Preform heating furnace and its heating doping methodTechnical field
The present invention relates to a kind of preform heating furnace and its heating doping methods, belong to optic fibre manufacturing technology field.
Background technique
Fiber optic communication has the characteristics that big transmission capacity, long transmission distance, transmission speed are fast, is widely used in long distance lineThe optical communication networks such as net, Metropolitan Area Network (MAN) and access net.The refractive index that optical fiber is typically designed to sandwich layer part is greater than covering, in favor ofThe conduction of light, for this reason, it may be necessary to increase sandwich layer refractive index or reduce the refractive index of covering.
The elements such as germanium, aluminium and titanium are mainly added in the method for increasing sandwich layer refractive index in manufacture raw material of quartz glass, butWith the increase of dopant content, optical fiber attenuation as caused by it also will increase, therefore sandwich layer dopant do not have to preferably orIt is as few as possible.In order to overcome the shortcomings that increasing sandwich layer refractive index, can be wrapped using the method for reducing or reducing cladding indexFluorine is added to reduce its refractive index in layer, meets required refringence between core covering.
In addition, cladding regions need to adulterate chlorine element, are mixed with Germanium in conjunction with micro- in sandwich layer for viscosity matches demandViscosity, it is ensured that have lesser mechanical stress in drawing optical fibers technique.
In conclusion preform doping halogen be it is highly important, doping way at this stage mainly utilizes high temperatureHeating furnace doping, but stove is strict with, because can activate under halogen (such as fluorine and chlorine) high temperature, corrode furnace body materialMaterial, furnace body not only need high temperature resistant, also want corrosion-resistant, generally use glass made of pure graphite or pure quartz glass(muffle) it manages, but its service life is still limited, needs replacing muffle pipe, muffle pipe size after a period of useGreatly, thus processing cost it is high, replacement trouble.
On the other hand, it is all in vitro to be all disposed within muffle pipe furnace for existing its heating element of preform heating furnace, justTemperature is spread outside to inside by fused silica powder stick when starting to warm up heating, i.e., Temperature Distribution is high outside and low outside.Enter furnace simultaneouslyInterior impurity gas is room temperature, can consume furnace interior and divide heat, be unfavorable for temperature and be uniformly distributed, the unevenness for causing heating to be adulteratedIt is even.
Summary of the invention
The technical problem to be solved by the present invention is to provide a kind of predispersed fiber in view of the deficiency of the prior artStick heating furnace processed and its heating doping method, it is not only conducive to fused silica powder stick uniform doping, but also is able to extend furnace bodyService life.
The present invention be solve the problems, such as it is set forth above used by heating furnace technical solution are as follows: include closed furnace body,It is connected with air inlet pipe below furnace body, is provided with exhaust pipe above furnace body, is installed on circumferential heating element in the periphery of furnace body,It is characterized in that being installed on intermediate heating element in the middle part of furnace chamber, thermally conductive protection sleeve pipe is set with outside intermediate heating element.
According to the above scheme, flue heating element is set at air inlet pipe, impurity gas is preheated.
According to the above scheme, the furnace body is cylindrical furnace, axis of the intermediate heating element along cylindrical furnaceLine is installed.
According to the above scheme, the intermediate heating element is rodlike or tubulose, is graphite resistance heating element.
According to the above scheme, the furnace body is made of pure quartz glass (muffle pipe) or solid graphite, and described is thermally conductiveProtection sleeve pipe is made of pure quartz glass or solid graphite.
According to the above scheme, the heating temperature of the intermediate heating element is 1000 ~ 1500 DEG C, the circumferential heating unitThe heating temperature of part is 700 ~ 1000 DEG C, and the heating temperature of the flue heating element is 500 ~ 800 DEG C.
According to the above scheme, the bottom side of furnace body is arranged in the air inlet pipe, and furnace body is arranged in the exhaust pipeTop.
The present invention heats the technical solution of doping are as follows: uses above-described heating furnace, will use outside vapor depositionHollow quartz glass powder stick made of (VAD or OVD) deposition is put into furnace chamber, is inserted in intermediate heating element；
Intermediate heating element and circumferential heating element are opened to heating simultaneously inside and outside hollow fused silica powder stick, whereinThe heating temperature of intermediate heating element is 1000 ~ 1500 DEG C, and the heating temperature of circumferential heating element is 700 ~ 1000 DEG C, is made hollowFused silica powder stick is heated to 1000 DEG C or more；
It opens flue heating element to preheat the impurity gas of current focus, and opens intake valve, keep impurity gas pre-Enter furnace chamber after heat, be doped and react with hollow quartz glass powder stick, the heating temperature of flue heating element is 500 ~ 800DEG C, the gas after reaction is discharged from exhaust pipe.
According to the above scheme, the heating temperature of the intermediate heating element is preferably 1000 ~ 1400 DEG C, intermediate heating elementHeating temperature is higher than the heating temperature of circumferential heating element, and the temperature difference controls within 500 DEG C；The heating temperature of flue heating elementLess than or equal to the heating temperature of circumferential heating element, the temperature difference is controlled within 200 DEG C.
According to the above scheme, the hollow quartz glass powder stick is inserted in intermediate heating element, outside intermediate heating elementThe gap of thermally conductive protection sleeve pipe is 0.1 ~ 3mm.
