阅读说明：本技术 光纤的拉丝方法 (Method for drawing optical fiber ) 是由 米泽和泰 川崎希一郎 于 2019-06-11 设计创作，主要内容包括：本发明提供光纤的拉丝方法,其在使用具有在炉芯部的上部设置有烟筒部的上烟筒型的框体的拉丝装置进行光纤的拉丝的情况下,能够在拉丝快要结束时抑制拉丝出的光纤的玻璃直径的变动变大。将构成为内侧部件(4b～7b)载置于外侧部件(4a～7a)之上的大于或等于一个遮蔽板(4～7)由装配棒(3)插入贯穿而能够移动地安装,并且在最下方的遮蔽板(7)和光纤母材(G)的上端之间安装防风板(11),伴随光纤(G1)的拉丝进行而光纤母材下降,外侧部件卡止于烟筒部(22)内的内径缩径部(24a～24d),由此遮蔽板(4～7)被卡止,由卡止的遮蔽板将烟筒部的空间在上下进行遮蔽,以防风板将与光纤母材的上端的距离保持恒定而下降的方式拉丝出光纤。(The invention provides a method for drawing an optical fiber, which can restrain the variation of the glass diameter of the drawn optical fiber from increasing when the drawing is finished when a drawing device with an upper chimney type frame body provided with a chimney part at the upper part of a furnace core part is used for drawing the optical fiber. One or more shielding plates (4-7) which are configured in such a manner that inner members (4 b-7 b) are placed on outer members (4 a-7 a) are movably mounted by inserting a mounting rod (3) therethrough, and a wind-shielding plate (11) is mounted between the lowermost shielding plate (7) and the upper end of an optical fiber base material (G), so that the optical fiber base material is lowered as the optical fiber (G1) is drawn, and the outer members are locked to inner diameter reducing portions (24 a-24 d) in a soot tube portion (22), whereby the shielding plates (4-7) are locked, and the space of the soot tube portion is shielded by the locked shielding plates in the vertical direction, and the optical fiber is drawn so that the distance from the upper end of the optical fiber base material is kept constant by the wind-shielding plates and is lowered.)

1. A method for drawing an optical fiber, wherein an optical fiber base material supported by an assembly rod is accommodated in an upper and lower liftable frame body by using a drawing device having the upper chimney type frame body provided with a chimney part at the upper part of a furnace core part, the optical fiber base material is heated and melted, and the optical fiber is drawn from the lower end of the optical fiber base material,

In the method for drawing an optical fiber,

A shielding plate having at least an outer member and an inner member and configured such that the inner member is placed on the outer member, the shielding plate being movably attached by inserting the attachment rod therethrough, and the wind-shielding plate being attached between the lowermost shielding plate and the upper end of the optical fiber base material,

The outer member is locked to an inner diameter-reduced portion in the soot body as the optical fiber is drawn downward, whereby the shielding plate is locked, the space in the soot body is shielded vertically by the locked shielding plate, and the optical fiber is drawn downward while keeping a distance from the upper end of the optical fiber base material constant by the wind-guard plate.

2. the method for drawing an optical fiber according to claim 1,

The windbreak plate is formed from quartz glass.

3. The method for drawing an optical fiber according to claim 1 or 2,

The diameter of the windproof plate is less than or equal to 0.98 times of the minimum inner diameter of the smoke tube part.

4. The method for drawing an optical fiber according to claim 1 or 2,

the diameter of the wind guard plate is greater than or equal to 0.80 times the diameter of the optical fiber preform.

5. The method for drawing an optical fiber according to claim 3,

The diameter of the wind guard plate is greater than or equal to 0.80 times the diameter of the optical fiber preform.

Technical Field

The present invention relates to a method for drawing an optical fiber.

Background

Patent document 1 describes an optical fiber drawing apparatus having an upper chimney type housing provided with a chimney portion at an upper portion of a furnace core portion, and the drawing apparatus is provided with a single partition plate for vertically dividing an upper space of an optical fiber base material.

Patent documents 2 to 4 describe an optical fiber drawing apparatus provided with a plurality of the above-described partition plates.

Patent document 1: japanese laid-open patent publication No. 5-147969

Patent document 2: japanese laid-open patent publication No. 11-343137

Patent document 3: japanese laid-open patent publication No. 2002-068773

patent document 4: japanese laid-open patent publication No. 2005-225733

when an optical fiber is drawn using a drawing apparatus having an upper chimney type housing, the glass diameter of the drawn optical fiber may fluctuate significantly near the end of drawing. As described above, if the variation in the glass diameter is large, the quality may be deteriorated, and the optical fiber drawn near the end of drawing must be discarded as a defective product.

