JPH0480860B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field> The present invention relates to a method for manufacturing a glass preform for optical fiber by a gas phase reaction using a multi-tube burner. <Prior art> In recent years, the VAD method has been used as a method for manufacturing optical fibers as it is superior in terms of quality and manufacturing, and the manufacturing technology is also becoming more sophisticated. This has become an essential condition for obtaining high-quality optical fiber for long-distance lines. The VAD method uses a multi-tube burner to burn vaporized glass raw materials and glass additives. A porous glass base material is obtained by introducing the glass particles together with an inert gas into a predetermined nozzle of a multi-tube burner, causing a reaction in front of the nozzle, chemically synthesizing glass particles, and depositing them on a target in the axial direction. Glass raw materials and glass additives include SiCl ₄ , GeCl ₄ ,
POCl ₃ , TiCl ₄ , AlCl ₃ and the like are used. These chemicals are usually liquid or solid at room temperature and cannot be fed directly to the burner. Therefore, conventional methods have been used in which raw material gas is forcibly vaporized using another gas, and then the raw material gas is maintained at a constant concentration using a concentration control device before being supplied to a burner. The vaporized glass raw material and glass additive are collectively referred to as raw material gas. Traditional
FIG. 1 shows an example of a gas burner and a raw material supply device for supplying raw material gas to the gas burner in the optical fiber manufacturing method using the VAD method. Usually, the gas supplied to the gas burner in the VAD method is classified into the following three types. (1) Raw material gas; vaporized glass raw materials such as silicon tetrachloride, germanium tetrachloride, phosphorous oxychloride, titanium tetrachloride, etc. or glass additives are mixed with the above chlorides such as argon, helium, hydrogen, etc. Gas when delivered with a non-reactive carrier gas. (2) Combustion/combustion auxiliary gas: A gas such as hydrogen or oxygen that generates glass particles by reacting with the raw material gas in (1) and at the same time generates H ₂ O in the reaction. (3) Seal gas: Although not directly involved in the glass reaction, this gas is used to prevent the nozzle from deteriorating due to a reaction occurring in front of the burner nozzle, and argon, helium, nitrogen gas, etc. are used. The problem in the present invention is the method of supplying the raw material gas. In FIG. 1, carrier gas (inert gas) is supplied from a supply source 1, maintained at a predetermined flow rate by a flow rate controller 2, and passes through a raw material supply tank 3 to vaporize glass raw materials or glass additives. Next, the vaporized raw material gas is controlled to a predetermined concentration by a raw material concentration adjusting device 4, and sent to a burner 6 via a pipe 5 heated by a pipe heating device 9. In the case shown in Fig. 1, for simplicity, one raw material system is shown as a raw material supply device that feeds one type of raw material gas to the burner nozzle, but in reality, it is more complicated, and multiple raw material gases are fed into one burner nozzle. Often connected to two nozzles. Note that 8 ₁ is a joint. In the conventional raw material supply device shown in Figure 1, the raw material gas supply system piping from the burner section and the raw material gas generator to the burner is maintained at a temperature at least higher than the saturation temperature of the raw material gas to prevent the raw material gas from liquefying and solidifying. need to be done. However, in the conventional method, the piping system is kept warm by wrapping tape-shaped heaters, nichrome wire, etc., and the heating effect is poor when the piping joint ₈₁ is used in thick-walled areas or the center nozzle of a multi-tube burner, etc. Often, the raw material gas tends to liquefy or solidify, making it impossible to keep the raw material gas at a specified value and supply it stably.
