JPS602254B2 - How to draw optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of drawing an optical fiber used as a bright transmission line.

[Subordinate technology]

Optical fibers are drawn using the crucible method, in which glass materials in multiple crucibles are heated with a heat source and the molten glass is drawn out from the nozzle of the crucible, and the crucible method, in which a separately prepared single or multi-layer pipe or There is a preform method in which a rod (preform) is heated and the molten glass is pulled out and drawn.

The optical fiber obtained by such a drawing method has locally weak mechanical strength, so a protective layer of polymeric material (hereinafter referred to as polymer) is applied to the outer peripheral surface of the optical fiber after or at the same time as drawing. Reinforcement is performed by coating (precoating). By precoating this polymer, defects in mechanical strength that were thought to be caused by air bubbles contained in the preform and scratches on the surface have been considerably improved. In addition, the polymer coating layer also had uneven thickness and uneven coating. In order to explore the causes of these defects, conventional manufacturing methods and manufacturing equipment were examined. First, we investigated a manufacturing method using a secondary device that coats the outer peripheral surface of an optical fiber with a polymer simultaneously with drawing as shown in FIG. As can be seen from FIG. 1, the preform 1 is heated and melted by the heat source 2 to become an optical fiber 9, which is wound around the drum 6.

The diameter of the optical fiber is detected by a detector 4 before it is wound around a drum, and then the outer peripheral surface of the optical fiber is coated (precoated) with polymer through a polymer coating bath 10 and a heating device 12. As a result of conducting various experiments using this series of devices, it was found that this manufacturing method includes the following problems.

'1) When detecting the diameter of the optical fiber 9, in order to prevent vibration of the optical fiber and increase the detection accuracy of the diameter, the optical fiber 9 is brought into contact with a metal (stainless steel) guide roller 4'. I had to make sure that I was able to pass in the same condition.

Furthermore, in order to uniformly coat the outer circumferential surface of the optical fiber with the polymer, it is necessary to minimize the vibration of the optical fiber 9 and the displacement of the optical fiber using the guide roller 4'. However, when the heated and melted optical fiber 9 passes through the guide roller 4', the surface temperature of the optical fiber is more than 100 pm and has not been cooled down sufficiently. Because the optical fiber with such a high surface temperature is drawn while creating friction with the metal guide roller, the surface of the optical fiber is scratched or deformed, and the optical fiber itself becomes mechanically brittle. . In addition, vibrations caused by axis misalignment and positional misalignment of the guide rollers are transmitted to the optical fiber, reducing the accuracy of detecting line fleas on the optical fibers, and the vibrations are also transmitted to the preform melting part, causing a change in the amount of deformation of the melting part. I was letting it happen. As a result, the amount of wire diameter variation was increased. (21) The optical fiber 9, which has been heated and drawn to 1900 to 230 mm inside the furnace core tube 3 (generally in an inert atmosphere), is pulled out into the open atmosphere with a very high surface temperature. Due to natural air cooling, there are many opportunities for contact with water vapor and alkali metal ions in the air, which causes the glass wire of the optical fiber to crystallize, become brittle, and otherwise deteriorate, reducing its mechanical strength. .

'31 Similar to the above (■), dust in the air is also likely to be adsorbed to the outer circumferential surface of the optical fiber.

As a result, the outer circumferential surface of the optical fiber that has passed through the polymer coating layer 10 and the heating device 12 is not uniformly coated with the polymer, resulting in uneven thickness and uneven wetting of the polymer coating layer. A polymer-coated optical fiber 13 was obtained. Furthermore, it has been found that because the optical fiber comes into contact with the polymer liquid at a temperature of 100 q or more, the polymer liquid is heated and boils, and the outer peripheral surface of the optical fiber is not uniformly coated with the polymer film. [Object of the Invention] The present invention aims to solve the above-mentioned problems.

That is, an object of the present invention is to provide a method for obtaining an optical fiber with high mechanical strength in a method of drawing optical fiber.
[General Description of the Invention] The present invention involves drawing an optical fiber material while heating and melting it with a heating source, and then winding the optical fiber onto a drum. This is a method of drawing an optical fiber in which a tube is provided that extends through the tube, the optical fiber is passed through the tube, and a gas is caused to flow inside the tube to cool the surface of the optical fiber.

By cooling the surface of the optical fiber in this manner, it is possible to suppress the diffusion of water vapor, alkali metal ions, etc. in the air into the optical fiber, and prevent a decrease in mechanical strength.

Furthermore, since the surface of the optical fiber is kept at a low temperature, the polymer can be coated uniformly and an optical fiber with strong mechanical strength can be obtained.

As described above, the present invention solves a conventional problem, that is, when an optical fiber is drawn out into an open atmosphere while its surface temperature is extremely high, water vapor, alkali metal ions, etc. in the air enter the optical fiber. Problems such as diffusion, causing crystallization or brittleness of the glass wire region of the optical fiber, and non-uniform coating of the polymer due to polymer coating at high temperatures can be solved.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

FIG. 2 shows an example of an optical fiber drawing apparatus used for carrying out the present invention.

