CN1284738C - Treating soot preforms with a reducing agent - Google Patents

Abstract

A silica soot preform (12) is inserted into a furnace (30). The preform is then treated with heat and carbon monoxide gas so as to reduce impurities that could effect the final product.

Description

Use reductive agent to handle soot preforms

Crossing relation with related application

Propose right of priority of the present invention in conjunction with the patent of applying for of following common transfer: number of patent application is 60/295,052 United States Patent (USP) (submission date is May 31 calendar year 2001) and number of patent application are 60/258,061 United States Patent (USP) (submission date is on December 22nd, 2000), the title of two pieces of patents all are " using reductive agent to handle soot preforms ".

The background of invention

FIELD OF THE INVENTION

The present invention relates to the preparation method of silica soot prefabricated rods, be specifically related to use reductive agent to handle soot preforms.

Background technology

In the production of optical fiber and other product of being made by soot preforms, the prefabricated rods that contains plurality of impurities can cause the various defectives of the finished product.The influence that these defectives produce can show as the decay of signal in the spread fiber, or when transmitting in the glassy product made from this prefabricated rods, significantly the weakening of the optical signal of certain wavelength.In the production of optical fiber, be necessary to reduce the attenuation degree of optical fiber, thereby will elimination can cause the product defects of signal attenuation the signal transmission.

Optical fiber contains a sign of impurity, and when being the length increase of employed optical fiber, optical fiber just increases the decay of the signal of certain wavelength.The effect that this decay increases is fairly obvious when wavelength is 1200 nanometers at least.

Previously in order to reduce the degree that above-mentioned optical fiber makes that signal attenuation increases, employed method comprises uses chlorine to make the prefabricated rods drying.In traditional treatment process, prefabricated rods is put into stove before fixedization.Be full of helium flow in the stove, wherein comprised about 2% chlorine, and stove will be heated to about 1000 ℃, holding time reaches about 2 hours.Yet this method with chlorine treatment can not reduce the increase of above-mentioned optical fiber to the signal transmission attenuation well.

Use another limitation of chlorine treatment soot preforms method, be this method can only to be used for chlorine treatment be metastable glass composition, the silica glass of silica glass and doped germanium etc. for example.Yet, be not that all components of silicate glass composition is stable to above-mentioned chlorine treatment method, for example comprise the glass composition of following component: aluminum oxide, antimony, alkalimetal oxide, the oxide compound of boron, the oxide compound of phosphorus, or alkaline earth metal oxide.Above-mentioned chlorine treatment method is verified can be removed aluminum oxide and comprise antimony, basic metal or alkaline earth metal compounds from prefabricated rods.

Above-mentioned chlorine treatment method more also will be carried out fluoridation after confirming further to use chlorine treatment intact to some glassy product also is unfavorable, even because mixed after the fluorine, the chlorine of bringing in still can more residual chlorine treatment processes in the prefabricated rods.The residual optical characteristics that can influence final glassy product of these chlorine.For example planography photomask blank just must not contain residual chlorine, and the existence of chlorine can weaken the transmission of the light of various operation wavelengths, and one of them operation wavelength is 157 nanometers.Experiment shows, only have only the existence of the chlorine of 75ppm will make wavelength be about 157 nanometers its transmission loss of light at least 50%.At least based on above reason, be necessary to develop a kind of method of new processing soot preforms.

In addition, the optical fiber of doped with fluorine has shown also that at some wavelength decay increases.The decay spectra of the optical fiber of doped with fluorine shows that (for example 1440nm, 1546nm, 1583nm and 1610nm) has absorption peak at certain some wavelength.At least be because wavelength 1583nm just in time in the L-band of transmission window, just is necessary to produce a kind of adulterated optical fiber of fluorine that does not have absorption peak at 1583nm or other aforementioned wavelength.

The general introduction of invention

The present invention relates to a kind of soot (soot) prefabricated rods that can be used to prepare optical articles and to the treatment process of soot preforms.First embodiment of the present invention is a kind of method of handling soot preforms, in this method, the soot preforms in the stove is contacted with free from chloride substantially air-flow, comprises a kind of reducing gas in the air-flow at least, in order to remove excess of oxygen in the stove.Reasonable a kind of reductive agent is CO.

An advantage of aforesaid method of the present invention is that it can be applicable to make fixedization of soot preforms under non-tangible well-oxygenated environment.This method also can be used to remove the excessive oxygen in the prefabricated rods, thereby produces the optical fiber that has better characteristic for a long time aspect decay.Another advantage that this method caused is to improve the speed of reeling off raw silk from cocoons of optical fiber.Using a fabulous embodiment of the present invention is that aforesaid method is applied in the production technique of non-zero dispersion displacement optical fiber.

In second method of the present invention, prefabricated rods is heated to certain temperature that is lower than 1000 ℃, and contacts with the air-flow of reductibility.A kind of air-flow of reductibility preferably comprises CO.An advantage of the above-mentioned embodiment of the present invention is that the prefabricated rods that root is produced accordingly can be prepared not chloride glassy product.Not chloride glassy product means never contacted chlorine in the production process of prefabricated rods at least.Fabulous purposes of not chloride glassy product is as the planography photomask blank, and this is because not chloride photomask can be propagated the light of wavelength less than 160nm preferably.Another advantage of aforesaid method of the present invention is that it can be used to handle following soot preforms, these soot preforms contain aluminum oxide, antimony, alkalimetal oxide, alkaline earth metal oxide or other some compounds, vapor away then or are transformed into the muriatic form of crystallization because their can react with chlorine.The advantage that aforesaid method of the present invention also has is that it can be used under the low occasion of temperature, and temperature can be lower than 1000 ℃.

The third method of the present invention is a kind of method of producing preform.This method comprises following step, and soot body is placed the air-flow that comprises CO, and this air-flow at least also comprises a kind of fluorochemicals, and (general formula is C _nF _2n+2, wherein " n " and positive integer preferably).Aforesaid method of the present invention being applied to have an advantage in the production technique of optical fiber in fluorine-containing district, is that the optical fiber of producing does not thus have absorption peak: 1440nm, 1546nm, 1583nm, 1610nm near following wavelength.

Other features and advantages of the present invention will describe in detailed description subsequently.Those skilled in the art describes according to this paper and can be readily seen that Partial Feature of the present invention and advantage, and described implementation method can easily be familiar with these features and method (to comprise following detailed, claims and accompanying drawing) perhaps according to the present invention.

Be appreciated that top general introduction and following detailed only are to illustrative explanation of the present invention, are used to provide overview and framework so that understand essence of the present invention and the feature that requirement is protected.Accompanying drawing is used for further understanding the present invention, its attached part that constitutes specification sheets in this manual.These description of drawings various embodiment of the present invention are used for explaining principle of the present invention and operation with specification sheets.

The accompanying drawing summary

Fig. 1 is the schematic cross-section that prefabricated rods places stove among the present invention.

Fig. 2 is the partial cross section synoptic diagram that the prefabricated rods after fixedization is reeled off raw silk from cocoons into optical fiber.

Fig. 3 is the partial cross section synoptic diagram that places stove among the present invention through the plug of soot deposit.

Fig. 4 is the skeleton view of the tubular preform after fixedization manufactured according to the present invention.

Fig. 5 is that tubular preform after fixedization manufactured according to the present invention is by the skeleton view after vertically cutting.

Fig. 6 is the skeleton view of the tubular preform after one section fixedization of stretching.

Fig. 7 is the side elevational view of prefabricated rods of one section fixedization of dangling.

Fig. 8 is optical fiber manufactured according to the present invention and control fiber cause decay under 1550nm after having placed 20 hours under 200 ℃ the condition a bar graph.

Fig. 9 is that hydrogen causes in the optical fiber that pulls under the different tension force that reels off raw silk from cocoons variation diagram in the decay of 1530nm, make the prefabricated rods of this optical fiber and after using halogenide to handle, further handled, and compare with the situation that does not have further to handle after using halogenide to handle with CO with CO.

Figure 10 is the decay pattern that optical fiber manufactured according to the present invention and control fiber have caused under 1550nm after having placed 20 hours under 200 ℃ the condition.

Figure 11 is decay and example of wavelength relationship figure of optical fiber, and this optical fiber is made according to conventional methods, includes the fluorine doped region.

Figure 12 is the schematic cross-section that prefabricated rods places stove in a certain method of the present invention.

Figure 13 is the decay of the optical fiber made of different prefabricated rods and the graph of a relation of wavelength, and wherein three prefabricated rods are that a kind of method at least according to the present invention is made another root contrast prefabricated rods.

Figure 14 is the refractive index profile of optical fiber, it is to represent with the relation of refractive index difference percentage ratio (Δ %) and radius, has shown the zone that specific refractory power has reduced among the figure.

The detailed description of invention

Will describe some embodiments preferably of the present invention below in detail, some embodiments wherein can be referring to accompanying drawing.In all accompanying drawings, use identical numeral as far as possible for identical or similar part.Fig. 1 has illustrated and has used reductive agent to handle an embodiment of soot preforms method among the present invention that integral body is represented with numeral 10.

The present invention relates to the creative method of a kind of soot preforms and several processing soot preforms.Reductive agent is used in the processing of soot preforms, preferably uses and contains CO or SO ₂And the reductive agent of not chloride compound.

Soot preforms

Shown among Fig. 1, a prefabricated rods (12) places stove (30).The soot body of making prefabricated rods (12) can be formed by various known methods.These formation methods comprise outside vapor deposition (OVD) at least, vapor axial deposition method (VAD) is improved chemical vapour sedimentation method (MCVD), plasma chemistry vapor deposition (PCVD), or other known method of production, for example colloidal sol changes the Gel Treatment method.OVD, VAD, MCVD, PCVD can be referred to as chemical vapour sedimentation method.Individual activation member is preferably arranged, and soot just is deposited on the activation member when forming prefabricated rods.The sooty particle that is deposited on the start assembly is generally less than 20 μ m, better is less than 10 μ m, is more preferably between 0.1 μ m and 1.0 μ m, preferably between 0.1 μ m and 0.3 μ m.

Prefabricated rods (12) contains a sandwich layer (14) and a covering (16), and some also can have a nearly clad region (not shown).There is a passage (18) at sandwich layer (14) center.Covering (16) is centered around sandwich layer (14) all around.Sandwich layer (14) generally is by SiO ₂Or the SiO of other material that mixed ₂Constitute.Some sandwich layer (14) has mixed germanium in order to improve its specific refractory power.Some sandwich layer (14) also can contain second kind of doping agent (for example fluorine), and individual ring-type fluorine doped region is preferably arranged.Other available soot doping agent comprises the mixture of alkalimetal oxide, alkaline earth metal oxide, transition metal, aluminum oxide, weisspiessglanz, boron oxide, gallium oxide, Indium sesquioxide, stannic oxide, plumbous oxide, phosphorus oxide, arsenic oxide arsenoxide, bismuth oxide, tellurium oxide, selenium oxide, titanium oxide and above material.Sandwich layer (14) can be by doped region and the multilayered structure formed of doped region not.

Covering (16) generally includes SiO at least ₂Covering (16) has than the lower specific refractory power of sandwich layer (14).The present invention is not limited to the material of foregoing formation sandwich layer (14) and covering (16), and any glass substance based on oxide compound all can constitute prefabricated rods (12).

As shown in Figure 1, an end of prefabricated rods (12) has the connection handle (20) that is fused to standard socket and ball joint handle (22), and the other end is stopper (24), and some stopper (24) also has kapillary (26).Prefabricated rods (12) is suspended from the stove (30) by connection handle (20).