Disclosure of Invention

An object of the present invention is to provide a method for drawing an optical fiber, which can suppress an increase in variation in the glass diameter of the drawn optical fiber immediately before the end of drawing, when the optical fiber is drawn using a drawing device having an upper-chimney-type housing in which a chimney portion is provided above a furnace core portion.

In a method for drawing an optical fiber according to an embodiment of the present invention,

Using a drawing device having an upper-chimney-type frame body in which a chimney is provided at the upper part of a furnace core part, an optical fiber base material supported by an assembly rod is accommodated in the frame body so as to be vertically movable, the optical fiber base material is heated and melted, and an optical fiber is drawn from the lower end of the optical fiber base material,

In the method for drawing an optical fiber,

A shielding plate having at least an outer member and an inner member and configured such that the inner member is placed on the outer member, the shielding plate being movably attached by inserting the attachment rod therethrough, and the wind-shielding plate being attached between the lowermost shielding plate and the upper end of the optical fiber base material,

The outer member is locked to an inner diameter-reduced portion in the soot body as the optical fiber is drawn downward, whereby the shielding plate is locked, the space in the soot body is shielded vertically by the locked shielding plate, and the optical fiber is drawn downward while keeping a distance from the upper end of the optical fiber base material constant by the wind-guard plate.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the optical fiber drawing method of the present invention, when the optical fiber is drawn using the drawing device including the upper chimney-type housing having the chimney portion provided at the upper portion of the furnace core portion, it is possible to suppress the increase in the variation in the glass diameter of the drawn optical fiber immediately before the end of drawing.

Drawings

Fig. 1 is a schematic diagram of a drawing apparatus using the optical fiber drawing method according to the embodiment of the present invention.

Fig. 2 is a diagram showing an example of a conventional drawing apparatus and a temperature distribution in a drawing furnace immediately before drawing is completed.

Fig. 3 is a diagram showing measurement data of the glass diameter of an optical fiber according to the lapse of drawing time in the case of drawing the optical fiber using a conventional drawing apparatus.

Description of the reference numerals

1: wire drawing device

2: wire drawing furnace

3: assembly rod

4. 5, 6, 7: shielding plate

4a, 5a, 6a, 7 a: outer part

4b, 5b, 6b, 7 b: inner part

10: connecting member

11: windproof plate

22: section of thick bamboo of cigarette section of thick bamboo

22 a: inner peripheral part

22 b: outer peripheral portion

23: furnace core

24a to 24 d: inner diameter reducing part

25: lower extension part

D: diameter of the windbreak panel

Dc: minimum inner diameter

And Dp: diameter of optical fiber preform

G: optical fiber preform

G1: optical fiber

Detailed Description

(description of embodiments of the invention)

First, embodiments of the present invention will be described.

in a method for drawing an optical fiber according to an embodiment of the present invention,

(1) using a drawing device having an upper-chimney-type frame body in which a chimney is provided at the upper part of a furnace core part, an optical fiber base material supported by an assembly rod is accommodated in the frame body so as to be vertically movable, the optical fiber base material is heated and melted, and an optical fiber is drawn from the lower end of the optical fiber base material,

In the method for drawing an optical fiber,

A shielding plate having at least an outer member and an inner member and configured such that the inner member is placed on the outer member, the shielding plate being movably attached by inserting the attachment rod therethrough, and the wind-shielding plate being attached between the lowermost shielding plate and the upper end of the optical fiber base material,

The outer member is locked to an inner diameter-reduced portion in the soot body as the optical fiber is drawn downward, whereby the shielding plate is locked, the space in the soot body is shielded vertically by the locked shielding plate, and the optical fiber is drawn downward while keeping a distance from the upper end of the optical fiber base material constant by the wind-guard plate.

According to the above method, the wind guard plate can prevent a strong updraft from occurring between the upper end and the lowermost shielding plate of the optical fiber preform. Thus, when an optical fiber is drawn using a drawing device having an upper-chimney-type housing in which a chimney portion is provided above a furnace core portion, it is possible to suppress an increase in variation in the glass diameter of the drawn optical fiber immediately before the end of drawing.

(2) The windbreak plate may be formed from quartz glass.

According to the above method, the wind-guard plate made of quartz glass is free from SiO generated from the optical fiber base material having a high temperature, such as graphite₂The steam and oxygen are oxidized and generate dust.

