Background technology
Preform is the starting material of drawing optical fiber, and its basic structure comprises sandwich layer and has the covering of more low-refraction (covering also can comprise inner cladding, surrounding layer).SiO
2be used to the main glass-former manufacturing preform, its specific refractory power can be changed by doping thus form waveguiding structure.Generally mix GeO in the core
2, make the specific refractory power of sandwich layer higher than the specific refractory power of the pure silica glass of covering.The relative difference of sandwich layer and cladding index adopts refractive index contrast Δ to represent, the specific refractory power of sandwich layer and covering is respectively
with
, the value of refractive index contrast Δ is provided by formula (1):
…………(1)
Sometimes in order to increase the bending resistance of optical fiber, the GeO by increasing in fiber core layer is needed
2content increases Δ value.But along with GeO
2the raising of content, can cause the increase of fiber Rayleigh scattering.If the GeO mixed
2too high levels, just easily forms GeO gas, produces bubble thereupon.This transmission performance for final optical fiber and intensity are all disadvantageous.For above-mentioned reasons, Δ value can be improved by the specific refractory power reducing covering.Mix B
2o
3the specific refractory power of covering can be reduced with fluorine.But, B
2o
3there is larger hangover at 1.2 μm to absorb, be unfavorable for the reduction of loss, therefore, preferably adopt and mix fluorine to reduce the specific refractory power of covering.In order to obtain same refractive index contrast Δ, by doped cladding layer fluorine, the GeO of sandwich layer can be reduced
2content does not even mix GeO
2, thus reduce the Rayleigh scattering that causes because of doping further.
The method of current manufacture preform comprises method (MCVD and PCVD) and the outer method of pipe (VAD and OVD) in pipe.Manage outer method not by the restriction of liner dimensions, sedimentation velocity is fast, and production efficiency is high, is suitable for the large-scale production of large-scale optical fiber prefabricating stick.Know adopt flame hydrolysis gaseous state fluorochemicals can be added in silica glass when depositing, but the method to exist sedimentation effect and the low shortcoming of doping content.Its reason may be: first, fluorine-containing SiO
2particle is not generate in torch flame at once, but diffuses into SiO the process of moving from blowtorch to prefabricated rods loose media along with fluorine
2particle.Diffusion needs the regular hour, causes SiO because the fluorine entering flame reaction is easily diffused in surrounding environment simultaneously
2circumgranular fluorine dividing potential drop is very low.Secondly, SiO
2oH in circumgranular a part of fluorine and flame
-reaction generates HF, therefore only has the fluorine of small part to be incorporated into SiO
2in particle.In addition, HF has corrosive nature to glass particle, the SiO that easy and flame hydrolysis generates
2particle reaction:
SiO
2(s)+2HF(g)→SiOF
2(g)+H
2O(g)…………(2)
SiO
2(s)+4HF(g)→SiF
4(g)+2H
2O(g)…………(3)
(s) and (g) in formula represents solid-state and gaseous state respectively.
These reactions prevent SiO
2the growth of particle, reduces SiO simultaneously
2the deposition of particle.Therefore, along with the increase of fluorochemicals flow, sedimentation effect and sedimentation velocity progressively reduce, and do not produce deposition the most at last.On the other hand, due to the high diffusibility of fluorine, the fluorine-containing loose media that deposition obtains, in sintering process, by the fluorine of loss 40%-50%, makes refractive index profile structure be destroyed, and has a strong impact on the performance of optical fiber after drawing.
In order to solve the problem, publication number be US2003/0101771 A1 U.S. patent applications disclose a kind of preform loose media deposition time mix the method for fluorine: adopt vapour deposition process to deposit loose media in advance, then fluoride gas is ejected on loose media by torch flame burning formation fluoro-gas and forms fluorine-containing atmosphere, now do not pass into silicon-containing compound in blowtorch, avoid generating SiO
2particle.Fluoro-gas realizes doping by diffusing into loose media.There is following problem in this method: because blowtorch is certain position from a direction, fluoro-gas being sprayed to loose media, is difficult to ensure the axis of Fluorin doped and radial homogeneity.Although this patent proposes to adopt multiple blowtorch and utilize the method for opening cover and heating to improve the homogeneity of mixing fluorine, the fluctuation of Oil repellent in axis and radial direction still may be there is.In addition, during fluorine-containing loose media sintering also can there is diffusion and run off in fluorine.
