JPH02243532A - Drawing furnace for fluoride optical fiber - Google Patents

Abstract

PURPOSE:To suppress secondary pollution by water and produce optical fiber having high strength by making possible to successively perform surface treatment and drawing of preform for fluoride optical fiber with installing fluorine gas supplying chamber in upper part, and discharging chamber and inert gas supplying chamber in lower part of a furnace core tube. CONSTITUTION:Preform 13 for fluoride optical fiber is set in a furnace core tube 12 drawn with heating and softening by a heater element 11 to form fluoride optical fiber 14. In said process, F2/Ar mixed gas is introduced from gas introducing tube 21 into gas suppling chamber 17 installed in upper part of the furnace core tube 12 and simultaneously dried N2 gas is introduced into inert gas supplying chambers installed in lower part of the furnace core tube 12, connected in series with shutters 24 and communicated through fiber drawing holes 24a, then gas introduced to inside of the inert gas supplying chamber is discharged through upper discharging chamber 25 to isolate atmosphere in the furnace core tube from outside air and subject the preform 13 to OH- removing treatment, thus the preform is drawn.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fluoride optical fiber drawing furnace for producing high-strength fluoride optical fibers.

<Prior art> Fluoride glass optical fiber (hereinafter referred to as "fluoride optical fiber") whose main component is Z r F4 has a transmission loss of 10-" dB/+m or less, which exceeds that of silica fiber. Development is underway with the aim of putting it into practical use as a future long-distance, high-capacity communication medium.

One approach is to improve the mechanical strength of fluoride optical fibers, but drawn optical fibers easily deteriorate, so high-intensity fluoride optical fibers with strength that can withstand practical use are No fibers have been fabricated.

The reason for this strength deterioration is that when the preform is heated during wire drawing, the hydrolyzed surface of the preform undergoes a dehydration reaction as shown in equation (1) below, and oxides are generated. This is because the substance becomes a crystal nucleus and crystal growth progresses significantly on the surface.

...(1) Conventionally, in order to improve the strength of fiber, H
Deterioration is prevented by surface treatment using F gas to remove the hydroxide layer formed on the surface of the preform.

(S, Sakaguehiat al; J, Mat
, Sei, Lett, , Vo16. P1440-144
2゜(19g?)).

<Problems to be Solved by the Invention> However, in the conventional processing method, a processing device for processing the preform and a drawing furnace are provided separately, and after processing the preform, the amount of water in the air is removed before drawing. Although it is hydrolyzed again by moisture and has improved strength compared to the conventional case where no treatment is applied at all, there is a problem in that it is not possible to achieve strength greater than IGPs (gigapascals).

In view of the above-mentioned circumstances, the present invention provides a drawing furnace for fluoride optical fibers that can suppress surface crystallization of oxides during drawing with a simple structure and can produce high-strength fluoride optical fibers. The purpose is to

Means for Solving the Problems> The configuration of the fluoride optical fiber drawing furnace of the present invention for achieving the above object includes installing a fluoride optical fiber preform in a furnace core tube, and A drawing furnace for fluoride optical fiber, which draws a fluoride optical fiber by stretching it while heating and softening it, comprising: a gas supply chamber provided above the furnace core tube and introducing a fluorine-based gas or an inert gas; At least two chambers are provided in the lower part of the furnace core tube and are connected in series through shutters and communicated through fiber extraction holes formed by each shutter, and at least one of the chambers is evacuated from gas. The present invention is characterized in that the exhaust chamber has an exhaust chamber and the lower side of the exhaust chamber is an inert gas supply chamber for supplying an inert gas.

With the above configuration, the fluorine-based gas or inert gas introduced into the furnace core tube is sent to the exhaust chamber provided at the bottom of the furnace core tube, and is also sent from the supply chamber provided below the exhaust chamber. An inert gas is also introduced into the exhaust chamber, where it is effectively exhausted to the outside, isolating the atmosphere inside the furnace tube from the outside air.

Embodiment Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of the drawing furnace for fluoride optical fiber of this embodiment. As shown in the figure, a drawing furnace for fluoride optical fiber (hereinafter referred to as "drawing furnace") 10 according to the present embodiment is provided with a heating element 11 and a furnace core tube 12. The fluoride optical fiber preform 13 is inserted into the upper opening 12a of the core tube 12, and the drawn fluoride optical fiber 14 is inserted into the lower opening 12b of the furnace core tube 12.
It is made to be cotton-pulled.

Here, a filter gas supply chamber 17 is provided in the upper opening 12 a of the furnace core tube 12 , which communicates with the inside of the furnace core tube 12 and is fixed by a bolt 16 via an O-ring 15 .

In the upper part of this gas supply chamber 17, a preform 1 is provided.
The support tube 18 for inserting and holding the O-ring 1
It is fixedly installed with bolts 20 via 9. Also,
A gas introduction pipe 21 for introducing a gas such as a fluorine-based gas or an inert gas into the gas supply chamber 17 and a pressure detection means P are provided on the wall surface of the chamber 17.

This furnace core IV! ! A furnace core tube support 23 is provided at the lower end of the furnace core tube 12 and is fixed with a cap screw 22 via an O-ring 15 to support the furnace core tube 12.

