JP2012087033A - Method for manufacturing glass perform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize characteristics of a glass perform by uniformizing the thermal history of a glass fine particle deposit by regulating a mountain-like temperature distribution in a heating furnace in the longitudinal direction.SOLUTION: The method for manufacturing a glass perform to obtain a transparent glass body by inserting a glass fine particle deposit 27 in a vessel 19, and heating the vessel interior by heaters 37 installed on the outer periphery of the vessel 19 includes heating the glass fine particle deposit 27 by a first heating step of heating the vessel interior in a mixed atmosphere of a halogen gas and an inert gas, and a second heating step of heating in a helium gas atmosphere. In the first heating step, the temperature distribution of a heating furnace 13 is uniformized across the longitudinal direction of the glass fine particle deposit 27. In the second heating step, while a part inside the heating furnace 13 is made to have a mountain-like temperature distribution and the mountain-like temperature distribution is regulated in the longitudinal direction during the transparent vitrification, the positional relation between the glass fine particle deposit 27 and the heaters is moved relatively in the longitudinal direction.

Description

  The present invention relates to a method for producing a glass base material in which a glass fine particle deposit is transparently vitrified in a heating furnace.

  In the method of manufacturing an optical fiber, a glass particulate deposit is produced by various methods including a gas phase axial method (VAD), an external method (OVD), and a multi-burner multilayer method (MMD). Each of the glass particulate deposits produced by these methods is formed of an aggregate of only glass particulates or a glass particulate deposited on the outer periphery of a transparent glass rod, and the formed glass particulate deposit is then sintered. The result is a transparent glass preform for optical fiber.

  In the VAD method, a burner is arranged under a rotating starting glass rod, a raw material gas is injected into an oxyhydrogen flame formed by the burner, glass particles are generated by a flame hydrolysis reaction, and the generated glass particles are started. A glass particulate deposit is produced by depositing in the axial direction of the rod. In the OVD method and the MMD method, for example, a burner is arranged on the outer periphery of a starting glass rod that rotates in a reaction vessel, a raw material gas is poured into an oxyhydrogen flame formed by the burner, and glass particles are obtained by a flame hydrolysis reaction. The produced glass fine particles are deposited on the outer periphery of the starting glass rod to produce a glass fine particle deposit.

  The transparent vitrification of the glass fine particle deposit is performed in a furnace core tube formed of a heat-resistant material such as carbon or quartz, and a heating furnace in which a heater is disposed on the outer periphery of the furnace core tube. In such a heating furnace, the temperature distribution of the heating range by the heater generally forms a mountain shape in which the central portion of the heater has the highest temperature.

Japanese Patent Laid-Open No. 3-109224 JP 2005-320197 A JP-A-9-110456 JP 2004-217472 A

However, the temperature distribution of the mountain shape changes every moment while the glass particulate deposit rises or falls. This is because the heat release amount and heat release direction of the heater (radiant heat) change depending on the relative positional relationship between the glass particulate deposit and the heater. In conventional heating furnaces (for example, Patent Document 1), there is no function of adjusting the temperature distribution of the mountain shape in the longitudinal direction during the heat treatment at all times. The heat history in the longitudinal direction of the body tends to be uneven.
In Patent Document 1, the temperature distribution is controlled by controlling the temperature of each heater when the heater is made into a three-stage structure when transparent glass is formed. However, the heater has a one-stage structure in the heat treatment before the transparentization. Because the temperature distribution in the heating furnace is not managed and the glass particulate deposit is not raised or lowered, it is considered that the heat history in the longitudinal direction of the finally obtained transparent glass body becomes non-uniform. . Moreover, in such a conventional structure, since the heater used at a 1st heating process and the heater used at a 2nd heating process are different, there exists a disadvantage that an installation cost becomes high.
In Patent Document 2, two or more heaters are installed in the longitudinal direction and the temperature of each heater is adjusted. However, since the heater temperature itself is controlled, there is a large deviation from the temperature of the glass particulate deposit. It is considered that the heat history of the obtained transparent glass body is not uniform in the longitudinal direction. Further, in paragraph [0022] of the same document 2, there is a description that “practically two heaters are desirable”, but it is difficult to control the temperature of the valley of the mountain-shaped temperature distribution with a two-stage heater. It is.
The configuration of Patent Document 3 in which the heater power is controlled by a thermocouple installed on the outer periphery of the heater is also largely different from the temperature of the glass particulate deposit itself, and as a result, the thermal history of the transparent glass body is not longitudinal in the same manner as described above. I think it tends to be uniform.
Furthermore, the configuration of Patent Document 4 is such that when the glass fine particle deposit is heated to a uniform temperature in the longitudinal direction in the heating process of dehydration and F addition, and is converted into a transparent glass, the heating elements installed in the longitudinal direction are placed one by one from the bottom. The temperature is raised and the glass is transparent. However, since the power control of the heating element is performed by a temperature sensor installed near the outer periphery of the heating element, it is considered that the thermal history of the transparent glass body obtained in this case is also likely to be non-uniform in the longitudinal direction. Moreover, since the heaters installed in the longitudinal direction are made transparent by raising the temperature one by one from the bottom when making transparent glass, the temperature distribution of the glass particulate deposit between the heaters and the glass in the heater part It is difficult to match the temperature distribution of the particulate deposit, which is also considered to be the cause of the thermal history becoming unstable in the longitudinal direction and the refractive index becoming unstable in the longitudinal direction.

