CN109437546B - Optical fiber preform heating furnace and heating doping method thereof - Google Patents
Optical fiber preform heating furnace and heating doping method thereof Download PDFInfo
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- CN109437546B CN109437546B CN201811468525.2A CN201811468525A CN109437546B CN 109437546 B CN109437546 B CN 109437546B CN 201811468525 A CN201811468525 A CN 201811468525A CN 109437546 B CN109437546 B CN 109437546B
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/01446—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
- C03B37/01453—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering for doping the preform with flourine
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/01446—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/01446—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
- C03B37/0146—Furnaces therefor, e.g. muffle tubes, furnace linings
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- Manufacturing & Machinery (AREA)
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- Organic Chemistry (AREA)
- Manufacture, Treatment Of Glass Fibers (AREA)
Abstract
The invention relates to an optical fiber perform heating furnace and a heating doping method thereof, wherein the heating furnace comprises a closed furnace body, an air inlet pipe is connected below the furnace body, an exhaust pipe is arranged above the furnace body, and a circumferential heating element is arranged on the periphery of the furnace body. The middle part of the furnace chamber is provided with the middle heating element, so that the inside and the outside of the hollow quartz glass powder rod are simultaneously heated, the temperature field of the hollow quartz glass powder rod is changed into a glass body with high middle and low outer edge by controlling a heating source, the corrosion of a furnace body muffle tube is ensured not to be corroded or to be corroded in a smaller level, the corrosion of a large-diameter pure quartz glass muffle tube is avoided and reduced, the service life of the furnace body is prolonged, only the heat conduction protective sleeve at the middle part needs to be replaced, and the maintenance cost is greatly reduced; the hollow quartz glass powder rod is heated inside and outside simultaneously, the temperature field distribution is more reasonable and uniform, and the doping uniformity is improved.
Description
Technical Field
The invention relates to an optical fiber preform heating furnace and a heating doping method thereof, belonging to the technical field of optical fiber manufacturing.
Background
Optical fiber communication has the characteristics of large transmission capacity, long transmission distance, high transmission speed and the like, and is widely applied to optical communication networks such as long-distance trunk networks, metropolitan area networks, access networks and the like. Optical fibers are generally designed such that a core portion has a refractive index greater than that of a cladding to facilitate light transmission, and for this reason, it is necessary to increase the refractive index of the core or decrease the refractive index of the cladding.
The method for increasing the refractive index of the core layer is mainly to add elements such as germanium, aluminum and titanium in the raw materials for manufacturing the quartz glass, but the attenuation of the optical fiber caused by the elements is increased along with the increase of the content of the dopants, so the dopants in the core layer are preferably not used or are as few as possible. In order to overcome the disadvantage of increasing the refractive index of the core layer, a method of reducing or decreasing the refractive index of the cladding layer can be adopted, namely fluorine is added into the cladding layer to decrease the refractive index of the cladding layer, so that the required refractive index difference between the core layer and the cladding layer is met.
In addition, the cladding region needs to be doped with chlorine element due to viscosity matching requirements, and the viscosity of the core layer slightly doped with germanium element can ensure that the optical fiber drawing process has smaller mechanical stress.
To sum up, the doping of the optical fiber preform is very important, the doping mode at the present stage mainly utilizes a high-temperature heating furnace for doping, but the strict requirements on the furnace are met, halogen elements (such as fluorine and chlorine) can be activated at high temperature to corrode the material of the furnace body, the furnace body needs to be resistant to high temperature and corrosion, a glass (muffle) tube made of pure graphite or pure quartz glass is usually adopted, the service life of the glass (muffle) tube is still limited, the muffle tube needs to be replaced after being used for a period of time, and the muffle tube is large in size, so that the processing cost is high, and the replacement is troublesome.
On the other hand, the heating elements of the existing optical fiber preform heating furnace are all arranged on the periphery of the muffle tube furnace body, and the temperature is diffused from the outside to the inside of the quartz glass powder rod when the temperature is just raised and heated, namely the temperature distribution is high outside and low inside. Meanwhile, the doping gas entering the furnace is at normal temperature, so that the heat in the furnace is consumed, the temperature is not uniformly distributed, and the heating doping is not uniform.
