JP3282925B2 - Manufacturing method of carbon coated optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As a method of producing a hermetic coated optical fiber, a method of synthesizing an inorganic material layer having a thickness of 200 to 1000 DEG by using a thermal CVD method on a surface of a bare optical fiber immediately after drawing is generally performed. . As the hermetic inorganic material layer manufactured by such a method, a layer of carbon and a carbon compound film is well known. Since this carbon film almost completely prevents H ₂ from entering, the hydrogen resistance of the optical fiber is significantly improved. At the same time, H ₂ O is prevented from penetrating, so that stress corrosion due to H ₂ O found in quartz glass does not occur and, as a matter of course, fatigue characteristics are significantly improved. Further, it is possible to manufacture a fiber having an initial strength of a carbon-coated optical fiber equal to or higher than that of a normal optical fiber, and the fiber is now being used in fields such as communication lines and optical components.

[0003]

In a conventional method for synthesizing a carbon film of an optical fiber, a raw material gas is thermally decomposed to form a carbon film on a cladding of an optical fiber made of quartz. Factors that determine various properties of the carbon-coated optical fiber, such as the breaking strength and hermetic properties, of the carbon-coated optical fiber having the carbon film formed thereon include the composition of the source gas, the concentration of the source gas, and the temperature during the thermal decomposition reaction. .

[0004] A carbon film coating apparatus for synthesizing a carbon film on-line during the process of drawing an optical fiber is usually provided with a thermal CVD reactor and a seal chamber for performing a thermal decomposition reaction of a raw material gas to coat the carbon film. I have. The seal chamber is filled with an inert gas such as Ar, He, and N ₂ or a gas that hardly reacts with the source gas even at a high temperature so that an external atmosphere does not flow into the thermal CVD reactor.

Conventionally, a seal gas A flowing into a seal chamber is used.
There is no means for determining an appropriate flow rate of an inert gas such as r, He, and N ₂ , and the seal gas is often constant regardless of the amount of the source gas flowing into the thermal CVD reactor. Thermal CVD
In order to prevent the outside atmosphere from flowing into the reactor, heat CV
In order to prevent a reaction gas such as a raw material gas, a reaction product gas, or a soot in the D reactor from leaking to the outside and adversely affecting the surrounding environment, a considerably large amount of a sealing gas is supplied.

In such a state, the pressure in the seal chamber is too high as compared with the thermal CVD reactor, and a large amount of seal gas flows into the thermal CVD reactor. When the sealing gas flows into the thermal CVD reactor, the concentration of the raw material gas in the thermal CVD reactor, particularly near the fiber in the vertical direction at the opening of the sealing chamber, decreases, and the thermal decomposition rate of the raw material gas decreases. It has been difficult to synthesize a carbon film of sufficient thickness and quality in a short time, which has been a cause of deteriorating the strength and hermetic properties of the carbon film. Also,
When a long carbon-coated optical fiber is drawn, soot is deposited in the thermal CVD reactor as the wire is drawn. The deposited soot changes the flow of the source gas in the thermal CVD reactor.
This change in the flow of the source gas changes the pressure difference between the opening of the sealing chamber and the thermal CVD reactor.
The amount of sealing gas flowing into the VD reactor changes with the amount of soot deposited in the reactor. Due to such influence, the raw material gas concentration in the thermal CVD reactor changes longitudinally, which is one cause of the characteristic change in the longitudinal direction of the long carbon-coated optical fiber.

[0007] The present invention solves the above-mentioned problems, and manufactures a carbon-coated optical fiber having excellent carbon film strength and hermetic characteristics by minimizing the amount of a sealing gas flowing from a sealing chamber into a thermal CVD reactor. It is intended to provide a method.

[0008]

The present invention has the following means to solve the above problems.

According to a first aspect of the present invention, there is provided a method for producing a carbon-coated optical fiber, comprising:
In a method for producing a carbon-coated optical fiber, wherein the surface of the optical fiber is coated with a carbon film by passing through a carbon-film coating apparatus having a reaction furnace, at least the carbon-film coating apparatus is provided with a thermal CVD reactor on an optical fiber insertion side. And an upper seal chamber filled with a seal gas for shutting off an external atmosphere. A pressure difference between the upper seal chamber and the thermal CVD reactor is measured to supply an optimal amount of the seal gas to the upper seal chamber. It is characterized by the following.

According to a second aspect of the present invention, in the method for manufacturing a carbon-coated optical fiber, the optical fiber immediately after drawing is subjected to thermal CVD.
In a method of manufacturing a carbon-coated optical fiber for coating a carbon film on the surface of the optical fiber by passing through a carbon-film coating apparatus having a reaction furnace, the carbon-film coating apparatus includes a thermal CVD reactor on an optical fiber insertion side. An upper seal chamber for filling a seal gas for shutting off an external atmosphere is provided, and a lower seal for filling a seal gas for shutting off the external atmosphere with the thermal CVD reactor on the optical fiber delivery side of the thermal CVD reactor. A chamber is provided, and at least a pressure difference between the lower seal chamber and the thermal CVD reactor is measured to supply an optimal amount of seal gas to the lower seal chamber.

According to a third aspect of the present invention, there is provided a method of manufacturing a carbon-coated optical fiber, comprising:
A seal gas is supplied to the seal chamber so that the pressure difference in the reactor becomes constant.

According to a fourth aspect of the present invention, in the method of manufacturing a carbon-coated optical fiber, the quality of the carbon film, such as the electrical resistance, of the carbon film coated on the surface of the optical fiber is monitored online so that the carbon film quality becomes constant. And supplying a seal gas to the seal chamber.

[0013]

According to the method for producing a carbon-coated optical fiber of the present invention, the optical fiber immediately after drawing is passed through a carbon film coating apparatus equipped with a thermal CVD reactor, and In a method of manufacturing a carbon-coated optical fiber for coating a surface of a carbon film, at least the carbon-film coating apparatus is provided with a thermal CVD reactor and an upper seal chamber filled with a seal gas for shutting off an external atmosphere on an optical fiber insertion side. At the same time, a lower seal chamber is provided at the optical fiber delivery side of the thermal CVD reactor for filling the thermal CVD reactor with a seal gas for shutting off an external atmosphere, and a pressure difference between at least one of the seal chambers and the thermal CVD reactor is reduced. By supplying the optimum amount of the sealing gas to the measured and measured sealing chamber, no extra sealing gas flows into the thermal CVD reactor. As a result, the concentration of the source gas in the vicinity of the optical fiber in the vertical direction of the opening of the seal chamber in the thermal CVD reactor is not reduced, so that the rate of thermal decomposition of the source gas in the thermal CVD reactor is ensured and sufficient film is formed. A carbon film having a thickness and a film quality can be synthesized, and the strength and hermetic characteristics of the carbon film are improved.

The sealing gas flowing from the sealing chamber of the carbon film coating apparatus to the thermal CVD reactor is the sealing gas flowing from the entire opening of the sealing chamber due to the pressure difference between the sealing chamber and the thermal CVD reactor, and especially the upper sealing gas. The vicinity of the boundary layer near the optical fiber is divided into a seal gas flowing into the thermal CVD reactor along with the optical fiber. Seal chamber and heat CV
Since the opening area between the D reactors is much larger than the cross-sectional area of the optical fiber, most of the seal gas flowing into the thermal CVD reactor is determined by the opening pressure difference and the opening area.

There are many restrictions when drawing an optical fiber for avoiding problems such as fluctuation of the optical fiber during drawing of the optical fiber. Because of these restrictions, it is difficult to reduce the opening area more than necessary. Therefore, it is necessary to reduce the pressure difference between the seal chamber and the thermal CVD reactor to reduce the heat CV of the seal gas.
This is a method for minimizing the flow into the D reactor, and is the only method for minimizing the decrease in the source gas concentration due to the seal gas regardless of the flow rate of the source gas.

