JP7164384B2 - Manufacturing method of glass body for optical fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an optical fiber glass body.

An optical fiber glass body is generally manufactured by dehydrating a porous glass body produced by a VAD (Vapor-phase Axial Deposition) method or the like, and then sintering the porous glass body for transparent vitrification. Silica (SiO ₂ ) is preferably used for the core in order to reduce the loss of the optical fiber. In this case, when a clad formed by adding fluorine, which is a down dopant, to _SiO2 is provided outside the core, the optical fiber glass body includes a core portion made of _SiO2 and fluorine added to the _SiO2 outside the core portion. It is composed of the cladding part to be added. However, in this case, the viscosity of the clad portion becomes low, and the viscosity difference between the core portion and the clad portion increases. For this reason, tensile stress concentrates on the core portion when the optical fiber glass body is drawn, and Rayleigh scattering increases in the core of the obtained optical fiber. Therefore, in order to reduce the viscosity difference between the core portion and the clad portion while maintaining the relative refractive index difference between the core portion and the clad portion in the optical fiber glass body, the amount of fluorine added to the clad portion is reduced. , chlorine may be added as an up-dopant to the core. Further, the optical fiber glass body may be composed of only the core portion or only the clad portion, and chlorine may be added to the core portion or the clad portion.

As a method for manufacturing an optical fiber glass body to which chlorine is added, a manufacturing method described in Patent Document 1 below, for example, is conventionally known. In the same document, a porous glass body is placed in the furnace core tube of a dehydration sintering apparatus, a dehydration processing gas obtained by mixing silicon tetrachloride (SiCl4) and an inert gas is supplied into the furnace core tube, and the inside of the furnace core tube is is exhausted through an exhaust pipe connected to a furnace core tube to perform dehydration treatment, followed by transparent vitrification treatment (sintering treatment) to produce an optical fiber glass body. .

JP-A-10-53423

However, although the method for manufacturing an optical fiber glass body described in Patent Document 1 can sufficiently add chlorine to the optical fiber glass body, it has the following problems.

That is, in the method for manufacturing an optical fiber glass body described in Patent Document 1, SiCl ₄ supplied during the dehydration process reacts with water adhering to the surface of the porous glass body to generate SiO ₂ powder. However, this SiO ₂ powder floats in the atmosphere and mixes with the exhaust gas, and tends to clog the exhaust pipe in a short period of time. As a result, it is necessary to stop the dehydration and sintering apparatus for exchanging or cleaning the exhaust pipe, which reduces the number of optical fiber glass bodies that can be continuously produced, and makes it impossible to efficiently produce optical fiber glass bodies. Gone.

Here, in order to suppress clogging of the exhaust pipe, SiCl4, which has a lower reactivity to the porous glass body than SiCl4, is used as the dehydration processing gas to be supplied to the core tube during the dehydration processing of the porous glass body. It is also conceivable to use a chlorine-based gas (eg chlorine). However, in this case, sufficient chlorine cannot be added to the optical fiber glass body.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing an optical fiber glass body to which chlorine is sufficiently added, which can be efficiently manufactured.

In order to solve the above problems, the present invention provides a dehydration treatment step of dehydrating a porous glass body in a furnace core tube , and heating and sintering the porous glass body with a heater to obtain an optical fiber glass body. and a sintering step, wherein in the dehydration step, while supplying a dehydration gas containing a chlorine-based gas into the furnace core tube , the gas in the furnace core tube is Exhaust is exhausted through an exhaust pipe connected to the furnace core tube , and the dehydration process includes a pre-dehydration process using a first chlorine-based gas as the chlorine-based gas and a post-dehydration process using a second chlorine-based gas as the chlorine-based gas. and a dehydration treatment step, wherein the reactivity of the second chlorine-based gas with respect to the porous glass body in the post-dehydration treatment step is determined by the reactivity of the first chlorine-based gas with respect to the porous glass body in the pre-dehydration treatment step. A method for manufacturing a glass body for optical fiber, which is made higher than reactivity.

According to the method for manufacturing an optical fiber glass body of the present invention, in the pre-dehydration process of the dehydration process, the reactivity of the first chlorine-based gas with respect to the porous glass body in the post-dehydration process is Since the reactivity is lower than that of the second chlorine-based gas, the concentration of SiCl ₄ generated by the reaction between the porous glass body and the first chlorine-based gas is low. Therefore, in the pre-dehydration step, even if the generated SiCl ₄ reacts with the water adhering to the surface of the porous glass body, the concentration of the generated SiO ₂ powder also becomes low. Therefore, even if the gas in the furnace core tube is exhausted through the exhaust pipe, clogging of the exhaust pipe is sufficiently suppressed. In the post-dehydration step, the reactivity of the second chlorine-based gas with respect to the porous glass body is higher than the reactivity of the first chlorine-based gas with respect to the porous glass body. Sufficient chlorine can be added. At this time, SiCl ₄ is generated by the reaction between the porous glass body and the second chlorine-based gas, but at this time, the water adhering to the surface of the porous glass body in the pre-dehydration step has been sufficiently removed. . Therefore, the concentration of SiO ₂ powder produced by the reaction between SiCl ₄ and moisture adhering to the surface of the porous glass body is sufficiently low. Therefore, even if the gas in the furnace core tube is exhausted through the exhaust pipe, clogging of the exhaust pipe is sufficiently suppressed. As described above, according to the optical fiber glass body of the present invention, an optical fiber glass body to which chlorine is sufficiently added can be efficiently produced.

In the method for manufacturing an optical fiber glass body, the second chlorine-based gas is different from the first chlorine-based gas, and the second chlorine-based gas has a temperature of the heater and a partial pressure ratio with respect to the dehydration gas. is the same for the first chlorine-based gas and the second chlorine-based gas, a gas having higher reactivity with respect to the porous glass body than the first chlorine-based gas. Preferably.

In this case, chlorine can be effectively added to the optical fiber glass body.

In the method for manufacturing an optical fiber glass body, the second chlorine-based gas is preferably the same as the first chlorine-based gas.

In this case, since the second chlorine-based gas is the same as the first chlorine-based gas, it is not necessary to switch the chlorine-based gas from the first chlorine-based gas to the second chlorine-based gas in the dehydration process. Therefore, the trouble of switching the chlorine-based gas can be saved, and the optical fiber glass body can be easily manufactured.

In the above-described method for manufacturing an optical fiber glass body, when the second chlorine-based gas is the same as the first chlorine-based gas, the pre-dehydration step and the post-dehydration step include It is preferable that the partial pressure ratios of the chlorine-based gases are different, and the partial pressure ratio of the second chlorine-based gas to the dehydration processing gas is higher than the partial pressure ratio of the first chlorine-based gas to the dehydration processing gas.

In this case, since the concentration of the chlorine-based gas in the dehydration gas increases in the post-dehydration process, the reactivity of the chlorine-based gas with respect to the porous glass body should be made higher than the reactivity of the chlorine-based gas in the pre-dehydration process. can be done. In addition, since the amount of increase in the relative refractive index difference with respect to SiO ₂ is generally proportional to the amount of increase in the partial pressure ratio of the chlorine-based gas to the power of 1/4, the partial pressure ratio of the chlorine-based gas in the post-dehydration process is By making the partial pressure ratio higher than the partial pressure ratio of the chlorine-based gas in the process, the refractive index of the obtained optical fiber glass body can be easily adjusted.

In the method for manufacturing an optical fiber glass body, when the second chlorine-based gas is the same as the first chlorine-based gas, the temperature of the heater is increased in the pre-dehydration step and the post-dehydration step. Differently, it is preferable that the temperature of the heater in the post-dehydration process is higher than the temperature of the heater in the pre-dehydration process.

In this case, in the post-dehydration process, the chlorine-based gas in the dehydration gas is heated to a higher temperature, so that the activity of the chlorine-based gas increases. Therefore, the reactivity of the chlorine-based gas with respect to the porous glass body can be increased more than the reactivity of the chlorine-based gas in the pre-dehydration step.

In the method for manufacturing an optical fiber glass body, the first chlorine-based gas is preferably chlorine.

In this case, among the chlorine-based gases, chlorine has relatively low reactivity with the porous glass body, and the concentration of SiCl ₄ produced by the reaction between the porous glass body and the first chlorine-based gas is particularly low. Therefore, in the pre-dehydration step, even if the generated SiCl ₄ reacts with moisture adhering to the surface of the porous glass body, the concentration of the generated SiO ₂ powder is also lower. Therefore, even if the gas in the furnace core tube is exhausted through the exhaust pipe, clogging of the exhaust pipe is more sufficiently suppressed.

In the present invention, "reactivity with respect to the porous glass body" refers to the ability to increase the relative refractive index difference of the porous glass body with respect to _SiO2 at a wavelength of 632.8 nm. Whether the reactivity to the body is higher than the reactivity to the porous glass body in the pre-dehydration process is determined by the relative refractive index difference at a wavelength of 632.8 nm of the glass body for optical fiber to _SiO2 after the pre-dehydration process. It can be determined by whether or not it is larger than the relative refractive index difference at a wavelength of 632.8 nm of the porous glass body with respect to _SiO2 . Here, the relative refractive index difference is defined as follows.
Relative refractive index difference = (n ₁ ² - n ₂ ² )/2n ₁ ²
(In the above formula, n1 indicates the refractive index of the porous glass body at _a wavelength of 632.8 nm, and _n2 indicates the refractive index of _SiO2 at a wavelength of 632.8 nm.)
The "reactivity to the porous glass body" can be changed by changing not only the type of chlorine-based gas but also the partial pressure ratio and temperature of the chlorine-based gas.

Moreover, in the present invention, the term "chlorine-based gas" refers to a gas containing chlorine atoms.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass body for optical fibers which can manufacture the glass body for optical fibers fully added with chlorine efficiently is provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross-sectional end view which shows an example of the dehydration-sintering apparatus for enforcing the manufacturing method of the glass body for optical fibers of this invention.

Hereinafter, embodiments of the method for manufacturing an optical fiber glass body of the present invention will be described in detail.

First, before describing the embodiment of the method for manufacturing an optical fiber glass body of the present invention, a dehydration sintering apparatus for carrying out the method for manufacturing an optical fiber glass body of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional end view showing an example of a dehydration and sintering apparatus for carrying out the method for producing an optical fiber glass body of the present invention.

As shown in FIG. 1 , the dehydration-sintering apparatus 100 includes a furnace core tube 1 for accommodating a porous glass body P and a heating furnace 2 surrounding the furnace core tube 1 . The core tube 1 has a core tube body 1a and a lid portion 1c that closes an upper end opening 1b of the core tube body 1a. An insertion hole 1d for inserting a support rod 4 for suspending the porous glass body P is formed in the lid portion 1c. A connection portion 5 for suspending the porous glass body P is attached to the lower end of the support rod 4 , and the connection portion 5 is connected to the porous glass body P. The furnace core tube 1 is formed with a gas supply port 1e for supplying dehydration processing gas containing a chlorine-based gas and an exhaust port 1f for exhausting the gas in the furnace core tube 1. As shown in FIG. An exhaust pipe 3 is connected to the exhaust port 1f, and the exhaust pipe 3 is provided with an exhaust gas treatment device (not shown).

The heating furnace 2 includes an outer wall portion 2a, a heater chamber 2b between the outer wall portion and the furnace core tube 1, and a heater 2c arranged in the heater chamber 2b so as to surround the furnace core tube 1. there is

Next, an embodiment of a method for manufacturing an optical fiber glass body using the dehydration sintering apparatus 100 will be described.

In the method of manufacturing the optical fiber glass body of the present embodiment, first, the porous glass body P is prepared. Here, the porous glass body P includes, for example, a soot portion and dummy glass rods extending from both ends of the soot portion. After the support rod 4 is pulled up to a position (not shown) where the porous glass body P can be attached, the prepared porous glass body P is hung from the support rod 4 through the connecting portion 5 . By lowering the support rod 4, the porous glass body P is accommodated in the furnace core tube 1, and the upper end opening 1b of the furnace core tube body 1a is closed with the lid portion 1c.

Next, the porous glass body P is dehydrated in the core tube 1 (dehydration process).

Next, the porous glass body P is sintered to obtain an optical fiber glass body (sintering step).

In the dehydration process, the gas in the furnace core tube 1 is discharged through the exhaust pipe 3 connected to the exhaust port 1f of the furnace core tube 1 while supplying the dehydration processing gas containing the chlorine-based gas into the furnace core tube 1. Vent to processing equipment. In the dehydration process, after performing a pre-dehydration process using a first chlorine-based gas as a chlorine-based gas, a post-dehydration process is performed using a second chlorine-based gas as a chlorine-based gas. Then, in the post-dehydration treatment step, the reactivity of the second chlorine-based gas with respect to the porous glass body P is made higher than the reactivity of the first chlorine-based gas with respect to the porous glass body P.