The preform 1 is fed into the heating source 2 at a speed vp. The preform heated and melted in the heat source 2 is stretched and wound onto the winding drum 6 at a speed vf. It is detected by the line width detector 4 of the optical fiber 9 and displayed on the line level measuring device 5. The wire diameter detector 4 irradiates a laser beam sinusoidally scanned by an optical deflector using a tuning fork and lenses from the x-axis direction onto an optical fiber 9 running along the Z-axis. A method is used in which each of the scattered square wave pulses is demodulated to obtain a wire diameter value. The accuracy of optical fiber wire measurement by the wire diameter measuring device 5 with respect to the positional deviation of the optical fiber 9 in the Y-axis direction has characteristics as shown in FIG. Therefore, in order to prevent the optical fiber 9 from shifting in the Y-axis direction, gas was blown onto the optical fiber 9 from the Y-axis direction through a flowmeter 19 as shown by the arrow 18. Reference numeral 20 denotes a gas pipe for flowing this gas around the optical fiber 9 along the axial direction of the optical fiber 9.

And an optical fiber 9 drawn into this gas pipe 20
The Y of the optical fiber is
To detect line fleas on an optical fiber while suppressing positional deviation in the axial direction. Furthermore, the optical fiber 9 is passed through a polymer coating tank 10 and a heating device 12 while being maintained in the gas 18'' atmosphere, and the precoated fiber 13 whose outer peripheral surface is coated with the polymer 11 is wound around the drum 6. In this embodiment, the gas pipe 201 shown in FIG. 4a is used. In FIG. 4a,
Gas was introduced from the gas introduction pipe 26, and the gas was made to come out from the optical fiber guide pipes 23 and 25. The gas introduction pipe 26 had an outer diameter of 8 on the side and an inner diameter of 6.5 on the side, with one side of the inner diameter 27 at the tip, and one side of the inner diameter of the tip. The optical fiber guide tubes 23 and 25 have an outer diameter of 1 mm, and an inner diameter 24 of the tapered part of 2 mm.
The 12th side was set as the 45th side. Then, while drawing the optical fiber (outer diameter: 150 cm), the gas (oxygen was used in this example, but Ar, N2, air, etc.) is sent in from the arrow 18.The flow rate and the Y-axis direction of the optical fiber 9 The relationship between the amount of positional displacement and the amount of displacement was measured. Figure 5 shows the results.
However, when the gas flow rate is 0, the amount of positional displacement of the optical fiber 9 in the Y-axis direction is set to 0. As is clear from the figure,
The position of the optical fiber could be adjusted by changing the gas flow rate. Furthermore, the vibration of the optical fiber 9 during running could be reduced. FIG. 6 is an example of a histogram of tensile breaking strength of precoated fibers. Figure a shows the results obtained by the conventional method, and Figure b shows the results obtained by the example method. This is made of silicone as Polymer 11 (product name: KEIO station TV).
sulfurizing agent), the nozzle length of the polymer coating layer 10 is approximately 0.2 mm, the length of the heating device is approximately 20 mm, the temperature is 700 ° C., the VF is approximately 20 mm/min, and the optical fiber 9 is heated. These are the results when the wire diameter is 150 ridges. and Figure 6b
In this case, the value of the flow meter 19 is set to 5/mjn. The bricoat fiber obtained by the method of this example has excellent tensile strength at break. The first reason for this is that the surface of the optical fiber was cooled by the gas flowing inside the gas pipe 20, which suppressed the diffusion of water vapor, alkali metal ions, etc. in the air into the optical fiber. . It can also be assumed that this is because the mechanical strength of the optical fiber 9 itself hardly deteriorated due to the fact that the optical fiber did not come into contact with a guide roller or the like in a high temperature state. Furthermore, since the surface of the optical fiber was kept at a low temperature and in a clean atmosphere, it can be assumed that the polymer could be coated uniformly. In FIG. 2, a solid line a and a dotted line b indicate a method of controlling the line of the optical fiber. When the output signal of the wire diameter measuring device 5 is fed back to the drum drive circuit 8 through the control circuit 17 as shown by the solid line a, the winding speed vf can be changed to control the winding diameter, and as shown by the dotted line b
When fed back to the gas flow rate control valve opening/closing device 16 as shown in the figure, the gas flow rate 14 sent into the furnace core tube 3
The wire diameter can be controlled by changing ′. The line drawing method of the present invention can be applied even when other line drawing control methods are used. Further, the gas sent from the arrow 18 through the flow meter 19 to the gas pipe 20 flows out in the directions of the arrows 18' and 18''. Reference numeral 21 is a stop for adjusting the gas flow rate.

22 is a tube for introducing gas into the furnace core tube 3.

4b, c, and d show other embodiments of the gas pipe 20. FIG.

