JPH07492B2 - Optical fiber manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an optical fiber including a step of depositing glass fine powder on a central member of glass, and particularly to depositing glass fine powder. The present invention relates to the surface treatment of the central member before the step of performing.

[Prior Art] When dust or the like is attached to the surface of the central member, fine glass powder is deposited on the dust, and after sintering, it remains as bubbles and does not become a low-loss optical fiber.

When polishing with an oxyhydrogen flame to remove dust on the surface, OH in the oxyhydrogen flame diffuses into the central member, so polishing with an anhydrous flame is performed.

[Problems to be Solved by the Invention] (1) Even when polishing with anhydrous flame, moisture in the air penetrates into the heated central member and is absorbed by OH, resulting in a low-loss optical fiber. Absent.

(2) In order to clean the surface of the central member, etching with an etching gas may be performed in addition to flame polishing.

Plasma is often used for the anhydrous flame, but if the etching gas is flown together with the plasma-generating gas in the plasma torch, not only will the flame become unstable, but in some cases it may be extinguished, so It is not possible to flow the etching gas.

Therefore, as in the case of (1), moisture in the air penetrates into the heated central member, suffers absorption loss due to OH, and does not become a low-loss optical fiber.

[Object of the Invention] (1) During flame polishing, a gas is passed to block moisture in the air to prevent OH absorption loss.

(2) An etching gas such as SF ₆ is used as a gas, and a large amount of this gas is blown into the glass rod at the highest temperature portion at a high flow rate to block the atmosphere from the high temperature portion, and at the same time, the glass is faster than the infiltration rate of moisture in the atmosphere. OH
Suppress absorption loss.

[Means for Solving the Problems] In the present invention, (1) the central member is heated from below with an anhydrous flame for flame polishing, and at that time, a large number of knurls are provided from around the anhydrous flame. A sealing gas is introduced into the flame, and the gas is used to carry out flame polishing while cutting off the heated portion of the central member from the surrounding atmosphere (the above is related to claim 1).

(2) Also, at least a part of the sealing gas is also used as an etching gas.

The details will be described below.

[Outline of Apparatus] In FIGS. 1a to 1c, reference numeral 10 denotes a central member, which is composed of, for example, a pure quartz glass rod which becomes a core when it is made into a fiber, or a quartz rod which becomes a part of a core and a clad. Of these, the former requires strict lowering of OH, but the latter does not necessarily require it.

12 is an anhydrous flame for polishing (a plasma flame in this figure, CO
+ O ₂ flame can also be used).

14 is a plasma torch for generating a plasma flame (other torches may be used), and 16 is a high frequency coil.

The plasma torch 14 can reciprocate in the direction of arrow 18.

20 is a nozzle. This is a plasma torch 14 as shown in Figure 1b.
Place a large number (for example, 12 pieces) at equal intervals. A sealing gas 22 is introduced into the plasma flame 12 by these nozzles 20.

As the sealing gas 22, N ₂ is used for simple flame polishing.
However, SF ₆ or the like is usually used in the sense that it also serves as etching. In that case, the following two ways can be considered.

When it is not necessary to strictly lower OH (for example, when the starting material is the core + clad): For example, one of the nozzles 20 is used as an etching gas,
Others are used with seal gas.

When it is necessary to strictly lower OH (for example, in the case of pure silica core fiber that is externally attached to the core material): A large amount of etching gas is supplied to all the nozzles 20.

[Operation] (1) When it is not necessary to strictly lower OH and the main purpose is to remove stains on the surface: Rotate the central member 10. The plasma torch 14 and the nozzle 20 are moved in parallel with the central member 10. Then, the surface of the central member 10 is etched with a small amount of etching gas from, for example, one of the plasma flame 12 and the nozzle 20.

At the same time, a large amount of the sealing gas 22 is introduced from the nozzle 20 into the plasma flame 12 (a small amount of the etch gas flows from one or two of the nozzles 20). Seal gas is cheap N ₂
The sealing gas 22 does not need to use a large amount of expensive etch gas (gas containing fluorine such as SF ₆ ) and flows so as to wrap around the high temperature portion 11 of the central member 10 directly heated by the plasma flame 12, Hot part
Isolate 11 from the open air. Therefore, moisture in the atmosphere is prevented from entering the high temperature portion 11 of the central member 10.

(2) Strictly low OH is required: Since the etching gas 22 which also serves as a sealing gas is sent into the plasma flame 12 from the outside by a large number of nozzles 20 (instead of flowing with the plasma generating gas). There is no concern that the plasma flame will become unstable even if a large amount is flown.

If a large amount of etching gas 22 that also serves as a seal gas is flowed,
As in the case of the above etching, the hot part of the central member 10
Isolates 11 from the outside air to prevent moisture in the atmosphere from entering the high temperature portion 11 of the central member 10, and because the etching rate is very fast, it is faster than the moisture in the atmosphere entering the rod. The glass can be scraped (or close to it), allowing etching with very little OH diffusion.

(3) Deposition of glass fine powder: After the above-described surface treatment of the central member 10, glass fine powder is deposited on the outside of the central member 10 by a normal VAD burner 24.

Although any combustion gas may be used for the flame of the burner 24, an anhydrous CO flame is preferably used when strictly considering low OH.

