JPH02137744A - Drawing of optical fiber - Google Patents

Abstract

PURPOSE:To improve workability by adjusting position of gas feed opening depending upon drawing speed so as to make specific part of optical fiber preform always exist higher than the gas feed opening. CONSTITUTION:Optical fiber preform 4 is introduced into a heating furnace 1 which is equipped with a gas feed opening 6A and sends a gas from the lower part of the feed opening 6A to the upper part, heated by a heater 5 and drawn to form part 7B of fiber 7, having <=10<7> poise. Position of the gas feed opening 6A is adjusted depending upon drawing speed of the fiber 7 in such a way that the part 7B of the optical fiber 7, which is being drawn and has <=10<7> poise, always exists higher than the position of the gas feed opening 6A and the fiber 7 is drawn while forming a solidification forming position 7A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of drawing an optical fiber.

[Prior Art] Conventionally, as shown in FIG. 3, optical fiber is drawn by inserting an optical fiber preform 4 into a vertically oriented furnace core tube 3 in a furnace body 2 of a heating furnace 1 in the axial direction. The optical fiber base material 4 is heated with a heater 5 made of carbon or the like, and
Inert gas is flowed from the lower gas supply port 6A into the upper part of the furnace core tube 3 through the gas supply line 6 to prevent air from entering the furnace, and in this state, the optical fiber is drawn from the optical fiber preform 4. The optical fiber 7 was manufactured using the same method. Note that 8 is a diaphragm cover provided at the exit of the optical fiber 7 to prevent air from entering.

In particular, when the gas flows from the bottom to the top, dust can be discharged upward, so that the dust does not adhere to the optical fiber 7 and the strength of the optical fiber 7 is improved.

In order to reduce fluctuations in the outer diameter of the optical fiber 7, it is necessary to constantly flow an inert gas into the furnace core tube 3.

However, in such a conventional optical fiber drawing method, when the drawing speed is about 120 m/min, for example, the solidification formation position of the optical fiber 7 and the point where the optical fiber has a predetermined outer diameter I
I) 7A is in the furnace core tube 3, but the linear speed is, for example, 240 m
/min, the solidified formation position 7A of the optical fiber 7 jumps out of the furnace core tube 3, so the gas from the gas supply port 6A directly hits the molten part of the optical fiber 7, causing temperature fluctuations and decreasing the fiber diameter. There were issues that were subject to change.

In order to solve these problems, the applicant first proposed the fourth
As shown in the figure, the position of the gas supply port 6A is such that the solidification formation position 7A of the optical fiber 7 having a viscosity of about 7.610 poise is always located above the gas supply port 6A. proposed an optical fiber drawing method in which drawing is performed by adjusting the speed of the optical fiber 7 according to the drawing speed of the optical fiber 7 (Japanese Patent Application No. 63-234884).

In this method, the linear speed of the optical fiber 7 is, for example, 240 m/
At the minute, the furnace core tube extension 3 is placed on the exit side of the optical fiber 7.
Correspondingly, a furnace body extension part 2Δ is provided concentrically, and a gas supply line extension part 6B is provided between the furnace core tube extension part 3A and the furnace body extension part 2A. Inert gas is supplied into the furnace core tube 3 from the gas supply port 6A at the tip of the tube extension 3A.

When the optical fiber 7 is drawn in this manner, the solidification position 7A of the optical fiber 7 is always located above the gas supply port 6A, and the molten portion of the optical fiber 7 is not directly exposed to the inert gas.

Figures 5 and 6 show two examples of how to extend the furnace. Figure 5 shows an example of one-stage extension, and Figure 6 shows an example of two-stage extension. . The first- and second-stage furnace core tube extensions 3A and 3B are connected by screw connections, and the first- and second-stage furnace body extensions 2A and 2B are connected by flanges. There is. The number of connection stages is increased depending on the drawing speed of the optical fiber 7, so that the solidification position ffff7A of the optical fiber 7 is not located below the gas supply port 6A.

[Problem to be solved by the invention] However, the solidification formation position 7 of such an optical fiber is
In the method of adjusting the position of the gas supply port 6A according to the drawing speed of the optical fiber 7 so that the position of the gas supply port 6A is always above the position of the gas supply port 6A, the length of the heating furnace 1 becomes longer than necessary. However, there was a problem with poor workability.

An object of the present invention is to provide an optical fiber drawing method that can draw an optical fiber by increasing the length of a heating furnace to the minimum necessary length.

