JP5170038B2 - Optical fiber drawing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for drawing an optical fiber by which a high-quality optical fiber can be obtained by suppressing the variation in outside diameter, and the cost is reduced by decreasing the consumption of an inert gas. <P>SOLUTION: An optical fiber drawing furnace 10 includes: a drawing furnace 11 housing an optical fiber preform 1 to be freely movable vertically; a plurality of partition plates 12-16 movable along a dummy rod 26 in the drawing furnace 11; a heater 17 for heating the optical fiber preform 1; a gas supply means 18 for supplying the inert gas into the drawing furnace 11; and a furnace internal pressure measuring instrument 20 for measuring the internal pressure of the drawing furnace 11. The quantity of the inert gas to be supplied by a gas supply means 18 is gradually reduced with the reduction of the volume in the drawing furnace 11 by being partitioned by the partition plates 12-16 by a control means 21 so that the pressure of the drawing furnace 11 is kept constant according to the measured value by the furnace internal pressure measuring instrument 20. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an optical fiber drawing method for drawing an optical fiber while heating and melting an optical fiber preform.

  As an example of a conventional optical fiber drawing method, a pressure detection means for detecting the drawing furnace internal pressure and a control means for controlling the flow rate of the inert gas introduced into the drawing furnace so that the pressure becomes a predetermined value are provided. A drawing apparatus has been proposed (see, for example, Patent Document 1).

  Also, as another example of a conventional optical fiber drawing method, a dummy rod for attaching an optical fiber preform that can be moved up and down, a heater that heats the lower end of the optical fiber preform attached to the dummy rod, An optical fiber drawing furnace provided with a plurality of partition plates slidable along a dummy rod has been proposed (see, for example, Patent Document 2).

  In the optical fiber drawing method disclosed in Patent Document 2 described above, the remaining length of the preform decreases as the preform, which is the optical fiber preform, is drawn. In order to prevent the internal pressure from fluctuating, a plurality of partition plates for partitioning the inside of the furnace in stages are provided.

JP-A-62-226834 JP 2002-68773 A

  However, the conventional optical fiber drawing apparatus disclosed in Patent Document 1 is controlled so that the pressure in the furnace is constant, but is feedback control, so control is performed in a situation where the volume changes greatly. It was difficult to make it follow quickly, causing a time delay. For this reason, the control could not catch up, the airflow in the furnace was disturbed, and the outer diameter of the optical fiber to be drawn sometimes caused an outer diameter fluctuation exceeding the allowable range. As a result, excessive inert gas may have been supplied.

Further, in the conventional optical fiber drawing method disclosed in Patent Document 2, since the supply amount of purge gas into the furnace is constant, it is difficult to keep the furnace pressure constant. In some cases, fluctuations have occurred and the outer diameter of the optical fiber to be drawn has an outer diameter fluctuation that exceeds an allowable range. In addition, since a predetermined amount of inert gas is constantly supplied, excessive inert gas may be supplied.
Usually, the fluctuation of the glass diameter is a fluctuation width of 0.1 μm or less with respect to the center value, but when the airflow in the furnace is disturbed, the fluctuation width is 0.5 μm or more.

  The object of the present invention has been made in view of the above-described circumstances, and can reduce the cost by reducing the amount of inert gas used while suppressing fluctuations in the outer diameter to obtain a high-quality optical fiber. An object of the present invention is to provide an optical fiber drawing method capable of achieving the above.

An optical fiber drawing method according to the present invention that can solve the above-described problem is that an optical fiber preform and a dummy rod for attaching an optical fiber preform are accommodated in a draw furnace so as to be movable up and down. The optical fiber preform is heated while being partitioned by a plurality of partition plates slidable along the dummy rod in the upper space of the draw furnace, and an inert gas is supplied into the draw furnace to supply the optical fiber preform. An optical fiber drawing method for drawing an optical fiber from a lower end of a material, wherein the drawing furnace volume is reduced by being partitioned by the partition plate so as to keep the pressure in the drawing furnace constant. The supply amount of the inert gas is gradually decreased based on a table stored in advance with the passage of time from the start of drawing .

