JPH0717736A - Method for stretching optical fiber preform - Google Patents

Abstract

PURPOSE:To maintain the characteristics of an optical fiber by rotating an optical fiber preform around its central axial line, thereby uniformizing heating in a circumferential direction and stretching the optical fiber preform to a completely round state. CONSTITUTION:The top end of the optical fiber preform 1 is clamped by a rotary lamp 5 and is so supported on an upper supporting bracket 6 that the optical fiber preform 1 is made freely rotable around its central axial line. The optical fiber preform 1 is heated by radiation heat of a heating furnace 3 heated by this heater 4. A roller 91 is rotatably supported in a bracket part 81 projecting to face the inner side of a hollow circular cylindrical or hollow prismatic rotary frame 8 and a heat resistant endless belt 92 is wound around plural rollers 91 isolated in the axial line direction of the rotary frame 8, by which a clamp rotating and feeding device 9 of an endless tracked vehicle type is constituted. A pulley 7 is fixed to the bottom end of the rotary frame 8 and is freely rotatably supported on a bottom end supporting bracket 10. The endless belt 92 is moved like an arrow by rotation of the rollers 91, by which the optical fiber preform 1 is clamped and stretched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drawing an optical fiber preform, and more particularly to a drawing method applied when an optical fiber preform formed by the VAD method is drawn before the external attachment process.

[0002]

2. Description of the Related Art An optical fiber preform to be subjected to a spinning process is formed by, for example, heating a base optical fiber preform formed by a VAD method or the like and cutting it into an appropriate length. It is manufactured by attaching soot to the base material by an external method.

This drawing step is conventionally carried out as shown in FIG. That is, first, as shown in FIG. 2A, the upper end of the optical fiber preform 1 to be stretched is clamped and fixed by the clamp device 101 (the portion of the dummy rod 2A), and the entire optical fiber preform 1 is heated by the heater 4. It is suspended vertically in a substantially hollow cylindrical heating furnace 3 that is heated from the surroundings, and the lower end portion (the portion of the dummy rod 2B) is grasped and extended vertically downward by a clamp device 102 that is linearly driven.

Next, when the lower end of the optical fiber preform 1 is stretched to such an extent that it can be applied to the clamp feed device 103, the grip of this lower end is switched to the grip by the clamp feed device 103 as shown in FIG. 2B. .

The clamp feeding device 103 includes a pair of rollers 1.
This is a caterpillar type feeder in which a heat-resistant synthetic resin belt 103B is wound around 03A, and the optical fiber preform 1 is stretched downward by feeding the belt 103B while sandwiching the optical fiber preform 1 from both sides. It is a thing. Reference numeral 104 indicates a rotary blade type cutting device used in the cutting process applied after the stretching process.

[0006]

However, according to the conventional drawing method, if the temperature distribution in the heating furnace 3 is uneven and the optical fiber preform 1 is not completely uniformly heated from the surroundings, the process shown in FIG. As indicated by reference numeral 1A, the cross section of the optical fiber preform 1 becomes thin so that the diameter becomes smaller in the direction in which the radiant heat of the heating furnace 3 is stronger, and the cross section does not become a perfect circle but deforms into an elliptical shape. There is a tendency that the characteristics of the optical fiber manufactured through the subsequent steps are deteriorated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the solution according to the invention of claim 1 is to provide an upper end portion of an optical fiber preform to be drawn, Gripping by a rotary clamp so that it can rotate around the central axis of the optical fiber preform, heating the optical fiber preform from the surroundings, and gripping the lower end of the optical fiber preform by a clamp rotary feed device. Then, the optical fiber preform is stretched downward while the optical fiber preform is rotated about its axis.

[0008]

Since the optical fiber preform is rotated around its central axis, the heating by the heating furnace becomes uniform in the circumferential direction.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENT An example of an apparatus for carrying out the method of the present invention will be described with reference to FIG. Reference numeral 5 designates a rotary clamp, which grips the upper end of the optical fiber preform 1 and supports the optical fiber preform 1 on the upper end support bracket 6 so that the optical fiber preform 1 is rotatable about its central axis.

Reference numeral 8 is a hollow cylindrical or hollow prism-shaped rotary frame, and a roller 91 is rotatably supported by a bracket portion 81 projecting inwardly so as to extend in the axial direction of the rotary frame 8. An endless belt 92 made of a heat-resistant synthetic resin is wound around a plurality of (two in the illustrated example) rollers 91 which are spaced apart from each other to form one caterpillar-type clamp rotary feed device 9. This is because the rotation of the roller 91 causes the endless belt 92 to move as shown by the arrow in the drawing to sandwich and stretch the optical fiber preform 1. Note that the rotary drive mechanism of the roller 91 is omitted in FIG.

A pulley 7 is coaxially fixed to the lower end of the rotary frame 8 and rotatably supported by a lower end support bracket 10. This pulley 7 is the lower end support bracket 1
The drive pulley 12 mounted on the spindle of the motor 11 provided at 0 is rotationally driven at a relatively low rotational speed.

When the method of the present invention is applied, it is preferable to attach a relatively long dummy rod 2B to the lower end of the optical fiber preform 1 to be stretched. This is to enable the lower end of the optical fiber preform 1 to be gripped by the clamp rotary feed device 9 from the beginning.

[0013]

According to the present invention, since the optical fiber preform is rotationally driven around its central axis during the drawing process,
Even if the heating state of the heating furnace is uneven in the circumferential direction, it is heated evenly in the circumferential direction, and as a result, the cross section can be stretched into a perfect circular state, and the characteristics of the final product optical fiber There is an effect that does not damage.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a side sectional view for explaining a conventional stretching method,
(A) shows a state where the clamp feeding device is hung, and (b) shows a state where the clamp feeding device is hung.

FIG. 3 is a transverse cross-sectional view showing non-circular cross-sectional deformation of a base material caused by a conventional method.

[Explanation of symbols]

 1 Optical fiber base material 1A Thin base material 2A, 2B Dummy rod 3 Heating furnace 4 Heater 5 Rotating clamp 6 Upper end support bracket 7 Pulley 8 Rotating frame 9 Clamp rotary feed device 91 Roller 92 Endless belt 10 Lower end support bracket 11 Motor 12 Drive pulley

Claims (1)

[Claims] 1. A step of gripping an upper end portion of an optical fiber preform (1) to be stretched so as to be rotatable about a central axis of the optical fiber preform (1), and the optical fiber preform (1). And a step of holding the lower end of the optical fiber preform (1) and drawing the optical fiber preform (1) downward while rotating it about its axis.