Handle the method for soot preforms

Temperature is at least 1000 ℃ treatment process

Handling first method of soot preforms, is to be used for eliminating the increase that when the length of using increases optical fiber is decayed at 1200nm or the above wavelength of 1200nm place.The increase of above-mentioned decay is a defective of finished product, and this is the germanium compound cause adjacent to each other owing to excess of oxygen and at least a lower valency in the optical fiber of extracting out.The germanium compound of lower valency be meant in the optical fiber element Ge not with optical fiber in oxygen element form four chemical combination keys.The germanium compound of a series of lower valencies that may exist in the optical fiber comprises (being not to have only these): Ge ^{+ 2}, GeO ^{+ 1}, Ge-Ge." adjacent to each other " is meant excessive oxygen in the scope of the about 5nm of distance lower valency germanium compound, better is in the scope of the about 1nm of distance lower valency germanium compound, preferably in the scope of the about 0.5nm of distance lower valency germanium compound.The possible cause that excess of oxygen exists in the optical fiber of extracting out is that fixedization of soot preforms is to exist under the environment of excessive oxygen to carry out.Fixedization is meant prefabricated rods (12) is heated to the process that following at least several effects take place more than 800 ℃: drying, doping and sintering.Excessive oxygen is meant the amount of oxygen that exists in the environment each total amount of needed oxygen on more than fixedization.Bring the possible cause of excessive oxygen to comprise and carry the oxygen that enters secretly, leak the oxygen that enters fixedization stove, and the oxygen that produces in the fixedization process.

In this method of the present invention, soot preforms better comprises a Ge-doped district, preferably two Ge-doped districts usually at least.Handling prefabricated rods (12) with reductive agent in stove (30) lining is in order to remove the excessive oxygen in the stove (30).Reductive agent flows into and contacts with prefabricated rods (12) along the direction of arrow (32), thereby removes excessive oxygen.One example reductive agent preferably is CO.Reductive agent preferably can react with excess of oxygen and generate stable reaction product, and consumes excess of oxygen.For example, CO can generate CO with the excessive oxygen reaction ₂Another example reductive agent preferably is buffered CO, for example is CO/CO ₂The mixture of gas.Except reductive agent, what have in the air-flow in the stove also includes rare gas element, helium for example, argon gas, nitrogen, or the mixture in it.Spendable inert substance is not limited to listed these.Preferably there is not chlorine-containing compound in the air-flow in the stove substantially.Comprise in flow of process air under the adulterated situation of CO and inert substance and prefabricated rods (12) fluorine of no use, the concentration of CO is at least 100ppm, and must not be higher than 3000ppm, is preferably and is at least 200ppm, preferably between 300ppm and 600ppm.

In the drying or sintering operation of prefabricated rods (12), reductive agent gas feeds in the stove (30).When stove (30) fed reductive agent gas, prefabricated rods (12) was heated between about 1000 ℃ to about 1200 ℃ at drying stage.Under this temperature, the drying process of prefabricated rods (12) continues about 1 hour to about 6 hours, preferably about 4 hours.In drying process, halide not in the air-flow in the stove (30).This method can be produced the significantly reduced prefabricated rods of foreign matter content (also being called blank) according to the present invention, thereby can make the optical fiber that does not have above-mentioned decay to increase shortcoming thus.

Sometimes, in drying or sintering process, prefabricated rods (12) can be mixed with fluorine.It is to realize by prefabricated rods (12) being heated to from about 1000 ℃ of doping temperature to 1600 ℃ of scopes that fluorine mixes.In case prefabricated rods (12) has been heated to suitable doping temperature, prefabricated rods (12) just contacts with impurity gas.Impurity gas preferably comprises a kind of fluoro-gas of following fluorochemical at least: the chloro-fluoride of CF4, SiF4, C2F6, SF6, F2, C3Fs, NF3, ClF3, BF3, carbon, and their mixture.Prefabricated rods (12) is approximately 1 hour to 6 hours with the duration of contact of impurity gas.Preferably have reductive agent in the impurity gas.Another available step in the processing of soot preforms is before fluorine doping step, or in fluorine doping step with before using these two steps of reductive agent treatment step, with halide-containing (Cl for example ₂Or GeCl ₄) the processing soot preforms.Reductive agent is being fed stove (30) before, preferably halide-containing is being blown down from the air-flow of stove (30).Halogen gas preferably includes the compound or the dihalide of metal halide.The optimal temperature of using halide-containing to handle prefabricated rods (12) is to arrive in about 1200 ℃ scope at about 800 ℃, preferably arrives in about 1100 ℃ scope at about 1000 ℃.The suitable time of using halide-containing to handle prefabricated rods (12) is to be up to preferably about 2 hours at about 1 hour in about 4 hours scope.In the step of using halide-containing to handle, the air-flow in the stove (30) also can comprise rare gas element, and example is helium as mentioned before, argon gas, or nitrogen.Using halide-containing to handle prefabricated rods (12) afterwards, the atmosphere in the most handy inert blowing gas prepurging (30), about at least 5 minutes of time, but be no more than about 2 hours.

After using reductive agent to handle prefabricated rods (12), centre channel (18) closure of prefabricated rods can be carried out sintering to prefabricated rods (12) then.The technology that passage (18) is closed is that centre channel (18) is vacuumized.For sintering prefabricated rods (12), sometimes reductive agent is discharged from stove (30), and stove (30) is heated to about 1200 ℃ to 1600 ℃, be more preferably about 1400 ℃ or more than 1400 ℃.Sometimes in sintering process, the air-flow in the stove (30) can comprise reductive agent.Air-flow in the sintering process preferably includes at least a rare gas element, helium for example, argon gas, or other rare gas element of mentioning of preamble.The suitable sintering time of prefabricated rods (12) is approximately 0.5 hour to about 6 hours.In a reasonable embodiment, sintering time is approximately 4 hours to about 6 hours.But suitable sintering time is subjected to the restriction of following factor: sintering temperature, the size of prefabricated rods and density and chemical constitution.Sintering process can be used same stove with drying process, also can use different stoves.Include at sandwich layer (14) under the situation of doping agent (for example germanium), because reductive agent and sedimentary GeO ₂Side-reaction consumes part germanium can take place, so preferably deposit excessive germanium.

