JPH0940438A - Production of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an optical fiber soot preform from being bent at the time of sinterization and transparent vitrification. SOLUTION: When the optical fiber soot preform A is hung in a furnace core pipe 1 arranged vertically, rotated and heated to apply sinterization and transparent vitrification, the bending during heating is prevented by supporting the bottom end of the optical fiber soot preform A rotatably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform by sintering an optical fiber soot preform in a porous state into a transparent glass.

[0002]

2. Description of the Related Art Generally, an optical fiber preform is manufactured by further sintering and transparent vitrifying a porous optical fiber soot preform manufactured by the VAD method or the OVD method. ing.

Conventionally, the sintering and transparent vitrification of optical fiber soot preforms have been performed as follows.
That is, as shown in FIG. 2, the optical fiber soot preform A is placed in a furnace core tube 50 made of a vertically arranged quartz tube.
Suspend and support. Then, after replacing the inside of the furnace core tube 50 with a mixed gas of He (helium) and Cl ₂ (chlorine), the optical fiber soot preform A is heated while being rotated. The heating is performed by the heater 51 arranged around the furnace core tube 50, and the heating temperature is about 1650 ° C. By heating the optical fiber soot preform in this way, the optical fiber soot preform is sintered and made into transparent glass.

In the figure, reference numeral 52 is a furnace shell that covers the heated portion, 53 is a mixed gas inlet, and 54 is a mixed gas outlet.

[0005]

However, the above conventional manufacturing method has the following problems. That is, the optical fiber soot preform A has the above-mentioned sintering
When the optical fiber preform is obtained through the transparent vitrification step, it shrinks by about 0.6 times in the radial direction. However, although the optical fiber soot preform A is constructed by concentrically arranging the clads around the start rod including the linear core, a slight eccentricity occurs between the two and a so-called eccentricity is caused. May occur. Therefore, when the uneven thickness portion contracts during the sintering / transparent vitrification process, the stress causes the rotation axis of the optical fiber soot preform A to sway, and as a result, as shown in FIG. 2, it is not supported. The lower end of the optical fiber soot preform A (here, it is sintered and made into transparent glass by heating) was bent.

Such bending of the optical fiber preform causes the inability to be housed in the device in the subsequent drawing process and the drawing process, and the contact with the inner peripheral surface of the device to cause damage. It was very inconvenient.

In order to prevent such inconvenience, it is possible to fix the curvature by fixing the sintered and transparent vitrified optical fiber preform A on a lathe before heating and heating it. However, the optical fiber preform A is in a state in which stress is accumulated inside due to contraction, and careless heating is likely to lead to damage of the optical fiber preform A ′, which cannot be easily corrected.

Therefore, it is an object of the present invention to prevent the optical fiber soot preform from being curved during sintering / transparent vitrification.

[0009]

In order to achieve such an object, the present invention provides an optical fiber soot preform in a furnace core tube in order to prevent the optical fiber soot preform from being bent during the sintering and transparent vitrification process. The lower end of the suspended optical fiber soot preform was further rotatably supported, and rotation and heating were applied to the optical fiber preform.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an apparatus used for carrying out the method for manufacturing an optical fiber preform according to an embodiment of the present invention.

This apparatus has a furnace core tube 1 made of a quartz tube. The furnace core tube 1 is vertically arranged and both ends are open. A cylindrical body 4a having a mixed gas exhaust port 3 is concentrically attached to the upper end of the furnace core tube 1, and the upper end of the cylindrical body 4a has an upper end supporting through hole 2 It is closed by the lid 4b. The upper end supporting through hole 2 is formed in the upper lid 4b so as to penetrate therethrough in the axial direction. In addition, the lower end of the furnace core tube 1 has a through hole 5 for supporting the lower end.
It is closed by a lower lid 7 having a mixed gas introduction hole 6. The lower end supporting through hole 5 is formed in the lower lid 7 so as to penetrate therethrough in the axial direction. The lower end supporting through hole 5 and the upper end supporting through hole 2 are provided at the upper and lower ends of the furnace core tube 1 and coaxially with each other. A seal member 5a made of silicon rubber or the like is attached to the inner peripheral surface of the through hole 5 for supporting the lower end. Further, a guide tube portion 7a is provided on the surface of the lower lid 7 facing the furnace core tube. The guide tubular portion 7a is provided on the surface of the lower lid 7 facing the furnace core tube, and is provided coaxially with the lower end supporting through hole 5 and radially outside thereof.