[Means for Solving the Problems] To explain in detail the present invention for achieving the above object, the present invention has a gas supply port provided at the bottom, and the gas supply port allows gas to flow from the bottom to the top. In the method of drawing an optical fiber, which manufactures an optical fiber by heating and drawing an optical fiber preform in a heating furnace, a portion of the optical fiber of 107 poise or less is always above the gas supply port. The optical fiber is drawn by adjusting the position of the gas supply port according to the drawing speed of the optical fiber.

[Function] Since the portion of the optical fiber below 107 poise is above the solidification formation position of the optical fiber, the optical fiber can be kneaded by extending the heating furnace to the minimum necessary extent.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG. Note that parts corresponding to those in FIGS. 3 to 6 described above are designated by the same reference numerals.

In this embodiment, the position of the gas supply port 6A of the optical fiber 7 is adjusted so that the portion 7B of 107 poise or less of the optical fiber 7 being drawn is always located above the position of the gas supply port 6A. The optical fiber 7 is drawn while adjusting according to the speed. The position of the gas supply port 6A is adjusted as shown in FIGS. 5 and 6 described above.

Optical fiber 7 at solidification formation position 7A of optical fiber 7
Although the viscosity of the optical fiber 7 is approximately 1+07.6 poise, experiments have shown that it is not necessary to stabilize the gas flow around the optical fiber 7 to this extent.

An example is shown in figure ff12. In Figure 2, position A is 15,611 IIm from the center of the heat zone if the gas supply port 6A is located, and position B is 2 m from the center of the heat zone.
When the gas supply port 6A is located at the position 20+++a, the relationship between the viscosity of the optical fiber 7 when the gas supply port is located at the position C is 280 mm from the center of the heat zone (optical fiber solidification formation position 7△). This is what is shown. When the gas supply port 6A is located at position A, the outer diameter variation of the optical fiber is approximately ±1 μm, and when the gas supply port 6A is located at position B, the outer diameter variation of the optical fiber 7 is approximately 0.4 μm. It is. Therefore, even if the gas supply port 6Δ is located at a place where the optical fiber 7 is a little softer than the assimilation formation position 7A, there will be no problem.
．． 6-6.8 No. Experiments have shown that when the gas supply port 6A is located at 10 10 poise, variations in the outer diameter of the optical fiber 7 do not pose a problem. Therefore, with a margin of 10
It is sufficient that a portion of 7 poise or less is above the gas supply port 6A.

As the drawing speed increases, the high temperature part of the optical fiber becomes longer and the low viscosity part extends downward. Accordingly, the position of the gas supply port 6A is adjusted further down as shown in FIG.

[Effects of the Invention] As explained above, in the optical fiber drawing method according to the present invention, the position of the gas supply port is adjusted so that the portion of the optical fiber having 107 poise or less is always above the gas supply port. Since the fiber is drawn while being adjusted according to the fiber drawing speed, the length of the heating furnace can be extended to the minimum necessary length, and the optical fiber can be drawn while preventing variations in its outer diameter. In this way, if the length of the heating furnace can be minimized, there is an advantage that workability will be improved.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing a schematic configuration of an example of a heating furnace for carrying out the method of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the length from the center of the heat zone and the viscosity of the optical fiber, and Fig. 3 and FIG. 4 are vertical cross-sectional views showing two examples of conventional heating furnaces, and FIGS. 5 and 6 are vertical cross-sectional views showing two examples of how to extend the heating furnace. DESCRIPTION OF SYMBOLS 1... Heating furnace, 2... Furnace body, 2A, 2B... Furnace body extension part, 3... Furnace core tube, 3A, 3B... Furnace core tube extension part, 4... Light Fiber base material, 5... Heater, 6...
- Gas supply system path, 6A... Gas supply port, 7... Optical fiber, 7A... Solidification formation position, 7B... Portion below 107 poise. Beast Kahema' CG field side (and kK) Figure Figure Figure Figure

Claims (1)

[Claims] A method of drawing an optical fiber in which an optical fiber base material is heated and drawn in a heating furnace in which a gas supply port is provided at the bottom and gas is flowed from the bottom to the top by the gas supply port to produce an optical fiber. 10 of the optical fibers
Drawing of an optical fiber is performed by adjusting the position of the gas supply port according to the drawing speed of the optical fiber so that a portion of ^7 poise or less is always above the gas supply port. Method.