Shown in 40 among Fig. 2, the prefabricated rods behind the sintering (42) is drawn as optical fiber (44).Specifically be that agglomerating prefabricated rods (42) is heated to more than 1800 ℃ or 1800 ℃, be drawn as optical fiber (44) then.Preferably the prefabricated rods behind the sintering (42) is transferred to drawing optic fibre (44) in the special fiber drawing furnace (46).More fortunately the exit of fiber drawing furnace (46) is equipped with a retort furnace.Optical fiber (44) is drawn by traction apparatus (50), deposits on the spool (52).Traction apparatus (50) is pressed the direction rotation shown in the arrow (54).Spool (52) is pressed the direction rotation shown in the arrow (56) around axle A.Wire drawing speed is about 10m/s or more than the 10m/s, preferably about 20m/s or more than the 20m/s.The suitable pulling force of pull optical fiber is that about 75g arrives about 200 grams, is preferably about 90g to about 150 grams.

In another embodiment of this method, just in sintering process, use the processing of reductive agent.Wherein sedimentary soot does not preferably have the adulterated soot of fluorine.In this embodiment, reductive agent is passed in the stove (30), then stove (30) is heated to about 1200 ℃ to about 1600 ℃, preferably, carried out sintering about at least 0.5 hour to about 6 hours about 1400 ℃ or the sintering temperature on 1400 ℃.The concentration of the reductive agent in the sintering air-flow is preferably about 300ppm to 600ppm at this moment.Sometimes after sintering process has been crossed, prefabricated rods (12) can be placed inertia to handle about half hour.

In another embodiment of preceding method, prefabricated rods (12) (as Fig. 1) is a prefabricated rods that plug is arranged, and that is to say that this prefabricated rods can be become remaining plug by wire drawing.In the present embodiment, after prefabricated rods is drawn as remaining plug, but the Dou soot is deposited on above it again.The sooty specific refractory power that deposition gets on preferably must not be higher than the specific refractory power in the sandwich layer district with maximum refractive index.The material that deposits on the plug better is SiO ₂SiO ₂During doping, can use the doping agent that improves specific refractory power or reduce specific refractory power.Deposit the sooty plug and also be called covering prefabricated rods or covering plug.

Shown in 60 among Fig. 3, the covering prefabricated rods is inserted in the stove, use reductive agent to handle then.Covering prefabricated rods (62) include plug (64) and at least one deck be deposited on soot layers (66) on it.Plug (64) preferably has been sintered into glass.Employed reductive agent is with previously described identical.Stove is heated to aforesaid temperature range (about 800 ℃ to 1200 ℃ or 1200 ℃ to 1600 ℃), keeps aforesaid for some time (about 0.5 hour to about 6 hours).Covering prefabricated rods (62) preferably contacts with reductive agent in sintering process.

Preceding method of the present invention can reduce to exist in the stove in fixedization process (30) possibility of excessive oxygen.Therefore, the optical fiber of being pulled out by the prefabricated rods of handling through aforesaid method does not have the shortcoming that aforesaid decay increases.

The aforesaid method that uses reductive agent to handle soot preforms has obtained fabulous application in the production of non-zero dispersion displacement optical fiber, healthy and free from worry (the Coning of group in New York for example, Incorporated of Corning, NewYork) the Corning Submarine LEAF optical fiber of Sheng Chaning.Non-zero dispersion displacement optical fiber is the optical fiber with the listed character of Table A, normally the multilayer doped core optical fiber.Have behind the Table A and explain.

Table A

Character	Suitable value	Better be worth	Best values
				Decay at 1550nm	≤0.28dB/km	≤0.23dB/km	≤0.18dB/km
Decay in the 1525-1575 wavelength region	≤0.28dB/km	≤0.23dB/km	≤0.18dB/km
				Mode field diameter at 1550nm	8.5-10μm	8.95-9.6μm	9.0-9.55μm
Total dispersion at 1560nm	(-4.0)- (-0.5) ps/nm·km	(-3.4)- (-1.0) ps/nm·km	(-3.4)- (-1.1) ps/nm·km
				Zero-dispersion wavelength (λ 0)	1560-1595nm	1567-1589nm	1580nm
Zero-dispersion slop (S 0)	≤ 0.15ps/nm 2 ·km	≤ 0.12ps/nm 2 ·km	≤ 0.11ps/nm 2 ·km
				Useful area (A eff)	≤200μm 2	≥65μm 2	≥71μm 2
Macrobending decay (bending diameter with 32mm encloses around 1) at 1550nm	≤0.50dB	＜0.50dB
				Bending decay (bending diameter with 75mm encloses around 100) at 1550nm	≤0.05dB	＜0.50dB

Following note is used for illustrating some above-mentioned character.

Explain

Following note is that the common usage according to this area illustrates.

Refractive index profile is the graph of a relation of the radius of specific refractory power and waveguide fiber.

The multilayer fibre core is to be divided at least the first and second waveguide cores part or sectional fibre core.Each part or segmentation are positioned at certain radical length position, substantially for the medullary ray symmetry of waveguide fiber, and have relevant index distribution.

Useful area A _Eff=2 π (∫ E ²Rdr) ²/ (∫ E ⁴Rdr), integrating range herein is from 0 to ∞, and E is the strength of electric field of the light propagated in the waveguide.Effective diameter D _EffCan be defined as follows:

A _eff＝π(D _eff/2) ²。

Big useful area is meant that the useful area of optical fiber is greater than 60 μ m ², be preferably greater than 65 μ m ², best is greater than 70 μ m ², useful area is greater than 80 to 90 μ m ²Optical fiber also be possible, effect can be better.