The wind guard plate made of quartz glass can transmit the radiation light from the upper end of the optical fiber preform to some extent. This can suppress an increase in the temperature difference between the upper and lower spaces of the wind guard plate in the flue pipe portion. By suppressing the temperature difference between the upper and lower spaces of the wind-guard plate, the turbulence of the air flow is suppressed, and the increase in the variation in the glass diameter of the drawn optical fiber can be further suppressed.

(3) The diameter of the windguard plate may be less than or equal to 0.98 times the minimum inner diameter of the chimney portion.

According to the above method, since the diameter of the wind-guard plate is less than or equal to 0.98 times the minimum inner diameter of the cylindrical portion, the wind-guard plate and the inner surface of the cylindrical portion are not substantially in contact with each other, and the wire drawing can be performed.

(4) The diameter of the wind guard plate may be greater than or equal to 0.80 times the diameter of the optical fiber preform.

According to the above method, since the diameter of the wind-guard plate is 0.80 times or more the diameter of the optical fiber base material, the variation in the glass diameter of the optical fiber can be more reliably suppressed.

(details of the embodiment of the present invention)

Next, a specific example of the optical fiber drawing method according to the embodiment of the present invention will be described with reference to the drawings.

The present invention is not limited to these examples, but is defined by the claims, and includes all modifications equivalent in content and scope to the claims.

Fig. 1 is a longitudinal sectional view showing an example of a drawing apparatus to which the optical fiber drawing method according to the embodiment of the present invention is applied.

As shown in fig. 1, the drawing apparatus 1 is an apparatus for drawing an optical fiber G1 from an optical fiber preform G. The drawing apparatus 1 includes: a drawing furnace 2 for vertically and freely storing the optical fiber preform G; and more than or equal to one (in this case 4) shutter plates 4, 5, 6, 7 able to move along the assembly bar 3 inside the drawing furnace 2. Further, the drawing apparatus 1 includes: a heater 8 for heating the optical fiber preform G; and a gas supply unit 9 that supplies an inert gas (e.g., helium gas) into the drawing furnace 2.

The drawing furnace 2 is an upper chimney type furnace (frame body) and includes: a cylindrical flue pipe part 22, the upper part of which is closed by a cover part 21; and a furnace core 23 disposed below the flue gas pipe section 22.

The drawing furnace 2 has a lower extension 25 below the core 23. The lower extension portion 25 has a cylindrical shape having a diameter smaller than that of the furnace core portion 23, and is provided continuously with the furnace core portion 23.

the heater 8 is assembled outside the furnace core 23. The gas supply portion 9 is connected to the flue pipe portion 22 in communication therewith. The gas supply unit 9 supplies an inert gas for suppressing oxidation and deterioration of the core part 23 accompanying heating by the heater 8 during drawing into the drawing furnace 2. For example, the inert gas supplied from the gas supply unit 9 is blown into a space between the flue gas cylinder 22 and the furnace core 23 through the gas passage 9a from the gas inlet 9 b.

the inner peripheral portion 22a of the smoke tube portion 22 is formed in, for example, an annular shape in a cross section perpendicular to the central axis of the attachment rod 3. The inner diameter of the circular cross section of the inner peripheral portion 22a is different depending on the position in the vertical direction. In the example of fig. 1, the inner peripheral portion 22a and the outer peripheral portion 22b of the flue pipe portion 22 are separate bodies, but may be integrated. In the inner peripheral portion 22a of the flue pipe portion 22, inner diameter-reduced portions (stepped portions having a reduced diameter in the lower portion in this example) 24a to 24d are formed at predetermined intervals in the vertical direction. Thus, the inner diameter of the circular cross section of the chimney portion 22 is configured to be smaller in each inner diameter reducing portion as going from the upper side to the lower side. In this example, the inner peripheral portion 22a of the tubular portion 22 is reduced in diameter in four steps in a downward direction.

The attachment rod 3 is inserted through the central portion of the lid member 21 in the smoke tube portion 22. The optical fiber base material G is assembled to the assembly rod 3 via the coupling member 10. The shielding plates 4, 5, 6, and 7 are movably disposed above the connecting member 10 through which the mounting rod 3 is inserted. Further, a wind guard plate 11 is disposed between the lowermost shielding plate 7 and the upper end of the optical fiber base material G. The windshield plate 11 is attached to, for example, the upper surface of the connecting member 10. Therefore, for example, when the optical fiber preform G to be drawn is positioned at the uppermost position in the drawing furnace 2, the shielding plates 4, 5, 6, and 7 are placed on the upper surface of the wind-guard plate 11 in a stacked state.

the shielding plates 4, 5, 6, 7 are respectively constituted by outer members 4a, 5a, 6a, 7a and inner members 4b, 5b, 6b, 7 b. The outer members 4a, 5a, 6a, and 7a and the inner members 4b, 5b, 6b, and 7b are, for example, disk-shaped plates having a hole formed in the center. The inner members 4b, 5b, 6b, 7b are disposed above the outer members 4a, 5a, 6a, 7a, respectively. The outer members 4a, 5a, 6a, and 7a and the inner members 4b, 5b, 6b, and 7b are made of a heat-resistant material such as quartz, graphite, or silicon carbide, and have a thickness of about several mm to ten and several mm.

the outer diameters of the outer members 4a, 5a, 6a, 7a of the shielding plates 4, 5, 6, 7 are set to diameters corresponding to the inner diameters of the stepped diameter reduction of the flue pipe portion 22. That is, the uppermost outer member 4a has a diameter corresponding to the inner diameter Dc1 of the portion of the flue pipe portion 22 that is not reduced in diameter, and has an outer diameter that can be placed on the step of the inner diameter reduced portion 24a that is the first step from above. The second outer member 5a has a diameter corresponding to the inner diameter Dc2 of the portion having a one-step reduced diameter from the top, and has an outer diameter (smaller diameter) that cannot be placed on the step of the inner diameter reduced portion 24a of the first step from the top and can be placed on the step of the inner diameter reduced portion 24b of the second step from the top. The outer diameters of the outer members 6a and 7a are set to diameters corresponding to the inner diameters Dc3 and Dc4 of the flue pipe section 22, and are set to sizes that can be placed on the steps of the inner diameter reduced portions 24c and 24d on the lower side in this order. The outer diameter of the lowermost outer member 7a is formed larger than the minimum inner diameter Dc of the portion of the flue pipe portion 22 having the largest diameter reduction. The inner diameter of the hole formed in the center of the outer member 4a, 5a, 6a, 7a is slightly larger than the diameter of the mounting rod 3.

The outer diameters of the inner members 4b, 5b, 6b, 7b of the shield plates 4, 5, 6, 7 are sufficiently larger than the inner diameter of the hole formed in the center of the mating outer members 4a, 5a, 6a, 7a, and are smaller than the outer diameters of the mating outer members 4a, 5a, 6a, 7 a.

the inner diameters of the holes formed in the central portions of the inner members 4b, 5b, 6b, and 7b are smaller than the inner diameters of the holes formed in the central portions of the outer members 4a, 5a, 6a, and 7a and slightly larger than the outer diameter of the attachment rod 3, and are formed slidably with respect to the attachment rod 3. Therefore, when the mounting rod 3 is inserted into the hole penetrating the center portion, the inner members 4b, 5b, 6b, and 7b are configured to be placed on the outer members 4a, 5a, 6a, and 7 a.

The wind guard plate 11 is a plate having a hole in the center, for example, a disk shape. The wind guard plate 11 is made of, for example, quartz glass, and has a thickness of about several mm to ten and several mm. The diameter D of the wind guard plate 11 is smaller than the minimum inner diameter Dc of the portion of the flue gas pipe section 22 having the largest diameter reduction. For example, the diameter D of the windshield plate 11 is less than or equal to 0.98 times the minimum inside diameter Dc. The diameter D of the wind-guard plate 11 is, for example, 0.80 times or more the diameter Dp of the optical fiber preform G.

Next, an example in which the optical fiber drawing method according to the present embodiment is applied to the drawing apparatus 1 will be described.

First, the optical fiber base material G is attached to the lower end of the mounting rod 3 via the connecting member 10, and the lower end of the optical fiber base material G is heated and melted by the heater 8. Then, an optical fiber G1 is drawn from the lower end of the molten optical fiber preform G. The drawn optical fiber G1 is drawn out from the lower extension 25. Since the optical fiber preform G becomes shorter as the optical fiber G1 is drawn, the lower end of the optical fiber preform G is always heated by the heater 8 by lowering the assembling rod 3. During drawing, an inert gas is supplied from the gas supply portion 9 to the inside of the drawing furnace 2. The upper portion of the flue gas duct portion 22 is covered with the lid member 21 so that the inert gas inside does not flow out.

