JPH107430A - Production of preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the productivity of the preform for an optical fiber by depositing fine particles of glass to the soot rod in both directions back and forth by reciprocating a plurality of burners. SOLUTION: The target rod 1 is vertically set and rotated, a plurality of burners A, B, C are vertically reciprocated, as they are vertically arranged at a certain interval and their jetting nozzles are directed toward the target rod 1. The moving rate of the burners are made to differ on ascending and on descending. The lower moving rate is set to >=25mm/sec, while the higher rate is to >=450mm/sec. Within the range of the moving rate, the deposition rate of the fine particles of glass per unit time becomes equal when the burner ascends to that when descending and the mutual interference, when the burners cross each other. Thus, fine particles of glass soot can be deposited on both ascending and descending of the burners.

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.

[0002]

2. Description of the Related Art As one method of manufacturing an optical fiber preform, a glass fine particle generator is reciprocated along a rotating target rod, and glass fine particles generated by the glass fine particle generator are deposited on the target rod. Several methods are known. As a device for generating fine glass particles, a device is generally used in which a raw material gas such as silicon tetrachloride is introduced into an oxygen / hydrogen flame of a burner to generate fine glass particles by flame hydrolysis. A torch or the like may be used. A glass rod, a refractory mandrel, or the like is used as the target rod. The porous optical fiber preform manufactured by this method is used for manufacturing an optical fiber after it is turned into a transparent glass by heating.

In order to increase the deposition efficiency of glass fine particles and increase the productivity of an optical fiber preform by this method, it is effective to use a plurality of glass fine particle generators. Conventionally, when a plurality of glass particle generators are used, when moving each glass particle generator from one end of the target rod to the other end, the outlet is slowly moved toward the target rod. When returning from the other end to the one end, a method has been proposed in which the outlet is quickly returned without directing the outlet toward the target rod (Japanese Patent Publication No. 5-57216).

[0004]

However, in this method,
When each of the glass particle generators returns from the other end to the one end, it becomes a wasteful time that does not contribute to the deposition of the glass particles. Therefore, there is a limit in improving the productivity.

[0005] When a plurality of glass fine particle generators are used to deposit glass fine particles both in the forward path and in the return path, it is difficult to avoid mutual flame interference when the glass fine particle generators pass each other. In particular, when the target rods are arranged horizontally, the glass particle generators pass each other up and down, so that flame interference is likely to occur. In addition, in the conventional manufacturing method, the moving speed of the glass fine particle generator when depositing the glass fine particles is low. The temperature of the produced glass particles becomes too high, and crystals are formed on the surface of the base material, so that good quality cannot be secured.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an optical fiber preform having excellent productivity, in which glass particles can be deposited using a plurality of glass particle generators in both the forward path and the return path.

[0007]

The moving speed of the glass particle generator when the glass particle generator is moved along the target bar to deposit the glass particles is about 2.5 mm / sec in the conventional method. (Tokuhei 5-572
No. 16). The present inventors have set the target rod vertically, and set the moving speed of the glass particle generator significantly higher than before so as to minimize the interference of the flame when the glass particle generators pass each other. The state of deposition was examined. As a result, the following became clear.

[0008] Even if the moving speed of the glass fine particle generator is increased, if the supply amounts of the fuel gas and the raw material gas to the glass fine particle generator are adjusted to match the speeds, it is possible to obtain a deposition rate equivalent to the conventional one. Is possible. When the target rod is arranged vertically, if the relative speed when the ascending glass particle generator and the descending glass particle generator pass each other is increased to a certain degree or more, the interference of the flame at the time of passing will be a problem-free level .

The present invention has been basically made based on such findings. That is, the manufacturing method of the optical fiber preform of the present invention, the target rod is vertically arranged and rotated, a plurality of glass particle generators, spaced apart in the vertical direction, with the outlet facing the target rod,
It is reciprocated vertically at different positions in the circumferential direction, and the supply conditions of the fuel gas and the raw material gas to the glass fine particle generator are the same at the time of ascending and descending, and the moving speed and lowering when the glass fine particle generator ascends The moving speed at the time of moving is such that when the ascending glass particle generator and the descending glass particle generator pass each other, a relative speed that does not cause a problem of mutual interference is obtained, and the glass per unit time when ascending and descending The method is characterized in that the amount of deposited fine particles is set to be substantially the same, whereby glass fine particles are deposited both when the glass fine particle generator rises and falls.

According to an experiment, the relative speed at the time of passing each other should be 475 mm / sec or more so that mutual interference does not become a problem when the ascending glass particle generating device and the descending glass particle generating device pass each other. I just found out. Therefore, when the moving speed of the glass particle generator is the same at the time of ascending and descending, 23
What is necessary is just to make it 7.5 mm / sec or more. This moving speed is about 100 times faster than the conventional method.

