JP3816268B2 - Method for producing porous glass base material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a porous glass preform, and more particularly, to a method for producing a porous glass preform used as an optical fiber or various optical materials.
[0002]
[Prior art]
Conventionally, a gas phase axis method (VAD method) is known as a method for producing a porous glass base material (hereinafter simply referred to as a porous base material). In this VAD method, a combustion gas and a glass raw material gas such as silicon tetrachloride (hereinafter simply referred to as a raw material gas) are introduced into a burner for synthesizing fine glass particles in a reaction vessel to perform a flame hydrolysis reaction or an oxidation reaction. Then, the generated glass fine particles are sprayed onto a starting base material (target) that is slowly pulled up while rotating, and are attached to and deposited on the surface of the starting base material (target), thereby producing a cylindrical porous base material.
In this method, in order to make the refractive index distribution of the optical fiber preform uniform in the longitudinal direction, the deposition position of the glass particles is detected using a laser beam or a CCD camera, etc., and the raw material gas is used so that the deposition position is constant. Generally, a method of controlling the flow rate is adopted.
[0003]
When correcting the glass raw material in such a manufacturing method, it is desirable to return to the reference pulling speed as quickly as possible in order to reduce the fluctuation of the refractive index distribution. That is, when there is a large fluctuation in the pulling speed, it is necessary to perform a large raw material correction correspondingly. However, in recent years, as efforts to improve productivity have been made, as the pulling speed of the base material is increased, cracks in the base material due to the correction of the raw material have frequently occurred.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to overcome the above-mentioned disadvantages that occur when a porous preform is produced at high speed, and to produce a glass body that does not crack during the production of the porous preform and has stable characteristics in the longitudinal direction. Another object of the present invention is to provide a method for producing a porous base material.
[0005]
[Means for Solving the Problems]
The present inventors investigated the cause of cracking on the surface of the porous base material during production, and the pulling rate changed suddenly just before the cracking occurred. It was found that a large increase / decrease correction was performed. Furthermore, it has been found that when the supply amount of the source gas is greatly increased or decreased, the bulk density locally changes greatly and cracks are generated. Based on these findings, further studies were conducted to complete the present invention.
[0006]
That is, in the method for producing a porous base material of the present invention, the glass raw material gas is supplied into the flame of the burner together with the fuel gas to be oxidized or flame hydrolyzed, and the generated glass fine particles are rotated at a pulling speed of 52 mm / In a method for producing a porous glass base material at a high speed by depositing it on a starting base material that is pulled up at a rate of hr or more, the starting point is that glass fine particles generated by supplying a reference amount of glass raw material gas are pulled up at a preset pulling rate. In order to detect the deposition position while depositing on the base material and control the pulling speed based on the amount of displacement from the reference deposition position, in order to return the pulling speed changed by the control to a preset pulling speed, when correcting the reference quantity the supply amount of the glass raw material gas, increasing by 10% or more with respect to the supply amount reference amount of the glass raw material gas to be determined by the amount of change in pulling speed If you are, it is characterized in that corrected by increasing or decreasing in the range of 10% or less.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in more detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an outline of a porous preform manufacturing apparatus. By feeding glass carrier gas 3 into silicon tetrachloride supply bubbler 1 and dopant supply bubbler 2 via mass flow controllers 4 and 5, silicon tetrachloride and a predetermined amount of dopant are gasified and mixed. A reaction vessel having an exhaust port 8 for supplying glass fine particles produced by a chemical reaction in the flame together with a predetermined amount of oxygen gas and hydrogen gas supplied from the combustion gas supply pipe 6 to the oxyhydrogen flame burner 7 The porous base material 12 is formed by depositing on the starting base material 11 which is accommodated in 9 and supported by the rotary pulling device 10.
During the formation of the porous base material 12, the tip of the porous base material 12 on which the glass fine particles are being deposited is monitored by the TV camera 13, so that the reference deposition position displayed on the TV display 14 is displayed from the base line 15. The amount of displacement of the position of the tip is detected. When a displacement from the reference deposition position is detected, this information is transmitted to the pulling control device 16, and the rotary pulling device 10 is operated to control the pulling speed to return to the original deposition position.
[0008]
The information on the pulling speed changed by this control is transmitted to the mass flow controller control device 17, and the amount of the raw material gas supplied to the oxyhydrogen flame burner 7 by adjusting the mass flow controllers 4 and 5 is set in advance. Adjusted to an appropriate value. This adjustment is performed by increasing or decreasing within 10% of the reference amount.
At this time, if the correction of the supply amount of the source gas exceeds 10%, the bulk density of the deposited portion is greatly changed and cracks are easily generated, and the porous base material is damaged.
When adjusting the amount of source gas, it is necessary to make the ratio of silicon tetrachloride and dopant constant, and thus a porous base material having a uniform shape and refractive index distribution can be easily obtained. Can do.
[0009]
【Example】
Hereinafter, the present invention will be described in more detail based on examples.