First, the 4 shielding plates 4, 5, 6, and 7 are stacked, and the optical fiber preform G is shortened as the optical fiber G1 is drawn, and the coupling member 10 to which the wind-guard plate 11 is attached is lowered together with the mounting rod 3. The 4-piece shield plates 4, 5, 6, and 7 are prevented from moving downward by inner diameter-reduced portions 24a to 24d, each having an inner diameter smaller than the outer diameter of each of the outer members 4a, 5a, 6a, and 7a, of the smoke tube portion 22. As a result, the shielding plates 4, 5, 6, and 7 are engaged with the inner diameter-reduced portions 24a to 24d in order from the upper shielding plate 4 to the lower shielding plate 7. As the optical fiber base material G becomes shorter, the space in the soot part 22 is sequentially divided vertically by the shielding plates 4, 5, 6, and 7, and thus drawing is performed in a state where the space capacity in the upper part of the optical fiber base material G is substantially constant.

On the other hand, the wind-guard plate 11 is lowered in the drawing furnace 2 together with the optical fiber base material G and the connecting member 10 while keeping a constant distance from the upper end of the optical fiber base material G without being locked to the inner diameter reducing portions 24a to 24 d.

Further, when an optical fiber is drawn using a drawing apparatus having an upper-chimney type drawing furnace in which a chimney portion is provided above a furnace core portion, the glass diameter of the drawn optical fiber may greatly vary near the end of drawing.

Fig. 2 is a diagram showing an example of a conventional drawing apparatus in which a change in glass diameter may occur near the end of drawing, and a temperature distribution in a drawing furnace near the end of drawing. Fig. 3 is a graph showing measurement data of the glass diameter of an optical fiber according to the lapse of drawing time in the case where the optical fiber is drawn by using a conventional drawing apparatus.

The drawing device 100 shown in fig. 2 does not have a windguard. As shown in fig. 2, if drawing is performed in the drawing apparatus 100, the 3 shielding plates 104, 105, and 106 provided are sequentially locked, and after the lowermost shielding plate 106 is locked, the optical fiber base material G continues to descend further downward.

The optical fiber preform G is directly heated by the heater 108 of the furnace core 123 at the lower end side of the optical fiber preform G, but the radiation light from the heater 108 is transmitted from the bottom to the top in the optical fiber preform G. Therefore, the upper end side of the optical fiber preform G functions as a heater that radiates heat of the radiated light by radiating the radiated light from the heater 108 from the upper end portion (shoulder portion having a reduced outer diameter) of the optical fiber preform G.

When the optical fiber is drawn and the drawing is nearly completed, the position of the upper end of the shortened optical fiber base material G is close to the position of the heater 108 in the furnace core 123. Thus, as shown in fig. 2, the temperature distribution H0 in the core part 123 has a distribution in which the temperature distribution H1 of the heating zone formed by the heater 108 and the temperature distribution H2 of the heating zone formed by radiant heat from the upper end of the optical fiber preform G overlap each other. Therefore, a temperature distribution different from that in drawing the lower and middle portions of the optical fiber base material G is formed in the drawing furnace 102, and a sharp temperature gradient is generated in the region S from the upper end portion of the optical fiber base material G to the lowermost shielding plate 106.

Due to the occurrence of this sharp temperature gradient, a strong updraft, for example, as shown by arrow P in fig. 2, occurs in the region S from the furnace core 123 toward the flue gas pipe 122. Then, due to the generation of the updraft, the inner member 106b of the lowermost shield plate 106 that has been closed is pushed, and the shielded state in the drawing furnace 102 is broken. Therefore, the pressure in the drawing furnace 102 fluctuates, and the glass diameter of the optical fiber fluctuates according to the fluctuation of the internal pressure. As a result, for example, as shown in fig. 3, the glass diameter of the optical fiber greatly fluctuates in a constant period T immediately after the completion of drawing.

in contrast, in the optical fiber drawing method according to the present embodiment, as shown in fig. 1, the optical fiber is drawn in a state where the wind-guard plate 11 is attached between the lowermost shielding plate 7 and the upper end of the optical fiber base material G. Therefore, the strong updraft generated in the area S can be suppressed by the wind guard plate 11, and the updraft can be prevented from directly hitting the inner member 7b of the lowermost shield plate 7. Therefore, when the optical fiber is drawn using a drawing apparatus having an upper-chimney-type housing in which a chimney portion is provided above a furnace core portion, it is possible to suppress an increase in variation in the glass diameter of the drawn optical fiber immediately before the end of drawing.