  The present invention has been made in view of the above situation, and the object thereof is a manufacturing method in which a glass fine particle deposit manufactured by a VAD method, an OVD method, an MMD method, or the like is transparently vitrified in a heating furnace. An object of the present invention is to provide a method for producing a glass base material that adjusts the temperature distribution of the mountain shape in the longitudinal direction, and to stabilize the characteristics of the glass base material by making the thermal history of the glass particulate deposit uniform. .

The above object of the present invention is achieved by the following configuration.
(1) A glass base material manufacturing method for obtaining a transparent glass body by inserting a glass particulate deposit body into a container of a heating furnace and heating the inside of the container with a heater installed on the outer periphery of the container, The glass fine particle deposit is heated by a first heating step for heating the substrate in a mixed atmosphere of a halogen-based gas and an inert gas and a second heating step for heating in a helium gas atmosphere. In the first heating step, the inside of the heating furnace is heated. Is uniformly controlled over the longitudinal direction of the glass fine particle deposit, and in the second heating step, a part of the heating furnace is made into a mountain-shaped temperature distribution, and the mountain-shaped temperature distribution is converted into a transparent glass. A method for producing a glass base material, wherein the positional relationship between the glass particulate deposit and the heater is relatively moved in the longitudinal direction while adjusting in the longitudinal direction.

According to this glass base material manufacturing method, since it has the function of adjusting the temperature distribution of the mountain shape, the temperature distribution can be kept constant while the glass particulate deposit is raised or lowered in the heating furnace. Thereby, the heat history of the longitudinal direction of the transparent glass body obtained can be made uniform. For example, when the glass particulate deposit is a glass base material for optical fiber containing GeO ₂ or the like, the diffusion amount / volatilization amount of GeO ₂ is stabilized in the longitudinal direction, so that the refractive index distribution in the longitudinal direction of the obtained transparent glass body Is stabilized, and the fiber characteristics in the longitudinal direction are stabilized.

(2) The glass base material manufacturing method according to (1), wherein the power adjustment of the heater is controlled based on the temperature measurement result of the outer surface of the glass particulate deposit. .

  According to this method for producing a glass base material, since the temperature distribution on the surface of the glass particulate deposit is directly measured and controlled, the deviation from the temperature of the glass particulate deposit can be reduced, and the resulting glass The thermal history in the longitudinal direction of the base material can be further stabilized.

(3) The method for manufacturing a glass base material according to (1), wherein the power adjustment of the heater is controlled based on a temperature measurement result of the outer surface of the container.

  According to this method for producing a glass base material, the temperature distribution at a location as close as possible to the glass fine particle deposit is measured and controlled, so that the deviation from the temperature of the glass fine particle deposit can be reduced as described above. The thermal history in the longitudinal direction of the glass base material to be obtained can be further stabilized.

(4) A method for producing a glass base material according to (1) to (3), wherein the heater in the first heating step is composed of three or more stages in the longitudinal direction. .

  According to this glass base material manufacturing method, since the heater is composed of three or more stages, the temperature distribution in the longitudinal direction in the first heating step can be made uniform.