This was a hindrance to manufacturing. <Object of the Invention> The present invention has been made in view of the drawbacks of the prior art, and provides a method for manufacturing a glass base material for optical fibers in which the raw material does not liquefy or solidify in the burner or the raw material supply system piping. The purpose is to <Specific means for solving the problem> The structure of the method for manufacturing a glass base material for optical fibers according to the present invention that achieves the above object is that in manufacturing the glass base material for optical fibers by a gas phase reaction, the boiling point is lower than room temperature. The raw material for the glass base material or the glass additive, which is expensive, is vaporized by the raw material supply device and fed to the burner nozzle as raw material gas,
This method is characterized in that the raw material gas is heated with gas heated by a heating device provided separately from the raw material supply device. There are two methods for heating the raw material gas with heated gas: one is to add heating gas that does not react with the raw material gas directly into the raw material gas piping and send it to the burner; There is a method of indirectly heating the raw material gas by feeding heated gas into adjacent nozzles so that the nozzle walls meet. <Example> A first example of the method for manufacturing a glass preform for optical fiber according to the present invention is shown in FIG. Figure 2 is
FIG. 2 is a configuration diagram of an apparatus for manufacturing a glass base material using a VAD method. In FIG. 2, 1a is a carrier gas supply source, 1b is a heating gas supply source, 2 is a carrier gas flow rate adjustment device, 3 is a glass raw material or glass additive supply device, 4 is a raw material gas concentration adjustment device, 5 ₁ ,
5 ₂ is the piping, 6 is the burner, 7 is the produced glass base material,
8 ₁ is a joint for the pipes 5 ₁ and 5 ₂ , and 10 is a heating device for heating gas. An inert gas is supplied as a carrier gas from a carrier gas device source 1a, and the flow rate is adjusted to a desired level by a carrier gas flow rate adjustment device _2.
is supplied to the glass raw material supply device 3 from the container in which it is stored. In the glass raw material supply device 3, the raw material glass at saturated vapor pressure is sent by carrier gas to the raw material concentration adjustment device 4, where it is made into a raw material gas with a desired concentration and sent to the burner 6 via the pipe ₅₁ . .
The raw material gas causes a reaction in the burner 6 and is deposited on the target as glass fine particles to form a glass base material 7. In FIG. 2, a desired flow rate of a heating gas such as an inert gas or a gas that does not change or react even when mixed with the raw material gas is supplied from the heating gas supply device 1b, and the heating device 10 supplies the raw material with a desired flow rate. The heated gas is heated to a high temperature equal to or higher than the saturation temperature of the gas, and the heated gas passes through the pipe 5 ₂ and joins the source gas fed through the pipe 5 ₁ at the branch joint 8 ₂ just before the burner 6 . The raw material gas is fed to the burner 6 in a dry state so that the heated gas directly heats the center of the burner, the joint _82, etc., where the temperature drops and the gas tends to liquefy. According to the method for manufacturing a glass base material according to the present invention shown in FIG. 2, by mixing the raw material gases and directly heating the raw material gases, the raw material gases are liquefied or solidified even at the pipe joints and the center of the burner nozzle. Since the raw material gas is supplied to the burner while keeping the desired concentration adjusted by the raw material concentration adjustment device 4, the concentration of glass raw materials and glass additives will fluctuate in the continuous production of glass base material by the burner. Glass preforms for optical fibers can be produced with a stable supply of raw materials. In the example shown in FIG. 2, an example was explained in which the branch joint 8 ₂ of the pipe 5 ₁ was provided just before the burner.
The heating gas may be supplied to the pipe 5 ₁ to heat the raw material gas fed to the pipe 5 ₁ and the burner 6 . In this case, it is possible to prevent the raw material gas from liquefying or solidifying inside the pipe 5 ₁ , the joint 8 ₁ , and the burner pipe. FIG. 3 shows the burner section in FIG. 2 in detail. In Fig. 3, nozzle 6 ₁ of the multi-tube burner
raw material gas, heating gas, and combustion gas are supplied to the nozzles 6 ₂ to 6n, and other gases, such as combustion gas (H ₂ ), auxiliary combustion gas (O ₂ ), and sealing gas (Ar, He
), and other raw material gases are supplied. still,
The raw material supply system shown in FIG. 2 corresponds to the part related to the raw material gas and heating gas supplied to the nozzle 6 ₁ in FIG. 3. A second embodiment of the present invention will be explained using a glass base material manufacturing apparatus shown in FIG. In FIG. 4, 1a is a carrier gas supply source, 1b is a heating gas supply source, 2 is a carrier gas flow rate adjustment device, 3 is a glass raw material or glass additive supply device, 4 is a raw material gas concentration adjustment device, and 5 ₁ and 5 ₂ are Piping, 6 is a burner, 7 is a produced glass base material, 8 ₁ is a joint, 9 is a heating device for piping, and 10 is a heating gas heating device.