Example 1
Using the equipment shown in Fig. 1, the combustion gas for glass fine particle synthesis is 5 L (liter) / min for oxygen, 10 L / min for oxygen, 2 L / min for argon, 0.2 L / min for silicon tetrachloride. And germanium tetrachloride (0.2 L / min) are supplied to the burner for forming the clad, and 40 L / min for hydrogen, 25 L / min for oxygen, 7 L / min for argon, 1.0 t L / min is supplied, glass particles generated by chemical reaction in this oxyhydrogen flame are deposited on the starting substrate, the starting substrate is pulled up at a speed of 52 mm / hr , and the diameter is 150 mmφ and the length is 1,600. A porous preform of mm was formed.
[0010]
For example, when the deposition position of the porous base material is detected by a CCD camera and it is detected that the deposition position is displaced from the set deposition position (baseline), the pulling speed is changed and the displacement of the deposition position is corrected. . Next, in order to average the pulling speed every 10 minutes and return the changed pulling speed to the preset pulling speed (reference speed), the supply amount of the glass source gas is increased or decreased by 10 % or more with respect to the reference amount. If you are, corrected in the range of 10% or less of the reference quantity the flow rate of silicon tetrachloride to the core forming burner. Determination of the correction amount at this time was increased or decreased in proportion to the amount of change in speed with respect to the specified speed.
When 20 porous base materials were produced under these conditions, no cracks occurred in the base material. When the obtained porous base material was vitrified, striae due to fluctuations in the relative refractive index difference were generated one by one in two of the glass bodies. When these two production records were confirmed, the raw material was corrected by 10% at the position where the striae occurred. This is because with the correction amount of 10%, it takes time to return to the reference pulling speed, and the temperature of the deposition surface that affects the relative refractive index difference fluctuates. This striae is not preferable as a glass body for optical fibers, but before the subsequent overcladding process, the striae is deleted in advance or the glass body is marked and the fiber drawing process Therefore, it is not a big problem in terms of cost as compared with the case where the base material is cracked by a correction exceeding 10% and one base material is completely lost.
[0011]
(Comparative Example 1)
A porous base material was manufactured under the same gas conditions as in the example, but the deposition position was corrected with a correction amount slightly exceeding 10% of the flow rate of the glass material relative to the reference amount of the source gas flow rate with respect to the displacement of the deposition position. went.
When 20 porous base materials were produced under these conditions, the two base materials were cracked. Looking at this production record, it was confirmed that the raw material correction was 12% and 14%, respectively, just before the cracking occurred, and that an excessive change in the raw material supply amount caused the cracking.
(Comparative Example 2)
When the same pulling speed of 48mm / hr was produced in the same way, cracks did not occur even when the flow rate of the glass raw material was corrected to exceed 10% of the reference amount of the raw material gas flow rate . There was striae in the glass body due to the relative refractive index difference.
[0012]
【The invention's effect】
According to the method of the present invention, in order to return the pulling speed changed by the control for keeping the deposition position constant to the preset pulling speed, when the supply amount of the glass raw material gas to the burner is corrected with respect to the reference amount. in the case where the supply amount of the glass raw material gas to be determined by the amount of change in pulling speed is increased or decreased by 10% or more with respect to the reference quantity, by correcting by increasing or decreasing in the range of 10% or less, conventional, Even when the pulling speed, which was around 45 mm / hr, was raised at a high speed of 52 mm / hr or higher, the porous base material could be manufactured without cracking, and the manufacturing cost could be greatly reduced. In addition, large-scale equipment renovation work to eliminate noise that leads to incorrect control of pulling speed is not required, and stable production is possible without breaking the glass base material even if noise occurs.
[Brief description of the drawings]
FIG. 1 is a schematic view of a porous base material manufacturing apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Silicon tetrachloride supply bubbler 2 ... Dopant supply bubbler 3 ... Glass raw material carrier gas 4, 5 ... Mass flow controller 6 ... Combustion gas supply pipe 7 ... Oxyhydrogen flame burner 8 ... Exhaust port 9 ... Reaction container
10 ... Rotary pulling device
11 ... Starting material
12 ... Porous matrix
13 ... TV camera
14 ... TV display
15 ... Baseline
16 ... Lifting control device
17 ... Mass flow controller controller

Claims (1)

Glass raw material gas is supplied into the burner flame together with the fuel gas to cause oxidation or flame hydrolysis reaction, and the generated glass fine particles are deposited on the starting substrate that is pulled up while rotating to pull up the porous glass base material at a speed of 52 mm. In a method of manufacturing at or above, the deposition position is detected while depositing glass fine particles generated by supplying a reference amount of glass raw material gas on a starting substrate that is pulled up at a preset pulling rate so that the deposition position becomes constant. In addition, after controlling the pulling speed based on the amount of displacement from the reference deposition position, in order to return the pulling speed changed by the control to a preset pulling speed, the supply amount of the glass raw material gas to the burner is set to the reference amount. when correcting for, when the supply amount of the glass raw material gas to be determined by the amount of change in pulling speed is increased or decreased by 10% or more with respect to the reference amount, 10% Method for producing a porous glass preform, characterized in that corrected by increasing or decreasing in the range below.

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