(5) A method for producing a glass base material according to any one of (1) to (4), wherein a second heating heater is used to adjust the temperature distribution of the mountain shape in the second heating step in the longitudinal direction. A method for producing a glass base material, characterized in that another auxiliary heater is added in the vicinity of both ends of the glass and the temperature distribution of the mountain shape is adjusted with the added auxiliary heater.

  According to this method for producing a glass base material, the temperature distribution of the mountain shape can be adjusted, and the temperature distribution can be managed to a desired distribution even while the glass fine particle deposit is moved in the heating furnace.

(6) A method for producing a glass base material according to any one of (1) to (4), wherein a second heating heater is used to adjust a mountain-shaped temperature distribution in the second heating step in the longitudinal direction. A method for producing a glass base material, characterized by introducing a gas in the vicinity of both ends of the glass to adjust the temperature distribution of the mountain.

  According to this glass base material manufacturing method, an inert gas is introduced in the vicinity of both ends of the heat zone, so that the temperature in the vicinity of both ends of the heat zone can be adjusted in a lower direction. Using a heater, it is possible to adjust the mountain-shaped temperature distribution with the center at the maximum temperature.

  According to the method for manufacturing a glass base material according to the present invention, in a manufacturing method for converting a glass fine particle deposit manufactured by a VAD method, an OVD method, an MMD method or the like into a transparent glass in a heating furnace, Therefore, the thermal history of the glass fine particle deposit can be made uniform, and the characteristics of the glass base material can be stabilized.

It is a block diagram which represented notionally the manufacturing apparatus used for the manufacturing method of the glass base material which concerns on this invention. It is process explanatory drawing which represented the procedure of the manufacturing method using the manufacturing apparatus shown in FIG. 1 to (a)-(d). It is a block diagram which represented notionally the manufacturing apparatus which concerns on 2nd Embodiment. It is a block diagram which represented notionally the manufacturing apparatus which concerns on 3rd Embodiment. It is a block diagram which represented notionally the manufacturing apparatus which concerns on the comparative example 1. FIG. 10 is a configuration diagram conceptually showing a manufacturing apparatus according to Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram conceptually showing a manufacturing apparatus used in the method for manufacturing a glass base material according to the present invention.
The glass base material manufacturing apparatus 11 used in the manufacturing method according to the present embodiment includes a heating furnace 13. The heating furnace 13 includes a furnace core tube 19 that is a container inside the furnace body 15. The core tube 19 is provided with a gas inlet 23 at the lower portion and an exhaust port 25 at the upper portion. A lid 29 for taking out the glass particulate deposit 27 is provided on the upper surface of the furnace tube 19. An elevating device 31 is installed above the core tube 19, and the elevating device 31 supports a suspension rod 33 penetrating the lid 29 so as to be movable up and down and rotatable. A dummy rod 35 is supported on the suspension bar 33. A glass particulate deposit 27 is attached to one end of the dummy rod 35.

  The core tube 19 is made of quartz material or carbon material. A plurality of heaters 37 are arranged on the outer periphery of the core tube 19 in a multistage shape along the longitudinal direction of the core tube 19. As the heater 37, for example, a resistance heater or induction heater made of carbon is used. The heater 37 is composed of at least three stages, and the temperature of each heater 37 can be adjusted.

  In this embodiment, heating is divided into a first heating step for dehydration reaction and a second heating step for transparent vitrification that is performed thereafter. The heater 37 in the first heating process is configured with three or more stages in the longitudinal direction. In order to make the temperature distribution in the longitudinal direction uniform in the first heating step, it is desirable to install three or more heaters 37 in the longitudinal direction.

  For example, the uppermost stage of the heater 37 is the second heater 39. The second heater 39 is also used for the first heating process in the first heating process. As described above, the second heating heater 39 in the second heating step is one of the heaters 37 in the first heating step, so that the equipment cost can be reduced. In order to adjust the mountain-shaped temperature distribution in the second heating step in the longitudinal direction, the second heater 39 is additionally provided with another auxiliary heater 41 as a temperature adjusting means near both ends. With this added auxiliary heater 41, the mountain-shaped temperature distribution can be adjusted.

