JPH11268926A - Production of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber preform so as to stably deposit soot from burner flame. SOLUTION: In this optical fiber preform-producing method for producing a soot preform 40 by depositing soot from burners 31 to 33 in a chamber 10, an inlet port 100A is provided in a part of a chamber 10 and outside air is introduced from the inlet port 100 to produce directed stream in the chamber 10. Thereby, occurrence of flickering, etc., of flames 31a, 32a and 33a of burners 31 to 33 is suppressed and the stabilization can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform in which soot, which is porous glass fine particles from a burner flame, is stably deposited.

[0002]

2. Description of the Related Art To manufacture a preform for an optical fiber (a so-called transparent optical fiber preform after sintering), first, a VA is used.
It is necessary to produce a soot preform (a so-called porous optical fiber preform before sintering) made of a porous glass fine particle laminate by the method D or the like, and to make it transparent.

Conventionally, in manufacturing the soot preform, as shown in FIG. 9, a rotating dummy rod (seed rod) 20 is generally hung in a chamber 10 and a plurality of burners 31, 32, 33 are provided at the lower end thereof. Flame 31a from
The soot preform 40 is grown by spraying 32a and 33a to attach and deposit soot. In addition,
The burner 31 is a core soot forming burner.
33 is a burner for forming a clad soot.

In this soot deposition, each burner 3
The flames 31a, 32a, 33a from 1, 32, 33 need to be burned and sprayed in a stable state.

For example, the flames 31a, 32a, 33a
If the soot becomes unstable due to fluctuations in the airflow in the chamber 10 or the like, uniform soot deposition cannot be obtained over the entire length of the soot preform 40. However, there is a problem that the characteristics vary. There is also a problem that the soot deposition efficiency is reduced due to the swing of the flames 31a, 32a, 33a. Further, while the amount of soot adhering to the wall surface in the chamber 10 increases, the adhering soot peels off and is deposited again on the soot preform 40 side. There were also problems such as becoming.

For this reason, in the chamber 10, it is necessary to pay close attention so that the flames 31a, 32a and 33a are stabilized without being shaken.

[0007]

However, in the conventional method shown in FIG. 9, the chamber 10 does not have an opening (suction port) for actively introducing outside air or the like from the outside, and the burners 31, 32, 33 are not provided. Flames 31a, 32a, 33a
What flows by the suction force from the exhaust port 11 side of the chamber 10 and passes while depositing soot on the soot preform 40 side, and guides the combustion gas and undeposited soot to the exhaust port 11 side and exhausts it. Met.

The suction force on the exhaust port 11 side is generally generated by an exhaust pump or an exhaust gas processing device connected thereto, and the suction force of the chamber 10 causes A small amount of outside air is sucked from the gap δ between the lid 12 a of the portion 12 and the dummy rod 20.

Therefore, once theoretically, the exhaust port 11
Due to the suction force on the side and the supply of the flame gas to the burners 31, 32, 33, the burners 31, 32,
An airflow is generated from the flames 31a, 32a, and 33a of the fuel cell 33 to the exhaust path 11, and the airflow is usually set to be weak. That is, if the suction force on the exhaust port 11 side is too strong, the flames 31a, 32a,
This is because 33a is drawn in more than necessary and becomes deformed or deformed, which is not preferable in soot deposition.

However, if the flow of the airflow in the chamber 10 is weak, the airflow tends to fluctuate in the chamber 10 due to slight disturbance or the like. Swings and becomes unstable, causing various adverse effects.

Therefore, the present inventor has provided an intake port (opening) for positively introducing outside air or the like from outside to a part of the chamber, so that an air flow directed into the chamber (for example, exhaust air from the burner flame side). It was found that when the airflow having a directional direction toward the mouth was positively generated, the flame could be stabilized and good results could be obtained.

The present invention has been made in view of the above point of view, and a method of manufacturing an optical fiber preform in which an intake port is provided in a part of a chamber so as to generate a directed air flow in the chamber. Is to be provided.