Further, by controlling the pressure difference to be constant over the length of the optical fiber during drawing, the thermal CVD of the seal gas is performed.
The flow into the reactor can be kept constant, and the raw material gas concentration can be kept constant during drawing of the optical fiber. However, if the flow rate of the sealing gas is controlled by using the above method, the flow rate of the sealing gas changes in the sealing chamber, and a delicate change occurs in the fiber surface temperature during the thermal decomposition reaction.
Therefore, if the sealing gas in the sealing chamber is controlled within the range of fulfilling the sealing function while measuring the quality of the carbon film such as the electric resistance of the carbon film, one of the conditions for forming the carbon film due to the change in the amount of the sealing gas flowing into the thermal CVD reactor is as follows. The raw material gas concentration, which is one of the conditions, and the temperature of the fiber surface, which is one of the conditions for forming the carbon film, are simultaneously changed.

When the electric resistance measurement is selected as the carbon film quality measuring means, when the electric resistance of the carbon film is to be increased (to reduce the film thickness of the carbon film), it is necessary to lower the raw material gas concentration and lower the reaction temperature. In order to reduce the electrical resistance of the carbon film (to increase the thickness of the carbon film), it is effective to increase the source gas concentration and increase the reaction temperature. The characteristics of the carbon film can be kept constant over the length of the optical fiber by the flow rate of the seal gas, and the change in the strength of the carbon film and the change in the length of the optical fiber in the hermetic characteristics can be further suppressed by changing the concentration of the raw material gas. .

[0018]

The present invention will be described in more detail with reference to the following examples.
You. The carbon film of the optical fiber was synthesized using the apparatus shown in FIG.
I went. GeO in the core _TwoIs added as a dopant
Single-mode optical fiber preform 1 with heater 2 inside
The optical fiber 4 having an outer diameter of 125 μm is drawn by the drawing furnace 3 to be wrapped
To The optical fiber 4 immediately after drawing is directly connected to the drawing furnace 3.
It is introduced into the carbon film coating apparatus 5 installed below. This carbon
Source gas is supplied from the source gas supply port 6 into the film coating apparatus 5.
Optical fiber immediately after drawing by thermal decomposition of this raw material gas.
A carbon film is formed on the surface of fiber 4 to form a carbon-coated light.
The fiber 8 is manufactured.

The carbon-coated optical fiber 8 is guided to a die 9 for applying a UV resin to the surface thereof, and is coated with the UV resin. Thereafter, the UV resin is cured in a curing device 10 having a UV lamp. The optical fiber coated with the carbon coating and the UV resin is taken by a take-up machine and taken up by a take-up machine (not shown). In the drawing, reference numeral 7 denotes a gas exhaust port, and reference numeral 11 denotes a carbon film electric resistance measuring instrument.

The carbon film coating apparatus 5 used in the present invention will be described in more detail with reference to FIG. Carbon film coating equipment 5
Is an upper seal chamber 21 in the upper part, and a thermal CVD reactor 2 in the central part.
2 and a lower seal chamber 23 in the lower part. The supply of the seal gas to the upper seal chamber 21 is performed from the inlet 24. The supply of the seal gas to the lower seal chamber 23 is performed through the inlet 27. The pressure difference between the upper seal chamber 21 and the thermal CVD reactor 22 is measured by the pressure measuring units 28 and 29. In the drawing, reference numeral 31 denotes a cooling water supply port, and 30 denotes a cooling water drain port.

In each of the examples and comparative examples described below, the resin-coated outer diameter is 250 μm, and the temperature of the drawing furnace 3 is about 2 μm.
The spinning speed was 350 m / min at 000 ° C., and the composition of the raw material gas supplied from the raw material gas supply port 6 was the same.

Example 1 A carbon-coated optical fiber was manufactured by the following method using the apparatus shown in FIGS. 1 and 2 described above. Example 1-1: The pressure in the upper seal chamber 21 was reduced by 0.80 m from the pressure in the thermal CVD reactor 22 using the pressure measuring units 28 and 29.
The seal gas was flowed into the upper seal chamber 21 so as to increase the amount by mH ₂ O, and the flow rate of the upper seal gas was set to 0.35 l / min. Example 1-2: The pressure in the upper seal chamber 21 was increased by 0.81 m from the pressure in the thermal CVD reactor 22 using the pressure measuring units 28 and 29.
The seal gas was flowed into the upper seal chamber 21 so as to increase the mH ₂ O content, and the flow rate of the upper seal gas was set to 0.90 l / min.