According to the method for manufacturing an optical fiber glass body of the present embodiment, the reactivity of the first chlorine-based gas with respect to the porous glass body P is increased to the second level with respect to the porous glass body P in the pre-dehydration treatment step of the dehydration treatment step. Since the reactivity is lower than that of the chlorine-based gas, the concentration of SiCl ₄ generated by the reaction between the porous glass body P and the first chlorine-based gas is low. Therefore, even if the generated SiCl ₄ reacts with moisture in the atmosphere in the pre-dehydration process, the concentration of the generated SiO ₂ powder is also low. Therefore, even if the gas in the furnace core tube 1 is exhausted through the exhaust pipe 3, clogging of the exhaust pipe 3 is sufficiently suppressed. In the post-dehydration process, since the reactivity of the second chlorine-based gas with respect to the porous glass body P is higher than the reactivity of the first chlorine-based gas with respect to the porous glass body P, the optical fiber glass Able to add enough chlorine to the body. At this time, SiCl ₄ is generated by the reaction between the porous glass body P and the second chlorine-based gas. It is Therefore, the concentration of the SiO ₂ powder produced by the reaction between SiCl ₄ and the moisture adhering to the surface of the porous glass body P becomes sufficiently low. Therefore, even if the gas in the furnace core tube 1 is exhausted through the exhaust pipe 3, clogging of the exhaust pipe 3 is sufficiently suppressed. As described above, according to the optical fiber glass body of the present invention, an optical fiber glass body to which chlorine is sufficiently added can be efficiently produced.

Next, the dehydration treatment process and the sintering process will be described in detail.

(A) Dehydration Process The dehydration process is a process of dehydrating the porous glass body P in the core tube 1 . The dehydration process includes a pre-dehydration process and a post-dehydration process, as described above.

The dehydration gas further contains an inert gas as a carrier gas in addition to the chlorine-based gas. As the inert gas, for example, He, Ne, Ar, _N2 , etc. can be used.

(Porous glass body)
The porous glass body P can be obtained by a soot method such as a VAD method or an external attachment method. In the soot method, a porous glass body P is obtained as follows. That is, first, a dummy rod having a shape that can be connected to the connection portion 5 at the lower end of the support rod 4 and a glass rod on which glass particles are to be deposited are welded together. Then, a burner is installed, and oxygen gas, hydrogen gas, and inert gas are flowed into the burner to cause a reaction. Into the flame, glass raw material gas such as SiCl ₄ is supplied to generate glass fine particles on the rotating glass rod. . A porous glass body P is thus obtained.

The porous glass body P may be composed of a core portion and a clad portion outside the core portion, may be composed of only the core portion, or may be composed of only the clad portion.

The porous glass body P contains, for example, _SiO2 .

(Pre-dehydration process)
In the pre-dehydration treatment step, the first chlorine-based gas is used as the chlorine-based gas. Examples of the first chlorine-based gas include chlorine, thionyl chloride (SOCl ₂ ), SiCl ₄ , carbon tetrachloride (CCl ₄ ), and the like.

Among them, chlorine is preferable as the first chlorine-based gas. In this case, OH groups on the surface of the porous glass body P and water attached to the surface are removed by the following formulas (1) and (2).

2SiOH (porous glass body P)+Cl ₂ →2Si—Cl+2HCl+O ₂ (1)
2H ₂ O+2Cl ₂ →4HCl+O ₂ (2)

On the other hand, chlorine causes the following reaction (3) with the porous glass body P.

SiO ₂ (porous glass body P)+2Cl ₂ →SiCl ₄ +O ₂ (3)

The SiCl ₄ generated at this time reacts with H ₂ O in the atmosphere according to the following formula (4) to generate SiO ₂ powder.

SiCl ₄ +2H ₂ O→SiO ₂ (powder)+4HCl (4)

However, among chlorine-based gases, chlorine has low reactivity with the porous glass body P, and the concentration of SiCl ₄ generated by the reaction between the porous glass body P and the first chlorine-based gas (reaction of formula (3)) is is particularly low. Therefore, in the pre-dehydration step, even if the generated SiCl ₄ reacts with the water adhering to the surface of the porous glass body P, the concentration of the generated SiO ₂ powder is also lower (equation (4 )reference). Therefore, even if the gas in the furnace core tube 1 is exhausted through the exhaust pipe 3, clogging of the exhaust pipe 3 is sufficiently suppressed.

The partial pressure ratio (R1) of the first chlorine-based gas to the dehydration gas is not particularly limited, but is preferably 0.01 or more. In this case, the porous glass body P can be dehydrated more efficiently than when the partial pressure ratio R1 is less than 0.01.

More preferably, the voltage division ratio R1 is 0.25 or more.

The temperature of the heater 2c is not particularly limited as long as it is a temperature lower than the sintering temperature of the porous glass body P and a temperature at which the OH groups on the surface of the porous glass body P and water adhering to the surface can be dehydrated. However, from the viewpoint of promoting the diffusion of the first chlorine-based gas into the porous glass body P, the temperature is preferably 1000° C. or higher. However, the temperature of the heater 2c is preferably 1200° C. or less from the viewpoint of promoting the diffusion of the first chlorine-based gas into the porous glass body P and sufficiently suppressing the softening of the porous glass body P.