In FIG. 4, an inert carrier gas is supplied from a carrier gas supply source 1a, and is adjusted to a desired flow rate by a carrier gas flow rate regulating device 2. In FIG. The carrier gas is further supplied to a glass raw material supply device 3 consisting of a container containing a glass raw material, for example, liquid silicon tetrachloride (SiCl ₄ ), and the vaporized glass raw material is sent as a raw material gas at saturated vapor pressure to a raw material concentration adjustment device 4. Piping 5 as raw material gas of desired concentration
₁ to the nozzle ₆₁ of the burner 6 as shown in FIG. The raw material gas undergoes a reaction in the burner 6 and is deposited on the target as fine glass particles.
A glass base material 7 is generated. In FIG. 4, a heating gas such as an inert gas is further supplied from the gas supply source 1b and heated to a high temperature higher than the saturation concentration of the raw material gas by the heating device 10, and the heated gas is supplied to the joint 8 ₁ ,
It is supplied to the nozzle 6 ₂ of the burner 6 via the pipe 5 ₂ as shown in FIG. Since there is a nozzle partition between the nozzles 6 ₁ and 6 ₂ , the raw material gas supplied to the nozzle 6 ₁ via the pipe 5 ₁ is indirectly heated via the nozzle partition. Therefore, unlike in the conventional case, the raw material gas supplied to the central nozzle does not liquefy or solidify due to insufficient temperature within the nozzle. In the embodiment shown in FIG. 4, the piping ₅₁ is heated by the piping heating device 9 as in the prior art to prevent the source gas from liquefying or solidifying at the piping and joints. FIG. 5 shows the structure of the burner 6 shown in FIG. 4 in more detail. The raw material gas supplied to the nozzle 6 ₁ of the burner 6 in the raw material supply system shown in FIG. 4 corresponds to the raw material gas supplied to the nozzle 6 ₁ of the multi-tube burner 6 in FIG. The heating gas supplied to the nozzle 6 ₂ of the burner in FIG. 4 corresponds to the heating gas supplied to the nozzle 6 ₂ of the multi-tube burner 6 in FIG. In addition, in FIG. 5, other gases for the other nozzles 6 ₃ to 6n of the multi-tube burner 6 include combustion gas (H ₂ ), auxiliary combustion gas (O ₂ ), sealing gas (Ar, He...), Other raw material gases etc. are supplied. The above two embodiments of the present invention are shown in FIGS. 2 and 4.
Although explained with reference to the figures, it is of course possible to use a combination of these two methods. For example, a specific raw material gas is mixed with heated gas, heated, and supplied to one nozzle of a burner, and the heated gas is supplied to an adjacent nozzle of the burner to liquefy the raw material gas.
Solidification can be prevented. Furthermore, when a plurality of raw materials are used in one multi-tube burner, it is also possible to use two types of heating methods according to the present invention, for example, for raw materials A and B, respectively. The multi-tube burner section in this case is shown in FIG. What is shown in FIG. 6 is that the raw material gas A and the heating gas are mixed and supplied to the nozzle ₆₁ of the multi-tube burner 6 according to the first embodiment method according to the present invention, and the raw material gas A and the heating gas are mixed and supplied to the nozzle 61 of the multi-tube burner 6 according to the method according to the second embodiment of the present invention. Accordingly, the raw material gas B is supplied to the nozzle 6 ₂ and the heating gas for heating it is supplied to the adjacent nozzle 6 ₃ to indirectly heat the raw material gas B. In Fig. 6, nozzles 6 ₄ ... 6n contain combustion gas (H ₂ ), auxiliary combustion gas (O ₂ ), seal gas (Ar,
He...), other raw material gases, etc. are supplied. Moreover, the method according to the present invention can of course be used in combination with a conventional heating method, that is, a method of heating the piping or the burner itself with an external heating device. A specific example of the method for producing a glass preform for optical fiber according to the present invention will be shown below. (1) A raw material gas containing vaporized SiCl ₄ (silicon tetrachloride) and AlCl ₃ (aluminum chloride) is supplied to a quartz glass seven-tube burner using stainless steel piping, and argon gas is used as a heating gas. The mixture was heated to 210° C. using the heating device 10 used, mixed directly with raw material gas (40° C.), and fed to a burner. At this time, the gas arrangement and flow rate conditions in the burner pipe are
Shown in the table. As a result, an extremely high-quality porous glass base material with a diameter of 70 mm and a length of 350 mm was obtained without liquefaction or solidification of the raw material in the burner section and without causing instability. Furthermore, the glass body made by heating this glass base material to make it transparent has a homogeneous structure in the longitudinal direction, and when it is spun, the loss is 1 dB/Km.