COMPARATIVE EXAMPLE 1-1 Using the pressure measurement units 28 and 29, the pressure in the upper seal chamber 21 was set to be higher than the pressure in the thermal CVD reactor 22 by 18.0 mmH ₂ O by 28.0 mmH ₂ O.
1 and the upper seal gas flow rate was 1.50.
l / min. Comparative Example 1-2: The pressure in the upper seal chamber 21 was set to be 20.0 m higher than the pressure in the thermal CVD reactor 22 using the pressure measurement units 28 and 29.
The seal gas was flowed into the upper seal chamber 21 so as to be higher by mH ₂ O, and the flow rate of the upper seal gas was set to 4.35 l / min.

Example 1-1, Example 1-2, Comparative Example 1
As the upper seal gas of Example 1 and Comparative Example 1-2, Ar heated to 1500 ° C., which is a pyrolysis reaction temperature, was used to prevent the surface temperature of the optical fiber 4 from changing. Example,
Table 1 shows the measurement results of the raw material gas flow rate, the upper seal gas flow rate, and various characteristics of the carbon film of the comparative example.

[0025]

[Table 1]

In Table 1, the conditions for measuring the 50% breaking strength were as follows: distance between evaluation points: 10 m; strain rate: 5% per minute; n = 49. Conditions for measuring hydrogen resistance were as follows: temperature 85 ° C, H ₂ partial pressure 1at
After exposure for 144 hours to the condition of m, the transmission loss increase amount at λ = 1.24 μm was defined as the amount of increase in transmission loss. The conditions for measuring the actual fatigue properties were as follows: the distance between the scores was 300 mm, the strain rate was 0.1% per minute, 0.3% per minute,
After measuring each speed level n = 19 at 1.0% / min, 3.3% / min and 10.0% / min, the n value was calculated from the median breaking strength.

Example 2 A carbon-coated optical fiber was manufactured by the following method using the apparatus shown in FIGS. 1 and 2 described above. Example 2: While the upper seal chamber 21 was filled with a seal gas so that the pressure difference between the upper seal chamber 21 and the thermal CVD reactor 22 was constant, drawing was performed for 500 minutes. In this example, immediately after coating the carbon film, the electric resistance of the carbon film was measured using the carbon film electric resistance measuring device 11.
FIG. 3 shows a longitudinal change in the pressure difference between the upper seal chamber 21 and the thermal CVD reactor 22 at this time. FIG. 4 shows the amount of the sealing gas flowing during drawing, and FIG. 5 shows the longitudinal change of the electric resistance of the carbon film.

Comparative Example 2: The upper seal chamber 21 is fixed (0.
Drawing was performed for 500 minutes while a seal gas (at a fixed rate of 5 l / min) was flowed. In this comparative example, similarly to Example 2, the electric resistance of the carbon film was measured using the carbon film electric resistance measuring device 11 immediately after the carbon film was coated. At this time, the upper seal chamber 21 and the thermal CVD reactor 22
6 shows the longitudinal change in the pressure difference, and FIG. 7 shows the longitudinal change in the electrical resistance of the carbon film. Table 2 shows the measurement results of the carbon film properties of the drawn carbon-coated optical fibers of Example 2 and Comparative Example 2 at the drawing start portion, the intermediate portion, and the drawing end portion.

[0029]

[Table 2]

In Table 2, the conditions for measuring the 50% strength at break, the conditions for measuring the hydrogen resistance, and the conditions for measuring the actual fatigue properties are the same as those in Table 1.

Example 3 A carbon-coated optical fiber was manufactured by the following method using the apparatus shown in FIGS. 1 and 2 described above. Example 3 Drawing was performed for 500 minutes so that the electric resistance measured by the carbon film electric resistance measuring device 11 became constant. In order to reduce the electric resistance of the carbon film, the upper seal chamber 21 is required.
The seal gas supplied to the upper seal chamber 21 was slightly increased in order to slightly reduce the seal gas supplied to the upper seal chamber 21 and to increase the electric resistance of the carbon film. FIG. 8 shows a longitudinal change in the pressure difference between the upper seal chamber 21 and the thermal CVD reactor 22 at this time.
Shown in FIG. 9 shows the amount of sealing gas flowing during drawing.
FIG. 10 shows the longitudinal change in the electrical resistance of the carbon film. In addition,
In the present embodiment, cooling water is supplied from the cooling water supply port 31,
The inner wall of the thermal CVD reactor 22 was cooled.