Relative refractive index percentage ratio Δ %=100 * (n _i ²-n _c ²)/2n _i ², n herein _iBe meant specific refractory power (unless referring to its meaning in addition), n in the maximum in i zone _cBe meant mean refractive index (unless referring to its meaning in addition) at clad region

α-distribution plan is meant a kind of refractive index profile of representing with Δ (b) %.B is a radius herein, and Δ (b) %=Δ (bo) (1-[|b-b _o|]/(b ₁-b _o)] ^α), b herein _oThe value of b when being Δ (b) % maximum, b ₁Be the value of Δ (b) % b when being zero, and the span of b is: b _i≤ b≤b _f, Δ herein described as defined above, b _iBe the starting point in α-distribution plan, b _fBe the terminating point in α-distribution plan, and α is an index that value is a real number.Be transfused in the computer model after starting point in α-distribution plan and terminating point are selected.If made α-distribution plan in the past earlier making step-refraction index distribution plan or other distribution plan, then the starting point that adopts of this place is the point of crossing of α-distribution plan and step-refraction index distribution plan or other distribution plan.

The measurement of above-mentioned decay can be according to U.S. Pat 5,534, and 994 (the open date is on July 9th, 1996) are carried out, and description taken in conjunction wherein is in herein.Other working method of measuring decay comprises FOTP-78, FOTP67, FOTP-20A, or TIA455-67.

This method of the present invention also can be applicable to contain the optical fiber of at least one Ge-doped district and at least one fluorine doped region.In a such embodiment, prefabricated rods (12) contains at least one Ge-doped district (preferably forming) and a fluorine doped region in the soot deposit step.Prefabricated rods (12) preferably also contains at least one fluorine doped region.The fluorine doped region can form in fluorine doping step as previously mentioned, also can form in the soot deposit step.Fluorine doping step can about 1100 ℃ or the temperature more than 1100 ℃ carry out.Ge-doped district and fluorine doped region can be two well-separated zones in prefabricated rods (12), also can crossover, and have at least a zone to contain germanium and fluorine simultaneously in the prefabricated rods, or above-mentioned array configuration.

In this embodiment, prefabricated rods (12) preferably uses reductive agent to handle in sintering step.But this embodiment of the present invention is not restricted to carry out the processing of reductive agent in sintering step.Sometimes prefabricated rods (12) can use reductive agent to handle in sintering step and fluorine doping step.The temperature of reductive agent air-flow is at least 1100 ℃, preferably is at least 1300 ℃.As previously mentioned, the compound that the reductive agent air-flow is preferably not chloride substantially or, also not chloride element.

For the adulterated prefabricated rods of fluorine, the concentration of the concentration of reductive agent fluorine dopant preferably and in the doping air-flow is on the same order of magnitude in the air-flow.Said herein numbers of poles is identical, is meant that the concentration of reductive agent in the reductive agent air-flow is at least (1/10th) of the concentration of fluorine dopant in the doping air-flow, and must not be higher than 3 times of concentration of fluorine dopant in the doping air-flow.For example, CF in the doping air-flow ₄Weight percentage concentration be 1%, the suitable weight percentage concentration of CO reductive agent is at least 0.5%, preferably is at least 1.0%.

The present invention is not limited to following example.

It is favourable using reductive agent to handle the adulterated prefabricated rods of fluorine, and a reason is that fluorine doping process can produce excess of oxygen in the doping air-flow.Fluorine is incorporated into and is based on following chemical equation in the prefabricated rods (12):

(1) ；

(2) 。

Reductive agent can form CO with the oxygen reaction of generation in the fluorine doping reaction ₂The amount of reductive agent is best in the air-flow presses the needed amount of stoichiometry more than the oxygen that generates in the fluorine doping reaction, so that excess of oxygen reaction in unnecessary reductive agent and the fixedization process is arranged.The possible cause of introducing excessive oxygen comprises (being not to have only these): carry the oxygen that enters secretly, leak the oxygen that enters fixedization stove, the oxygen that produces in the fixedization process, and remaining oxygen in the fixedization furnace gases.The processing of reductive agent can consume all excessive oxygens that exist in the fixedization stove.

Sometimes, prefabricated rods (12) can use chlorine-containing gas to handle before fluorine doping or reductive agent processing.The chlorine-containing gas treatment step is preferably described identical with preamble.The chlorine-containing gas treatment step must not carry out in this method of the present invention.

The optical fiber that contains the fluorine doped region that root is produced does not accordingly have the above-mentioned shortcoming that decay increases when optical fiber uses length to increase.The step of prefabricated rods (12) drawing optic fibre as hereinbefore.

The present invention also can be used to eliminate the absorption peak in the fluorine doped fiber decay spectra.Absorption peak is one section zone that decay departs from the baseline decay in the decay spectra, and general departing from is that decay increases.Shown in Figure 11 is with the decay spectra of the optical fiber that contains the fluorine doped region of ordinary method production, represents with 110.The result of this spectrum is shown solid line (112).Decay spectra (110) has an absorption peak (114) at about 1440nm place, and second absorption peak (116) is at about 1546nm place, and the 3rd absorption peak (118) is at about 1580nm place, and the 4th absorption peak (119) is at about 1610nm place.What these absorption peaks shown in Figure 11 (114,116,118,119) were represented is that actual pad value has departed from the baseline of (110), and these baselines are expressed as dotted line 120,122,124,126.Absorption is that the transform light energy of optical signal becomes heat energy and the part of the decay that causes.

The method of measuring the decay spectrogram of optical fiber has many kinds.A data source about existing measuring method is that Stewart E.Miller and Alan G.Chynoweth write " Optical FiberTelecommunications ".This paper is with reference to the content of having quoted this this book 214-218 page or leaf.The instrument type that can be used for carrying out above-mentioned measurement comprises GN Nettest of Hopkinton, the PK decay worktable that MA produces, and the model of a suitable PK decay worktable is PK-2500.