For above problem, the patent No. be US4629485 U.S. patents disclose the method that fluorine is mixed in the vitrifying of a kind of preform loose media: good for the vapour deposition loose media containing hole is put into vitrifying stove and heats, pass into fluoride gas flow through loose media surface and make it fully diffuse into loose media, finally loose media glass is changed into and transparent mix fluorine glass.Concrete steps are: first adopt OVD method to deposit pure SiO
2loose media, then loose media is put into vitrifying stove and carry out dehydration vitrifying, then the plug after vitrifying is extended, adopt again on OVD method pure silicon dioxide plug after extension and deposit surrounding layer, after the loose media that deposition obtains dewaters in vitrifying stove, pass into fluoride gas, then after vitrifying, obtain the prefabricated rods of doped cladding layer fluorine.The method mixes that fluorine speed is fast and doping content is high, but the preform sandwich layer hydroxy radical content manufactured through the method is higher, and the transmission loss of the optical fiber 1383nm wavelength of drawing reaches more than 2dB/km.Its reason is: the pure silicon dioxide plug after (1) vitrifying is surperficial by OH in extension process
-pollute, OH
-at high temperature diffuse into plug.(2) plug after extending deposits covering through flame hydrolysis, the OH that hydrolysis reaction produces
-sandwich layer is diffused under follow-up hot environment (vitrifying and wire drawing).In order to reduce OH
-pollution, when producing plug, not only manufacture sandwich layer also fabrication portion covering (inner cladding).And cored ratio (ratio of plug cladding diameter and sandwich layer diameter) must be controlled more than 4.0 when adopting flame hydrolysis outsourcing to manufacture preformod of optical fiber with low water peak.Problem brought thus is: because the sandwich layer of plug that deposits and covering are all the loose medias containing a large amount of hole, when fluorine is mixed in vitrifying, fluorine not only diffuses into covering, and enters sandwich layer, causes fluorine to be difficult to optionally to mix covering and forms refractive index profile structure.
For this reason the patent No. be the United States Patent (USP) of US4620861, publication number to be the U.S. Patent application of US2002/0073740 A1 and application number be 00805475.4 Chinese patent application propose the method that when fluorine is mixed in vitrifying, plug refractive index profile controls respectively.The patent No. doping agent that to be the method for the United States Patent (USP) of US4620861 be mixes different concns by plug deposition process center core layer and covering makes its softening temperature lower than the softening temperature of pure silica glass, after heating, doping sandwich layer and the covering that do not adulterate (or sandwich layer is different with the concentration of clad doped dose) form different density and porosity thus realize plug optionally vitrifying, pass into fluoride gas afterwards, fluorine optionally mixes covering.But the method is not suitable for the manufacture of pure-silica-core fiber prefabricated rods.Although the sandwich layer doping post softening temperature of plug declines, after heating, density increases, and porosity reduces, thus when making vitrifying mix fluorine, fluorine effectively cannot diffuse into sandwich layer.But when sandwich layer and clad doped agent concentration are more or less the same, sandwich layer and covering cannot form effective interface, thus fluorine is made to be difficult to invariably can diffuse into sandwich layer.And publication number be US2002/0073740 A1 U.S. patent applications disclose a kind of method that relation according to fluorochemical speed of response and velocity of diffusion controls plug refractive index profile: when fluorine is mixed in loose media vitrifying, the speed that fluoride gas and loose media react and the speed that fluoride gas spreads in loose media are all the functions of temperature, along with the rising of temperature, fluoride gas and loose media speed of response are faster than the speed of fluoride gas at loose media internal diffusion.Therefore, by controlling the temperature and time mixing fluorine, parameter Ф>=1(Ф is defined as
, wherein
for the radius of loose media,
for the spread coefficient of fluoride gas in loose media,
reaction rate constant for fluoride gas and loose media), thus control the radial doping depth of fluorine in loose media.But the method is clearly difficult to the refractive index profile structure forming step change type.Application number for the method disclosed in the Chinese patent application of 00805475.4 is: loose media vapour deposition obtained passes into CF after dehydrating in vitrifying stove
4flow through the outside surface of loose media, the time of doping and temperature are enough to make and CF
4the Fluorin doped concentration on the loose media surface of contact is minimum, and increases progressively to center gradually.Obviously, the method and publication number are the same refractive index profile structure being difficult to be formed step change type of method of the U.S. Patent application of US2002/0073740 A1.
Summary of the invention
The technical assignment of the technical problem to be solved in the present invention and proposition is the defect overcoming prior art existence, provides a kind of optical fiber prefabricating stick cladding to mix the method for fluorine.