As can be seen from the first embodiment, the method of manufacturing the carbon-coated optical fiber of the present invention is such that the upper seal chamber 21 is filled with a seal gas in accordance with the flow rate of the raw material gas, thereby allowing the upper seal chamber 21 to react with the thermal CVD reaction. Since the pressure difference between the furnaces 22 is properly maintained and the dilution of the raw material gas by the seal gas is suppressed, the reduction of the rate of thermal decomposition reaction of the raw material gas is small, and the carbon-coated optical fiber 8 having both sufficient strength and good hermetic characteristics is provided. Can be manufactured.

In Example 1, when the pressure difference between the upper seal chamber 21 and the thermal CVD reactor 22 was about 0.8 mmH ₂ O, a carbon-coated optical fiber having good characteristics was obtained.
The shape of the thermal CVD reactor 22 and the upper seal chamber 21 greatly affects the shape.
The external atmosphere flows into the thermal CVD reactor along with the optical fiber drawn into the D reactor 22, which is not preferable because the properties of the carbon film are impaired. Unless the external atmosphere flows into the thermal CVD reactor, the upper seal chamber 21
As the value of the pressure difference in the thermal CVD reactor 22 decreases, the flow rate of the seal gas into the thermal CVD reactor decreases, so that the control of the raw material gas concentration is facilitated and the deterioration of the characteristics of the carbon-coated optical fiber is easily prevented. There is a tendency.

The appropriate pressure difference shown in the embodiment is shown in FIG.
Is the value in the carbon film coating apparatus 5 having the shape shown in FIG. 1, and is appropriate due to the influence of the flow of products such as raw material gas and soot in the seal gas or the thermal CVD reactor 22 as the shape of the carbon film coating apparatus 5 changes. Values can change. Furthermore, since the degree of the influence of the flow of products such as gas or soot in the seal gas or the thermal CVD reactor 22 differs depending on the position of the pressure measurement unit,
It is preferable to measure the pressure as close to the opening as possible.

As is apparent from the second and third embodiments, when the long carbon-coated optical fiber 8 is manufactured, the strength is reduced by about 20% in the longitudinal direction in the comparative example, and the hermetic characteristics are considerably deteriorated. However, the use of the present invention greatly suppresses the deterioration of hermetic characteristics. Particularly, in Example 3, no reduction in strength and hermetic characteristics was observed.

When the quality of the carbon film such as electric resistance is measured and the sealing gas flow rate is controlled based on the measurement result as in the third embodiment, the amount of the sealing gas is reduced and the thermal CVD reactor 22 is used.
Upper seal chamber 21 to prevent gas and soot from leaking from
It is preferable to set the minimum value of the pressure difference while monitoring the pressure difference between the reactor and the thermal CVD reactor 22 so that the flow rate of the seal gas is not further reduced.

In the embodiment described above, the pressure difference between the upper seal chamber 21 and the thermal CVD reactor 22 was measured and only the flow rate of the upper seal gas in the upper seal chamber 21 was described. Even if the pressure difference of the CVD reactor 22 is measured to control the flow rate of the lower seal gas in the lower seal chamber, the effect of the present invention can be obtained. In particular, when the present invention is used to control the flow rate of the lower seal gas when producing the carbon-coated optical fiber while introducing the raw material gas from the lower part of the thermal CVD reactor 22, the effect is remarkable. Also, the effect of the present invention can be obtained by controlling the flow rate of the seal gas in both the seal chambers by measuring the pressure difference between the two seal chambers and the thermal CVD reactor 22.

[0038]

As described above, according to the method for producing a carbon-coated optical fiber of the present invention, the optical fiber immediately after drawing is passed through a carbon film coating apparatus equipped with a thermal CVD reactor to reduce the optical fiber. In a method of manufacturing a carbon-coated optical fiber having a surface coated with a carbon film, at least a carbon film coating apparatus is provided on an optical fiber insertion side with a thermal CVD reactor and an upper seal chamber 2 filled with a seal gas for shutting off an external atmosphere.
1 and a thermal CV on the optical fiber delivery side of the thermal CVD reactor.
D. Provide a lower seal chamber filled with a seal gas for shutting off the external atmosphere from the reactor, measure the pressure difference between at least one of the seal chambers and the thermal CVD reactor, and determine the optimal seal gas for the measured seal chamber. The supply minimizes the flow of the seal gas into the thermal CVD reactor.