We have obtained a long-distance optical fiber with extremely low loss (1.6 μm). (2) Using vaporized SiCl ₄ (silicon tetrachloride), GeCl ₄ (germanium tetrachloride), and TiCl ₄ (titanium tetrachloride) as the raw material gas, and using fluororesin and stainless steel piping ₅₁ , the outer diameter φ = A mixed gas of helium and argon was heated to 150°C and supplied to the nozzle of a 50 mm multiple quartz glass burner, and the raw material gas was heated to produce a glass base material. The gas arrangement and flow rate conditions at this time are shown in Table 2. As a result, the raw material gas did not liquefy or solidify in the burner section, causing no instability, and an extremely good porous glass base material with a diameter of 75 mm and a length of 350 mm was obtained. The glass body made by heating this base material to make it transparent has a homogeneous structure in the longitudinal direction,
The difference in refractive index of the glass body with respect to silica was about 3%. When this glass body was spun, an optical fiber for long-distance lines with extremely low loss of 20 dB/Km (1.6 μm) was obtained.

[Table] Others / minute

【table】

[Table] Others per minute <Effects of the Invention> According to the method for producing a glass base material for optical fiber according to the present invention, the raw material gas produced by the raw material supply device is directly or indirectly heated using separately heated gas. Because of the heating process, the raw glass does not liquefy or solidify in the piping or burner, and therefore, the quality of the glass base material obtained is extremely stable in the length direction, even during long-term continuous operation. did it.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a burner and raw material supply device for producing a glass preform by the conventional VAD method, and FIG. 2 is a diagram of an apparatus for explaining a first embodiment of the method for producing a glass preform for optical fibers according to the present invention. The configuration diagram, Figure 3, is
FIG. 4 is a detailed diagram of the burner section in FIG. 2, FIG. 4 is a configuration diagram of an apparatus explaining another embodiment of the present invention, FIG. 5 is a detailed diagram of the burner section shown in FIG. 4, and FIG. 6 is a detailed diagram of the burner section shown in FIG. Figures illustrating the configuration of a burner section when two embodiments of the invention method are used together are shown. In the drawing, 1 is a gas supply source, 1a is a carrier gas supply source, 1b is a heating gas supply source, 2 is a carrier gas flow rate supply device, 3 is a raw material supply device, 4 is a raw material gas concentration adjustment device, 5 ₁ and 5 ₂ are Piping, 6 is a burner, 7 is a glass base material, 8 ₁ is a joint, 8 ₂ is a branch joint, 9 is a heating device for piping, and 10 is a heating gas heating device.

Claims (1)

[Claims] 1. In a method for producing a glass preform for optical fibers by a gas phase reaction, the raw material for the glass preform or a glass additive having a boiling point higher than room temperature is heated and vaporized by a raw material supply device to produce a raw material gas. A method for producing a glass preform for an optical fiber, which comprises feeding the raw material gas to a burner nozzle and heating the raw material gas with gas heated by a heating device provided separately from the raw material supply device. 2. The gas heated by a heating device provided separately from the raw material supply device is a gas that does not change in quality within the range of use even if mixed with the raw material gas, and the heated gas is mixed with the raw material gas. 2. The method for producing a glass preform for optical fiber according to claim 1, wherein the raw material gas is heated by heating the raw material gas. 3. The method of manufacturing a glass preform for optical fiber according to claim 2, wherein the heating gas is an inert gas. 4 Heat the raw material gas through the wall of the nozzle by flowing gas heated by a heating device provided separately from the raw material supply device through a nozzle adjacent to a nozzle through which the raw material gas flows through a burner nozzle. Claim 1 characterized in that
A method for manufacturing a glass base material for optical fibers as described in .