For this reason, the present invention is by the following technical solutions:
Optical fiber prefabricating stick cladding mixes a method for fluorine, it is characterized in that comprising the following steps:
Target rod deposits sandwich layer loose media;
The outside surface heating described sandwich layer loose media forms tight zone, makes the density of described tight zone higher than the density of described sandwich layer loose media inside;
The mandrel loose body comprising sandwich layer loose media, inner cladding loose media is formed at described tight zone external sediment inner cladding loose media;
Detach described target rod and be formed centrally centre hole in mandrel loose body;
Described mandrel loose body is put into vitrifying stove and at dehydration atomosphere thermal dehydration, while heating, in described centre hole, passes into dehydrated air;
In fluorochemical atmosphere, heat described mandrel loose body, make fluorine optionally mix in inner cladding loose media;
Mandrel loose body described in vitrifying, the centre hole shrinkage cavity described in order, sandwich layer loose media form sandwich layer, inner cladding loose media forms inner cladding, form plug.
As optimization technique means:
At described inner cladding external sediment surrounding layer loose media;
Described surrounding layer loose media is put into vitrifying stove and at dehydration atomosphere thermal dehydration in company with plug;
In fluorochemical atmosphere, heat described surrounding layer loose media, make fluorine mix in surrounding layer loose media;
Vitrifying surrounding layer loose media, makes surrounding layer loose media form surrounding layer.
As optimization technique means: the Ratio control of the diameter of described inner cladding and the diameter of sandwich layer is more than 4.0; The density of described tight zone is greater than 1.2g/cm
3.
As optimization technique means: contain Cl in described dehydration atomosphere and dehydrated air
2gas and He gas; Heating temperature in vitrifying stove is 1100 DEG C-1400 DEG C.
As optimization technique means: described dehydrated air flows through described centre hole from top to bottom.
As optimization technique means: described fluorochemical atmosphere contains SiF
4, CF
4, SF
6, C
2f
6, C
2f
2cl
2, F
2, C
3f
8, NF
3, SOF
2, SO
2clF one or more combination wherein.
As optimization technique means: described fluorochemical atmosphere contains He.
As optimization technique means: deposit sandwich layer loose media by after target rod tubular handle, and pipe handle is positioned at one end of post-depositional sandwich layer loose media.Further, after detaching target rod, a tubular elongate handle is welded on pipe handle, then tubular elongate handle is installed on the fixture above vitrifying stove and slow mandrel loose body being dropped in the middle of vitrifying stove carries out vitrifying.
The invention has the beneficial effects as follows: in the inventive method plug deposition process, the interface of sandwich layer loose media and inner cladding loose media forms tight zone (namely heating the tight zone that sandwich layer loose media outside surface is formed), and sandwich layer loose media and inner cladding loose media are still porosity and looseness state, pass into dehydrated air by centre hole in dehydration, significantly reduce the OH in sandwich layer
-content, thus the decay greatly reducing optical fiber 1383nm.Secondly, due to the existence of the tight zone at sandwich layer loose media and inner cladding loose media interface, when fluorine is mixed in vitrifying, fluoride gas optionally diffuses into inner cladding loose media and cannot enter sandwich layer loose media, thus forms Stepped-index distribution.Relative to prior art, owing to being doping and vitrifying in fluorochemical atmosphere, fluorine is evenly distributed in covering radial direction, and refractive index profile can not be caused due to the loss of fluorine to be destroyed.Finally, it is fast that method of the present invention mixes fluorine speed, and doping content is high, is suitable for the large-scale production of large-scale optical fiber prefabricating stick.
Embodiment
Below in conjunction with Figure of description, the present invention will be further described.
Optical fiber prefabricating stick cladding of the present invention mixes the method for fluorine, comprises the following steps:
Target rod deposits sandwich layer loose media;
The outside surface heating described sandwich layer loose media forms tight zone, makes the density of described tight zone higher than the density of described sandwich layer loose media inside;
The mandrel loose body comprising sandwich layer loose media, inner cladding loose media is formed at described tight zone external sediment inner cladding loose media;
Detach described target rod and be formed centrally centre hole in mandrel loose body;
Described mandrel loose body is put into vitrifying stove and at dehydration atomosphere thermal dehydration, while heating, in described centre hole, passes into dehydrated air;
In fluorochemical atmosphere, heat described mandrel loose body, make fluorine optionally mix in inner cladding loose media;
Mandrel loose body described in vitrifying, the centre hole shrinkage cavity described in order, sandwich layer loose media form sandwich layer, inner cladding loose media forms inner cladding, form plug.
As optimization technique means:
At described inner cladding external sediment surrounding layer loose media;
Described surrounding layer loose media is put into vitrifying stove and at dehydration atomosphere thermal dehydration in company with plug;
In fluorochemical atmosphere, heat described surrounding layer loose media, make fluorine mix in surrounding layer loose media;
Vitrifying surrounding layer loose media, makes surrounding layer loose media form surrounding layer.
