JPH0421547A - Apparatus for producing hermetically coated optical fiber - Google Patents

Abstract

PURPOSE:To reduce the discharge speed of a gas for protecting the interior of a furnace from a taking out port by providing the lower part of a wire drawing furnace for optical fiber with an air-permeable porous lid having a fiber taking outlet. CONSTITUTION:A protective gas is fed from a feed pipe 17 for the protective gas in the upper part into the furnace body (2A) of a wire drawing furnace 2 and a sealing gas is fed from a sealing gas feed pipe 20 into a sealing chamber 19 installed in the top of the furnace body (2A) and blown off from an inserting hole 21 of an optical fiber preform 1 to seal the top of the furnace body (2A). On the other hand, the protective gas for the interior of the furnace is discharged through an air-permeable porous lid 22 such as a carbon felt attached to the bottom of the wire drawing furnace 2 and the resultant drawn optical fiber (3A) is led out of a fiber taking outlet 18 formed in the center of the lid 22.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention is characterized in that the surface of an optical fiber is coated with carbon, carbide (SiC,
The present invention relates to a hermetic-coated optical fiber production apparatus for producing a hermetic-coated optical fiber provided with a hermetic coating of (TiC, etc.).

"Prior art" Providing a hermetic coating on the surface of an optical fiber can prevent the intrusion of H2 and H2O from the outside.This greatly improves the fatigue characteristics of the optical fiber, and at the same time improves the H2 resistance. .

FIG. 6 shows the structure of a conventional hermetic coated optical fiber manufacturing apparatus. In this device, the tip of an optical fiber preform 1 is heated and melted in a drawing furnace 2, and an optical fiber 3A is kneaded from the molten part.
After measuring the outer diameter of A with the outer diameter measuring device 4, it is passed through the reaction chamber 5A in the reaction tube 5. In the reaction tube 5, a heating furnace 6 is disposed on the outer periphery of the central portion thereof, and a heating zone 7 is provided in the reaction chamber 5A. At the bottom of the reaction tube 5, there is a raw material gas supply port 8A.
A raw material gas supply pipe 8 is connected to the raw material gas supply port 8A, and the raw material gas for hermetic coating sent through the raw material gas supply pipe 8 is passed through the raw material gas supply port 8A to the reaction chamber 5A. is being supplied to. An exhaust port 9A is provided at the top of the reaction tube 5, and an exhaust pipe 9 is connected to the exhaust port 9A, so that the exhaust gas from the reaction chamber 5A is exhausted from the exhaust pipe 9 via the exhaust port 9A. ing. Further, small-diameter seal portions 10A and IOB are provided at the upper and lower ends of the reaction tube 5, and sealing inert gas such as N2 gas is supplied to these seal portions from seal gas introduction tubes 11A and IIB. , outside air is prevented from entering the reaction chamber 5A. In the reaction tube 5A, a hermetic coating is provided on the surface of the optical fiber 3A by a gas phase chemical reaction, thereby obtaining a hermetic coating optical fiber 3B. The hermetically coated optical fiber 3B is passed through a resin coater 12, and its surface is coated with resin, thereby forming a hermetically coated optical fiber core 3C. The hermetic coated optical fiber core wire 3C is passed through a hardener 13 to harden the coating resin, and then wound up by a winder 14.

In this case, the raw material gas is usually hydrocarbons (CH4
, C2H6+ c2H2, C3H,, C4H1o, etc.)
gas is used. The raw material gas flows along the optical fiber 3A in the reaction chamber 5A occupying a region shown by hatching in FIG. It becomes a hermetic coating. When coating with a hermetic coating made of SiC or TiC, a raw material gas prepared by adding SiH4, TiCJQ4, etc. to hydrocarbon gas is used.

C and SiC generated by high-temperature heating in heating zone 7.

A part of the TIC and the like is deposited on the surface of the optical fiber 3A to form a hermetic coating, which is a high-density layer, but most of it is exhausted from the exhaust port 9A.

However, when using such a hermetic coated optical fiber manufacturing apparatus to provide a hermetic coat on the surface of the optical fiber 3A through a gas phase chemical reaction of the raw material gas by heating in the heating furnace 6, as shown in FIG. , reaction chamber 5
C, SiC in A.

A soot-like reaction product 15 in the form of particles such as TIC is generated and adheres to the surface of the optical fiber 3A to form a low-density hermetic coating, or adheres to the exhaust port 9A or the exhaust pipe 9 and clogs it. There was a problem. Note that a low-density hermetic coating is easily peeled off from the optical fiber 3A, and cannot be expected to be effective as a film for preventing the intrusion of N20 or N2.

In order to improve this problem, in recent years, the heating furnace 6 has been omitted, and instead the optical fiber 3A is drawn at high speed, so that the optical fiber 3A is guided into the reaction chamber 5A before it is cooled, and the light is A device has also been developed that provides a high-density hermetic coating on the surface of the optical fiber 3A by chemically reacting the raw material gas using the heat of the fiber 3A.

Conventionally, the drawing furnace 2 of this type of device has a carbon heater 16 built into the furnace body 15 as shown in FIG. 3, and the heater 16 and other carbon parts are protected from wear and tear. Therefore, inside the furnace body 15, N2. The furnace body 15 is supplied with an in-furnace protective gas made of an inert gas such as Ar, and the furnace body 15 is prevented from being discharged from the fiber outlet 18 at the bottom of the furnace body 15.
A sealing chamber 19 is formed at the lower end, and sealing is performed by supplying an inert gas such as N2 gas as a sealing gas through a sealing gas supply pipe 20 and blowing it out to the fiber outlet 18. Instead, the protective gas inside the furnace was configured to be discharged to the outside of the furnace from the optical fiber preform insertion port 21 in the upper part of the furnace body 15.

However, since such a drawing furnace 2 blows out the sealing gas from the fiber outlet 18, the optical fiber 3A drawn out from the fiber outlet 18 or the broken line 22
The temperature of the optical fiber 3A entering the reaction chamber 5A decreases, resulting in the problem that only a very thin hermetic coating can be deposited. Also,
Since the furnace protection gas supplied from the lower side of the furnace body 15 also rises from the bottom to the top inside the furnace body 15 without being sufficiently heated, the optical fiber 3A is also cooled by this furnace protection gas. There were some problems.

In order to improve such problems, in recent bow furnaces 2, as shown in FIG. Furnace body 15
A sealing chamber 19 is provided at the upper end, and the sealing gas supplied from the sealing gas supply pipe 20 to the sealing chamber 19 is blown out from the optical fiber preform insertion port 21 to seal the upper part of the furnace body 15. Accordingly, the gas for protecting the inside of the furnace is discharged from the fiber outlet 18 to the outside of the furnace.

In such a drawing furnace, the optical fiber 3A is not cooled because the sealing gas is blown out from the optical fiber preform insertion port 21 at the upper end of the furnace body 15. In addition, the furnace protection gas is supplied from the upper part of the furnace body 15, and is discharged from the fiber outlet 18 in a sufficiently heated state during the descending process, so that the optical fiber 3A is heated by the furnace protection gas. It's not even cooled down. Therefore, the optical fiber 3A enters from the drawing furnace 2 into the reaction chamber 5A of the reaction tube 5 below it with almost no cooling.

[Problems to be Solved by the Invention] However, when the drawing furnace 2 as shown in FIG. 4 is used, if the diameter of the fiber outlet 18 is made small,
There was a problem that the thickness of the hermetic coating became thin and the H2 resistance of the hermetic coating became insufficient.

A detailed investigation into the cause revealed the following. That is, when the diameter of the fiber outlet 18 is reduced, the flow rate of the furnace protective gas released from the fiber outlet 18 increases, and as shown in FIG. It was found that the thickness of the hermetic coating was reduced in order to reduce the concentration of the raw material gas.

In order to avoid this, if the diameter of the fiber outlet 18 of the drawing furnace 2 is increased, the hermetic coating can be formed thicker, but air may enter the furnace body 15 through the fiber outlet 18 and the wire This is not preferable because the carbon parts in the furnace 2 will be consumed by oxidation.

An object of the present invention is to provide a hermetic coated optical fiber manufacturing apparatus that can reduce the outflow rate of the protective gas inside the furnace from the fiber outlet of a drawing furnace, and can also prevent air from entering the furnace body from the fiber outlet. Our goal is to provide the following.

[Means for Solving the Problems] To explain in detail the present invention for achieving the above object, the present invention provides an in-furnace protective gas that is supplied into the furnace, and that the in-furnace protective gas is supplied to the lower fiber drawer. It has a drawing furnace that is discharged from the mouth, heats and melts the lower part of the optical fiber preform in the drawing furnace, and draws the optical fiber from the lower part of the molten optical fiber preform. , in an apparatus for producing a hermetic coated optical fiber by pulling out the optical fiber from the fiber outlet to the outside of the furnace and passing it into a reaction tube, and applying a hermetic coating to the surface of the optical fiber using a raw material gas supplied into the reaction tube. A porous lid having air permeability is provided at the lower part of the drawing furnace, and the fiber outlet is provided in the porous lid.

[Function] When the porous lid is provided at the lower part of the drawing furnace in this manner, the gas for protecting the inside of the furnace can be discharged to the outside of the furnace through the porous lid by utilizing its breathability. Therefore, even if the diameter of the fiber outlet is made small, the flow rate of the furnace protection gas discharged from the fiber outlet can be reduced. Therefore, it is possible to suppress the in-furnace protective gas discharged from the lower part of the drawing furnace from entering the reaction chamber of the reactor, and it is possible to avoid a decrease in the thickness of the hermetic coating. Furthermore, if the diameter of the fiber outlet is made smaller, it is possible to suppress air from entering the furnace body.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG. Note that parts corresponding to those in FIG. 5 described above are designated by the same reference numerals.