Disclosure of Invention
The invention aims to solve the technical problem of providing an optical fiber preform heating furnace and a heating doping method thereof aiming at the defects of the prior art, which are not only beneficial to uniformly doping a quartz glass powder rod, but also can prolong the service life of a furnace body.
The heating furnace adopted by the invention for solving the problems comprises the following technical scheme: the heating furnace comprises a closed furnace body, an air inlet pipe is connected below the furnace body, an exhaust pipe is arranged above the furnace body, and a circumferential heating element is arranged on the periphery of the furnace body.
According to the scheme, the pipeline heating element is arranged at the air inlet pipe to preheat the doping gas.
According to the scheme, the furnace body is a cylindrical furnace body, and the middle heating element is arranged along the axis of the cylindrical furnace body.
According to the scheme, the middle heating element is a rod-shaped or tubular graphite resistance heating element.
According to the scheme, the furnace body is made of pure quartz glass (a muffle tube) or compact graphite, and the heat-conducting protective sleeve is made of the pure quartz glass or the compact graphite.
According to the scheme, the heating temperature of the middle heating element is 1000-1500 ℃, the heating temperature of the circumferential heating element is 700-1000 ℃, and the heating temperature of the pipeline heating element is 500-800 ℃.
According to the scheme, the air inlet pipe is arranged on one side of the bottom of the furnace body, and the exhaust pipe is arranged on the top of the furnace body.
The technical scheme of the heating doping of the invention is as follows: the heating furnace is adopted, the hollow quartz glass powder rod deposited by the external vapor deposition method (VAD or OVD) is placed into the furnace chamber, and the middle heating element is sleeved;
starting a middle heating element and a circumferential heating element to heat the inside and the outside of the hollow quartz glass powder rod simultaneously, wherein the heating temperature of the middle heating element is 1000-1500 ℃, the heating temperature of the circumferential heating element is 700-1000 ℃, and the hollow quartz glass powder rod is heated to more than 1000 ℃;
and (3) starting a pipeline heating element to preheat the recently focused doping gas, opening an air inlet valve to enable the doping gas to enter the furnace chamber after being preheated, carrying out doping reaction with the hollow quartz glass powder rod, wherein the heating temperature of the pipeline heating element is 500-800 ℃, and the gas after the reaction is discharged from an exhaust pipe.
According to the scheme, the heating temperature of the middle heating element is preferably 1000-1400 ℃, the heating temperature of the middle heating element is higher than that of the circumferential heating element, and the temperature difference is controlled within 500 ℃; the heating temperature of the pipeline heating element is lower than or equal to that of the circumferential heating element, and the temperature difference is controlled within 200 ℃.
According to the scheme, the middle heating element is sleeved with the hollow quartz glass powder rod, and the gap between the hollow quartz glass powder rod and the heat-conducting protective sleeve outside the middle heating element is 0.1-3 mm.
The invention has the beneficial effects that: 1. the middle part of the furnace chamber is provided with a middle heating element, so that the inside and the outside of the hollow quartz glass powder rod are simultaneously heated, the temperature field of the hollow quartz glass powder rod is changed into a glass body with high middle and low outer edge by controlling a heating source, the temperature of the furnace body is controlled below 1000 ℃, the temperature of the muffle tube of the furnace body is reduced to the temperature which does not react with halogen, the muffle tube is ensured not to be corroded or corroded in a smaller level, the corrosion to a large-diameter pure quartz glass muffle tube is avoided and reduced, the service life of the furnace body is prolonged, only a heat-conducting protective sleeve at the middle part needs to be replaced, and the maintenance cost is greatly reduced; 2. the hollow quartz glass powder rod is heated inside and outside simultaneously, the temperature field distribution of the hollow quartz glass powder rod is more reasonable and uniform, the diffusion of halogen elements into the glass rod is facilitated, and the doping uniformity is improved; 3. the halogen-doped gas enters the heating furnace after being heated, so that the temperature of the quartz glass powder rod is balanced, the temperature field distribution in the furnace is more uniform and stable, the doping uniformity and the doping amount of the quartz glass powder rod are further improved, and the doping efficiency is improved.