As optimization technique means: the Ratio control of the diameter of described inner cladding and the diameter of sandwich layer is more than 4.0; The density of described tight zone is greater than 1.2g/cm
3.
As optimization technique means: contain Cl in described dehydration atomosphere and dehydrated air
2gas and He gas; Heating temperature in vitrifying stove is 1100 DEG C-1400 DEG C.
As optimization technique means: described dehydrated air flows through described centre hole from top to bottom.
As optimization technique means: described fluorochemical atmosphere contains SiF
4, CF
4, SF
6, C
2f
6, C
2f
2cl
2, F
2, C
3f
8, NF
3, SOF
2, SO
2clF one or more combination wherein.
As optimization technique means: described fluorochemical atmosphere contains He.
As optimization technique means: deposit sandwich layer loose media by after target rod tubular handle, and pipe handle is positioned at one end of post-depositional sandwich layer loose media.Further, after detaching target rod, a tubular elongate handle is welded on pipe handle, then tubular elongate handle is installed on the fixture above vitrifying stove and slow mandrel loose body being dropped in the middle of vitrifying stove carries out vitrifying.
Describe the preferred embodiments of the invention in detail below with reference to accompanying drawings.
Fig. 1 is preform schematic cross-section.Preform is formed by post-depositional loose media vitrifying.Preform is made up of plug 1 ' and surrounding layer 4 ', and wherein plug 1 ' comprises sandwich layer 2 ' and inner cladding 3 '.The specific refractory power of sandwich layer 2 ' higher than the specific refractory power of inner cladding 3 ' with surrounding layer 4 ', thus forms waveguiding structure.Have excellent optical property in order to ensure optical fiber, when producing plug 1 ', not only will manufacture sandwich layer 2 ' also must fabrication portion covering (inner cladding 3 ').
Fig. 2 is OVD depositing operation (equipment) schematic diagram for the manufacture of mandrel loose body.Target rod 5 tubular handles 6 are installed to (not shown) on lathe.Target rod 5, while rotation, is also carried out straight line relative at least one blowtorch 7 and moves around (also can be undertaken by the mode of blowtorch 7 relative to target rod 5 movement).Gaseous halide raw material (SiCl
4deng) react with oxyhydrogen flame or methane flame, produce a large amount of SiO
2particle, its particle diameter from a few nanometer to hundreds of nanometer not etc., grow up gradually along with cohesion, and then particle deposits along with air-flow and thermophoresis effect are brought on target rod 5 by particle.Along with moving back and forth of barred body, SiO
2particle is in layer deposited on the outside surface of mandrel loose body 1.The two ends of loose media need to add two taillight (not shown)s and heat, and ftracture in deposition process to prevent loose media.In order to obtain refringence, also need to mix other materials in the feed in deposition sandwich layer loose media 2 process.Modal is exactly mix GeO
2, for improving the specific refractory power of sandwich layer loose media 2.After sandwich layer loose media 2 has deposited, supply gas halide feedstock is stopped in blowtorch 7, carrying out heating with oxyhydrogen flame or methane flame to the outside surface of sandwich layer loose media 2 makes its vitrifying form tight zone 8, and the density of tight zone 8, higher than the density of sandwich layer loose media 2 inside, is preferably more than 1.2g/cm
3, be more preferably greater than 1.8g/cm
3.Need during heating to ensure that the outside surface of whole sandwich layer loose media 2 and the equal vitrifying of inactive portion at two ends form tight zone, thus when preventing vitrifying doped cladding layer fluorine, fluorine diffuses into sandwich layer loose media 2.Also other can make the method for tectorium densification can to adopt process furnace heating, LASER HEATING etc. to tight zone 8.The gauge control of tight zone 8 is at 0.01mm-0.5mm.Then, continue sedimentary inner envoloping layer loose media 3 at the outside surface of tight zone 8, now only pass into SiCl in oxyhydrogen flame or methane flame blowtorch
4gas raw material.Fig. 3 is the schematic cross-section of mandrel loose body 1, and sandwich layer loose media 2 and inner cladding loose media 3 are isolated by the interface that tight zone 8 is positioned at sandwich layer loose media 2 and inner cladding loose media 3.In order to prevent the OH introduced in surrounding layer loose media 4 manufacturing processed
-diffuse into sandwich layer 2, need the ratio (as shown in Fig. 5, Fig. 6 and Fig. 7) of inner cladding loose media 3 diameter and sandwich layer loose media 2 diameter to control more than 4.0, preferably control more than 4.5, more preferably control more than 5.0.