According to the optical fiber drawing method configured in this way, from the start of drawing according to the decrease in the drawing furnace volume by being partitioned by the partition plate so as to keep the pressure in the drawing furnace constant. The supply amount of the inert gas is gradually reduced based on a table stored in advance as time elapses . Thereby, the airflow in the furnace is not disturbed by convection due to the heat in the furnace during drawing, and a high-quality optical fiber that suppresses fluctuations in the outer diameter can be manufactured. Further, since the supply amount of the inert gas is reduced according to the decrease in the volume in the drawing furnace, the supply amount of the inert gas can be saved, and the cost can be reduced.

  According to the method for drawing an optical fiber according to the present invention, it is possible to obtain a high-quality optical fiber by suppressing fluctuations in the outer diameter, and to reduce costs by reducing the amount of inert gas used. it can.

1 is a longitudinal sectional view of an optical fiber drawing furnace to which an optical fiber drawing method according to an embodiment of the present invention is applied.

  Hereinafter, an optical fiber drawing method according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, an optical fiber drawing furnace 10 to which an optical fiber drawing method according to an embodiment of the present invention is applied draws an optical fiber 2 from an optical fiber preform 1. A drawing furnace 11 that accommodates the material 1 so as to be movable up and down, and a plurality of partition plates 12, 13, 14, 15, and 16 that can move in the drawing furnace 11 along a dummy rod 26 described later. .
The optical fiber drawing furnace 10 includes a main heater 17 for heating the optical fiber preform 1, a gas supply means 18 for supplying an inert gas (for example, He) into the drawing furnace 11, and a drawing furnace. And a control means 21 for controlling the supply amount of the inert gas based on the furnace pressure.

The drawing furnace 11 has an outer tube 23 whose upper portion is closed by a cover member 22, a core tube 24 disposed below the outer tube 23, and a lower portion of the core tube 24. A core tube lower extension 25 is provided. The outer tube 23 has a dummy rod 26 inserted through the center of the lid member 22.
The dummy rod 26 is assembled with the optical fiber preform 1 via the connecting member 27. The partition plates 12, 13, 14, 15, and 16 are inserted into the dummy bar 26 and disposed on the upper portion of the connecting member 27.

  When the drawing of the optical fiber 2 proceeds and the optical fiber preform 1 is shortened, the optical fiber member 1 is lowered together with the dummy rod 26. Accordingly, the partition plates 12, 13, 14, 15, 16 are stepped into step portions 28, 29, 30, 31, 32 formed at predetermined intervals above and below the inner peripheral portion of the outer tube 23. Engaged.

  By arranging the plurality of partition plates 12, 13, 14, 15, 16, the furnace space volume in the outer tube 23 is made substantially constant. Thereby, generation | occurrence | production of the convection by the temperature difference in the up-down direction in the outer cylinder pipe 23 is suppressed, and the outer-diameter fluctuation | variation of the optical fiber 2 is suppressed.

The main heater 17 is assembled to the outside of the furnace core tube 24.
An auxiliary heater 33 is assembled on the uppermost part of the outer tube 23. Unlike the main heater 17 for heating and melting the lower end portion of the optical fiber preform 1, the auxiliary heater 33 is disposed to further stabilize the airflow in the drawing furnace 11.

  The gas supply means 18 is connected in communication with the outer tube 23. The gas supply means 18 supplies an inert gas into the drawing furnace 11 for suppressing oxidation deterioration of the furnace core tube 24 due to heating by the main heater 17 during drawing. In the gas supply means 18, the supply amount of the inert gas is controlled by the control means 21.