The temperature distribution in the second heating step is a temperature distribution in which a part of the heating furnace has a mountain shape, and the temperature distribution of the mountain shape is adjusted in the longitudinal direction. The mountain-shaped temperature distribution changes while the glass particulate deposit 27 moves in the length direction. This is because the heat release amount and heat release direction of the heater (radiant heat) change depending on the relative positional relationship between the glass particulate deposit 27 and the heater 37. In the present embodiment, the mountain-shaped temperature distribution can be adjusted, so that the temperature distribution can be managed to a desired distribution even while the glass particulate deposit 27 is moved in the heating furnace. Thereby, the heat history of the longitudinal direction of the transparent glass body obtained becomes uniform. For example, when the glass particulate deposit 27 is an optical fiber glass base material containing GeO ₂ or the like, the volatilization amount of GeO ₂ (2GeO ₂ → 2GeO + O ₂ ) is stabilized in the longitudinal direction, so that the length of the transparent glass body to be obtained is The refractive index distribution in the direction is stabilized, and the fiber characteristics are stabilized in the longitudinal direction.

  In the vicinity of the installation position of the heater 37, a radiation thermometer 43 as a temperature detecting means is used for each heater. The radiation thermometer 43 measures the temperature by measuring the intensity of infrared rays or visible rays emitted from the glass particulate deposit 27. For this reason, the window part 45 which permeate | transmits infrared rays to the heating furnace 13 is provided corresponding to each heater. A control device 49 is connected to the radiation thermometer 43, and the control device 49 controls the heater 37, the second heater 39, and the auxiliary heater 41 based on the temperature detection value from the radiation thermometer 43. The radiation thermometer 43 measures the temperature distribution on the surface of the glass fine particle deposit corresponding to each heater 37. This is because in order to stabilize the thermal history in the longitudinal direction of the glass particulate deposit 27, it is better to control the temperature distribution at a location as close as possible to the glass particulate deposit 27.

  In the second heating step, the glass fine particle deposit 27 is heated to become transparent vitrified. At this time, it is necessary to make the outer peripheral atmosphere of the glass fine particle deposit 27 be a helium gas atmosphere. When heating is performed in another inert gas atmosphere, the gas remains inside the glass fine particle deposit 27, and it becomes difficult to form a transparent glass. However, there is no problem even if a gas other than helium is mixed as long as the amount is small.

  In the first heating step, the peripheral atmosphere of the glass particulate deposit 27 is made to be a mixed atmosphere of a halogen-based gas and helium gas before the glass particulate deposit 27 is converted into a transparent glass in the heating furnace 13. Thereby, OH groups in the glass fine particle deposit can be removed. The same effect can be obtained even in a mixed atmosphere with an inert gas other than helium (for example, nitrogen).

  The glass base material manufacturing apparatus 11 is configured in this manner, whereby the glass particulate deposit 27 is inserted into the core tube 19 of the heating furnace 13, and the inside of the core tube 19 is heated by the heater 37 installed on the outer periphery of the core tube 19. Is heated to form a transparent glass.

FIG. 2 is a process explanatory view showing the procedure of the manufacturing method using the manufacturing apparatus shown in FIG. 1 in (a) to (d).
For example, the dummy rod 35 of the glass particulate deposit 27 shown in FIG. 2A formed by the VAD method is supported by the suspension rod 33 of the lifting device 31 and inserted into the core tube 19. The electric power supplied to each heater 37, 39, 41 measures the surface temperature of the glass particulate deposit with a radiation thermometer 43 (see FIG. 1) and controls the measured temperature to be a desired temperature. In the first heating step, heating is performed without moving the glass particulate deposit 27 in the longitudinal direction.

In the first heating step, the glass particulate deposit 27 is heated in a mixed atmosphere of, for example, a chlorine-based halogen gas (Cl ₂ , SiCl _4, etc.) and an inert gas. Then, OH groups (impurities) in the glass fine particle deposit are removed by a dehydration reaction (Si—OH + Cl ₂ → Si—Cl + HClO). On the other hand, in the case of glass particles deposit 27, including GeO _2, simultaneously GeO ₂ is diffused and vaporized and dehydration _{(GeO 2 + 2Cl 2 ⇔GeCl 4} + O 2). Therefore, if the temperature distribution of the glass particulate deposit 27 becomes non-uniform in the first heating step, the GeO ₂ concentration distribution becomes unstable in the longitudinal direction and the radial direction.

