JPH05147969A - Optical fiber drawing furnace - Google Patents

Abstract

PURPOSE:To suppress the fluctuation in the diameter of the optical fiber to a lower level even if a large-sized base material is drawn by providing a partition plat for vertically delineating the part exclusive of the part near the circumferential wall surface of a drawing chamber in a space upper than the optical fiber base material of the drawing chamber. CONSTITUTION:The disk-shaped partition plate 20 is detained at the mid-point of a dummy bar 9 to delineate the space above the optical fiber base material 10 of the drawing chamber 8 in a vertical direction. The space of the part exclusive of the spacing (d) between the peripheral surface of the partition plate 20 and an inside cylinder pipe 7 is vertically segmented by the partition plate 20. The drawing chamber 8 is segmented to the space A upper than the partition plate 20, the space B between the partition plate 20 and the optical fiber base material 10 and the space C on the lower side of the optical fiber base material 10. The spacing B between the partition plate 20 and the optical fiber base material 10 is not changed in size even if the optical fiber base material 10 diminishes on progressing of the drawing of the optical fiber 14. A fitting member 15 connects the dummy bar integrated with the optical fiber base material 10 and a separately prepd. dummy bar.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber drawing furnace capable of obtaining an optical fiber having a small wire diameter variation from a large-sized optical fiber preform.

[0002]

2. Description of the Related Art Conventionally, an optical fiber drawing furnace has been used to obtain an optical fiber by heating and melting an optical fiber preform (hereinafter also simply referred to as a preform) and drawing it.

An example of this optical fiber drawing furnace is shown in FIG. As shown in the figure, the drawing furnace is composed of a furnace core portion 1 and a chimney portion 2. The furnace core portion 1 has a structure in which a heater 4 is provided around a furnace core tube 3 made of carbon or the like, and an upper lid portion 5 and a lower lid portion 6 having a water cooling structure inside are provided on the upper and lower sides thereof.
It is divided by. Further, the chimney portion 2 is made of carbon or the like, and has an inner cylindrical tube 7 having the same diameter as the furnace core tube 3, and the surrounding area is usually water-cooled for safety. And
A cylindrical drawing chamber 8 is formed by the furnace core tube 3 and an inner cylindrical tube 7 that communicates with the furnace core tube 3, and an optical fiber preform supported by a dummy rod 9 from above is formed in the drawing chamber 8. 10 is inserted. Further, an inert gas ejection port 11 is uniformly formed in the circumferential direction on the upper wall surface of the inner cylindrical pipe 7, and is supplied from the outside through an inert gas passage 12 formed outside the inner cylindrical pipe 7. The inert gas to be introduced is continuously introduced into the drawing chamber 8. In addition, 13 in the figure is a lid that closes the upper opening of the chimney part 2 and prevents the inflow of external air.

Using such a drawing furnace, an inert gas jet 1
1 from the lower end of the optical fiber preform 10 by continuously flowing the inert gas from 1 to fill the inside of the drawing chamber 8 with the inert gas and heating the furnace core tube 3 with the heater 4.
4 can be delineated. The variation of the diameter of the optical fiber 14 drawn in this way is usually ± 0.3
It was about μm, and had a practically sufficient performance.

[0005]

By the way, in recent years, the optical fiber preform 10 has become larger due to mass production of optical fibers and cost reduction. However, for example, diameter 125mm, length 1
When a large base material of about 20 mm is used for wire drawing, the variation in wire diameter becomes large at ± 3 to 10 μm, and there is a problem that it cannot be used in the optical communication field and the like where high performance is required.

In view of such circumstances, it is an object of the present invention to provide an optical fiber drawing furnace capable of suppressing a change in wire diameter even when a large preform is drawn.