[0013]

According to a first aspect of the present invention, there is provided a method of manufacturing an optical fiber preform for manufacturing a soot preform by depositing soot from a burner in a chamber. A method for manufacturing an optical fiber preform, characterized in that an air inlet is provided so as to generate a directed air flow in the chamber.

According to a second aspect of the present invention, there is provided a method of manufacturing an optical fiber preform for manufacturing a soot preform by depositing soot from a burner in a chamber. A method for manufacturing an optical fiber preform, characterized in that an opening is provided to generate a directed airflow in the chamber.

According to a third aspect of the present invention, an air flow control guide comprising a plate-like piece for directing an intake air flow is provided on the inside or outside of the suction port portion of the chamber, or on both the inside and outside. The method for producing an optical fiber preform according to claim 1 or 2, wherein:

[0016]

1 and 2 show an example of an apparatus system for carrying out a method for manufacturing an optical fiber preform according to the present invention. This device system is also basically similar to that shown in FIG. 9 except that a part of the chamber 10, that is, a side opposed to the exhaust port 11 side, and a horizontally long intake port 100 </ b> A is provided above the burner 33. Is different.

As shown in FIG. 3, an air flow control guide 110 composed of a plate-like piece that is opened upwardly inclined is provided outside the intake port 100A.
As shown in FIG. 4, an airflow control guide 120 formed of a plate-like piece bent downward and formed in an L-shape is provided.

With this configuration, during operation of the present system, outside air such as air outside the chamber 10 (including an inert gas other than air) is obliquely controlled as shown by an arrow A in FIG. The guides 110 and the L-shaped airflow control guides 120 are directed downward by the guiding action of each of the burners 33 and 3.
2, 31 side, each burner 33, 32,
In the form of passing through the soot preform 40 from near the tip of 31, it reaches the exhaust port 11 side, and each burner 33, 32,
It acts on the 31 flames 31a, 32a, 33a as directed airflow (directional airflow).

Of course, the strength of the air flow directed by the outside air is adjusted so that the amount of the outside air introduced is appropriately adjusted so that the flames 31a, 32a, and 33a do not become unstable due to the swinging of the flames. Set the strength to enhance the original flow. When the original flow of the flame is smoothly enhanced in this way, even if airflow fluctuations are likely to occur in the chamber 10 due to a disturbance factor due to any cause, a good fluctuation suppressing effect is obtained, and as a result, a stable flame is obtained. 31
a, 32a and 33a are obtained.

Further, in order to smoothly introduce the outside air from the intake port 100A, the internal pressure in the chamber 10 may be suppressed to be slightly lower than the pressure of the outside air. For example, the pressure inside the chamber is set to be lower than the external force by about 25 Pa, although the pressure varies slightly depending on the model of the chamber 10.
Monitoring is always performed using 0 or the like.

Incidentally, the present inventor carried out the method of manufacturing an optical fiber preform according to the present invention by using the apparatus system shown in FIG. FIG. 5 shows the mode field diameter (MFD note) in the longitudinal direction of the optical fiber obtained as a result. In other words, it can be seen that the fluctuation range of the MFD is small (difference between the maximum value and the minimum value = 0.18 μm), and the fluctuation of the flame is effectively suppressed.

On the other hand, for reference, a conventional method for manufacturing an optical fiber preform is carried out by the apparatus system shown in FIG. In the longitudinal direction of the optical fiber obtained
FIG. 6 shows the state of D. That is, MFD
Is large (difference between the maximum value and the minimum value = 0.46 μm).
m), it can be seen that the flame sway and the like are not sufficiently suppressed.

When the method of manufacturing an optical fiber preform according to the present invention was carried out by the apparatus shown in FIG. 1, the soot deposition efficiency was about 78%. Further, in the optical fiber obtained from the soot preform 40, 1
Only two bubbles in 00 km were found, and it was also found that the adhesion of soot to the inner wall surface of the chamber 10 was effectively suppressed.