In the present invention, the temperature distribution of the entire length of the glass particulate deposit 27 is made uniform in the first heating step, so that the amount of diffusion and volatilization of GeO ₂ is stabilized in the longitudinal direction, and as a result, the refractive index distribution is stabilized. The first heating step is not only dehydration in which OH groups are removed with a chlorine-based halogen gas, but even if a heating step in which fluorine is added into the glass particle deposition body in a fluorine-based halogen gas atmosphere is added after dehydration, The rate stabilizes.

  The second heating step is a step of heating the glass particulate deposit 27 to form a transparent glass. In the second heating step, the outer peripheral atmosphere of the glass particulate deposit 27 needs to be a helium gas atmosphere. When heating is performed in another inert gas atmosphere, the gas remains inside the glass fine particle deposit 27, making it difficult to form a transparent glass. However, there is no problem even if a gas other than helium is mixed as long as the amount is small.

  In the second heating step, the glass particulate deposit 27 is moved in the longitudinal direction and heated. A part of the temperature distribution in the longitudinal direction in the furnace core tube is a mountain-shaped temperature distribution, and the mountain-shaped temperature distribution is adjusted during the transparent vitrification and heated.

  As shown in FIG. 2B, after pulling up the glass particulate deposit 27 once and maintaining the inside of the furnace tube in a temperature distribution that becomes a predetermined mountain shape by, for example, a heater 39, as shown in FIG. The glass fine particle deposit 27 is lowered to a desired position. At this time, the auxiliary heater 41 is used to control the adjustment of the mountain-shaped temperature distribution. After the glass fine particle deposit 27 reaches a desired position, the transparent glass base material is pulled up as shown in FIG.

  As described above, in the manufacturing method according to the present embodiment, the thermal history of the glass fine particle deposit 27 can be made uniform by adjusting and controlling the temperature distribution of the mountain shape in the heating furnace. This is because, for example, when the temperature distribution of the mountain shape changes over time, the heating amount in the longitudinal direction of the glass fine particle deposit cannot be made uniform, but by constantly controlling the temperature distribution of the mountain shape, This is because it can cope with a change in temperature distribution.

Thereby, for example, when the glass particulate deposit 27 is an optical fiber glass preform containing GeO ₂ or the like, the diffusion amount / volatilization amount of GeO ₂ is stabilized in the longitudinal direction, so that the longitudinal direction of the transparent glass body to be obtained is This stabilizes the refractive index distribution and stabilizes the fiber characteristics in the longitudinal direction.

  Therefore, according to the manufacturing method of the glass base material according to the present embodiment, in the manufacturing method in which the glass fine particle deposit 27 manufactured by the VAD method, the OVD method, the MMD method or the like is made into a transparent glass in a heating furnace, Since the temperature distribution of the mountain shape in the furnace can be adjusted in the longitudinal direction, the thermal history of the glass fine particle deposit can be made uniform, and the characteristics of the glass base material can be stabilized.

Next, a second embodiment of the present invention will be described.
FIG. 3 is a configuration diagram conceptually showing the manufacturing apparatus according to the second embodiment. In the following embodiments, the same members as those shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.
In the manufacturing apparatus 11A according to this embodiment, a thermocouple 47 is used instead of the radiation thermometer 43 as the temperature adjusting means. A controller 49 is connected to the thermocouple 47, and the controller 49 controls the heater 37, the second heater 39, and the auxiliary heater 41 based on the temperature detection value from the thermocouple 47. The thermocouple 47 measures the temperature distribution near the outer surface of the core tube 19. In the case of this configuration, the window portion 45 for the radiation thermometer provided in the heating furnace 13 is not necessary. Other configurations are the same as those of the manufacturing apparatus 11 of the above embodiment.

Next, a third embodiment of the present invention will be described.
FIG. 4 is a configuration diagram conceptually showing the manufacturing apparatus according to the third embodiment.
The glass base material manufacturing apparatus 11B according to this embodiment is provided with gas introducing portions 57 as temperature adjusting means near both ends of the second heater 39, and introduces an inert gas to adjust the temperature distribution.
By introducing an inert gas in the vicinity of both ends of the heat zone of the glass particulate deposit 27, the temperature in the vicinity of both ends of the heat zone can be adjusted to be lowered, and the temperature distribution can be adjusted without using the auxiliary heater 41. .
According to the glass base material manufacturing apparatus 11B, the second heating heater 39 can be easily controlled, and the supplied inert gas can be used effectively. Originally, the inert gas is used as a purge gas to prevent oxidative deterioration of carbon parts used in the furnace, but it can also be used to control the temperature distribution in the furnace, thereby extending the life of the carbon parts and increasing the inside of the furnace. It becomes possible to achieve both temperature distribution control.