Further, the optical fiber preform G made of quartz glass is drawn while being melted in the drawing furnace 2, and the wind-guard plate 11 is used in the high-temperature portion exceeding 1000 ℃ in the drawing furnace 2 as described above. Therefore, for example, when graphite is used as the material of the wind guard plate 11, SiO generated from the optical fiber preform G having a high temperature is generated₂The windbreak plate 11 may be oxidized to generate dust by the steam and oxygen. On the other hand, when quartz glass is used as the material of the wind guard plate 11, there is no concern about dust generation due to oxidation, and it is possible to suppress occurrence of glass diameter variation due to adhesion of dust to the optical fiber preform G and the optical fiber G1.

Further, if the windbreak plate 11 blocks the radiation light from the upper end of the optical fiber base material G, the temperature difference between the upper and lower sides of the windbreak plate 11 becomes excessively large, and a large disturbance of the air flow may occur. Therefore, by forming the wind guard plate 11 of quartz glass, the radiant light can be transmitted to some extent, and the temperature difference between the upper and lower sides of the wind guard plate 11 can be suppressed from increasing. This can suppress the occurrence of turbulence in the air flow, and further suppress the increase in variation in the glass diameter of the drawn optical fiber G1.

(Experimental example of wind-guard plate)

Next, an experimental example of the wind guard plate in which the diameter D of the wind guard plate 11 in the drawing device 1 was changed and the optical fiber was drawn by the method of drawing the optical fiber according to the present embodiment will be described.

In the wind guard plate experimental example, in the case of examples 1 to 9 in which the same optical fiber base material and the wind guard plates 11 having different diameters D were used in the same drawing apparatus 1, drawing was performed. The diameter D of the wind guard plate 11 of examples 1 to 9 is represented by a ratio (D/Dc) to the minimum inner diameter Dc of the cylindrical portion 22 and a ratio (D/Dp) to the diameter Dp of the optical fiber preform G. In each example, whether or not drawing is possible was examined for 100 optical fiber base materials G. Then, the glass diameter of the optical fiber G1 was measured with respect to the drawn optical fiber G1 in accordance with the lapse of the drawing time, and it was checked from the measurement result (for example, a graph such as fig. 3) whether or not a change in glass diameter larger than or equal to a predetermined size occurred.

Table 1 shows the results of wire drawing in each of examples 1 to 9.

[ TABLE 1 ]

TABLE 1

In example 1 where D/Dc is 1.00, the wind guard plate 11 and the inner surface of the cylindrical portion 22 were in contact with each other by the automatic adjustment of the position of the drawing route line (horizontal movement of the attachment rod 3), and drawing was not performed at all.

In example 2 where D/Dc is 0.98, the wind-guard plate 11 does not contact the inner surface of the soot body 22 in 98% of the optical fiber preform G, and the fiber can be drawn.

In the case where D/Dc is 0.95 or less and 0.38 or more (examples 3 to 9), the wind-guard plate 11 does not contact the inner surface of the soot body 22 in all the optical fiber preform G, and the fiber can be drawn. When D/Dc is 0.70 or less (examples 7 to 9), D/Dp is 0.74 or less, and a part of the drawn optical fiber G1 has a glass diameter varying by a predetermined amount or more.

On the other hand, when the D/Dp is 0.80 or more and 1.03 or less (examples 2 to 6), no change in the glass diameter of a predetermined size or more occurred in all the optical fibers G1 obtained by drawing. When the D/Dp was 1.05 (example 1), the D/Dc was 1.00, and the windbreak plate 11 and the inner surface of the chimney 22 were in contact as described above, and drawing was not performed at all, and therefore, the optical fiber G1 was not examined for fluctuations in glass diameter.

According to the method of drawing an optical fiber according to the present embodiment, as shown in the above-described wind guard plate experimental example, for example, by setting the diameter D of the wind guard plate 11 to be equal to or less than 0.98 times the minimum inner diameter Dc of the soot body 22 (D/Dc is equal to or less than 0.98), the wind guard plate 11 and the inner surface of the soot body 22 are substantially not in contact with each other, and the optical fiber G1 can be drawn. Further, for example, by setting the diameter D of the wind guard plate 11 to be 0.80 times or more (D/Dp is 0.80 times or more) the diameter Dp of the optical fiber preform G, it is possible to sufficiently suppress a strong updraft and to more reliably suppress variation in the glass diameter of the optical fiber G1.

While the present invention has been described in detail and with reference to the specific embodiments, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. The number, position, shape, and the like of the components described above are not limited to those of the above embodiments, and may be changed to those suitable for carrying out the present invention.