JPS6034721B2 - Method for reducing optical fiber diameter variation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber drawing method using the Lubbo method to obtain an optical fiber with less variation in line flea and a diameter controlled with higher precision. .

Research on optical fibers has progressed rapidly over the past few years, and it has become possible to realize ultra-low loss values of several dB/second.

At the same time, we have gradually entered the stage where various practical characteristics of optical fibers, such as ease of connection, stress resistance characteristics, and broadband characteristics, are being discussed. One of the important keys to elucidating and evaluating these properties is the uniformity of the diameter of the optical fiber. The uniformity of the bran diameter of this optical fiber depends on the optical fiber drawing device. Conventionally, optical fiber drawing methods include a preform method and a crucible method. Currently, the crucible method has the problem that it is difficult to obtain optical fibers with low loss compared to the preform method, but it is possible to draw long optical fibers (about several tens of fibers) continuously at high speed. This is a promising line drawing method because it is suitable for mass production. FIG. 1 shows an outline of the conventional optical fiber drawing method using the Luppo method. The figure is an example of the double crucible method.
By placing a glass material that will become the core material of the optical fiber in the inner crucible 1 and a glass material that will become the cladding material of the optical fiber in the outer crucible 2 and heating the crucibles with the heat source 5, the crucibles are heated. The inserted glass is melted, and the molten glass is drawn out from the rubbo nozzles 6, 6' to form an optical fiber 7. The optical fiber 7 is attached to the drum 12 at a predetermined winding speed vr (motor controller 1
Set at 1. ). and drum 12
While the optical fiber is being wound, the diameter of the optical fiber is detected by the detector 8 and displayed on the twill measuring device 9. One of the problems with this drawing method is that the diameter of the optical fiber varies due to the following factors. '11
Wire diameter variation due to glass temperature variation during drawing. ■ The wire diameter changes due to the drop in the glass liquid level in Rubbo and the change in the amount of glass flowing out as the drawing time increases. As an example of the analysis of the above-mentioned fluctuation in line density (for example, Masagaki et al.: Study of fibers for optical communication, materials from the Kodoji Electronics Research Group), we can see that changes in core diameter a and cladding flea b due to fluctuations in glass temperature T, ΔA (T) and Δb(T) are expressed by the following equations.

Q1 Three things 2 = Back {pM+QJ+(; Table; Nu}△T〇2△Things 2
＝Kyo {p's ten snake T ten; Kurage;}△T However, Q, A, B
, To are constants, po is the density at a temperature of 0° C., and suffixes 1 and 2 are quantities related to the core glass and clad glass, respectively.

Furthermore, since the core diameter and cladding diameter are also proportional to the square root of the position of the liquid level of the glass, the position of the liquid level of the glass decreases with the drawing time, and the wire diameter changes.

For this purpose, conventionally, the output signal of the detector 8 is transferred to the control circuit 10.
feeds back to the motor controller 11 through
Wire winding control is performed by changing the winding speed vf of the optical fiber. By this control method, it is possible to suppress to a certain extent the line flow fluctuation due to slow periodic fluctuations in the glass temperature T and the line flow fluctuation due to changes in the amount of glass flowing out.
However, in reality, with this drawing method, the temperature of the molten glass near the Lubbo nozzle becomes irregular due to fluctuations in the density of the outside air due to the movement of workers or objects during drawing, or due to forced disturbances. , and it was found to fluctuate extremely sensitively in short periods. It was also found that the line mosaic also fluctuates irregularly and extremely sensitively in short periods. Therefore, it has been difficult to suppress this bran diameter variation by the above-mentioned line flea control. This is because the rise and fall times of the wire flow variation are slightly shorter (both on the order of seconds) than the rise and fall times of the wire diameter response to a step change in the winding speed vf.
Therefore, the present invention suppresses fluctuations in the temperature of molten glass near the nozzle of Rubbo due to fluctuations in the density of the outside air due to the movement of objects or workers during drawing, or forced disturbances. As a result, it is an object of the present invention to provide a method for suppressing the irregular and extremely short period fluctuations in wire diameter caused by the temperature fluctuations. That is, in this method, a gas introduction passage is provided between the rubbo and the inside of the heat source, and the gas is flowed along the outer circumferential surface of the rubbo, and the wire is drawn in such a state that the flow of molten glass and the gas flow always become a waste flow. Also,
The present invention also provides a method for linearly controlling fluctuations caused by fluctuations in the set temperature of the heating source and fluctuations in the position of the liquid level of the glass by changing the flow rate of the gas. The method of the present invention will be explained below using Examples. FIG. 2 shows a schematic diagram of an embodiment of the optical fiber drawing method of the present invention.