Next, the glass fine particle deposit is made into a transparent glass with the same configuration as each of the embodiments described above, and the variation in the relative refractive index difference between the core portion and the clad portion is compared.
FIG. 5 is a block diagram conceptually showing the manufacturing apparatus according to Comparative Example 1, and FIG. 6 is a block diagram conceptually showing the manufacturing apparatus according to Comparative Example 2. The same members as those shown in FIG. 1 are denoted by the same reference numerals. The manufacturing apparatus 501A according to Comparative Example 1 uses a single heating source 37 as the heating source, and the manufacturing apparatus 501B according to Comparative Example 2 includes only the second heater 37 and the multistage heater 37 that does not include the auxiliary heater. Is used.
[Example 1]
A glass fine particle deposit with an effective portion having a core / cladding length of 1000 mm is formed by the VAD method, and this glass fine particle deposit is inserted into a heating furnace shown in FIG. 1 to produce a glass base material. The heating source is a carbon heater having a six-stage configuration in the longitudinal direction, and the power supplied to each heater controls the temperature at which the surface of the glass particulate deposit is measured with a radiation thermometer. Further, the upper second heater is provided with auxiliary heaters for adjusting the temperature distribution above and below it so that the temperature distribution of the second heater can be adjusted.

First, a glass particulate deposit is placed in a heating furnace, and a mixed gas of Cl ₂ : 1 (L / min) and He: 20 (L / min) is flowed into the furnace, and the temperature is raised simultaneously to deposit the glass particulates. Heat the whole body to 1100 ° C for 1H. Subsequently, the glass fine particle deposit is pulled up to the upper end, and He gas is introduced into the furnace at 20 (L / min). At the same time, only the second heating heater is heated, the second heating heater is controlled to 1550 ° C., and the upper and lower ends of the temperature distribution are set to 1450 ° C. using auxiliary heaters added above and below the second heating heater. Control to have a mountain-shaped temperature distribution. When the desired temperature distribution is reached, the glass fine particle deposit is moved downward from the upper end at a speed of 4 mm / min. During the movement of the glass particulate deposit, the temperature distribution of the second heater is adjusted, and each heater is controlled so as to maintain the mountain-shaped temperature distribution. After the glass particulate deposit reaches the lowest end, the transparent glass base material is pulled up. When the relative refractive index difference of the glass base material is measured at each position in the longitudinal direction, it can be suppressed to a variation of 0.35 ± 0.0008%.

[Comparative Example 1]
The same glass fine particle deposit as in Example 1 is heated in a single-stage heating furnace with the heater shown in FIG. 5 to produce a glass base material. The power supplied to the heater controls the temperature at which the heater surface is measured with a radiation thermometer.
First, in a state where the glass fine particle deposit is kept waiting at the upper end, a mixed gas of Cl ₂ : 1 (L / min) and He: 20 (L / min) is allowed to flow into the furnace, and the temperature is raised simultaneously. Is controlled at 1100 ° C. When the heater reaches a desired temperature, the glass fine particle deposit is moved from above to below at a speed of 5 mm / min. After the glass particulate deposit reaches the lower end, the glass particulate deposit is lifted to the upper end, and He gas is introduced into the furnace at 20 (L / min). At the same time, the temperature is raised and the heater is controlled at 1550 ° C. When the heater reaches a desired temperature, the glass fine particle deposit is moved downward from the upper end at a speed of 4 mm / min. After the glass particulate deposit reaches the lowest end, the transparent glass base material is pulled up. When the relative refractive index difference of the glass base material is measured at each position in the longitudinal direction, it is 0.35 ± 0.007%.

[Example 2]
The same glass fine particles as in Example 1 are heated in a heating furnace shown in FIG. 3 to produce a glass base material. A thermocouple is installed on the outer surface of the quartz furnace core tube, and the power supplied to each heater is controlled with respect to the temperature measured by the thermocouple. Other manufacturing conditions and equipment configurations are the same as those in the first embodiment.
The relative refractive index difference of the obtained glass base material is 0.35 ± 0.001%.