(Post-dehydration process)
In the post-dehydration process, the second chlorine-based gas is used as the chlorine-based gas. SOCl ₂ , SiCl ₄ , CCl ₄ or the like can be used as the second chlorine-based gas, for example. As the second chlorine-based gas, a gas different from the first chlorine-based gas is used in this embodiment. In this case, the second chlorine-based gas is the first chlorine-based gas when the temperature of the heater 2c and the partial pressure ratio to the dehydration processing gas are the same for the first chlorine-based gas and the second chlorine-based gas. A gas having higher reactivity with respect to the porous glass body P than the system gas is preferable. In this case, chlorine can be effectively added to the optical fiber glass body. For example, when chlorine is used as the first chlorine-based gas, SOCl ₂ , SiCl ₄ , CCl ₄ or the like can be used as the second chlorine-based gas. The reactivity of the chlorine-based gas with respect to the porous glass body P under the condition that the temperature of the heater 2c and the partial pressure ratio to the dehydration treatment gas are the same is 1/4 of the partial pressure ratio of the chlorine-based gas. The slope of the straight line that indicates the relationship between the power and the relative refractive index difference of the optical fiber glass body with respect to SiO ₂ can be used as an index.

The partial pressure ratio (R2) of the second chlorine-based gas to the dehydration gas depends on the type of the second chlorine-based gas, so it cannot be generalized. For example, when the second chlorine-based gas is thionyl chloride, It is preferably 0.03 or more. In this case, chlorine can be added to the porous glass body P more efficiently than when the partial pressure ratio R2 is less than 0.03.

For example, when the second chlorine-based gas is thionyl chloride, the partial pressure ratio R2 is more preferably 0.05 or more.

However, the partial pressure ratio R2 is the partial pressure ratio at which the partial pressure of the second chlorine-based gas is the same as the saturated vapor pressure of the second chlorine-based gas at the temperature of the piping for supplying the second chlorine-based gas into the core tube 1. It is preferably smaller than Ra. In this case, unlike the case where the partial pressure ratio R2 is Ra or more, condensation of the second chlorine-based gas can be suppressed in the piping when the second chlorine-based gas is supplied into the furnace core tube 1 through the piping, Corrosion and deterioration of piping due to dew condensation can be sufficiently suppressed. Further, when the partial pressure ratio R2 is smaller than Ra, a predetermined amount of the second chlorine-based gas can be supplied into the core tube 1 .

The temperature of the heater 2c is not particularly limited, but from the viewpoint of sufficiently adding chlorine to the porous glass body P, it is preferably 1100° C. or higher. However, the temperature of the heater 2c is preferably 1200° C. or less from the viewpoint of promoting the diffusion of the second chlorine-based gas into the porous glass body P and sufficiently suppressing the softening of the porous glass body P. .

(B) Sintering Step The sintering step is a step of sintering the porous glass body P to obtain an optical fiber glass body. In the sintering process, a sintering process gas is supplied into the furnace core tube 1 from the gas supply port 1e, and the gas in the furnace core tube 1 is exhausted through an exhaust pipe 3 connected to the exhaust port 1f of the furnace core tube 1. Vent to processing equipment. In the sintering process, after the porous glass body P that has undergone the dehydration treatment process is moved above the heater 2c, the lower end of the porous glass body P is placed inside the heater 2c, and the porous glass body P is moved to the heater 2c. or by heating the porous glass body P with the heater 2c without moving the porous glass body P that has undergone the dehydration treatment step.

In the sintering step, the temperature of the heater 2c is set to the sintering temperature of the porous glass body P or higher. Here, the sintering temperature of the porous glass body P is the lowest value of the temperature of the heater 2c capable of vitrifying the porous glass body P into transparent glass. The sintering process gas contains an inert gas.

For example, He, Ar, or the like can be used as the inert gas. The inert gas may be the same as or different from the inert gas used in the dehydration process.

The present invention is not limited to the above embodiments. For example, in the above embodiment, in the post-dehydration process, a gas different from the first chlorine-based gas is used as the second chlorine-based gas, but the second chlorine-based gas may be the same as the first chlorine-based gas. In this case, in the post-dehydration process, the partial pressure ratio (R2) of the second chlorine-based gas with respect to the dehydration gas needs to be greater than the partial pressure ratio R1 of the first chlorine-based gas. That is, the ratio of R2 to R1 should be greater than one. In this case, since the concentration of the chlorine-based gas in the dehydration gas increases in the post-dehydration process, the reactivity of the chlorine-based gas with respect to the porous glass body P is made higher than the reactivity of the chlorine-based gas in the pre-dehydration process. be able to. In addition, since the amount of increase in the relative refractive index difference with respect to _SiO2 glass is generally proportional to the amount of increase in the partial pressure ratio of the chlorine-based gas to the power of 1/4, the partial pressure ratio of the chlorine-based gas in the post-dehydration process is By making the partial pressure ratio higher than the partial pressure ratio of the chlorine-based gas in the treatment step, the refractive index of the obtained optical fiber glass body can be easily adjusted.