On the other hand, when the conventional method for manufacturing an optical fiber preform is performed by the apparatus shown in FIG.
The soot deposition efficiency was about 69%. Further, in the optical fiber obtained from the soot preform 40, as many as 112 bubbles were found out of 100 km and it was found that the adhesion of the soot to the inner wall surface of the chamber 10 was hardly suppressed.

FIG. 7 shows another example of an apparatus system for carrying out the method of manufacturing an optical fiber preform according to the present invention. This device system is also basically similar to that of FIG. 9 described above, except that a part of the chamber 10, that is, a side opposed to the exhaust port 11 side, and a horizontally long intake port 100 </ b> B Is different.

Inside the intake port 100B, there is provided an air flow control guide 130 composed of a plate-like piece that is opened upward and inclined.

With this configuration, during operation of the present system, outside air such as air outside the chamber 10 (including inert gas other than air) is obliquely controlled as shown by an arrow B in FIG. The guide 130 guides upward and is introduced into the upper side of the chamber 10, passes through the soot preform 40, and reaches the exhaust port 11 side, where the flames 31 a and 31 a of the burners 33, 32 and 31 are turned. 32a, 33a
Acts as an airflow directed from above. Therefore, substantially the same effects as in the case of the apparatus system shown in FIGS. 1 and 2 can be obtained.

Incidentally, the present inventor carried out the method of manufacturing an optical fiber preform according to the present invention using the apparatus system of FIG. In the longitudinal direction of the optical fiber obtained
The fluctuation range of D was small (difference between maximum value and minimum value = 0.2
3 μm). From this, it can be seen that the sway of the flame is effectively suppressed.

When the method of manufacturing an optical fiber preform according to the present invention was carried out using the apparatus shown in FIG. 7, the soot deposition efficiency was about 74%. Further, in the optical fiber obtained from the soot preform 40, 1
Only one bubble per 00 km was found, and it was also found that the adhesion of soot to the inner wall surface of the chamber 10 was effectively suppressed.

FIG. 8 shows still another example of an apparatus system for performing the method of manufacturing an optical fiber preform according to the present invention. This device system is also basically similar to that of FIG. 9 described above, except that a part of the chamber 10, that is, a side opposed to the exhaust port 11 side, and a horizontally long intake port 100 Is different.

Inside the intake port 100C, there is provided an air flow control guide 140 made of a plate-like piece which is opened downwardly inclined.

With this configuration, during operation of the apparatus system, outside air such as air outside the chamber 10 (including an inert gas other than air) is obliquely provided as shown by an arrow C in FIG. Due to the guiding action of 140, it is directed downward to the bottom side of the chamber 10, passes through the soot preform 40 and reaches the exhaust port 11 side, and the flames 31 a, 32 a of the burners 33, 32, 31. , 33a
Acts as an airflow directed from below. Therefore, substantially the same effects as in the case of the apparatus system shown in FIGS. 1 and 2 can be obtained.

By the way, the present inventor carried out the method of manufacturing an optical fiber preform according to the present invention by using the apparatus system of FIG. 8 to obtain a soot preform 40, which was made transparent, and then converted into an optical fiber. MF of the optical fiber obtained in the longitudinal direction
The fluctuation range of D was small (difference between maximum value and minimum value = 0.2
5 μm). From this, it can be seen that the sway of the flame is effectively suppressed.

When the method for manufacturing an optical fiber preform according to the present invention was carried out by the apparatus shown in FIG. 8, the soot deposition efficiency was about 77%. Further, in the optical fiber obtained from the soot preform 40, 1
Only five bubbles were found out of 00 km, and it was also found that the adhesion of soot to the inner wall surface of the chamber 10 was effectively suppressed.

In each of the above embodiments, the intake port 10
Although one of OACs is provided on the side of the chamber 10 opposite to the exhaust port 11 side, the present invention is not limited to this, and is configured to generate a desired directed airflow in the chamber 10. If necessary, a plurality may be provided if necessary.
In addition, the present invention is not limited to the side facing the exhaust port 11 side, and may be provided on an adjacent side surface (one or both sides may be provided). It is also possible.