[Example 3]
The same glass fine particle deposit as in Example 1 is heated in a heating furnace shown in FIG. 4 to produce a glass base material. A thermocouple is installed on the outer surface of the core tube, and the power supplied to the heater is controlled with respect to the temperature of the thermocouple. Nitrogen gas is blown on the top and bottom of the second heater for 1 to 10 L / min to control the temperature distribution of the second heater. Other manufacturing conditions are the same as those in Example 1.
The relative refractive index difference of the obtained glass base material is 0.35 ± 0.003%.

[Comparative Example 2]
The same glass fine particle deposit as in Example 1 is heated in a six-stage heating furnace with a heater shown in FIG. 6 to produce a glass base material. The power supplied to the heater controls the temperature at which the heater surface is measured with a radiation thermometer.
First, a glass particulate deposit is placed in a heating furnace, and a mixed gas of Cl ₂ : 1 (L / min) and He: 20 (L / min) is flowed into the furnace, and the temperature is raised simultaneously to deposit the glass particulates. Heat the whole body to 1100 ° C for 1H. Next, 20 (L / min) of He gas is introduced into the furnace. At the same time, the temperature is raised and the lower heater is controlled at 1550 ° C. When the lower heater reaches the desired temperature, hold 1H. Thereafter, the temperature of the lower heater is lowered, the temperature of the second heater from the bottom is increased to 1550 ° C., and held for 1H. Such a temperature increase / decrease is repeated, and when the heating by the upper heater is completed, the transparent glass base material is pulled up. When the relative refractive index difference of the glass base material is measured at each position in the longitudinal direction, it is 0.35 ± 0.006%.

In Examples 1, 2, 3, the heating step is carried out heating in a mixed gas atmosphere of Cl ₂ and He, even by heating in an inert gas atmosphere other than Cl ₂ and He, the same effect can be obtained . In addition, the heating process in which heating is performed in a He gas atmosphere can achieve the same effect even if a small amount of nitrogen gas is mixed.

11 Glass Base Material Manufacturing Equipment 13 Heating Furnace 19 Core Tube (Container)
27 Glass particulate deposit 37 Heater 39 Second heater 41 Auxiliary heater (temperature adjusting means)
57 Gas introduction part (temperature adjustment means)

Claims (6)

A glass base material manufacturing method for obtaining a transparent glass body by inserting a glass particulate deposit body into a container of a heating furnace and heating the inside of the container with a heater installed on the outer periphery of the container,
Heating the glass particulate deposit by a first heating step of heating the inside of the container in a mixed atmosphere of a halogen-based gas and an inert gas and a second heating step of heating in a helium gas atmosphere;
In the first heating step, the temperature distribution in the heating furnace is uniformly controlled over the longitudinal direction of the glass particulate deposit,
In the second heating step, a part of the inside of the heating furnace is formed into a mountain-shaped temperature distribution, and the positional relationship between the glass particulate deposit and the heater is adjusted in the longitudinal direction while adjusting the mountain-shaped temperature distribution in the longitudinal direction during the vitrification. A method for producing a glass base material, wherein the glass base material is moved relatively. A method for producing a glass base material according to claim 1,
A method for producing a glass base material, wherein the power adjustment of the heater is controlled based on a temperature measurement result of an outer surface of the glass particulate deposit. A method for producing a glass base material according to claim 1,
A method for producing a glass base material, wherein power adjustment of the heater is controlled based on a temperature measurement result of an outer surface of the container. It is a manufacturing method of the glass base material given in any 1 paragraph of Claims 1-3,
The method for producing a glass base material, wherein the heater of the first heating step is composed of three or more stages in the longitudinal direction. It is a manufacturing method of the glass base material given in any 1 paragraph of Claims 1-4,
In order to adjust the mountain-shaped temperature distribution in the second heating step in the longitudinal direction, another auxiliary heater is added near both ends of the second heating heater, and the mountain-shaped temperature distribution is adjusted with the added auxiliary heater. A method for producing a glass base material. It is a manufacturing method of the glass base material given in any 1 paragraph of Claims 1-4,
In order to adjust the temperature distribution of the mountain shape in the second heating step in the longitudinal direction, a glass base material is characterized in that gas is introduced near both ends of the heater for second heating to adjust the temperature distribution of the mountain shape. Manufacturing method.