Although the above ratio (R2/R1) is not particularly limited as long as it is greater than 1, it is preferably 1.5 or more. In this case, chlorine can be added to the porous glass body P more efficiently than when the ratio is less than 1.5. The ratio (R2/R1) is more preferably 2.5 or more, and even more preferably 16.5 or more.

Alternatively, when the second chlorine-based gas is the same as the first chlorine-based gas, in the post-dehydration process, the temperature (T2) of the heater 2c is set higher than the temperature (T1) of the heater 2c in the pre-dehydration process. may That is, the temperature ratio of T2 to T1 (T2/T1) must be greater than one. In this case, in the post-dehydration process, the chlorine-based gas in the dehydration gas is heated to a higher temperature, so that the activity of the chlorine-based gas increases. Therefore, the reactivity of the chlorine-based gas with respect to the porous glass body can be increased more than the reactivity of the chlorine-based gas in the pre-dehydration step.

Although the temperature ratio is not particularly limited as long as it is greater than 1, it is preferably 1.08 or more. In this case, chlorine can be added to the porous glass body P more efficiently than when the temperature ratio is less than 1.08. In the above temperature ratio (T2/T1), T1 and T2 are absolute temperatures.

However, the temperature ratio is preferably 1.16 or less. In this case, blockage of the exhaust pipe 3 can be suppressed more sufficiently than when the temperature ratio exceeds 1.16.

EXAMPLES The content of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Examples 1 to 11)
First, a porous glass body P was produced as follows. That is, first, a dummy rod having a shape connectable to the connection portion 5 at the lower end of the support rod 4 and a glass rod on which glass particles are to be deposited were prepared and welded. Then, a burner was installed, and oxygen gas, hydrogen gas, and inert gas Ar _were flowed through the burner to cause a reaction. A soot portion was formed. At this time, the glass rod was composed of _SiO2 . Thus, a porous glass body P was obtained. The obtained porous glass body P was composed of a soot portion and dummy glass rods extending from both ends of the soot portion.

The resulting porous glass body P had a soot portion with a total length of 300 mm and a diameter of 30 mm. After the support rod 4 was pulled up to a position (not shown) where the porous glass body P could be attached, the prepared porous glass body P was suspended from the support rod 4 via the connecting portion 5 . By lowering the support rod 4, the porous glass body P was accommodated in the furnace core tube 1, and the upper end opening 1b of the furnace core tube body 1a was closed with the lid portion 1c (see FIG. 1).

Next, the porous glass body P was sequentially subjected to a dehydration treatment step and a sintering step in the dehydration sintering apparatus 100 .

In the dehydration process, first, the porous glass body P was subjected to a pre-dehydration process. Specifically, the support rod 4 was lowered to insert the porous glass body P inside the heater 2c. Then, a dehydration treatment gas composed of the first chlorine-based gas shown in Table 1 and He as an inert gas is supplied into the furnace core tube 1 from the gas supply port 1e at a flow rate of 3 L/min. was exhausted to the exhaust gas treatment device through the exhaust pipe 3 connected to the exhaust port 1f. At this time, the partial pressure ratio R1 of the first chlorine-based gas to the dehydration gas was set as the partial pressure ratio of the first chlorine-based gas in the pre-dehydration process in Table 1. The partial pressure ratio R1 is the partial pressure ratio of the first chlorine-based gas when the pressure of the dehydration gas is 1. Table 1 shows the temperature T1 of the heater 2c in the pre-dehydration process.

After 3 hours had passed, a post-dehydration treatment step was performed. Specifically, a dehydration treatment gas composed of the second chlorine-based gas shown in Table 1 and He as an inert gas was supplied from the gas supply port 1e into the core tube 1 at a flow rate of 3 L/min. At this time, the exhaust gas treatment apparatus was kept in operation, and the gas in the furnace core tube 1 was exhausted to the exhaust gas treatment apparatus through the exhaust pipe 3 connected to the exhaust port 1f. At this time, the partial pressure ratio R2 of the second chlorine-based gas to the dehydration gas was set as the partial pressure ratio of the second chlorine-based gas in the post-dehydration process shown in Table 1. The partial pressure ratio R2 is the partial pressure ratio of the second chlorine-based gas when the pressure of the dehydration processing gas is set to 1. Table 1 shows the temperature T2 of the heater 2c in the post-dehydration process.