By analyzing the various optical fiber that contain the fluorine doped region, find that such optical fiber has four absorption peaks at least.The wavelength that absorption peak occurs is included in 1410nm and (generally is at least 1400nm, better be to be at least 1410nm, preferably be at least 1420nm, and generally be no more than 1470nm, better be to be no more than 1460nm, preferably be no more than 1450nm), (generally being at least 1520nm, better is to be at least 1530nm at 1546nm, preferably be at least 1540nm, and generally be no more than 1560nm, better be to be no more than 1555nm, preferably be no more than 1550nm), (generally be at least 1565nm at 1583nm, better be to be at least 1570nm, preferably be at least 1575nm, and generally be no more than 1595nm, better be to be no more than 1590nm, preferably be no more than 1585nm), and at 1610nm (generally being at least 595nm, better is to be at least 1600nm, preferably be at least 1605nm, and generally be no more than 1525nm, better be to be no more than 1520nm, preferably be no more than 1515nm) nominal wavelength.

The present invention finds to cause that a reason of above-mentioned absorption peak is to have mixed to have general formula C in fixedization process _nF _2n+2Fluorochemicals, here " n " is positive integer.Verified, the above-mentioned absorption peak that occurs in spectrum analysis figure is owing to there be a kind of of following at least compound in the optical fiber: CO, CO ₂, COF ₂, COClF, C _nF _2n+2, the perhaps mixture of above-mentioned substance.With CF ₄For example illustrates how aforesaid compound forms, its total reaction equation following (not trim):

" x " is the numerical value between 1 to 4 herein, usually between 1 to 3.

Confirm also that simultaneously be not more than the optical fiber of-0.35% (normally being not more than-0.38%) for Δ %, absorption peak can be bigger.Δ % is a relative refractive index percentage ratio, Δ %=100 * (n _i ²-n _c ²)/2n _i ², n herein _iBe meant largest refractive index (unless referring to its meaning in addition), n in the i zone _cBe meant mean refractive index (unless referring to its meaning in addition) at clad region.The value of above-mentioned Δ % is the reduction amount of a maximum for the zone that specific refractory power in the optical fiber reduces.An example like this is 140 among Figure 14.Figure 14 is the refractive index profile of optical fiber, represents that with the relative refractive index percentage ratio (Δ %) and the variation of radius refractive index profile (140) has the Δ % value of a maximum, and it is worth less than-0.4, is designated as (142).Eliminating an embodiment of the method for above-mentioned absorption peak, generally is a method of producing preform.This method comprises to be used CO and at least aly has a general formula C _nF _2n+2The air-flow of the fluorochemicals soot body of mixing, here " n " is positive integer.Contain preferably in the doping air-flow at least that percent by volume concentration is 5%, be preferably 10%, more preferably 15%, be preferably 20% fluorochemicals.Also require the percent by volume concentration of the fluorochemicals in the doping air-flow must not be greater than 50%.Soot body herein can be any aforementioned example of soot preforms shown in Figure 1 (12).An embodiment of this method of the present invention is shown in Figure 12.Figure 12 is different with Fig. 1, be when the gas that comprises CO and fluorochemicals when the direction of arrow (32) feeds in the stove, just the outside along prefabricated rods (12) enters, and the do not pass prefabricated rods center of (12).But the present invention is not limited to embodiment shown in Figure 12.Available fluorochemical preferably comprises (being not to have only these): CF ₄, C ₂F ₆, or C ₃F ₈, first-selection is CF ₄

Aforesaid method preferably adds a step, soot body is exposed to comprise CO and substantially not in the air-flow of halide.This exposing step is preferably carried out before the doping step.Sometimes exposing step is carried out later in the available chloride treatment step.Between chloride treatment step and available exposing step preferably with the stove blowing purification.In addition, exposing step can be carried out in that the temperature of soot preforms progressively is warmed up to the process of fluoridizing the doping temperature from the outlet temperature of chloride treatment step.The temperature and time of chloride treatment step and doping step is identical with previously described corresponding steps.In an embodiment of this method of the present invention, the air-flow in the exposing step is free from chloride substantially air-flow.Usually the temperature of prefabricated rods is at least 1000 ℃ in the exposing step, better is at least 1100 ℃, preferably is at least 1200 ℃.

Comprise progressively the stage of heating up in exposing step, the temperature of stove will be heated to above 1200 ℃ from being higher than 1000 ℃ usually, better is to be heated to and to be at least 1200 ℃ from being at least 1000 ℃, preferably is heated to and is at least 1300 ℃ from being at least 1000 ℃.

The time of exposing step can be any for some time from 15 minutes to 60 minutes, and best exposure duration comprises 30 minutes, 45 minutes, and 60 minutes.The temperature of stove rises with the speed of 2 ℃ to 10 ℃ of per minutes, and concrete heat-up rate will depend on the circumstances.The process of heat temperature raising need not be that successive rises in whole process-exposed yet in the process-exposed.But, the present invention's be not limited in process-exposed, must to raise temperature of stove.Process-exposed also can be carried out under isothermal condition, or a part of process wherein is under isothermal condition.

The air-flow that is exposed in the stove preferably is made of inert substance and CO, and the ratio of CO and inert substance is at least 0.0012, and preferably is not more than 0.48.Inert substance can be any rare gas element, for example (but being not only these): argon gas, nitrogen, helium, or their mixture.In addition, in process-exposed, the concentration of CO is at least 300ppm usually in the stove, better is at least 600ppm, preferably is at least 1200ppm.Have, the concentration of CO is not more than 4800ppm usually in the stove again, better is not more than 4000ppm, preferably is not more than 3000ppm.

The concentration of CO can be got with regard to any concentration in the described CO concentration range of process-exposed in the stove in the doping step.The concentration of CO not necessarily needs identical with the concentration of the CO of process-exposed in the stove in the doping step.The CO in the above-mentioned process-exposed and the proportional range of inert substance also are applicable to the doping step, but CO does not need with process-exposed identical with the ratio of inert substance in the doping step.