Mandrel loose body 1 after having deposited is in loose porous state, and its density is 0.1-1.2g/cm
3, preferably, its density is 0.2-0.8g/cm
3, more preferably, its density is 0.4-0.6g/cm
3.Next detach target rod 5, tubular elongate handle 9 is welded on pipe handle 6, then utilize tubular elongate handle 9 to hang mandrel loose body 1 and be put in the middle of vitrifying stove and carry out vitrifying.
Vitrifying stove is by heating member 14(resistance furnace or other heating unit) heat pure quartzy furnace core tube 13, heating zone length is 400mm when temperature fluctuation ± 25 DEG C, and the speed of rotation of mandrel loose body 1 is 3-10rpm, and decline enters heating zone gradually.A large amount of OH can be introduced in process due to hydrolysis reaction deposition loose media
-, and prefabricated rods particularly mandrel loose body 1 couple of OH
-requirement high especially, in order to obtain low OH
-the mandrel loose body 1 of content, must through the process of dehydration.Cl in dehydration
2, O
2enter vitrifying stove with He from air feed port 15, and from bottom to top (arrow 17) flows through mandrel loose body 1 surface, then flows out from vitrifying fire grate gas port 16.After mandrel loose body 1 has deposited, detach target rod 5 meeting at intermediate formation centre hole 10, therefore, in dehydration, except the outside surface making gas flow through mandrel loose body 1, also must by Cl
2, O
2centre hole 10(arrow 18 is passed into from tubular elongate handle 9 top with He), to ensure the abundant dehydration of sandwich layer loose media 2; Cl
2effect be dewatering agent, its reaction equation is:
2Cl
2+ 2H
2O = O
2+ 4HCl………………………(4)
2Si-OH + 2Cl
2= 2Si-Cl + O
2+ 2HCl…………(5)
The cardinal principle of dehydration is exactly in fact use Cl
-replace isolated OH
-halogenating reaction process, reaction result causes the generation of Si-Cl key, and the fundamental vibration absorption peak due to this key is positioned near 25 μm, away from current optical communication operating wavelength area, so to the attenuation by absorption in Optical Fiber Transmission process and moment-less influence; The Main Function of He is auxiliary dehydration, and because He has, atomic volume is little, diffusivity is high, stable performance, so it penetrates into inside easily via the hole in mandrel loose body 1 and can not have an impact to the performance of prefabricated rods, He mono-brings Cl in aspect
2, O
2, make it fully to contact with mandrel loose body 1, on the other hand, the waste gas of dehydration reaction and moisture brought out; O
2effect be to prevent doped element (such as Ge) and Cl
2there is halogenating reaction to volatilize away, cause Ge to run off.Dehydrate step to carry out under lower than mandrel loose body 1 second-order transition temperature, dehydration temperaturre is 1100 DEG C-1400 DEG C.Temperature is too high, easily causes mandrel loose body 1 closing of pores, Cl
2effectively cannot enter mandrel loose body 1 inside to dewater.Temperature is too low, then the required time is oversize, is not suitable for suitability for industrialized production.Time of drying is 0.5-5 hour.After dehydrating, mandrel loose body 1 again progressively declines and enters heating zone, simultaneously passes into fluoride gas from air feed port 15 and flows through mandrel loose body 1 surface (arrow 17) and be wrapped inside layer loose media 3 and mix fluorine.Preferably, diluent gas is preferably contained in vitrifying stove as helium.Because the sandwich layer loose media 2 of mandrel loose body 1 and inner cladding loose media 3 interface exist tight zone 8, the fluoride gas diffusing into inner cladding loose media 3 cannot enter sandwich layer loose media 2.A capillary 11 is contained in the lower end of mandrel loose body 1, enters (now tubular elongate handle 9 top can pass into rare gas element as He) the centre hole 10 of mandrel loose body 1 to prevent the gas in vitrifying stove from mandrel loose body 1 bottom.Fluoride gas is at least SiF
4, CF
4, SF
6, C
2f
6, C
2f
2cl
2, F
2, C
3f
8, NF
3, SOF
2, SO
2the combination of ClF wherein a kind of or at least two kinds.Mixing fluorine temperature can be identical with dehydration temperaturre, carries out at temperature that also can be different with dehydration temperaturre.Fluoride gas accounts for the 1-30% of total gas flow rate.The time of mixing fluorine is enough to fluorine is diffused into fully and is evenly distributed in inner cladding loose media 3.Time controling is at 0.5-5 hour.Then He, O is passed into
2carry out vitrifying, vitrified temperature range is 1400-1600 DEG C.Owing to being mixed with fluorine in inner cladding loose media 3, second-order transition temperature can be made to decrease.According to the difference of mandrel loose body diameter, length and second-order transition temperature and speed, vitrified time is 0.5-8 hour.After vitrifying completes, because capillary bore 12 at high temperature molten contracting is closed, the bottom of mandrel loose body is sealed.Then the transparent plug 1 ' with centre hole 10 is promoted to outside vitrifying stove and cools.Then be installed on equipment extending longitudinally by the plug 1 ' with centre hole 10, vacuumize from tubular elongate handle 9 one end to centre hole 10, plug sealed end stove is heated to more than 1900 DEG C, progressively makes its centre hole 10 close.The target rod that the solid transparent plug 1 ' of gained deposits as surrounding layer loose media 4 is installed on OVD lathe.Gas raw material SiCl in blowtorch