Then, after 3 hours passed and the dehydration process was completed, the sintering process was performed. Specifically, the porous glass body P was left as it was without being moved, and the heater 2c was heated to 1450° C. to sinter it. The sintering temperature of the porous glass body P was 1450°C. Thus, an optical fiber glass body having a total length of 150 mm was produced.

(Comparative Examples 1 to 8)
In the pre-dehydration process, the type of the first chlorine-based gas, the partial pressure ratio R1, and the temperature T1 are set as shown in Table 1, and in the post-dehydration process, the type of the second chlorine-based gas, the partial pressure ratio R2, and the temperature T2 of the heater 2c are set to As shown in Table 1, the same procedure as in Example 1 was performed except that the type of the first chlorine-based gas and the type of the second chlorine-based gas, the partial pressure ratio R1 and the partial pressure ratio R2, and the temperatures T1 and T2 were the same. An optical fiber glass body was produced by

[evaluation]
The effect of adding chlorine and the effect of suppressing exhaust pipe clogging were evaluated in the following manner for the methods of manufacturing optical fiber glass bodies of Examples 1 to 11 and Comparative Examples 1 to 8.

(Chlorine addition effect)
The refractive index at a wavelength of 632.8 nm of the optical fiber glass bodies obtained in Examples 1 to 11 and Comparative Examples 1 to 8 was measured, and the relative refractive index difference was calculated based on the following formula. was taken as an index of the chlorine addition effect. Table 1 shows the results.
Relative refractive index difference = (n ₁ ² - n ₂ ² )/2n ₁ ²
(In the above formula, n1 indicates the refractive index of the optical fiber glass body at _a wavelength of 632.8 nm, and _n2 indicates the refractive index of _SiO2 at a wavelength of 632.8 nm.)
At this time, the acceptance criteria for the chlorine addition effect were as follows.

(Acceptance Criteria) The relative refractive index difference of the glass body for optical fiber is 0.050% or more.

The relative refractive index difference of the optical fiber glass body obtained in Comparative Example 3 (partial pressure ratio R1 of chlorine as the first chlorine-based gas: 0.30, temperature T1: 1200° C.) was 0.041%. On the other hand, the relative refractive index difference of the optical fiber glass bodies obtained in Examples 1 to 3 (partial pressure ratio R1 of chlorine, which is the first chlorine-based gas: 0.30, temperature T1: 1200° C.) was Since it was 0.050 to 0.080%, in the post-dehydration process of Examples 1-3, the reactivity of thionyl chloride (SOCl ₂ ), which is the second chlorine-based gas, was used in the pre-dehydration process. It can be seen that the reactivity is higher than that of chlorine, which is the first chlorine-based gas used. Further, the relative refractive index difference of the optical fiber glass body obtained in Comparative Example 5 (partial pressure ratio R1 of thionyl chloride (SOCl ₂ ) as the first chlorine-based gas: 0.01, temperature T1: 1200° C.) is 0.043%, the light obtained in Examples 4 to 6 (partial pressure ratio R1: 0.01 of thionyl chloride (SOCl ₂ ), which is the first chlorine-based gas, temperature T1: 1200 ° C.) Since the relative refractive index difference of the fiber glass body was 0.050 to 0.057%, in the post-dehydration process of Examples 4 to 6, thionyl chloride (SOCl ₂ ), which is the second chlorine gas, was used. It can be seen that the reactivity is higher than that of thionyl chloride (SOCl ₂ ), which is the first chlorine-based gas used in the pre-dehydration process. Further, the relative refractive index difference of the optical fiber glass body obtained in Comparative Example 7 (partial pressure ratio R1: 0.05 of thionyl chloride (SOCl ₂ ) as the first chlorine-based gas, temperature T1: 1000° C.) is 0.040%, whereas the optical fiber obtained in Example 7 (partial pressure ratio R1 of thionyl chloride (SOCl ₂ ), which is the first chlorine-based gas: 0.05, temperature T1: 1000 ° C.) _The relative refractive index difference of the glass body was 0.057%. It can be seen that the reactivity is higher than that of thionyl chloride (SOCl ₂ ), which is the first chlorine-based gas used in . Furthermore, the relative refractive index difference of the optical fiber glass body obtained in Comparative Example 2 (partial pressure ratio of chlorine as the first chlorine-based gas: 0.30, temperature: 1150° C.) was 0.040%. On the other hand, the relative refractive index difference of the optical fiber glass bodies obtained in Examples 8 to 11 (partial pressure ratio of chlorine, which is the first chlorine-based gas: R1: 0.30, temperature T1: 1150° C.) is 0.050. 0.080%, in the post-dehydration process of Examples 8-11, the reactivity of thionyl chloride (SOCl ₂ ), which is the second chlorine-based gas, was lower than that of the second chlorine-based gas used in the pre-dehydration process. It can be seen that the reactivity is higher than that of chlorine, which is a monochlorine gas.