Drawings
FIG. 1 is a schematic structural view of a heating furnace according to an embodiment of the present invention.
FIG. 2 is a temperature profile of doping heating according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples and the accompanying drawings.
One embodiment of the heating furnace of the present invention is shown in fig. 1, and comprises a closed cylindrical furnace body 2 made of pure quartz glass (muffle tube), an air inlet pipe 7 connected to one side of the bottom of the furnace body, an exhaust pipe 8 arranged on the top of the furnace body, a circumferential heating element 1 arranged on the periphery of the furnace body, a graphite resistance heating element arranged on the circumferential heating element, a middle heating element 5 arranged in the middle of the furnace chamber, the middle heating element being rod-shaped or tubular and being graphite resistance heating element, and a graphite resistance heating element arranged in the middle of the furnace chamberThe heating element is arranged along the axis of the cylindrical furnace body, and the middle heating element is sleeved with a heat-conducting protective sleeve 4 which is made of pure quartz glass, so that the middle heating element is isolated from the furnace chamber. A pipe heating element 3 is provided at the gas inlet pipe for preheating the dopant gas. During doping work, the heating temperature of the middle heating element is preferably 1000-1400 ℃, the heating temperature of the middle heating element is higher than that of the circumferential heating element, and the temperature difference is controlled within 500 ℃; the heating temperature of the pipeline heating element is lower than that of the circumferential heating element, and the temperature difference is controlled within 200 ℃. The halogen gas for doping the optical fiber preform can be mainly divided into a fluorine-containing gas and a chlorine-containing gas, wherein the fluorine-containing gas is mainly F2、SiF4、SF6、CF4、C2F6Etc. chlorine-containing gas is mainly Cl2、SiCl4、CCl4And the like.
One embodiment of the heating doping of the present invention is as follows: the hollow silica glass powder rod was produced by VAD method, and had an outer diameter of 100mm, an inner diameter of 35mm and a length of 1.5 m. The hollow silica glass powder rod was moved into the heating furnace shown in fig. 1, and as shown in the figure, the hollow silica glass powder rod 6 was subjected to a chlorine doping treatment by the following method: chlorine gas is introduced into the furnace body from an air inlet pipe at the lower part of the furnace body for 1L/min and nitrogen gas is introduced into the furnace body for 25L/min, the temperature of the gas reaches 900 ℃ after the gas is heated by a pipeline heating element, the gas enters a furnace chamber, and meanwhile, an exhaust pipe is arranged above the furnace body to keep the stable pressure of the gas in the furnace; the heating temperature of the circumferential heating element is 900 ℃, the heating temperature of the middle heating element is 1300 ℃, the gap between the heat-conducting protective sleeve outside the middle heating element and the hollow quartz glass powder rod is 2.0mm, and the actually measured temperature field is distributed as shown in figure 2, wherein the distance from the middle position of the hollow quartz glass powder rod to the muffle tube of the furnace body is normalized, the middle position of the furnace body is 0, the position of the muffle tube is 1, and the outer edge position of the hollow quartz glass powder rod (root rod) is 0.8. The chlorine doping time is 8h, the solid glass body is formed by subsequent melting, the chlorine content in the tested glass is 10000ppm, and the maximum difference value of the chlorine content is 500 ppm.