4siO is generated by hydrolysis reaction
2particle deposition forms loose media to the outside surface of target rod.Reach after the external diameter of setting and stop deposition, and again put into vitrifying stove and carry out vitrifying.Conventional production technique surrounding layer loose media 4 vitrifying does not need through dehydration, OH when mixing fluorine to prevent vitrifying in fluoride gas and vitrifying stove
-reaction generates HF and corrodes pure quartzy furnace core tube 13, and surrounding layer loose media 4 of the present invention vitrifying needs the OH thoroughly removing loose media inside
-, and then according to aforementionedly mixing fluorine, vitrified step carries out surrounding layer loose media 4 and mixes fluorine and vitrifying, finally obtains the transparent prefabricated rods of doped cladding layer fluorine.Prefabricated rods is drawn into step type single mode optical fiber by drawing process conveniently.
embodiment 1:
Mandrel loose body 1 adopts the manufacture of OVD method.Target rod 5 tubular handles 6 are installed on lathe.Gaseous halide raw material SiCl
4, GeCl
4be hydrolyzed reaction in oxyhydrogen flame, produces a large amount of SiO
2doped with Ge O
2particle deposition is on target rod 5.Along with moving back and forth of target rod 5, SiO
2-GeO
2particle is in layer deposited on mandrel loose body 1 outside surface of rotation.After sandwich layer loose media 2 has deposited, in blowtorch 7, stop supplying raw material SiCl
4and GeCl
4, heat with the outside surface of oxyhydrogen flame to sandwich layer loose media 2, make its vitrifying form tight zone 8.In blowtorch 7, the flow of hydrogen and oxygen is respectively 200slpm and 90slpm.Then, raw material SiCl is passed in blowtorch 7
4, at the outside deposition inner cladding loose media 3 of tight zone 8.After inner cladding loose media 3 has deposited, the ratio of inner cladding loose media 3 diameter and sandwich layer loose media 2 diameter is shrink in proportion after the vitrifying of 4.5(loose media, and the ratio t/a of inner cladding 3 ' diameter and sandwich layer 2 ' diameter is still 4.5, as shown in Figure 5).The external diameter of mandrel loose body 1 is 120mm, and length is 1500mm.
Detach the target rod 5 of loose media core, tubular elongate handle 9 is welded on pipe handle 6, then tubular elongate handle 9 is installed to (not shown) on the fixture above vitrifying stove, and slow mandrel loose body 1 being dropped in the middle of vitrifying stove carries out vitrifying.Vitrifying stove heats pure quartzy furnace core tube 13 by heating member 14, and heating zone length is 400mm when temperature fluctuation ± 25 DEG C.The speed of rotation of mandrel loose body 1 is 3rpm, and decline enters heating zone gradually.First pass into inert nitrogen gas to purge, then pass into Cl
2, O
2dehydrate with He, to remove the OH in mandrel loose body 1
-.Dehydrated air enters vitrifying stove from air feed port 15, and from bottom to top (arrow 17) flows through mandrel loose body 1 surface, flows out from vitrifying fire grate gas port 16.In order to remove the OH in sandwich layer loose media 2
-, Cl
2, O
2centre hole 10(arrow 18 is passed into from tubular elongate handle 9 top with He), flow out from mandrel loose body 1 lower end; Dehydration temperaturre is 1100 DEG C.Dewatering time is 3 hours.After dehydrating, mandrel loose body 1 again progressively declines and enters heating zone, passes into SF from air feed port 15 simultaneously
6gas and He flow through mandrel loose body 1 surface (arrow 17) and are wrapped inside layer loose media 3 and mix fluorine.Due to mandrel loose body 1 sandwich layer loose media 2 and inner cladding loose media 3 interface there is tight zone 8 and centre hole 10 lower end is provided with kapillary 11, the fluoride gas diffusing into inner cladding loose media 3 cannot enter sandwich layer loose media 2, fluoride gas and also cannot enter centre hole 10.Tubular elongate handle 9 top passes into rare gas element He and kapillary 11 through centre hole 10 lower end is discharged, to enter from centre hole 10 lower end the centre hole 10 of mandrel loose body 1 (if do not pass into rare gas element He from tubular elongate handle 9 top and kapillary 11 through centre hole 10 lower end is discharged, then the lower end shutoff of centre hole can be realized fluoride gas and cannot enter centre hole 10) to prevent the gas in vitrifying stove.The temperature of mixing fluorine is 1200 DEG C.SF
6gas accounts for 15% of total gas flow rate.The time of mixing fluorine is 2 hours, thus fluorine is fully diffused in inner cladding loose media 3.Then He, O is passed into
2carry out vitrifying, vitrified temperature is 1450 DEG C, and vitrified time is 5 hours.After vitrifying completes, plug 1 ' makes its reduced diameter to 30mm through central pipe.Plug 1 ' after extension is installed on OVD lathe as the target rod that surrounding layer loose media 4 deposits and deposits SiO
2surrounding layer loose media 4, and again put into vitrifying stove and carry out dewatering, mixing fluorine and vitrifying.Finally obtain sandwich layer 2 ' and mix the transparent optical fiber preform that germanium, inner cladding 3 ' and surrounding layer 4 ' mix fluorine.Through the test of PK2600 prefabricated rods comprehensive tester, as shown in Figure 5, Δ value reaches 1.1% to the refractive index profile of preform.Draw by ordinary method and obtain the optical fiber that numerical aperture is 0.22.