(Exhaust pipe clogging suppression effect)
Optical fiber glass bodies were continuously produced in Examples 1 to 11 and Comparative Examples 1 to 8, and the number of optical fiber glass bodies continuously produced until the exhaust pipe was closed was measured. At this time, the number of optical fiber glass bodies at this time was used as an index of the effect of suppressing blockage of the exhaust pipe. Table 1 shows the results. At this time, the acceptance criteria for the effect of suppressing blockage of the exhaust pipe were as follows.

(Acceptance Criteria) The number of continuously manufactured optical fiber glass bodies is 20 or more.

From the results shown in Table 1, it was found that the methods for producing the optical fiber glass bodies of Examples 1 to 11 satisfied the acceptance criteria in terms of the effect of adding chlorine and the effect of suppressing clogging of the exhaust pipe. On the other hand, it was found that the manufacturing methods of the optical fiber glass bodies of Comparative Examples 1 to 8 did not meet the acceptance criteria in terms of either the effect of adding chlorine or the effect of suppressing clogging of the exhaust pipe.

From the above, it was confirmed that the method for producing an optical fiber glass body of the present invention can efficiently produce an optical fiber glass body to which chlorine is sufficiently added.

DESCRIPTION OF SYMBOLS 1... Furnace tube 2c... Heater 3... Exhaust pipe P... Porous glass body

Claims (4)

a dehydration treatment step of heating the porous glass body with a heater and dehydrating it in the furnace core tube;
a sintering step of heating and sintering the porous glass body with the heater to obtain an optical fiber glass body, comprising:
In the dehydration step, gas in the furnace core tube is exhausted through an exhaust pipe connected to the furnace core tube while supplying a dehydration gas containing a chlorine-based gas into the furnace core tube,
The dehydration step includes a pre-dehydration step using a first chlorine-based gas as the chlorine-based gas and a post-dehydration step using a second chlorine-based gas as the chlorine-based gas,
making the reactivity of the second chlorine-based gas with respect to the porous glass body higher in the post-dehydration process than the reactivity of the first chlorine-based gas with respect to the porous glass body in the pre-dehydration process;
The second chlorine-based gas differs from the first chlorine-based gas in that the temperature of the heater and the partial pressure ratio of the second chlorine-based gas to the dehydration gas are the same as the first chlorine-based gas and the second chlorine-based gas. A method for manufacturing an optical fiber glass body, wherein the gas has a higher reactivity with the porous glass body than the first chlorine-based gas when placed under the same conditions as the system gas. a dehydration treatment step of heating the porous glass body with a heater and dehydrating it in the furnace core tube;
a sintering step of heating and sintering the porous glass body with the heater to obtain an optical fiber glass body, comprising:
In the dehydration step, gas in the furnace core tube is exhausted through an exhaust pipe connected to the furnace core tube while supplying a dehydration gas containing a chlorine-based gas into the furnace core tube,
The dehydration step includes a pre-dehydration step using a first chlorine-based gas as the chlorine-based gas and a post-dehydration step using a second chlorine-based gas as the chlorine-based gas,
making the reactivity of the second chlorine-based gas with respect to the porous glass body higher in the post-dehydration process than the reactivity of the first chlorine-based gas with respect to the porous glass body in the pre-dehydration process;
The second chlorine-based gas is the same as the first chlorine-based gas,
The partial pressure ratio of the chlorine-based gas to the dehydration gas differs between the pre-dehydration process and the post-dehydration process, and the partial pressure ratio of the second chlorine-based gas to the dehydration gas is different from that of the dehydration gas. is at least three times the partial pressure ratio of the first chlorine-based gas ,
The method for manufacturing an optical fiber glass body, wherein the first chlorine-based gas is thionyl chloride (SOCl ₂ ) . 3. The production of an optical fiber glass body according to claim 2, wherein the partial pressure ratio of said second chlorine-based gas to said dehydration gas is five times or less the partial pressure ratio of said first chlorine-based gas to said dehydration gas. Method. 2. The method for manufacturing an optical fiber glass body according to claim 1 , wherein said first chlorine-based gas is chlorine.

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