[0007]

An optical fiber drawing furnace according to the present invention that achieves the above object has a drawing chamber filled with an inert gas continuously introduced from above, and the drawing chamber is provided. In an optical fiber drawing furnace that heats and melts an optical fiber preform that is inserted by being supported by a dummy rod from the upper end opening of the optical fiber and draws an optical fiber from the lower end thereof, the drawing chamber is provided in the middle of the dummy rod. The above-mentioned optical fiber preform, characterized in that it comprises a partition plate that defines in the vertical direction in the space above the peripheral wall surface of the drawing chamber, and in the above configuration, penetrates the partition plate in the vertical direction. And the partition plate has a diameter smaller than the inner diameter of the drawing chamber and larger than the diameter of the optical fiber preform.

[0008]

The inert gas flowing in from the upper part of the drawing chamber flows between the partition plate of the drawing chamber and the optical fiber preform through the gap between the peripheral surface of the partition plate and the wall surface of the drawing chamber. Flowing into the space,
After being heated, it flows into the lower side of the optical fiber preform through the gap between the periphery of the optical fiber preform and the wall of the drawing chamber. As a result, the disturbance of the temperature and the disturbance of the gas flow around the drawn portion at the lower end of the optical fiber preform are less likely to occur, and the diameter of the drawn optical fiber is stabilized.

When a plurality of through holes are provided in the partition plate, the rectified inert gas flows through the through holes between the partition plate and the optical fiber preform, and this is the lower side of the optical fiber preform. The gas turbulence around the drawn portion at the lower end of the optical fiber preform is further reduced because it flows into the.

On the other hand, when the partition plate is not provided,
The flow of the inert gas is turbulent in the space above the optical fiber preform, and there is convection with the upper cold part, so the temperature is low overall. Therefore, it is considered that the inert gas flowing into the lower side of the optical fiber preform has a low temperature and the flow is disturbed, so that the drawing cannot be performed uniformly.

[0011]

EXAMPLES The present invention will be described below based on examples.

FIG. 1 shows an outline of an optical fiber drawing furnace according to an embodiment. In the figure, members having the same functions as those in FIG. 4 are designated by the same reference numerals, and overlapping description will be omitted.

As shown in FIG. 1, in this embodiment, a disk-shaped partition plate 20 is locked in the middle of the dummy rod 9 to vertically define a space above the optical fiber preform 10 in the drawing chamber 8. Is made. More specifically, as shown in FIG. 3A, the partition plate 20 is made of quartz and has a diameter larger than the diameter of the optical fiber preform 10 but smaller than the inner diameters of the inner tube 7 and the furnace core tube 3. It is a disk and has a locking hole 20a for locking the dummy rod 9 in the center. Therefore, the space other than the gap d between the peripheral surface of the partition plate 20 and the inner tubular pipe 7 is vertically divided by the partition plate 20, and the drawing chamber 8 is positioned above the partition plate 20. Is divided into a space A, a space B between the partition plate 20 and the optical fiber preform 10, and a space C below the optical fiber preform 10. The space B between the partition plate 20 and the optical fiber preform 10 does not change in size as shown in FIG. 2 even if the drawing of the optical fiber 14 advances and the optical fiber preform 10 becomes smaller. . In addition, reference numeral 15 in the drawing denotes a fitting member for connecting a dummy rod integrally formed with the optical fiber preform 10 and a dummy rod prepared separately.

The material of the partition plate 20 is not limited to quartz as long as it has heat resistance, and carbon, silicon carbide (SiC) or the like may be used.

In the optical fiber drawing furnace described above,
The drawing chamber 8, particularly the space C, is heated by the heater 4, and the inert gas is continuously introduced from the inert gas jet port 11 to fill the drawing chamber 8 with the inert gas. Then, the partition plate 2
In the space A above 0, a flow of a relatively low temperature inert gas (convection in the vertical direction) occurs, and a part of this gas flows into the space B from the gap d around the partition plate 20. At this time, since the gap d is small, the flow of the inert gas is rectified. Further, since the inert gas is considerably heated in the space B, a relatively heated gas flow (convection) occurs in the space B, and the flow is not disturbed. Then, since the inert gas, which has been heated considerably and has a stable flow, flows into the space C from the periphery of the optical fiber preform 10, the temperature change in the space C and the turbulence of the flow are small, and stable drawing can be performed. it can.