As previously mentioned, this method also can further comprise the step of sintering prefabricated rods.Sintering prefabricated rods of the present invention also can be carried out in comprising the air-flow of CO.Add the CO in the sintering air-flow, the mode of sintering prefabricated rods is said identical with the front.What the range of concentrations of CO can be with described in the process-exposed in the sintering air-flow is identical, but also not necessarily identical.

Have, the present invention also comprises the process with the prefabricated rods drawing optic fibre again.When the optical fiber that goes out from stove lira leaves stove preferably by a cell that is full of the lower gas of relative helium thermal conductivity.The temperature of gas better is lower than the temperature of the optical fiber of pulling out, and is preferably consistent with room temperature or lower.Thermal conductance is that the low gas of rate number comprises nitrogen, argon gas, air or their mixture.The position of this cell can be close to the optical fiber outlet of fiber drawing furnace, also the downstream position that can export at the optical fiber of fiber drawing furnace.This cell can be called the retort furnace (LEM) of handling stove or lower end extension.Incorporated herein in the United States Patent (USP) (title is " method and apparatus of preparation optical fiber ", and date of presentation is May 30 calendar year 2001) about other description references of LEM.

A specific embodiments of the present invention is after prefabricated rods 12 is put into stove, and furnace is raise, and about 10 minutes of time, 5 minutes better, and 3 minutes best.Stove preferably has two independently temperature control zones, 1 (also claiming fixedization district) of zone and regional 2 (also claiming the sintering zone).In the stove zone 1 be heated to 1200 ℃ or more than, can be heated to 1225 ℃ or above better.In the stove zone 2 be heated to 1300 ℃ or more than, can be heated to 1325 ℃ or above better, can be heated to 1350 ℃ or abovely also will get well, can be heated to 1380 ℃ or above best.Between temperature raising period, in stove, feed rare gas element, flow is 10 standard liter/min (slpm), and 15slpm is better, and 20slpm is best.

Prefabricated rods is positioned over stove zone 1 when handling, and is in chloride 2.2% the atmosphere at least 30 minutes, and 45 minutes better, and 60 minutes best.In the stove temperature rise period, it is identical that furnace temperature preferably keeps.The treatment stage of chlorine, in stove, feed the helium of 20slpm and the chlorine of 0.45slpm.After finishing the treatment stage of chlorine, the gas in the stove is discharged.

Next step, prefabricated rods 12 contacts maintenance 15 minutes to 45 minutes with the helium of said temperature and the atmosphere of CO.The atmosphere that is contacted comprises helium and CO, is 19.00slpm toward the interior flow that feeds helium of stove, 19.24slpm better (19.48slpm also will get well, and 19.76slpm is best); The flow of CO is 1.00slpm, (0.76slpm is better, and 0.52slpm also will get well, and 0.45slpm is best).Be more preferably, CO accounts for 10% in helium and CO mixture.

Another embodiment of the invention comprises and prefabricated rods 12 is being contained helium, CO and CF ₄Atmosphere in mix.Toward the interior flow that feeds helium of stove is 14.00slpm, and 14.5slpm is better, and 15.0slpm also will get well, and 15.76slpm is best.In stove, feed CF ₄Flow 2slpm at least, 3slpm is better at least, 4slpm is best at least.The flow of the interior feeding of past stove CO is 0.020slpm at least, and 0.0243slpm is better at least.The time of doping step was at least 30 minutes, and at least 45 minutes better, also will get well at least 60 minutes, and at least 90 minutes best.

This embodiment also comprises discharges stove with impurity gas.When exhaust, the temperature in stove zone 2 is brought up at least 1400 ℃, and at least 1420 ℃ better, and at least 1450 ℃ best.Furnace atmosphere comprises helium and CO during exhaust.Be at least 19.0slpm toward the interior flow that feeds helium of stove, 19.5slpm is better at least, and 19.76slpm is best at least.Be at least 0.020slpm toward the interior flow that feeds CO of stove, 0.024slpm is better at least.The evacuation time of doping atmosphere at least 10 minutes, at least 20 minutes are better, and at least 30 minutes are best.

Next step, the sintering of prefabricated rods, translational speed 4mm/ minute are at least carried out in the zone 2 that prefabricated rods is moved to stove.Translational speed can be more preferably 8mm/ minute up to 12mm/ minute.The temperature in stove zone 2 remains at least 1400 ℃, and at least 1420 ℃ better, and at least 1440 ℃ best.The prefabricated rods agglomerating time was at least 120 minutes, and at least 150 minutes better, and at least 170 minutes best.The sintering stage feeds helium and CO in stove.Be at least 19.0slpm toward the interior flow that feeds helium of stove, 19.5slpm is better at least, and 19.76slpm is best at least.Be at least 0.020slpm toward the interior flow that feeds CO of stove, 0.024slpm is better at least.

After the dawn prefabricated rods moved in the zone 2 of stove fully, sintering step promptly came to an end, and the time that prefabricated rods keeps in 2 helium atmospheres of stove zone will be less than 5 minutes, be less than 3 minutes better, be less than 2 minutes and also will get well, be less than 1 minute best.In this step, the flow that feeds helium in freezing of a furnace is that 20slpm is better.

A specific embodiments of the present invention has an end in end step.In ending phase, the temperature in stove zone 2 is reduced to and is lower than 1400 ℃, be lower than 1390 ℃ better, be lower than 1380 ℃ best.In end step, it is better that the interior atmosphere of stove also has argon gas., better toward the interior flow that feeds argon gas of stove greater than 15slpm greater than 10slpm, best greater than 20slpm.The decay spectra of gained optical fiber is presented at wavelength 1565nm in the 1595nm scope, and decaying offset is not more than 0.012dB/km.It is better that skew is not more than 0.006dB/km, is not more than 0.003dB/km and also will gets well, and skew is zero best.Wavelength region is that 1570nm is better to 1590nm, and 1575nm is best to 1585nm.