The figure consists of a triple Lupo, with an arrow 14 on the outer crucible 13.
Gas is fed through the gas introduction pipe 15 from the arrow 14.
It is made to flow in the direction of ^. The gas flow rate passing through the outer rubbo 13 and flowing in the direction of the arrow 14'' is within the laminar flow range where the flow rate distribution does not become turbulent. The temperature is set to be sufficiently larger than the change in natural convection due to turbulence.Therefore, it is possible to suppress the temperature fluctuations of the molten glass near the Rubbo nozzle, and the irregular and extremely sensitive fluctuations in short periods due to this can be suppressed. That is, when the molten glasses 3 and 4 in Rubbo 1 and Rubbo 2 flow out of the nozzle, the method of the present invention can suppress the flow of the molten glass and the fluctuation of the molten glass. The flow of gas on the outer surface is always maintained in a laminar flow state, making it an extremely ideal wire drawing method.In addition, gas is constantly blown onto the outer surface of the molten glass flowing from the nozzle to maintain a clean atmosphere while drawing the wire. Therefore, low-loss optical fibers can be expected.Furthermore,
If cooled gas is sent from the optical fiber 14, a cooling effect on the outer circumferential surface of the optical fiber can be expected, and it becomes possible to wind the optical fiber onto the drum 12 without impairing its mechanical strength. FIG. 3 shows an embodiment of the gas introduction section 15 used in FIG. 2. In the figure, 16 is a gas supply pipe, and 17 is a ring pipe. Reference numeral 18 denotes a gas outlet, from which the gas is uniformly sent into the outer rubbo 13 shown in FIG. Note that the gas introduction part in Figure 3 is replaced by 3 in Figure 2.
When installed in a heavy Lubbo, a large gas outlet may be provided at the bottom of the ring pipe 17 so that gas can be evenly blown into Lubpo 1 and Lubbo 2 (an example is shown in Fig. 4). . In this way, the glass is melted while being maintained in a clean gas atmosphere, thereby preventing contamination during glass melting and making it easier to realize a low-loss optical fiber. Also, blowing gas into crucibles 1 and 2 corresponds to applying pressure inside crucibles 1 and 2, and the amount of molten glass flowing out from the nozzles of the crucibles is reduced when no gas pressure is applied. It is also possible to compare and make it continuous. The gas sent from arrow 14 is 02, Ar.
, N2, He, etc. can be used. FIG. 5 is a schematic diagram showing an embodiment of the optical fiber line control method of the present invention.