At the bottom of the furnace core tube holder 23, there are two chambers zs,
Each zs has a shutter of 24JS! The optical fibers are connected in series in the drawing direction of the optical fibers through the O-rings 15 so as to maintain airtightness. This chamber 25,2
6 is a fiber extraction hole 2 formed by each shutter 24;
4a.

Among the chambers 25 and 26, the furnace core tube 12
The lower chamber 25 is used as an exhaust chamber for gas exhaust, and the lower chamber 26 of this exhaust chamber 25 is used as an inert gas supply chamber for supplying an inert gas such as He or N2. An exhaust pipe 27 and pressure detection means P are provided on the wall of the exhaust chamber 25 for exhausting the gas introduced into the drawing furnace to a gas processing device (not shown). In addition, the inert gas supply chamber 26
A gas introduction pipe 28 for supplying an inert gas such as He, N2, etc. and a pressure detection means P are provided on the wall surface.

In the drawing furnace 1o having such a configuration, each pressure detection means P is constantly detected, and the gas supply chamber 17 and the furnace core tube 12 are constantly detected.
t so that the inside of the inert gas supply chamber 26 provided at the lower end of the wire drawing furnace 10 has a positive pressure, and the inside of the exhaust chamber z5 provided at the lower part of the furnace core tube 12 has a positive pressure. I am trying to adjust each of these.

In this embodiment, materials other than the O-rings 15 and 19 were made of aluminum.

Next, an example in which a fluoride optical fiber is drawn using the cotton drawing furnace 1o of this embodiment will be described below. It can be performed.

Composition ZrF4 (62 mol%)-BaF2 (30 mol%)
-LaF3 (4% Le%) -A1. A fluoride optical fiber free form 13 of F3 (4 mol %) was placed in the furnace core tube 12 and heated to 290° C. by the heating element 11. At this time, F, (10%) - Ar (90%)
) was introduced, and at the same time, dry N2 gas was introduced from the internal gas introduction pipe 28 of the inert gas supply chamber 26 at the lowest end of the drawing furnace. Further, the gas introduced inside was exhausted from the exhaust nozzle 27 of the exhaust chamber 25 below the furnace core v:12. The amount of gas introduced and the amount of gas exhausted at this time is determined by measuring the pressure detection means P provided in each chamber. The pressure was adjusted so that 25 was a positive pressure. As a result, the furnace core If! It was possible to perform OH treatment by separating the 7g atmosphere from the outside air.

Here, HF, ClF3. SF6. A mixed gas of NF and an inert gas may also be used.

After performing this OH removal treatment for 3 hours, the preform 13 was heated to 380° C., and the preform 13 was drawn. The atmosphere inside the furnace core tube 12 during wire drawing was the same as that during the above treatment.

Thereafter, the drawn optical fiber 14 was coated with an ultraviolet curing resin to obtain a fiber core.

When the strength of the obtained fiber core wire was determined by bending strength measurement, the strength of the fiber was found to be 1.5 GPa. This is the strength of the fiber (0,5
0Pa), the strength will be improved by about three times.

In this embodiment, aluminum was used as the material for the parts other than the O-ring 15 and the heating element 11, but the present invention is not limited to this, and each member does not corrode even when fluorine-containing gas is introduced. Any metal may be used as long as it is suitable, and examples thereof include fluorine-resistant metals such as nickel, Monel alloy, and copper.

In addition, in this embodiment, a shutter 24 is provided at the bottom of the furnace core tube.
Although the number of chambers provided through the drawing furnace is two, the present invention is not limited to this, and it is also possible to provide a drawing furnace with even higher airtightness by providing two or more chambers.

Furthermore, in this example, after the OH removal treatment, only the temperature of the heating element 11 was increased to draw the wire under the same conditions.
It is also possible to perform wire drawing by switching the introduced fluorine gas to an inert gas.

<Effects of the Invention> As described above in detail together with the examples, the drawing furnace for fluoride optical fiber of the present invention has a simple structure and can continuously perform surface treatment and drawing of a preform for fluoride optical fiber. This has the advantage that secondary contamination due to moisture, which could not be prevented by conventional methods, can be suppressed and a high-strength fluoride optical fiber can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the drawing furnace for fluoride optical fiber of this embodiment. In the drawing, 10 is a drawing furnace for fluoride optical fiber, 12 is a furnace core tube, 13 is a free form for fluoride optical fiber, 14 is an optical fiber, 17 is a gas supply chamber, 24 is a shutter, 25 is an exhaust chamber, 26 is an inert gas supply chamber.

Claims (1)

[Scope of Claims] A drawing furnace for fluoride optical fiber in which a preform for fluoride optical fiber is installed in a furnace core tube, and the preform is heated and softened while being stretched and drawn into a fluoride optical fiber, comprising: A gas supply chamber provided in the upper part of the furnace core tube to introduce fluorine-based gas or inert gas, and a fiber extraction hole connected in series through a shutter to the lower part of the furnace core tube and formed by each shutter. at least two chambers communicating with each other via the chamber, and at least one of the chambers is an exhaust chamber for exhausting gas, and the lower side of the exhaust chamber is an inert gas supply chamber for supplying an inert gas. This is a drawing furnace for fluoride optical fiber.