[0011] Results of examining the variation in the outer diameter of the porous optical fiber preform when the moving speed of the glass particle generating apparatus is set to various levels and the target rod is arranged vertically and horizontally. Was as shown in FIG. From this result, it was confirmed that when the target rod was arranged vertically, the fluctuation of the outer diameter could be significantly reduced.

By the way, if the moving speed of the glass particle generator is made much higher than before, the glass particles can be deposited both at the time of ascending and at the time of descent, and efficient production becomes possible. When the moving speed at the time of descent is the same as that at the time of descent, the following problems were found. That is, the density of the glass fine particle deposition layer is reduced, and cracks are easily generated in the base material.

[0013] Therefore, the moving speed of the glass particle generating apparatus is made different between ascending and descending (moving speed is increased in one of the ascending and descending directions, and decreased in the other), and as a result of further experiments, The findings as shown in FIG. 5 were obtained. The graph of FIG. 5 shows that the higher moving speed of the glass fine particle generator is set to be 10 times the lower moving speed, and that the lower the moving speed, the larger the amount of the glass fine particles deposited per unit time is. The gas and fuel gas supply amounts are set (the gas supply conditions are the same even at the higher moving speed). For each moving speed, the amount of glass particles deposited per unit time at the higher moving speed is lower. 7 is a plot of a ratio of the moving speed to the amount of glass particles deposited per unit time. According to this result, when the moving speed of the glass particle generator is increased to a certain level or more (the lower moving speed is set to 25 mm /
It can be seen that there is a region where the amount of glass particles deposited per unit time hardly changes even if the moving speed of the glass particle generator is changed between rising and falling. It was also found that in this region, the density of the glass fine particle deposition layer did not decrease and no cracks occurred. Therefore, if glass particles are deposited in this area on both the outward path and the return path, extremely efficient deposition can be performed.

Therefore, in the present invention, the moving speed of the glass fine particle generating device is made different between the rising time and the falling time,
It is preferable to set the lower moving speed so that the amount of glass particles deposited per unit time is substantially the same as that of the higher moving speed. In this case, the lower moving speed is 25 mm / sec or more, and the higher moving speed is 450 mm / sec.
mm / sec or more (the relative speed at the time of passing each other is 475 mm / sec or more).

Next, FIG. 6 shows the result of examining the outer diameter variation of the obtained porous optical fiber preform when the moving speed of the glass fine particle generator is made different between the rising time and the falling time. . According to this, the lower moving speed is 25 mm /
It is preferable that the higher moving speed be 500 mm / sec.

[0016]

1 and 2 show an embodiment of the present invention. In this embodiment, the target rod 1 is arranged vertically, and three burners A, B, and C are attached to the target rod 1.
It is reciprocating up and down with facing. Reference numeral 2 denotes a glass fine particle deposition layer deposited on the surface of the target rod 1. The upper end of the target rod 1 is gripped by a chuck 3 and rotated by a motor (not shown). The lower end of the target rod 1 is held at a fixed position by an anti-sway guide 4.
FIG. 1A shows a state where the burners A, B and C rise, FIG. 1B shows a state where the burners A descend, and FIG. 2 shows the positions of the burners A, B and C in the circumferential direction. It is the state seen from.

The three burners A, B, and C move up and down at intervals in both the ascending and descending directions.
FIG. 3 shows the movement. The burners A, B and C rise at a constant speed which is relatively slow when ascending, and descend at a constant speed which is considerably faster than when ascending. The source gas and the fuel gas are supplied to the burners A, B, and C under the same conditions when ascending and descending. That is, the conditions of flame hydrolysis are the same when the moving speed is high and low. The interval between the burners A, B and C is kept constant by adjusting the stop time when the glass particle generator turns around at the upper end and the lower end. The intervals between the burners A, B and C at the time of ascent and at the time of descent may be the same or different. However, in the normal case, the intervals at the time of descent (when the moving speed is high) are wider.

In this method, since the burners A, B, and C temporarily stop when turning at the upper end and the lower end, the deposition density of the glass fine particles becomes high in that portion, and the optical fiber preform Can not be used as For this reason, the direction change of the burners A, B, and C is performed at a place where the diameter of the burner is overrun by 1/2 or more from the limit of the effective deposition range (the range used as the optical fiber preform).
In this way, the glass particle deposition density within the effective deposition range becomes constant.

When the burners A, B and C are reciprocated,
Passing of the ascending burner and the descending burner occurs. It has been confirmed by experiments that the influence of the flame interference at the time of passing each other decreases as the relative speed of the passing burners increases, and no problem occurs when the relative speed becomes 475 mm / sec or more. Therefore, when the lower moving speed than the graph of FIG. 5 is set to 25 mm / sec,
The higher moving speed may be set to 450 mm / sec or more. From FIG. 6, the higher moving speed is 50.
It is preferable to set the speed to 0 mm / sec or more.