The figure shows an arrow 14 indicating a gas flow rate control valve opening/closing device 20.
, the flow meter 19, and the outer crucible 13 through the gas introduction part 15.
The flow rate of gas is flowed within the chamber at a flow rate that is sufficiently larger than the change in natural convection caused by the density fluctuation of the air and forced turbulence. The method for controlling the bran diameter of the optical fiber is to feed back the signal detected by the detector 8 to the valve opening/closing device 20 for controlling the gas flow rate through the wire diameter measuring device 9 and the control circuit 10, thereby changing the gas flow rate passing through the flow meter 19. This is a method of controlling the line length. The details of this optical fiber line flea control will be described below. If the wire diameter d of the optical fiber fluctuates by 10△d% due to a change in the outflow amount of glass, the detector 8 detects this wire diameter fluctuation, and the wire diameter is measured by the voltage (or current) using the twill measuring device 9. ) and sends the output signal to the control circuit 10. Then, the case where Δd=0 is compared with the control circuit, and if the wire diameter of the optical fiber is smaller than the reference value, the valve of the gas flow rate control valve opening/closing device 20 is closed and the gas flow rate passing through the flow meter 19 is adjusted. Control circuit 1 to reduce
An output signal of 0 is sent to the gas flow rate control valve opening/closing device 20. Conversely, if the diameter of the optical fiber is larger than the reference value, the output signal of the control circuit 10 is changed to open the valve of the gas flow rate control valve opening/closing device 20 to increase the gas flow rate passing through the flow meter 19. This is a method of controlling the wire diameter of the optical fiber by sending it to the flow rate control valve opening/closing device 20. This control method is an application of the method previously proposed by the present inventor (Machigao No. 50-1151825). FIG. 6 is a schematic diagram showing an embodiment of the optical fiber drawing method of the present invention. This is a method of drawing an optical fiber consisting of a three-layer glass structure, which is composed of four-layer Rubbo. In this case, the core glass material 3 is placed in the center crucible 1, the intermediate layer glass material 4 is placed in the Lupo 2, and the crucible 21 is filled with the glass material 3 for the core.
A glass material 22 for cladding is placed in the outer receptacle 13, and gas is fed from the arrow 14 through the gas introduction part 15 and flows out in the direction of the arrow 14''.The above explanation As can be seen from the figure, the method for reducing line fluctuations in optical fibers of the present invention involves providing a gas introduction passage between the Rubbo and the heating source, flowing the gas along the outer peripheral surface of the Rubbo, and reducing the amount of molten glass flowing out of the Rubbo nozzle. It is characterized by drawing the flow and the flow of gas on the outer surface of the molten glass to always maintain a laminar flow, and as a result, it is possible to suppress fluctuations in the melting temperature of the molten glass flowing out of the Lubbo nozzle. It can be expected that line fluctuations caused by this can be almost completely eliminated.

Further, it is possible to control the wire diameter fluctuation caused by the change in the outflow amount of glass by changing the gas flow rate, and it is possible to expect an optical fiber with small wire diameter fluctuation.

[Brief explanation of the drawing]

Fig. 1 shows an outline of the conventional Lubbo method for drawing optical fibers, Fig. 2 is a schematic diagram of an embodiment of the optical fiber drawing method of the present invention, and Figs. 3 and 4 show the present invention. An embodiment of the gas introduction part used in the optical fiber drawing apparatus of the invention, FIG. 5 is a schematic diagram showing an embodiment of the optical fiber diameter control method of the invention, and FIG. It is a schematic diagram showing an example of a line drawing method. Tsutomu Figure 1 Tsutomu Figure 3 Figure 4 Hidezu Figure Tsutomu Figure 6

Claims (1)

[Claims] 1. Heat the crucible with a heat source, pull out the molten glass in the crucible through the nozzle of the crucible to form a thin optical fiber, and wind this around a rotating drum to form a long optical fiber. A method for reducing wire diameter variation of an optical fiber, characterized in that the optical fiber is drawn while flowing gas along the outer circumferential surface of the molten glass drawn out from a nozzle of a crucible in the drawing direction of the molten glass. 2. In the method for reducing wire diameter variation according to claim 1, a gas introduction passage is provided between the crucible and the heating source, and the gas flowing along the outer circumferential surface of the crucible is drawn out from the nozzle of the crucible for melting. A method for reducing wire diameter variation of an optical fiber, characterized in that the molten glass flows along the outer circumferential surface of the glass in the drawing direction of the molten glass.