As a result, the rate of thermal decomposition of the raw material gas in the thermal CVD reactor is assured, and a carbon film having a sufficient film thickness and quality can be synthesized, and the carbon coating light having excellent strength and hermetic properties of the carbon film. Fiber production becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an apparatus used in a method for producing a carbon-coated optical fiber of the present invention.

2 (a) is an explanatory view of a longitudinal section showing an example of a carbon film coating apparatus used in the method of manufacturing the carbon-coated optical fiber of FIG. 1, and FIG. 2 (b) is an explanation of a transverse section viewed from above the apparatus. FIG.

FIG. 3 shows an upper seal chamber 21 and thermal CVD in Example 2.
It is a figure of a longitudinal change of the pressure difference of a reactor.

FIG. 4 is a diagram showing a longitudinal change in the flow rate of an upper seal gas flowing during drawing in Example 2.

FIG. 5 is a diagram showing a longitudinal change in the electrical resistance of a carbon film in Example 2.

FIG. 6 is a diagram showing a longitudinal change in a pressure difference between an upper seal chamber and a thermal CVD reactor in Comparative Example 2.

FIG. 7 is a diagram showing a longitudinal change in the electrical resistance of a carbon film in Comparative Example 2.

FIG. 8 is a diagram showing a longitudinal change in a pressure difference between an upper seal chamber and a thermal CVD reactor in Example 3.

FIG. 9 is a diagram showing a longitudinal change in the flow rate of an upper seal gas flowing during drawing in Example 3.

FIG. 10 is a diagram showing a longitudinal change in the electrical resistance of a carbon film in Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single mode optical fiber preform 3 Drawing furnace 4 Optical fiber 5 Carbon film coating device 6 Raw material gas supply port 8 Carbon coated optical fiber 21 Upper seal chamber 22 Thermal CVD reactor 23 Lower seal chamber 27 Seal gas inlet 28,29 Pressure measurement section

Claims (4)

(57) [Claims] 1. A method for producing a carbon-coated optical fiber, wherein the optical fiber immediately after drawing is passed through a carbon film coating apparatus equipped with a thermal CVD reactor to coat the surface of the optical fiber with a carbon film. The film coating apparatus is provided on the optical fiber insertion side with an upper seal chamber filled with a seal gas for shutting off the thermal CVD reactor and the outside atmosphere,
A method for producing a carbon-coated optical fiber, comprising: measuring a pressure difference between the upper seal chamber and the thermal CVD reactor, and supplying an optimal amount of seal gas to the upper seal chamber. 2. The method for producing a carbon-coated optical fiber, wherein the optical fiber immediately after drawing is passed through a carbon-film coating apparatus equipped with a thermal CVD reactor to coat the surface of the optical fiber with a carbon film. The coating apparatus is provided with an upper seal chamber on the optical fiber insertion side, which is filled with a seal gas for shutting off the thermal CVD reactor and the external atmosphere,
The thermal CVD is provided on the optical fiber delivery side of the thermal CVD reactor.
A lower seal chamber filled with a seal gas for shutting off a reactor and an external atmosphere is provided, and a pressure difference between at least the lower seal chamber and the thermal CVD reactor is measured, and an optimum amount of the seal gas is supplied to the lower seal chamber. And a method for producing a carbon-coated optical fiber. 3. A seal gas is supplied to the seal chamber so that the pressure difference between the seal chamber and the thermal CVD reactor is constant while monitoring the pressure in the seal chamber and the pressure in the thermal CVD reactor. The method for producing a carbon-coated optical fiber according to claim 1 or 2, wherein 4. A method of monitoring the quality of a carbon film such as electric resistance of a carbon film coated on the surface of an optical fiber on-line, and supplying a sealing gas to a sealing chamber so that the film quality of the carbon film is constant. The method for producing a carbon-coated optical fiber according to any one of claims 1 to 3.