[0020]

EXAMPLE A quartz glass rod for a core having a diameter of 30 mm was used as a target rod, and the rod was vertically arranged at 150 rpm.
And rotated. Three oxyhydrogen burners were reciprocated up and down toward the target rod. The reciprocating range is 1500 mm. The diameter of the burner is 60 mm, and the distance from the tip of the burner to the surface of the target rod is 120 m.
m. Each burner receives 200 hydrogen from the gas supply.
1 liter / minute and 80 liter / minute of oxygen were supplied to generate an oxyhydrogen flame. 100 g / min of silicon tetrachloride was introduced into the flame from a gas supply device, and SiO.
_Two glass particles were produced. The glass particles were deposited on a target rod to produce a porous optical fiber preform.

First, the moving speed of the burner was increased and lowered, and the moving speed was changed to examine the amount of glass particles deposited per unit time. As a result, it was found that even if the moving speed was significantly increased, the amount of glass particles deposited per unit time could be obtained. The flame of the burner spreads vertically due to the buoyancy of hydrogen. However, since the moving direction of the burner is the vertical direction, the interference of the flame when the burners pass each other is relatively small, and the relative speed is 475 mm / sec or more, which is no problem It was confirmed that.

From this result, the moving speed of each burner is
The same 250 mm / sec was set for both ascending and descending (gas supply conditions to the burner were the same as above), and an optical fiber preform was manufactured. As a result, the length was 1500 mm and the outer diameter was 220
mm base metal could be manufactured in about 10 hours.

Next, the moving speed of the burner is made different between the ascending and descending times, and the higher moving speed is set to one of the lower moving speeds.
The supply conditions of the source gas and the fuel gas are set so that the amount of glass particles deposited per unit time is maximized when the moving speed is lower (the gas supply condition is also higher when the moving speed is higher). 5) For each moving speed, as a result of examining the amount of glass fine particles deposited per unit time at the higher moving speed and the amount of glass fine particles deposited per unit time at the lower moving speed, FIG. Such a result was obtained.

From these results, the moving speed of each burner was calculated as
An ascending 25 mm / sec and a descending 475 mm / sec were set (gas supply conditions to the burner were the same as above), and an optical fiber preform was manufactured. As a result, a base material having a length of 1500 mm and an outer diameter of 220 mm could be manufactured in about 10 hours.

[0025]

As described above, according to the present invention, a plurality of glass fine particle generators can be reciprocated along the target rod, and glass fine particles can be deposited on both the forward path and the return path. Can greatly improve productivity.

[Brief description of the drawings]

FIG. 1 is a front view showing a state in which three burners are rising, and FIG. 1B is a state in which three burners are falling, in the manufacturing method of the present invention.

FIG. 2 is a plan view showing an arrangement of three burners around a target rod.

FIG. 3 is a graph showing a state in which three burners reciprocate vertically.

FIG. 4 is a graph showing the variation in the outer diameter of the optical fiber preform when the target rod is arranged vertically and horizontally.

FIG. 5 is a graph showing a change in the amount of deposited glass particles when the moving speed of the burner is different between when the burner moves up and when it moves down.

FIG. 6 is a graph showing the presence or absence of a change in the outer diameter of the optical fiber preform when the moving speed of the burner is different between when ascending and when ascending.

[Explanation of symbols]

 1: Target rod 2: Glass fine particle deposition layer A, B, C: Burner

Claims (5)

[Claims] 1. A target rod is vertically arranged and rotated, and a plurality of glass particle generators are vertically spaced at different positions in a circumferential direction while leaving an outlet facing the target rod at intervals in the vertical direction. The conditions for supplying the fuel gas and raw material gas to the glass particle generator are the same both when rising and lowering.The moving speed when the glass particle generator rises and when moving down increases. The relative speed is such that mutual interference is not a problem when the falling glass particle generator and the descending glass particle generator pass each other, and the amount of glass particles deposited per unit time during ascending and descending is substantially the same. The optical fiber motherboard is characterized in that glass particles are deposited both when the glass particle generator rises and when it descends. The method of manufacturing the material. 2. The moving speed of the glass fine particle generating device is the same both when ascending and when descending, and the relative speed when the ascending glass fine particle generating device and the descending glass fine particle generating device pass each other is 475 mm / sec or more. The method for producing an optical fiber preform according to claim 1, wherein 3. The moving speed of the glass fine particle generator differs between rising and lowering, and the amount of glass fine particles deposited per unit time is substantially the same as when the lower moving speed is the higher moving speed. The method for producing an optical fiber preform according to claim 1, wherein the optical fiber preform is set to be as follows. 4. The method of manufacturing an optical fiber preform according to claim 3, wherein the lower moving speed is at least 25 mm / sec, and the higher moving speed is at least 450 mm / sec. 5. The direction change of the glass fine particle generator at the upper end and the lower end is performed when the glass fine particle generator overruns at least 1/2 of the diameter of the glass fine particle generator from the limit of the effective deposition range. The method for producing an optical fiber preform according to any one of claims 1 to 4, wherein: