JPH01197340A - Production of optical fiber and device therefor - Google Patents

Abstract

PURPOSE:To uniformize the diameter of a drawn optical fiber by practically equalizing the clearance between a furnace core tube and a preform to the clearance between the furnace core tube and a pipe, heating and melting the lower end of the preform, and drawing an optical fiber. CONSTITUTION:The pipe 6 is made of the same material as that of the furnace core tube 3, and heated by the radiant heat from the furnace core tube 3 to almost the same temp. In addition, since the clearance between the preform 1 and the furnace core tube 3 is almost equalized to the clearance between the pipe 6 and the furnace core tube 3, an eddy current of gaseous nitrogen is not caused. Accordingly, the gaseous nitrogen shown by the arrow A1 is kept at a uniform temp. and forms a stabilized current, and hence nonuniformity is not caused even in the gas current shown by the arrow A2. In addition, even when the drawing stage proceeds and the preform 1 is shortened, the preform 1 and the pipe 6 are simultaneously moved by a slider 9, and an eddy current, etc., are not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber manufacturing method and a manufacturing apparatus used therein.

[Conventional technology]

An optical fiber is drawn from a preform (base material) as shown in FIG. 2, for example.

As shown in the figure, a preform 1 is constituted by an inner part 1a with a high refractive index to serve as a core and an outer part 1b with a low refractive index to serve as a cladding, and this preform 1 is fixed to a support rod 2 made of, for example, quartz. has been done. Such a preform 1 is inserted into a furnace core tube 3 made of carbon, for example. Here, a heater 4 is installed in a predetermined portion of the furnace tube 3.
The lower end of the preform 1 is heated and melted, and the optical fiber 5 is drawn. In the drawing process of the optical fiber 5, nitrogen (N2) gas, for example, is supplied to the furnace tube 3 as an atmospheric gas in the direction indicated by the arrows Al,
It will be distributed like A2.

Then, the optical fiber 5 after being drawn with this nitrogen gas is
is now being cooled.

[Problem to be solved by the invention]

However, in the above-described conventional technology, the temperature of the nitrogen gas changes or fluctuates near the lower end of the main body 1.
Or it may vary depending on location. This is considered to be because the clearance between the preform 1 and the furnace core tube 3 is significantly different from the clearance between the support rod 2 and the furnace core tube 3.

That is, between the support rod 2 and the furnace core tube 3, the flowing nitrogen gas is not heated uniformly by the furnace core tube 3, and in the upper part of the preform 1, which is indicated by the dotted line interior B in the figure, a vortex flow of nitrogen gas occurs. This is thought to be due to the fact that this is likely to occur.

In this way, when non-uniformity occurs in the nitrogen gas temperature near the lower end of the preform 1, the diameter of the drawn optical fiber 5 fluctuates. This tendency became more pronounced as the diameter of the preform 1 became larger. Further, as the drawing of the optical fiber 5 progresses and the preform 1 becomes shorter, the problem becomes more noticeable.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical fiber manufacturing method that can make the diameter of a drawn optical fiber uniform.

Another object of the present invention is to provide an optical fiber manufacturing apparatus suitable for carrying out the above manufacturing method.

[Means to solve the problem]

The optical fiber manufacturing method according to the present invention involves inserting a preform fixed to a support rod into a furnace tube, and heating and melting the lower end of the preform while circulating atmospheric gas from above into the furnace tube, thereby producing light. In an optical fiber manufacturing method in which fiber is drawn, a pipe whose lower open end touches or is close to the upper shoulder of a preform is inserted into the core tube through a support rod, and the gap between the core tube and the preform is inserted into the core tube. It is characterized in that the gap is approximately the same as the gap between the pipes.

Further, the optical fiber manufacturing apparatus according to the present invention includes a furnace core tube in which a heater is disposed at a predetermined position and an atmospheric gas is circulated from above, and a support fixed to a lower end of a preform to be inserted into the furnace core tube. It is characterized by comprising a support mechanism that supports the rod, and a pipe that is disposed within the reactor core tube so as to move up and down together with the support rod via the support mechanism, and whose outer diameter is approximately the same as the outer diameter of the preform.

[Effect]

According to the present invention, in the pipe made of, for example, carbon, the cross-sectional area of the atmospheric gas flow path is made approximately the same in the preform portion and the support rod portion. Therefore, the atmospheric gas is heated uniformly, and fluctuations in temperature due to the generation of eddy currents are also reduced.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to FIGS. 1 and 2 of the accompanying drawings. In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 is a side view, in cross section, of a part of a drawing apparatus for applying an optical fiber manufacturing method according to an embodiment of the present invention. As shown in the figure, the preform 1 is placed in the furnace tube 3.
is inserted, and a pipero is inserted above this.

The outer diameter of this pipero is approximately the same as the outer diameter of the preform 1, and its lower open end is close to or in contact with the upper shoulder of the preform 1. The upper end of the support rod 2 to which the preform 1 is fixed is gripped by a support rod chuck 7a, and the upper end of the pipe is gripped by a pipe chuck 7b, which are fixed to the slider 9 via arms 8a and 8b. Ru. This slider 9 is attached to a threaded shaft 10, so that both the preform 1 and the pipero can move up and down.

Next, the operation of the above embodiment will be explained.

In FIG. 1, the pipero is made of the same material as the furnace core tube 3, so when the furnace core tube 3 is made of carbon, the pipero is also made of carbon.

Therefore, the pipes are heated to approximately the same temperature by the radiant heat from the core tube 3. In addition, preform 1 and furnace tube 3
Since the clearance between the pipe and the furnace core tube 3 is approximately the same as that between the pipro and the furnace core tube 3, no swirl of nitrogen gas is generated.

Therefore, the nitrogen gas indicated by the arrow A1 in the figure has a uniform temperature and a stable flow, so the nitrogen gas indicated by the arrow A1 in the figure
Even in the gas flow shown by , no temperature non-uniformity appears.

Furthermore, even when the preform 1 becomes shorter as the wire drawing process progresses, the preform 1 and pipero are simultaneously moved by the slider 9, so the clearance between the furnace core tube 3 and the support rod 2 is limited even in the preform 1 part. Since it remains constant even in the area, there is no room for eddy currents to occur. Therefore, if the pipe has a sufficient length, the nitrogen gas will be stably heated between the reactor core tube 3 and the pipe, and the temperature will be stabilized at a uniform temperature.

The present invention is not limited to the above embodiments, and various modifications are possible.

For example, the material of the pipero is preferably the same as that of the furnace tube 3, such as carbon, but is not limited to this, and the same material as that of the preform 1, such as quartz, may be used. Further, a support rod chuck 7a constituting a support mechanism,
Pipe chuck 7b.

The arms 8a, 8b, slider 9, etc. are not limited to those shown in the drawings, and may have any configuration as long as they can keep the upper shoulder of the preform 1 and the lower open end of the pipero in contact with or close to each other.

The present inventor conducted the following comparative experiment in order to confirm the effectiveness of the invention.

First, as a conventional example, a preform having a diameter of 80 m was spun at a line speed of 600 m/min using an apparatus as shown in FIG. In this case, the diameter variation σd of the obtained optical fiber is
was about 3 μm. Next, as an example, when the furnace core tube and pipe were made of carbon in the apparatus shown in Fig. 1, and a preform with a diameter of 80 mm was spun at a line speed of 600 m/min, the wire diameter variation was σ, -0.15 μm.

As a result, it has been found that according to the present invention, the atmospheric gas can stably flow at a uniform temperature, and therefore, variations in the diameter of the optical fiber can be significantly reduced.

〔Effect of the invention〕

As described in detail above, in a pipe made of, for example, carbon, the cross-sectional area of the atmospheric gas flow path is approximately the same in the preform portion and the support rod portion. Therefore, the atmospheric gas is heated uniformly, and fluctuations in temperature due to the generation of eddy currents are also reduced. Therefore, the diameter of the drawn optical fiber can be made uniform.

Further, the present invention can provide an optical fiber manufacturing apparatus that is suitable for carrying out the above manufacturing method and has a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional side view of a part of a drawing apparatus to which an optical fiber manufacturing method according to an embodiment of the present invention is applied;
FIG. 2 is a sectional view of a main part of a conventional wire drawing device. DESCRIPTION OF SYMBOLS 1... Preform, 2... Support rod, 3... Furnace tube, 4... Heater, 5... Optical fiber, 6...
Pipe, 7a... Support rod chuck, 7b... Pipe chuck, 9... Slider. Patent applicant: Sumitomo Electric Industries, Ltd. Representative Patent Attorney Yoshiki Hase Figure 1 Figure 2

Claims (1)

[Claims] 1. A preform fixed to a support rod is inserted into a furnace tube, and while atmospheric gas is passed from above into the furnace tube, the lower end of the preform is heated and melted to form an optical fiber. In the method of manufacturing an optical fiber, a pipe whose lower open end abuts or is close to the upper shoulder of the preform is inserted into the core tube through the support rod, and the pipe is inserted into the core tube and the preform is connected to the core tube. A method for manufacturing an optical fiber, characterized in that the gap is made substantially the same as the gap between the furnace core tube and the pipe. 2. A furnace core tube in which a heater is arranged at a predetermined position and atmospheric gas is circulated from above, a support mechanism that supports a support rod to which a preform to be inserted into the furnace core tube is fixed at its lower end, and this support mechanism. An optical fiber manufacturing apparatus comprising: a pipe disposed within the furnace core tube so as to move up and down together with the support rod, and having an outer diameter substantially the same as an outer diameter of the preform. 3. The optical fiber manufacturing apparatus according to claim 2, wherein the pipe is made of the same material as the furnace tube.