When the optical fiber preform 10 having a diameter of 125 mm and a length of 120 mm was drawn using the optical fiber drawing furnace shown in FIG. 1, the fluctuation of the diameter of the optical fiber 14 was ± 0.3.
It was as good as about μm. On the other hand, when the partition plate 20 was removed and the wire was similarly drawn, a wire diameter variation of ± 0.3 μm or more occurred.

The partition plate 20 may be mounted at a position where the above-described effects can be obtained, that is, a position where a space B in which a stable gas flow is formed by heating to some extent can be formed. It is not particularly limited. Further, if the diameter of the partition plate 20 is made larger than the diameter of the optical fiber preform 10, the above-described effects are obtained, and it is preferable that the diameter is close to the inner diameter of the inner cylindrical tube 7 or the furnace core tube 3. The thickness of the partition plate 20 itself does not need to be so large as long as the strength can be maintained, and therefore the diameter thereof can be made very close to the inner diameter of the inner cylindrical tube 7 or the furnace core tube 3.

As the partition plate, a partition plate 21 having a large number of through holes 21b other than the dummy rod locking hole 21a as shown in FIG. 3B can be used.

When the partition plate 21 is used, the inert gas in the space A flows into the space B from the through hole 21b as well as the gap d between the peripheral surface of the partition plate 21 and the inner cylindrical tube 7 or the furnace core tube 3. Therefore, it is in a fairly rectified state. Therefore, the gas flow in the space B becomes more stable, which further suppresses the turbulence of the gas flow in the space C. That is, the partition plate 2
Since 1 has a stronger rectifying action than the partition plate 20, the gas heating effect in the space B as described above does not necessarily have to occur. In any case, when the partition plate 21 is used, the fluctuation of the optical fiber diameter can be suppressed to be as small as or more than that when the partition plate 20 is used.

[0020]

As described above, according to the present invention,
The partition plate defines the upper space of the optical fiber preform in the up-down direction, and a space with relatively high temperature and no gas flow disturbance can be formed immediately above the optical fiber preform, so that a large preform can be formed. Even if it is used, it is possible to continuously manufacture an optical fiber having no fluctuation in wire diameter.

[Brief description of drawings]

FIG. 1 is a schematic view of an optical fiber drawing furnace according to an embodiment.

FIG. 2 is a schematic view showing a usage state of the optical fiber drawing furnace of FIG.

FIG. 3 is an explanatory diagram showing an appearance of a partition plate.

FIG. 4 is a schematic view of a conventional optical fiber drawing furnace.

[Explanation of symbols]

 1 Drawing part 2 Chimney part 3 Furnace core tube 4 Heater 7 Inner cylinder tube 8 Drawing chamber 9 Dummy rod 10 Optical fiber base material 11 Inert gas ejection port 14 Optical fiber 20,21 Partition plate 20a, 21a Dummy rod locking Hole 21b through hole

Claims (3)

[Claims] 1. An optical fiber preform, which has a drawing chamber filled with an inert gas continuously flowed in from an upper portion and is supported by a dummy rod from an upper end opening of the drawing chamber and is melted by heating. Then, in an optical fiber drawing furnace for drawing an optical fiber from the lower end thereof, provided in the middle of the dummy rod and in the space above the optical fiber preform of the drawing chamber except near the peripheral wall surface of the drawing chamber. An optical fiber drawing furnace, characterized in that it comprises a partition plate that defines the vertical direction. 2. The optical fiber drawing furnace according to claim 1, wherein the partition plate has a plurality of through holes penetrating in the vertical direction. 3. The optical fiber drawing furnace according to claim 1, wherein the partition plate has a diameter smaller than the inner diameter of the drawing chamber and larger than the diameter of the optical fiber preform.