JPH06235828A - Heating furnace for drawing optical fiber preform - Google Patents

Abstract

PURPOSE:To provide a heating furnace to draw an optical fiber preform. CONSTITUTION:The heating furnace to heat, melt and draw an optical fiber preform 1 is equipped with several independent heaters 2 arranged in a ring shape around the optical fiber preform 1. More preferably, the furnace is equipepd with such means to control each heater 2 at same temp. in the circumference direction or to control temp. of each heater to keep the position of drawn optical fiber constant. Thus, the optical fiber having small non-circular percentage (difference of outer diameter/outmeterX100(%)) is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace for drawing an optical fiber, and more particularly to a heating furnace capable of drawing an optical fiber preform in a perfect circle.

[0002]

2. Description of the Related Art An optical fiber is usually formed by heating and melting an optical fiber preform in a heating furnace while stretching and drawing. As such a drawing heating furnace (hereinafter sometimes abbreviated as a heating furnace), an electric resistance heating furnace using carbon, which is relatively easy to maintain and has good thermal stability, is generally adopted. A cross-sectional shape of an example of a conventional heating device is shown in FIG. On the outer circumference of the optical fiber preform (1) in the center of the case (6), the upper end of the ring-shaped carbon heater (2) that generates heat by its own electric resistance by supplying electricity from the power supply (5). Are attached via electrodes (3). An insulating material (4) such as carbon or felt is annularly arranged between the case (1) and the carbon heater (2).
This prevents the heat from radiating to the outside of the case (6).
[Reference: WIRE JOURNAL (APRIL 19
81) p86-90]

[0003]

In the conventional heating furnace, due to the change in the cross-sectional area of the carbon heater in the circumferential direction and the nonuniformity of the thickness of the heat insulating material annularly arranged outside the carbon heater, The temperature is not uniform in the circumferential direction, and the non-circularity of the drawn fiber (in the present specification, "non-circularity (%)" means "non-circularity (%) = outer diameter difference / outer diameter x 100
(Defined by the formula (%)) becomes worse. The non-circular shape of the fiber is an important factor for reducing the splice loss, and the smaller one (that is, the cross section closer to a perfect circle) is more preferable. An object of the present invention is to provide a heating furnace for drawing an optical fiber preform capable of obtaining a fiber whose cross-sectional shape is close to a perfect circle after drawing.

[0004]

As a means for solving the above problems, the present invention is a heating furnace for heating, melting and stretching an optical fiber preform, in which a plurality of independent heaters are provided on the outer periphery of the optical fiber preform. Provided is a heating furnace for drawing an optical fiber preform, which is arranged in a ring shape. As a particularly preferred embodiment of the present invention, the heating furnace for drawing the optical fiber preform is provided which has means for measuring the temperatures of the plurality of independent heaters and controlling the temperatures to be the same in the circumferential direction. be able to. As another particularly preferred embodiment of the present invention, the above heating,
Means for measuring the position of the optical fiber drawn by melting and drawing, and means for controlling the temperature of the individual heaters so that the position of the drawn optical fiber becomes constant according to the measurement value obtained by the measuring means. The heating furnace for drawing the optical fiber preform can be mentioned.

[0005]

Operation and Examples A heating furnace for drawing an optical fiber preform according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the present invention. (1) shows an optical fiber preform, (2) shows a carbon heater, and (4) shows a heat insulating material. In the example of FIG. 1, four carbon heaters (2) are connected to a power source (5), respectively, and are arranged in a ring shape around the optical fiber preform (1). Each carbon heater (2) can measure the heat of the heater radiated by the measurement hole (9) provided in the case (6) and the heat insulating material (4) with the thermometer (7). Although not shown, this measured value is sent to the control system as a signal, and the control system can control the temperature of all the heaters to be the same. This allows
The temperature of the optical fiber preform becomes uniform in the circumferential direction, and the cross section of the stretched optical fiber (10) becomes very close to a perfect circle. Specifically, a radiation thermometer is used as the temperature system (7) and, for example, carbon felt or the like is used as the heat insulating material (4). The case (6) is made of, for example, stainless steel or the like and has a structure that can be water-cooled.