embodiment 2
Mandrel loose body 1 adopts OVD method to manufacture as described in Example 1.Unlike, pass into raw material SiCl when sandwich layer loose media 2 deposits
4be hydrolyzed the SiO of reaction, generation in oxyhydrogen flame
2particle deposition to target rod 5 forms pure SiO
2sandwich layer loose media 2.Sedimentary inner envoloping layer loose media 3 is continued after adding thermosetting tight zone 8 as described in Example 1.After having deposited, the ratio of inner cladding loose media 2 diameter and sandwich layer loose media 2 diameter is 5.0.The external diameter of mandrel loose body 1 is 100mm, and length is 1800mm.
Detach target rod 5, tubular elongate handle 9 is welded on pipe handle 6, then tubular elongate handle 9 is installed to (not shown) on the fixture above vitrifying stove, and slow mandrel loose body 1 being dropped in the middle of vitrifying stove carries out vitrifying.The speed of rotation of mandrel loose body 1 is 5rpm, and decline enters heating zone gradually.First pass into inert nitrogen gas to purge, then pass into Cl
2dehydrate with He, to remove the OH in mandrel loose body 1
-.Dehydrated air enters vitrifying stove from air feed port 15, and from bottom to top (arrow 17) flows through mandrel loose body 1 surface, then flows out from vitrifying fire grate gas port 16.In order to remove the OH in sandwich layer loose media 2
-, Cl
2centre hole 10(arrow 18 is passed into from tubular elongate handle 9 top with He), flow out from mandrel loose body 1 lower end; Dehydration temperaturre is 1300 DEG C.Dewatering time is 7 hours.After dehydrating, mandrel loose body 1 again progressively declines and enters heating zone, passes into SiF from air feed port 15 simultaneously
4gas and He flow through mandrel loose body 1 surface (arrow 17) and are wrapped inside layer loose media 3 and mix fluorine.Due to mandrel loose body 1 sandwich layer loose media 2 and inner cladding loose media 3 interface there is tight zone 8 and centre hole 10 lower end is provided with kapillary 11, the fluoride gas diffusing into inner cladding loose media 3 cannot enter sandwich layer loose media 2, fluoride gas and also cannot enter centre hole 10.Tubular elongate handle 9 top passes into rare gas element He and kapillary 11 through centre hole 10 lower end is discharged, to enter from centre hole 10 lower end the centre hole 10 of mandrel loose body 1 (if do not pass into rare gas element He from tubular elongate handle 9 top and kapillary 11 through centre hole 10 lower end is discharged, then the lower end shutoff of centre hole can be realized fluoride gas and cannot enter centre hole 10) to prevent the gas in vitrifying stove.The temperature of mixing fluorine is 1350 DEG C.SiF
4gas accounts for 30% of total gas flow rate.The time of mixing fluorine is 3 hours, thus fluorine is fully diffused in inner cladding loose media 3.Then pass into He and carry out vitrifying, vitrified temperature is 1500 DEG C, and vitrified time is 8 hours.After vitrifying completes, plug 1 ' makes its reduced diameter to 30mm through central pipe.Plug 1 ' after extension is installed on OVD lathe as the target rod that surrounding layer loose media 4 deposits and deposits SiO
2surrounding layer loose media 4, and again put into vitrifying stove and carry out dewatering, mixing fluorine and vitrifying.Finally obtain sandwich layer 2 ' for pure SiO
2, inner cladding 3 ' and surrounding layer 4 ' mix the transparent optical fiber preform of fluorine.Through the test of PK2600 prefabricated rods comprehensive tester, as shown in Figure 6, Δ value is 0.32% to the refractive index profile of preform.Draw by ordinary method and obtain ultra-low-loss fiber, its 1550nm decays to 0.170dB/km, and 1383nm decays to 0.248dB/km.