  The in-furnace pressure measuring device 20 is attached in the vicinity of the lower end portion of the core tube lower extension 25 with little pressure fluctuation. The in-furnace pressure measuring device 20 measures the in-furnace pressure at predetermined time intervals and sends the measurement information to the control means 21. It should be noted that the attachment position of the furnace pressure measuring device 20 may be attached to the upper end portion of the core tube lower extension 25.

  The control means 21 includes an electronic component with a built-in arithmetic circuit (not shown). The control means 21 determines the supply amount of the inert gas based on a prestored table as time elapses from the start of drawing. The table is corrected by using the measured value of the furnace pressure of the furnace pressure measuring device 20, and is reflected in the flow rate control at the next drawing. The gas supply means 18 supplies the determined supply amount of inert gas.

  Next, an optical fiber drawing method using the optical fiber drawing furnace 10 will be described.

  First, the optical fiber preform 1 is attached to the lower end of the dummy rod 26 via the connecting member 27, and the lower end of the optical fiber preform 1 is heated and melted by the main heater 17. And the optical fiber 2 is drawn from the lower end of the optical fiber preform 1 heated and melted. Since the optical fiber preform 1 becomes shorter as the drawing of the optical fiber 2 progresses, the dummy rod 26 is lowered so that the lower end of the optical fiber preform 1 is always heated by the main heater 17.

  When heating and melting by the main heater 17 starts, the control means 21 determines the supply amount of the inert gas based on a table stored in advance as time elapses from the start of drawing. And the gas supply means 18 supplies the determined predetermined amount of inert gas.

  At this time, the furnace space is partitioned in stages by the partition plates 12, 13, 14, 15, and 16 so that the furnace space volume in the outer tube 23 is substantially constant. As the volume in the drawing furnace 11 decreases, the supply amount of the inert gas is gradually decreased. Thereby, the airflow in a furnace is not disturbed by the convection by the heat in a furnace during drawing, and the outer diameter fluctuation | variation of the optical fiber 2 drawn can be suppressed.

  Next, an example carried out to confirm the operation and effect of the optical fiber drawing method according to the present invention will be described.

The optical fiber was drawn by the optical fiber drawing method according to the present invention.
In the examples, drawing was performed while gradually reducing the He gas, and the glass outer diameter (fluctuation) was measured at an interval of 1 hour from the start of drawing with an outer diameter measuring device under the drawing furnace. Further, the pressure in the furnace at this time was measured. On the other hand, in the comparative example which is a conventional drawing method, the furnace pressure and the glass outer diameter (variation) were measured by the same method while supplying a certain amount of He gas. The results are shown in Table 1. In the He gas, the flow rate at the start of drawing is 100 (l / min) in both the examples and the comparative examples, and the amount of change is represented by a difference Δ from the initial flow rate at the start of drawing.

  As shown in Table 1, it can be seen that in the example in which the He flow rate was gradually reduced, the furnace pressure was substantially constant, and the fluctuation of the glass outer diameter was small. On the other hand, in the conventional example in which the supply amount of He gas is constant, it can be seen that the furnace pressure gradually increases as the drawing progresses, and the fluctuation of the glass outer diameter increases accordingly.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

DESCRIPTION OF SYMBOLS 1 Optical fiber base material 2 Optical fiber 10 Optical fiber drawing furnace 11 Drawing furnace 12-16 Partition plate 17 Heater 18 Gas supply means 20 Furnace pressure measuring instrument 21 Control means

Claims (1)

An optical fiber preform and an optical fiber preform mounting dummy rod are accommodated in the drawing furnace so as to be movable up and down, and a plurality of partitions are slidable along the dummy rod in the upper space of the drawing furnace. Heating the optical fiber preform while partitioning by a plate, supplying an inert gas into the drawing furnace, and drawing an optical fiber from a lower end of the optical fiber preform,
Based on a table stored in advance as time elapses from the start of drawing, according to a decrease in the volume of the drawing furnace by being partitioned by the partition plate so as to keep the pressure in the drawing furnace constant. , line引方technique of the fiber, characterized in that to gradually decrease the supply amount of the inert gas.

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