[0036]

As is clear from the above description, the following excellent effects can be obtained by the method of manufacturing an optical fiber preform according to the present invention.

(1) Since an air inlet is provided in a part of the chamber, outside air can be appropriately introduced into the chamber.
In addition, it is possible to appropriately adjust the airflow in the chamber so as to have a desired direction. Therefore, an effect such as enhancing the original flow of the flame can be obtained, and even if there is a disturbance factor due to some cause, the air flow fluctuation in the chamber can be effectively suppressed, and a stable burner flame can be obtained.

As a result, uniform soot deposition is obtained over the entire length of the soot preform, and when the optical fiber is later formed into an optical fiber, the characteristic fluctuation in the longitudinal direction of the optical fiber can be effectively suppressed.

(2) Further, since the burner flame is stabilized as described above, the soot deposition efficiency is improved and the production cost can be reduced.

(3) Further, since the burner flame is stabilized as described above, the adhesion of soot to the inner wall surface of the chamber can be effectively suppressed, and the generation of air bubbles when an optical fiber is formed is greatly reduced. Can be.

(4) Since the burner flame is stabilized as described above, the temperature fluctuation of the surface of the soot preform which is the target is reduced and stabilized, so that cracking of the soot preform during manufacturing is also effective. Can be prevented.

(5) In addition, as a result of stabilizing the burner flame, soot adhesion to the inner wall surface of the chamber is effectively suppressed. In a method for manufacturing an optical fiber preform in which imaging is performed and image processing is performed to control the optical fiber preform, the transparency is improved, so that improvement in control performance can be expected.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing an example of an apparatus system for carrying out a method for manufacturing an optical fiber preform according to the present invention.

FIG. 2 is a cross-sectional view of the device system of FIG.

FIG. 3 is a partial perspective view from the outside of an intake port in the apparatus system of FIG. 1;

FIG. 4 is a partial perspective view from the inside of an air inlet in the apparatus system of FIG. 1;

FIG. 5 is a graph showing a variation range of an MFD of an optical fiber obtained by a method of manufacturing an optical fiber preform according to the present invention.

FIG. 6 is a graph showing a variation range of an MFD of an optical fiber obtained by a conventional method of manufacturing an optical fiber preform.

FIG. 7 is a partial longitudinal sectional view showing another example of an apparatus system for performing the optical fiber preform manufacturing method according to the present invention.

FIG. 8 is a partial longitudinal sectional view showing another example of an apparatus system for performing the method of manufacturing an optical fiber preform according to the present invention.

FIG. 9 is a partial longitudinal sectional view showing an apparatus system for implementing a conventional optical fiber preform manufacturing method.

[Explanation of symbols]

 Reference Signs List 10 Chamber 11 Exhaust port 20 Dummy rod (seed rod) 31, 32, 33 Burner 31a, 32a, 33a Flame 40 Soot preform 50 Differential pressure gauge 100A-C Inlet port 110-140 Air flow control guide

Claims (3)

[Claims] 1. A method of manufacturing an optical fiber preform for manufacturing a soot preform by depositing soot from a burner in a chamber, wherein a part of the chamber is provided with an air inlet and is directed into the chamber. A method for producing an optical fiber preform, characterized in that an airflow is generated. 2. A method of manufacturing an optical fiber preform for manufacturing a soot preform by depositing soot from a burner in a chamber, wherein an intake port is provided on a side of the chamber opposite to an exhaust port side, and the chamber is provided with an intake port. A method for manufacturing an optical fiber preform, characterized in that a directed air flow is generated therein. 3. An air flow control guide comprising a plate-like piece for directing an intake air flow inside or outside the air inlet portion of the chamber, or on both the inside and the outside thereof. 3. The method for producing an optical fiber preform according to 2.