After the deposition of the fine glass powder, sintering is performed to obtain a preform, which is spun into an optical fiber.

[Examples] (1) In the case of a fiber base glass rod in which a part of the core and the clad are made: By the VAD method, fully dehydrated and extremely high-purity pure quartz having an outer diameter of 7 mmφ and a length of 500 mm is used. The central portion of the SM fiber serving as the base was produced and used as the central member 10.

The plasma flame used was a mixed plasma of Ar and O ₂ , with an oscillation output of 30 kW and a frequency of 3.5 MHz. Flow rate is 30 / min for Ar and O ₂
10 / min.

Twelve nozzles 20 are arranged around the plasma torch 14. Sealing gas N ₂ at 30 / min for 11 of them, 1 left
SF ₆ as an etching gas was fed into the book at a rate of 1 / min to perform flame polishing.

During this time, the plasma torch 14 and the nozzle were moved at a speed of 2500 mm / h.
I made 20 round trips.

After that, the plasma flame was extinguished, the feeding of the sealing gas and the etching gas was also stopped, and SiCl ₄ was introduced into the oxyhydrogen flame together with the carrier gas to deposit glass fine powder.

At this time, H ₂ 12.8 / min, O ₂ 9 / min, seal gas (Ar) 1 / min, and raw material carrier Ar 300 cc / min were flown into the burner at a moving speed of 800 mm / h.

This was sintered in a chlorine atmosphere or, if necessary, in a fluorine atmosphere to obtain a glass rod having an outer diameter of 40 mmφ.

This was further stretched, the same process was performed, the outer diameter was adjusted, and it was set as a SM fiber rod.

This was spun into an optical fiber.

The fiber thus obtained has a fiber diameter variation of ± after spinning.
The average rupture length was about 30 km, and the 2% proof test was very good.

(2) When externally mounted on the pure water quartz glass rod of the core part: By the VAD method, fully dehydrated and extremely high purity pure quartz with an outer diameter of 6 mmφ and a length of 500 mm was prepared, and this was used as the central member.
It was 10.

The plasma flame used was a mixed plasma of Ar and O ₂ , with an oscillation output of 30 kW and a frequency of 3.5 MHz. The flow rate is Ar 30 / min. O ₂ is
10 / min.

Twelve nozzles 20 are arranged around the plasma torch 14. SF ₆ also serving as a sealing gas is sent to them at 20 / min,
Etched.

During this time, plasma torch 14, nozzle 2 at a speed of 2500 mm / h
One round trip of 0.

After that, the plasma flame was extinguished, the feeding of SF ₆ was also stopped, and SiCl ₄ was introduced into the oxyhydrogen flame together with the carrier gas to deposit fine glass powder.

At this time, H ₂ 12.8 / min, O ₂ 9 / min, seal gas (Ar) 1 / min, and raw material carrier Ar 300 cc / min were flown into the burner at a moving speed of 800 mm / h.

This was sintered in a fluorine atmosphere to obtain a glass rod having an outer diameter of 40 mmφ.

This was further stretched in an electric furnace and the steps described above were performed to adjust the outer diameter to obtain a rod having a core / clad ratio of 1:12.

This was spun into an optical fiber.

The fiber thus obtained has a very low loss of 0.18 dB / km at a wavelength of 1.55 μm and an OH at a wavelength of 1.38 μm.
The peak loss was 0.9 dB / km, and the one with very little OH contamination was obtained.

Further, since no bubble was generated at the boundary between the central member 10 and the fine glass powder, the fiber diameter variation after spinning was not more than ± 1 μm at all.

[Advantages of the Invention] (1) Since flame polishing can be performed while sending a large amount of sealing gas 22, air is blocked and OH is prevented from entering.

(2) When the etching gas also serves as the sealing gas, the high temperature rod portion is shielded from the atmosphere, and a large amount of etching gas can be sent without impairing the stability of the anhydrous flame, which enables high-speed etching. Therefore, even if OH enters from the outside air, etching can be performed faster than the diffusion rate, and OH diffusion is extremely small.

[Brief description of drawings]

FIG. 1a is a schematic elevation view of an example of an apparatus used for carrying out the present invention, FIG. 1b is its plan view, and FIG. 1c is a side view seen from the right side. 10: central member, 11: high temperature part 12: anhydrous flame, 14: plasma torch 16: high frequency coil, 20: nozzle 22: sealing gas, 24: burner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryozo Yamauchi, 1440 Rokuzaki, Sakura City, Chiba Prefecture, Sakura Factory, Fujikura Cable Co., Ltd. 56) References JP-A 63-25241 (JP, A) JP-A 1-96040 (JP, A)

Claims (2)

[Claims] 1. A method of manufacturing an optical fiber including a step of depositing glass fine powder on a glass central member, wherein the central member is placed from below in an anhydrous flame before the step of depositing the glass fine powder. In addition to heating and flame-polishing at that time, at that time, a sealing gas is introduced into the flame from a plurality of nozzles from around the anhydrous flame, and the heated portion of the central member is heated by the gas to the surrounding atmosphere. A method of manufacturing an optical fiber, in which flame polishing is performed while blocking from the inside. 2. The method for producing an optical fiber according to claim 1, wherein at least a part of the sealing gas also serves as an etching gas.