In the hermetic coated optical fiber manufacturing apparatus of this embodiment, a porous lid 22 having air permeability such as carbon felt is attached to the lower part of the drawing furnace 2, and a fiber outlet 18 is formed in the center of the porous lid 22. has been done. The other points are the same as in FIG. 2.

When such a drawing furnace 2 is used, the gas for protecting the inside of the furnace can be discharged to the outside of the furnace through the porous lid 22 by utilizing its breathability. Therefore, even if the diameter of the fiber outlet 18 is made small, the flow rate of the furnace protection gas discharged from the fiber outlet 18 to the outside of the furnace can be reduced. Therefore, it is possible to suppress the in-furnace protective gas discharged from the lower part of the drawing furnace 2 from entering the reaction chamber 5A of the reaction furnace 5, and it is possible to avoid thinning of the hermetic coating. Furthermore, when the diameter of the fiber outlet 18 is reduced, it is possible to suppress air from entering the furnace body 15.

Experimental example The diameter of the fiber outlet 18 was 10 as the porous lid 22.
mm carbon felt was used, and the distance between the porous lid 22 and the upper end of the reaction tube 5 was 50 mm. The reaction tube 5 used had an inner diameter of 30 mm and a length of 450 mm. C2H4 gas is supplied as a raw material gas from the raw material gas supply pipe 8 at a rate of 2.0°C/min, and the seal portions IQA and IOB are
N2 gas was supplied as a sealing gas from the sealing gas introduction pipes 11A and 11B at 5β/min. An optical fiber 3A with an outer diameter of 125 μm is placed in the reaction chamber 5A at a linear velocity of 500 m/m.
A hermetic coating made of a carbon film was formed on the surface of the optical fiber 3A. The obtained hermetic coated optical fiber 3B is passed through the resin coater 12,
The surface thereof was coated with an ultraviolet curing resin to obtain a hermetic coated optical fiber core wire 3C. The resin coating was removed from the thus obtained hermetically coated optical fiber core wire 3C, and the thickness of the hermetic coating made of the carphone film was measured using a transmission electron microscope. Further, the temperature of the drawing furnace 2 was lowered, and the oxidation state of the carbon parts in the furnace was visually examined.

Further, as a comparative example, similar evaluations were conducted using a drawing furnace 2 as shown in FIG. 5, with the fiber outlet 18 having a diameter of 10, and other conditions being the same as in the experimental example described above.

The results are shown in the table. That is, according to the present invention, the drawing furnace 2
The hermetic coated optical fiber 3B having a thick hermetic coating could be manufactured without oxidizing the carbon parts.

Table [Effects of the Invention] As described above, in the hermetic coated optical fiber manufacturing apparatus according to the present invention, since a porous lid is provided at the lower part of the drawing furnace,
The gas for protecting the inside of the furnace can be discharged from the porous lid by utilizing its breathability. Therefore, even if the diameter of the fiber outlet is made small, the flow rate of the furnace protection gas discharged from the fiber outlet can be reduced. Therefore, it is possible to suppress the in-furnace protective gas discharged from the lower part of the wire bow furnace from entering the reaction chamber of the reactor, and it is possible to avoid a decrease in the thickness of the hermetic coating. Furthermore, by reducing the diameter of the fiber outlet, it is possible to suppress air from entering the furnace body.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a drawing furnace in a first embodiment of the apparatus according to the present invention, FIG. 2 is a vertical cross-sectional view showing a schematic configuration of a conventional device, and FIGS. 3 and 4 5 is a longitudinal sectional view showing two types of conventional drawing furnaces, and FIG. 5 is a longitudinal sectional view showing the flow of gas in the drawing furnace shown in FIG. 4. 1... Optical fiber base material, 2... Drawing furnace, 3A...
Optical fiber, 3B...hermetic coated optical fiber
3C... Hermetic coated optical fiber core, 5...
Reaction tube, 5A...Reaction chamber, 6...Heating furnace, 8A...
- Raw material gas supply port, 9A...exhaust port. Blasphemy ′) wo′! Figure Figure procedure amendment (discharge) March 18, 1991 2゜3゜4゜1990 Patent Application No. 121922 Name of the invention Relationship to the case of a person making amendments to hermetic coated optical fiber manufacturing equipment Patent application Person (529) Furukawa Electric Co., Ltd.

Claims (1)

[Claims] It has a drawing furnace in which a furnace protective gas is supplied into the furnace and discharged from the fiber outlet at the bottom, and the optical fiber preform is formed in the drawing furnace. The lower part is heated and melted, an optical fiber is drawn from the lower part of the melted optical fiber preform, and the optical fiber is pulled out of the furnace from the fiber outlet and passed into a reaction tube, and the raw material is supplied into the reaction tube. In an apparatus for manufacturing a hermetic coated optical fiber by applying a hermetic coating to the surface of the optical fiber using gas, a porous lid having ventilation is provided at the lower part of the drawing furnace, and the porous lid is provided with a porous lid for drawing out the fiber. A hermetic coated optical fiber manufacturing device characterized by being provided with a port.