Figure b is characterized in that the inner diameter of the tip of the gas introduction pipe 26 is elliptical. By making it elliptical in this way, even if the optical fiber shifts slightly in the x-axis direction, the amount of displacement of the optical fiber in the Y-axis direction can be kept constant by the gas blown from the Y-axis direction. It is. In addition, in FIG. 3c, the gas fed from the gas introduction pipe 26 is easily separated into the optical fiber guide pipes 23 and 25 by the tip protrusion 28. As a result, it is possible to suppress vibration of the optical fiber 9 while it is running due to the gas flow rate. In FIG. 4D, the gas sent from the gas introduction pipe 26 is separated and flows out to the optical fiber guide pipes 23 and 25, and also flows out from the hole 29. This is also designed to suppress the vibration of the optical fiber 9 while it is running, as in the case c of the same figure. As described above, in order to suppress the displacement of the optical fiber, the gas pipe is not limited to this embodiment as long as it has a structure that allows the gas to uniformly collide with the traveling optical fiber. Further, the inner diameter 24 may be larger than the diameter of the optical fiber. Furthermore, arrow 18
It is advantageous that the higher the pressure of the gas sent from the y-axis, the greater the displacement layer of the optical fiber 9 in the Y-axis direction. FIG. 7 shows another embodiment of the line drawing method of the present invention.

In this case, gas sent from an arrow 18 is sent into a gas pipe 20 through a gas flow rate regulating valve opening/closing device 31 and a flow meter 19. Then, the amount of displacement of the optical fiber in the Y-axis direction is detected by the optical non-contact detector 29, and is fed back to the gas flow rate adjustment valve opening/closing device 31 through the control circuit 30, so that the optical fiber is always directed to the center of the scanning beam of the linear detector. It was designed so that fibers would come. Another method that does not use the optical non-contact detector 29 is to use a method for setting the position of the optical fiber obtained from the line measuring device 17 (for example, when using a laser line measuring device manufactured by Anritsu Electric Co., Ltd.). You can use an instruction signal. That is, when this instruction signal reaches its maximum value, the optical fiber is brought to the center of the scanning beam of the wire diameter detector. Therefore, the control circuit 30
The maximum value of the above instruction signal is used as the reference signal, the above instruction signal is input as the input signal, and the signal is compared and amplified with the reference signal. If an erroneous Hatakeashi signal is generated, the valve opening/closing device for gas flow rate adjustment is activated. All you have to do is make it so that the gas increases or decreases. The method of the present invention includes a crucible method, a crucible method, and a preform method. Needless to say, this method can also be applied to combination methods of multi-purpose methods.

In the above explanation, the method of displacing the optical fiber in the Y scale direction and the method of controlling it so that the amount of displacement is constant has been explained. The accuracy of line measurement with respect to positional deviation in direction) has characteristics as shown in FIG.

Therefore, in order to improve the accuracy of line measurement for the positional deviation in the optical axis direction, gas is blown onto the optical fiber running in the Z-axis direction from the x-axis direction through the gas pipe as shown in Figures 2 and 7. A method of suppressing fiber position shift may be used in combination with the above method, or may be used alone. [Effects of the Invention] As explained above, according to the present invention, the mechanical strength of the optical fiber can be increased.

[Brief explanation of the drawing]

Fig. 1 shows a conventional optical fiber drawing device, Fig. 2 shows an example of an optical fiber drawing device used in the implementation of the present invention, and Fig. 3 shows lines in the scanning direction of the line deviation measuring device used in the implementation of the present invention. An example of diameter measurement accuracy, FIG. 4 is an example of a gas pipe used in the practice of the present invention, FIGS. 5 and 6 are examples of results obtained by the optical fiber drawing method of the present invention, and FIG. Another example of the optical fiber drawing device used in practice, FIG. 8 shows an example of the accuracy of measuring the line depression in the optical axis direction of the wire diameter measuring device. 1...preform, 2...heat source, 6...
... Winding drum, 9 ... Optical fiber, 10 ... Polymer coating tank, 13 ... Precoated fiber, 20.
...Gas pipe. Many figures, many six figures, many two figures, inferior figure, Figure 4, '4i, Tsutomu I figure, too.'

Claims (1)

[Claims] 1. In an optical fiber drawing method in which an optical fiber material is drawn while being heated and melted, and the optical fiber is wound around a drum, the optical fiber is exposed to light after leaving a heating source that heats the material. 1. A method for drawing an optical fiber, which comprises passing a gas through a tube extending along the axial direction of the fiber and causing gas to flow through the tube to cool the surface of the optical fiber. 2. The optical fiber drawing method according to claim 1, wherein an oxidizing gas or an inert gas is used as the gas. 3. A method for drawing an optical fiber according to claim 1, characterized in that the outer peripheral surface of the optical fiber that has passed through the tube is coated with a coating material. 4. In the method for drawing an optical fiber according to claim 1, the gas is introduced into the tube so as to be blown onto the optical fiber from a direction perpendicular to the running direction of the optical fiber, and the gas is introduced into the guide tube. A method for drawing an optical fiber, characterized in that the surface of the optical fiber is cooled by flowing the fiber. 5. A method for drawing an optical fiber according to claim 4, characterized in that the gas is blown onto the optical fiber to displace the optical fiber. 6. An optical fiber drawing method according to claim 5, characterized in that the diameter of the optical fiber is detected in a non-contact state without using a guide roller.