The present inventors have also found that the temperature uniformity in the circumferential direction of the optical fiber preform can be achieved also by keeping the position of the stretched optical fiber constant.
That is, as shown in FIG. 2, if there is temperature nonuniformity in the circumferential direction, the optical fiber preform is stretched asymmetrically, and the position of the optical fiber at the exit of the heating furnace changes. Since the temperature of the carbon heater on the right side in FIG. 2 is high, the right side of the optical fiber preform is more melted, the preform is asymmetrically extended, and the optical fiber (10) moves toward the left side. The position of the optical fiber (10) is measured by a position measuring device (8) to raise the temperature of the carbon heater on the moving side of the optical fiber (10) via a control system (not shown), or Conversely, by limiting the amount of electricity supplied to the carbon heater so as to lower the temperature of the carbon heater on the non-moving side, it is possible to keep the optical fiber (10) always at the center of the heating furnace. A uniform temperature distribution was obtained, and it became possible to draw an optical fiber with a small non-circularity.

[Examples] [0007] According to the present invention, an outer diameter of 24 is controlled by controlling the temperature of the heater on the outer circumference of the optical fiber in the circumferential direction to be 2100 ± 2 ° C by using the heating furnace having the configuration of Fig. 1.
The mmφ optical fiber preform was drawn and spun into an optical fiber having an outer diameter of 125 μm. A radiation thermometer was used as the thermometer at this time. Non-circularity of the obtained optical fiber [outer diameter difference / outer diameter x
100 (%)], the optical fiber was as small as 0 to 0.2%.

[Comparative Example] An optical fiber having a 125 μm outer diameter was spun by the conventional heating furnace shown in FIG. The non-circularity of the obtained optical fiber was 0.3 to 0.6%, which was higher than that of the inventive product of the example.

[0009]

In the heating furnace for drawing an optical fiber preform of the present invention, a plurality of carbon heaters are arranged in a ring shape on the outer periphery of the optical fiber preform, and the drawing is performed while controlling the temperature of each heater to be the same. Since the fiber can be spun, the temperature distribution on the circumference of the base material can be made uniform, and it is possible to manufacture an optical fiber with a small non-circularity. Etc. are easy and very effective.

[0010]

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a heating furnace for drawing an optical fiber preform according to an embodiment of the present invention in a direction perpendicular to an axial direction of the preform.

FIG. 2 is a schematic cross-sectional view in the axial direction of the preform showing another example of the present invention, in which the position of the optical fiber is controlled by a position measuring device to uniformly heat the outer circumference of the preform.

FIG. 3 is a schematic diagram illustrating a conventional heating furnace.

[Explanation of symbols]

1 optical fiber base material, 2 carbon heater, 3 electrodes, 4 heat insulating material, 5 power source, 6 case, 7 thermometer, 8 position measuring instrument, 9 measuring hole, 10 optical fiber.

Claims (3)

[Claims] 1. A heating furnace for heating, melting and stretching an optical fiber preform, wherein a plurality of independent heaters are arranged in a ring shape on the outer periphery of the optical fiber preform. Drawing furnace heating furnace. 2. A means for measuring the temperature of the plurality of independent heaters, and a means for controlling the individual heaters to have the same temperature in the circumferential direction based on the measurement values obtained by the measuring means. A heating furnace for drawing an optical fiber preform according to claim 1. 3. A means for measuring the position of the optical fiber stretched by heating, melting and stretching, and the above-mentioned individual so that the stretched optical fiber position becomes constant according to the measurement value obtained by the measuring means. The heating furnace for drawing an optical fiber preform according to claim 1 or 2, further comprising means for controlling the temperature of the heater.