The beneficial effects of the present invention are: 1, it furnace chamber in the middle part of is installed on intermediate heating element, so that hollow quartz glassGlass powder stick is inside and outside to be heated simultaneously, by controlling heating source, by the temperature field of hollow quartz glass powder stick be changed to height among vitreum,Outer rim is low, and the temperature of furnace body is controlled at 1000 DEG C hereinafter, reduce the temperature of furnace body muffle pipe to the temperature that do not react with halogen,Guarantee muffle pipe does not corrode or the corrosion of smaller rank, avoids and reduce the corruption to major diameter pure quartz glass muffle pipeErosion, extends the service life of furnace body, it is only necessary to replace the thermally conductive protection sleeve pipe in intermediate position, maintenance cost substantially reduces；2, hollow quartzy glassGlass powder stick is inside and outside to be heated simultaneously, and hollow quartz glass powder stick thermo parameters method is more reasonable and uniform, is conducive to promote halogenIt diffuses into inside glass bar, improves the uniformity of doping；3, it enters back into heating furnace, is convenient for after doping halogen gas is heatedThe temperature of balanced fused silica powder stick further improves quartz glass so that temperature field in furnace more uniformly spreads and stablizesPowder stick uniform doping and doping quality, and facilitate the promotion of doping efficiency.
Detailed description of the invention
Fig. 1 is the structural schematic diagram of heating furnace one embodiment of the present invention.
Temperature profile when Fig. 2 is present invention doping heating.
Specific embodiment
Below with reference to embodiment and attached drawing, the present invention is described in further detail.
One embodiment of heating furnace of the invention is as shown in Figure 1, include closed circular tubular furnace body 2, furnace body is pure stoneFurnace body made of English glass (muffle pipe), the bottom side of furnace body are connected with air inlet pipe 7, exhaust are provided at the top of furnace bodyPipe 8 is installed on circumferential heating element 1 in the periphery of furnace body, and circumferential heating element is graphite resistance heating element, in furnace chamberPortion is installed on intermediate heating element 3, and it is graphite resistance heating element that the intermediate heating element, which is rodlike or tubulose, intermediateHeating element is installed along the axis of cylindrical furnace, thermally conductive protection sleeve pipe 4 is set with outside intermediate heating element, by pure quartz glassIt is made, so that intermediate heating element is isolated with furnace chamber.At air inlet pipe be arranged flue heating element 3, to impurity gas intoRow preheating.When adulterating work, the heating temperature of the intermediate heating element is preferably 1000 ~ 1400 DEG C, intermediate heating elementHeating temperature be higher than the heating temperature of circumferential heating element, the temperature difference controls within 500 DEG C；The heating temperature of flue heating elementDegree is lower than the heating temperature of circumferential heating element, and temperature difference control is within 200 DEG C.The halogen gas of doped optical fiber prefabricated rod is mainFluoro-gas and chlorine-containing gas can be divided into, wherein fluoro-gas is mainly F2、SiF4、SF6、CF4、C2F6Deng chlorine-containing gas is mainFor Cl2、SiCl4、CCl4Deng.
One embodiment that the present invention heats doping is as follows: hollow quartz glass powder stick is made in VAD method, and outer diameter is100mm, internal diameter 35mm, length 1.5m.This hollow quartz glass powder stick is moved into the heating furnace in Fig. 1, as shown in the figure,Hollow fused silica powder stick 6 is carried out to mix chlorine processing, it is as follows to mix chlorine processing method: being passed through chlorine 1L/ from lower portion of furnace body air inlet pipeMin and nitrogen 25L/min, gas temperature is up to 900 DEG C after flue heating element heats, into furnace chamber, while above furnace bodyEquipped with exhaust pipe, the pressure for keeping furnace gas stable；The heating temperature of circumferential heating element is 900 DEG C, intermediate heating elementHeating temperature be set as 1300 DEG C, the thermally conductive protection sleeve pipe outside intermediate heating element and the gap of hollow quartz glass powder stick are2.0mm, observed temperature field distribution from hollow fused silica powder stick middle position to furnace body muffle as shown in Fig. 2, will wherein manageRange normalization, furnace body middle position are that 0, muffle pipe position is 1, hollow quartz glass powder stick (soot stick) outer edge positionIt is 0.8.Mixing the chlorine time is 8h, and for subsequent collapsing at solid glass body, testing chlorinity in glass is 10000ppm, and chlorinity is maximumDifference value is 500ppm.
Second embodiment is as follows: OVD method formation hollow quartz glass powder stick, outer diameter 200mm, internal diameter 45mm,Length is 1.5m.This hollow quartz glass powder stick is moved into the collapsing furnace in Fig. 1, as shown in the figure, to hollow fused silica powderStick carries out fluorine doped processing, wherein heating furnace structure is the same as in embodiment 1.Fluorine doped processing method is as follows: being passed through from lower portion of furnace bodyThe nitrogen of the CF4 and 25L/min of 1L/min, gas temperature is up to 1000 DEG C after flue heating element heats, into furnace chamber, furnaceExhaust pipe is equipped with above body, the pressure for keeping furnace gas stable；The heating temperature of circumferential heating element is set as 1000 DEG C, inBetween the temperature setting of heating element be 1200 DEG C, the middle thermally conductive protection sleeve pipe by outside heating element and hollow quartz glass powder stickGap is 1.5mm.The fluorine doped time is 4h, and subsequent collapsing is at solid glass body, and testing fluorine content in glass is 15000ppm, and fluorine containsAmount maximum different value is 650ppm.
Since halogen gas is being higher than critical-temperature Shi Huiyu pure quartz glass muffle tube reaction, corrode, andThe critical reaction temperature of fluorine and chlorine is 1000 DEG C, therefore the temperature for controlling circumferential heating element heats is no more than 1000 DEG C.