The second embodiment is as follows: the OVD process formed a hollow quartz glass frit rod with an outer diameter of 200mm, an inner diameter of 45mm and a length of 1.5 m. The hollow silica glass powder rod was moved into the collapsing furnace shown in FIG. 1, and fluorine-doping treatment was performed on the hollow silica glass powder rod as shown in the drawing, wherein the furnace structure was the same as that in example 1. The fluorine doping treatment method comprises the following steps: introducing 1L/min CF4 and 25L/min nitrogen from the lower part of the furnace body, heating by a pipeline heating element to reach 1000 ℃, and introducing the gas into the furnace chamber, wherein an exhaust pipe is arranged above the furnace body to keep the stable pressure of the gas in the furnace; the heating temperature of the circumferential heating element is set to 1000 ℃, the temperature of the middle heating element is set to 1200 ℃, and the gap between the heat-conducting protective sleeve outside the heating element and the hollow quartz glass powder rod is 1.5 mm. The fluorine doping time is 4h, the subsequent melting and shrinking are carried out to obtain a solid glass body, the fluorine content in the test glass is 15000ppm, and the maximum difference value of the fluorine content is 650 ppm.
Since the halogen gas reacts with the high-purity quartz glass muffle tube above the critical temperature to cause corrosion, and the critical reaction temperature of fluorine and chlorine is 1000 ℃, the heating temperature of the circumferential heating element is controlled not to exceed 1000 ℃.
Claims (10)
1. The utility model provides an optical fiber perform heating furnace, is including the confined furnace body, and the below of furnace body is connected with the intake pipe, and the top of furnace body is provided with the blast pipe, has installed circumference heating element in the periphery of furnace body, and its characterized in that installs middle heating element at the middle part of furnace chamber, and middle heating element overcoat is equipped with heat conduction protective case.
2. The furnace of claim 1, wherein a tube heating element is provided at the inlet for preheating the dopant gas.
3. A furnace for heating an optical fiber preform according to claim 1 or 2, wherein said furnace body is a cylindrical furnace body, and said intermediate heating element is disposed along an axis of the cylindrical furnace body.
4. The furnace according to claim 1 or 2, wherein the intermediate heating element is rod-shaped or tubular and is a graphite resistance heating element.
5. The furnace for heating an optical fiber preform according to claim 1 or 2, wherein said furnace body is made of pure silica glass or dense graphite, and said heat conductive protective sleeve is made of pure silica glass or dense graphite.
6. The furnace of claim 2, wherein the intermediate heating element is heated to a temperature of 1000 to 1500 ℃, the circumferential heating element is heated to a temperature of 700 to 1000 ℃, and the tube heating element is heated to a temperature of 500 to 800 ℃.
7. The furnace for heating an optical fiber preform according to claim 1 or 2, wherein the inlet pipe is provided at a bottom side of the furnace body, and the outlet pipe is provided at a top of the furnace body.
8. A method for heating and doping an optical fiber preform, characterized in that a hollow silica glass soot rod deposited by an external vapor deposition method is placed in a furnace chamber and sheathed with an intermediate heating element by using the heating furnace of any one of claims 2 to 7;
starting a middle heating element and a circumferential heating element to heat the inside and the outside of the hollow quartz glass powder rod simultaneously, wherein the heating temperature of the middle heating element is 1000-1500 ℃, the heating temperature of the circumferential heating element is 700-1000 ℃, and the hollow quartz glass powder rod is heated to more than 1000 ℃;
and opening the pipeline heating element to preheat the doping gas at the gas inlet pipe, opening the gas inlet valve to enable the doping gas to enter the furnace chamber after being preheated, carrying out doping reaction with the hollow quartz glass powder rod, wherein the heating temperature of the pipeline heating element is 500-800 ℃, and the reacted gas is discharged from the exhaust pipe.
9. The method for heating and doping an optical fiber preform according to claim 8, wherein the heating temperature of the intermediate heating element is preferably 1000 to 1400 ℃, the heating temperature of the intermediate heating element is higher than that of the circumferential heating element, and the temperature difference is controlled within 500 ℃; the heating temperature of the pipeline heating element is lower than or equal to that of the circumferential heating element, and the temperature difference is controlled within 200 ℃.
10. The method of heating and doping an optical fiber preform according to claim 8 or 9, wherein the hollow silica glass soot rod is inserted into the intermediate heating element with a gap of 0.1 to 3mm from the heat-conductive protective sleeve outside the intermediate heating element.
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| CN201811468525.2A CN109437546B (en) | 2018-12-03 | 2018-12-03 | Optical fiber preform heating furnace and heating doping method thereof |
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