embodiment 3
Mandrel loose body 1 adopts OVD method to manufacture as described in Example 2.The tight zone 8 at sandwich layer loose media 2 and inner cladding loose media 3 interface adopts process furnace to add thermosetting, obtains pure SiO
2the mandrel loose body 1 of sandwich layer, the ratio of its inner cladding loose media 3 diameter and sandwich layer loose media 2 diameter is 5.0.The external diameter of mandrel loose body 1 is 100mm, and length is 1200mm.
Detach target rod 5, tubular elongate handle 9 is welded on pipe handle 6, then tubular elongate handle 9 is installed to (not shown) on the fixture above vitrifying stove, and slow mandrel loose body 1 being dropped in the middle of vitrifying stove carries out vitrifying.The speed of rotation of mandrel loose body 1 is 10rpm, and decline enters heating zone gradually.First pass into inert nitrogen gas to purge, then pass into Cl
2dehydrate with He, to remove the OH in mandrel loose body 1
-.Dehydrated air enters vitrifying stove from air feed port 15, and from bottom to top (arrow 17) flows through mandrel loose body 1 surface, then flows out from vitrifying fire grate gas port 16.In order to remove the OH in sandwich layer loose media 2
-, Cl
2pass into centre hole 10 with He from tubular elongate handle 9 top, flow out (arrow 18) from mandrel loose body 1 lower end; Dehydration temperaturre is 1400 DEG C.Dewatering time is 2 hours.After dehydrating, mandrel loose body 1 again progressively declines and enters heating zone, passes into CF from air feed port 15 simultaneously
4gas and He flow through mandrel loose body 1 surface (arrow 17) and are wrapped inside layer loose media 3 and mix fluorine.Due to mandrel loose body 1 sandwich layer loose media 2 and inner cladding loose media 3 interface there is tight zone 8 and centre hole 10 lower end is provided with kapillary 11, the fluoride gas diffusing into inner cladding loose media 3 cannot enter sandwich layer loose media 2, fluoride gas and also cannot enter centre hole 10.Tubular elongate handle 9 top passes into rare gas element He and kapillary 11 through centre hole 10 lower end is discharged, to enter from centre hole 10 lower end the centre hole 10 of mandrel loose body 1 (if do not pass into rare gas element He from tubular elongate handle 9 top and kapillary 11 through centre hole 10 lower end is discharged, then the lower end shutoff of centre hole can be realized fluoride gas and cannot enter centre hole 10) to prevent the gas in vitrifying stove.The temperature of mixing fluorine is 1300 DEG C.CF
4gas accounts for 30% of total gas flow rate.The time of mixing fluorine is 3 hours, thus fluorine is fully diffused in inner cladding loose media 3.Then pass into He and carry out vitrifying, vitrified temperature is 1550 DEG C, and vitrified time is 5 hours.After vitrifying completes, plug 1 ' makes its reduced diameter to 30mm through central pipe.Plug 1 ' after extension is installed on OVD lathe as the target rod that surrounding layer loose media 4 deposits and deposits SiO
2surrounding layer loose media 4, and again put into vitrifying stove and carry out dewatering, mixing fluorine and vitrifying.The present embodiment surrounding layer loose media 4 is mixed when Funing tablet mixes fluorine lower than embodiment 2(surrounding layer loose media 4 and is passed into CF in vitrifying stove by reduction
4the flow of gas thus reduce mix Funing tablet), finally obtain sandwich layer 2 ' for pure SiO
2, inner cladding 3 ' and surrounding layer 4 ' mix the transparent optical fiber preform of fluorine.Through the test of PK2600 prefabricated rods comprehensive tester, as shown in Figure 7, Δ value is 0.33% to the refractive index profile of preform.Draw by ordinary method and obtain ultra-low-loss fiber, its 1550nm decays to 0.175dB/km, and 1383nm decays to 0.253dB/km.
It should be noted that, the mode of above-described embodiment is only limitted to describe embodiment, but the present invention is not confined to aforesaid way, and those skilled in the art can modify accordingly without departing from the scope of the present invention easily, therefore scope of the present invention should comprise disclosed principle and the maximum range of new feature.