplied as a gas at a rate of 5 min to create a laminar flow inside the reaction tube. Then set the heating temperature to 60
A carbon film was formed on the surface of the bare optical fiber by varying the temperature in the range of 0 to 1500°C, and the formation of the carbon film was confirmed using an Auger electron spectrometer. Also the 6th
In the figure, the relationship between the heating temperature and the thickness of the carbon film is shown by a solid line.

(Example 2) A carbon film was formed on the surface of a bare optical fiber in exactly the same manner as in Example 1, except that seal gas was supplied at a rate of 15 a/min to create a turbulent flow inside the reaction tube. This result is shown in FIG. 6 by a dotted line.

(Comparative Example 3) A bare optical fiber was coated at a linear speed of 20 m/min using a fiber coating device similar to that shown in Fig. 5, in which an infrared concentrator was installed outside a reaction tube with a diameter of 36IIIn and a length of 800IllI11. , 10vo with argon gas as raw material gas
Chloroethylene diluted to 1% was supplied at a flow rate of 200 am'/min, and the heating temperature in the reaction tube was set at 600 to 1500.
A carbon film was formed on the surface of the bare optical fiber by changing the temperature in the temperature range of ℃, but the carbon film had a thickness of 0.1 μm or more to prevent soot from adhering to the inside of the reaction tube and sufficiently exert the hydrogen permeation blocking effect. was not obtained. The results are shown in FIG. 6 by a dashed line.

From the relationship between the thickness of the carbon coating and the heating temperature shown in FIG. 6, it can be seen that by using the optical fiber coating apparatus of the present invention, a carbon coating with a sufficient thickness can be formed on the surface of the bare optical fiber even at low heating temperatures. It has been found that it is possible to significantly improve the decomposition efficiency of the raw material gas and the formation efficiency of the carbon film compared to the conventional method.

(Example 4) A carbon film was formed on the surface of a bare optical fiber in the same manner as in Example 1, except that the heating temperature was 700° C. and the linear velocity of the optical fiber PIAIa was varied from 0 to 40 m7 minutes. The relationship between the linear speed of the bare optical fiber and the thickness of the formed carbon film is shown by the solid line ζ in FIG.

(Example 5) A coating apparatus similar to that shown in FIG. 2 was manufactured by attaching an infrared concentrator furnace as a heating element for preheating to the outside of the reaction tube of the coating apparatus used in Example 1. A carbon film was formed on the surface of a bare optical fiber in the same manner as in Example 4 except that this device was used. This result is shown in FIG. 7 by a dotted line.

From the results of Examples 4 and 5, in Example 4, which does not have a heating element for preheating the raw material gas and the bare optical fiber, in order to obtain a carbon film with a thickness of 0.1 μm or more, the linear speed of the bare optical fiber must be increased. However, in Example 5, the preheating heating element can sufficiently heat the raw material gas and the bare optical fiber, so the linear speed of the bare optical fiber can be increased to 25 m/min. It was confirmed that the drawing speed of the optical fiber can be further improved by providing a heating element for preheating.

(Example 6) Using the same optical fiber coating equipment as used in Example 1, a bare optical fiber with a diameter of 125 μm was coated at a linear speed of 25 m.
/min, a carbon film with a thickness of 0.1 μm was formed on the surface, and then an ultraviolet curable resin was applied on top of it to make an optical fiber core with a fiber diameter of 0.25 μm. . Twenty of these optical fibers were prepared and stretched under the conditions of a gauge length of 10 m and a strain rate of 10% for 7 minutes, and their Weibull strength distribution was measured. The results are shown in Figure 8.

(Example 7) A coating device similar to that shown in FIG. 3 was manufactured by connecting a bulge prevention tube with a diameter of 1011% and a length of 200 mm to the bottom of the reaction tube of the optical fiber coating device used in Example 6. did. A cored optical fiber coated with a carbon coating and an ultraviolet curable resin was produced in exactly the same manner as in Example 6 except that this coating device was used.

The Weibull intensity distribution of the fiber core wire was then measured under exactly the same conditions as in Example 6, and the results are indicated by ◯ in FIG.

From Examples 6 and 7, when a wire blur prevention tube for preventing wire wobbling of the bare optical fiber is provided in the reaction tube, a carbon film can be formed with a uniform thickness on the surface of the bare optical fiber.
It was confirmed that it is possible to further improve the mechanical strength of the pre-fiber core wire.

[Effects of the Invention] As explained above, the optical fiber coating apparatus according to claim I of the present invention generates heat inside the reaction tube that thermally decomposes the raw material gas to form a carbon film on the surface of the bare optical fiber. Since it is equipped with a body, the raw material gas can be heated efficiently, and the carbon film obtained by thermal decomposition of the raw material gas can be deposited with high efficiency on the surface of the bare fiber end.

Furthermore, by supplying a sealing gas into the reaction tube, it is possible to prevent carbon film or soot from adhering to the inner wall of the reaction tube. Further, by providing a heating element for preheating, the raw material gas can be sufficiently heated and a carbon film can be deposited on the surface of the optical fiber with high efficiency, so that the tip fiber can be drawn at a high drawing speed.

Furthermore, the optical fiber coating apparatus according to claim 2 of the present invention includes the optical fiber coating apparatus according to claim I, which prevents line wobbling from one end of the reaction tube to which the cracked gas exhaust pipe is connected toward the inside of the reaction tube. Since it is an extended tube, it is possible to prevent wire wobbling due to convection generated in the reaction tube by decomposition gas and sealing gas, and to form a carbon film with a uniform thickness on the surface of the bare optical fiber. An optical fiber core wire with even higher mechanical strength can be obtained.

[Brief explanation of the drawing]

1 and 2 are both schematic configuration diagrams showing an embodiment of the optical fiber coating apparatus according to claim 1 of the present invention, and FIGS. 3 and 4 are both claim 2 of the present invention. FIG. 5 is a schematic configuration diagram showing an embodiment of the optical fiber coating device described above, FIG. 5 is a schematic configuration diagram of a conventional optical fiber coating device, and FIG. Figure 7 is a graph showing the relationship between the heating temperature and the thickness of the carbon film formed when forming a carbon film on the surface of a bare optical fiber using a fiber coating device. FIG. 8 is a graph showing the relationship between the thickness of the carbon film and the drawing speed of the optical fiber when the carbon film is formed on the surface of the end fiber using a device, and FIG. 8 shows the coating of the optical fiber according to claim 2 of the present invention. It is a graph showing the Weibull distribution of the breaking strength of the optical fiber core wire produced using the apparatus. I: Bare optical fiber, 3: Reaction tube, 5: Heating element, 6: Raw material gas supply pipe, 7: Decomposition gas exhaust pipe, 8: Seal gas supply pipe, l0111.12, I
3... Optical fiber coating device, 14... Line blur prevention tube.

Claims (2)

[Claims] (1) A reaction tube is connected to a raw material gas supply pipe at one end and a cracked gas exhaust pipe at the other end, and thermally decomposes the raw material gas from the raw material gas supply pipe to form a carbon film on the surface of the bare optical fiber. An optical fiber coating device comprising: a heating element provided inside the reaction tube; (2) The optical fiber coating device according to claim 1, further comprising a line blur prevention tube extending from one end of the reaction tube to which the cracked gas exhaust tube is connected toward the inside of the reaction tube.