The apparatus also includes a heating section 8.
The heating unit 8 includes a furnace shell 9 that covers the central portion of the furnace core tube 1 in the longitudinal direction.
And a heater 10 housed inside the furnace shell 9.

Next, the steps of sintering and vitrifying an optical fiber soot preform using the above apparatus will be described.

First, the upper lid 4b and the lower lid 7 are removed from the furnace core tube 1. In this state, the optical fiber soot preform A is inserted into the furnace core tube 1 from the upper end side of the furnace core tube 1.
Then, the upper lid 4b is attached to the auxiliary rod D1 located above the optical fiber soot preform A projecting from the upper end of the core tube 1. Further, the lower end supporting through hole 5 of the lower lid 7 is inserted through the auxiliary rod D2 located on the lower end side of the optical fiber soot preform A protruding from the lower end of the furnace core tube 1. In this insertion work, the guide cylinder 7a provided on the lower lid 7 serves as a guide when the auxiliary rod D2 is inserted.
Can be done smoothly without causing damage. In this way, the optical fiber soot preform A is inserted to the position where the lower end position thereof faces the heater 10.

Then, the upper lid 4b and the lower lid 7 are connected to the tubular body 4a and the core tube 1. When housed in this manner, the optical fiber soot preform A will be rotatably supported at both ends within the furnace core tube 1, and
The gap between the auxiliary rod D2 and the lower end supporting through hole 5 is completely sealed by the sealing material 5a.

In this state, the mixed gas of helium / chlorine is introduced into the furnace core tube 1 through the mixed gas introduction hole 6 and the mixed gas exhaust hole 3 to replace the inside of the furnace core tube 1 with the mixed gas. . Further, the upper end of the optical fiber soot preform A protruding from the furnace core tube 1, that is, the auxiliary rod D
The lower end side of the optical fiber soot preform A in the furnace core tube 1 is heated by the heating unit 8 while rotating the optical fiber soot preform A at a very low speed by rotating 1 about its axis. Further, while heating and rotating the optical fiber soot preform A, by pulling down the tip of the auxiliary rod D2, the position where the optical fiber soot preform A faces the heater 10 is gradually changed from the lower end position. Move to the top position. As a result, the heating position of the optical fiber soot preform A is changed from its lower end position to its upper end position.
The whole is evenly sintered and made into transparent glass.

At this time, since the lower end of the optical fiber soot preform A is rotatably supported by the lower lid 7, the optical fiber soot preform A which is sintered and made into vitrified glass and contracts, and the auxiliary. The stick D2 does not bend.

[0019]

As described above, according to the present invention, the following effects can be obtained. That is, since both ends of the optical fiber soot preform are rotatably supported during the work, the optical fiber soot preform does not bend due to the contraction stress due to heating. Therefore, it was possible to reliably prevent the optical fiber preform, which was sintered and made into a vitrified glass, from being unable to be housed in the device or damaged in the subsequent drawing process and drawing process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an apparatus used in manufacturing an optical fiber soot preform according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of an apparatus used in a method for manufacturing a conventional optical fiber soot preform.

[Explanation of symbols]

 1 Furnace core tube 7 Lower lid A Optical fiber soot preform

Claims (1)

[Claims] 1. An optical fiber soot preform is suspended and supported in a vertically arranged furnace core tube, and the optical fiber soot preform is heated while being rotated along its axial direction to be sintered and transparent vitrified. A method for manufacturing an optical fiber preform that forms an optical fiber preform, wherein the optical fiber soot preform is rotated and heated while rotatably supporting the lower end of the optical fiber soot preform. Manufacturing method of optical fiber preform.