The decay spectra of product optical fiber, in the 1470nm scope, decaying offset is not more than 0.012dB/km at wavelength 1400nm, and it is better to be not more than 0.006dB/km, is not more than 0.003dB/km and also will gets well, and skew is zero best.Wavelength region is that 1410nm is better to 1460nm, and 1420nm is best to 1450nm.

The decay spectra of product optical fiber, in the 1560nm scope, decaying offset is not more than 0.010dB/km at wavelength 1520nm, and it is better to be not more than 0.006dB/km, is not more than 0.003dB/km and also will gets well, and is zero best.Wavelength region is that 1530nm is better to 1555nm, and 1540nm is best to 1550nm.

The decay spectra of product optical fiber is presented at wavelength 1595nm in the 1625nm scope, and decaying offset is not more than 0.012dB/km, and it is better to be not more than 0.006dB/km, is not more than 0.003dB/km and also will gets well, and is zero best.Wavelength region is better to 1620nm for decay 1600nm, and 1605nm is best to 1615nm.

The spectrum of pulling out optical fiber do not occur at least one aforementioned absorption peak (nominal wavelength is at about 1440nm, 1543nm, 1583nm, 1610nm), it is better at least two aforementioned absorption peaks not occur, it is best any one aforementioned absorption peak not occur.

Peak excursion also can be represented with rootmean-square (RMS).RMS can calculate in order to following equation:

$\mathrm{RMS}={\left((1/n)\underset{{\mathrm{\λ}}_l}{\overset{\mathrm{\λn}}{\mathrm{\Σ}}}{\left({\mathrm{attn}}_i\right)}^2\right)}^{\frac{1}{2}}$

" n " is the space-number in the setted wavelength scope in the formula, and " λ n " is the upper limit of wavelength, and " λ l " is the lower limit of wavelength, " attn _i" be the decay of optical fiber in arbitrary given length, " i " is between " n " and " l ".For example at 1583 absorption peaks that occur, wavelength region can be 1565nm to 1595nm.It is 0.0090 better that RSM is not more than, and is not more than 0.0088 better, is not more than 0.0086 best.

Aforesaid each method can be used for making the whole technological process of optical fiber.For example, aforesaid method can be used to produce (managed) optical fiber of big optical fiber of useful area and chromatic dispersion manipulation.The doping agent that the optical fiber that chromatic dispersion is handled has at least one zone to comprise specific refractory power is descended, the maximum Δ % in this zone be-0.35% or littler ,-0.38% or littler just better ,-0.40% or also will get well forr a short time ,-0.42% or littler best.Can consult following U.S. Patent application about the further describing of optical fiber that chromatic dispersion is handled, its reference in content is incorporated into this: be filed in 60/208342 of on May 31st, 2000; Be filed in 60/217967 of on May 31st, 2000; Be filed in 60/193080 of on March 30th, 2000.

Be not higher than 1000 ℃ processing in temperature

Method comprises prefabricated rods 12 heating that will hang in the stove 30, and temperature is lower than 1000 ℃.The Heating temperature of soot preforms 12 be lower than 800 ℃ better, also to get well for 25 ℃ to 600 ℃, be not more than 400 ℃ best.

As shown in Figure 1, in stove 30, feed reductive agent gas.Reductive agent contacts with prefabricated rods 12 along the aspect inflow of arrow 32.Reductive agent be a kind of can be the compound of the oxide compound reaction of MxOy with its molecular formula, " M " is at least a following component that is selected from the formula: period of element atom sequence number is 21-30,39-48,57-79, the element of 89-107 and their mixture." O " is oxygen, and " x " and " y " is the integer greater than 0.Be more preferably M " be at least a following component that is selected from:: the element of Zr, Ni, Fe, Ti, V, Cr, Mn, Co, Cu, Zn or its mixture.

A kind of preferred reductive agent is CO.Be more preferably this reductive agent and can contain a kind of carbonyl (product CO) at least with MxOy compound reaction generation.For example, prefabricated rods 12 contains nickel oxide, and this nickel oxide can react with reductive agent CO, generates Ni (CO) ₄Be more preferably, under normal pressure, just can volatilize being lower than under 200 ℃ of temperature as the carbonyl compound of reaction product.A kind of reductive agent of replaceable use is SO ₂Except reductive agent, also for example helium, nitrogen, argon gas or their mixture and reductive agent feed stove 30 simultaneously with a kind of rare gas element.The invention is not restricted to listed rare gas element.The time that prefabricated rods 12 contacts with reductive agent is preferably 1 hour to 4 hours.

Soot preforms 12 mainly comprises silicate, better contains to be selected from alkalimetal oxide alkaline earth metal oxide, aluminum oxide, at least a component of weisspiessglanz and composition thereof.Be more preferably, prefabricated rods 12 comprises the oxide compound of at least a element that is selected from following element: Sb, Al, B, Ga, In, Ti, Ge, Sn, Pb, P, As, Bi, Te, Se and composition thereof.Prefabricated rods 12 also can form from the soot batch of material that is used for glass smelting.Suitable soot batch of material for example comprises silicon, aluminium and alkali-metal oxide compound and at least a other oxide compounds above-mentioned.

Also can be prefabricated rods 12 with after reductive agent gas contacts, carry out fluorine and mix.Prefabricated rods 12 is heated to 1000 ℃-1600 ℃ of doping temperature carries out the fluorine doping.Prefabricated rods 12 just contacts with impurity gas after being heated to suitable doping temperature.Impurity gas comprises at least a following component that is selected from: following fluoro-gas: CF ₄, SiF ₆, C ₂F ₆, SF ₆, F ₂, C ₃F ₈, NF ₃, ClF ₃, chloro-fluorocarbon compound and composition thereof.The time that prefabricated rods 12 contacts with impurity gas is 1 hour to 6 hours.

Prefabricated rods 12 is heated to 1200 ℃ to 1600 ℃ sintering temperature then, is sintered into glass.For the adulterated prefabricated rods of fluorine, prefabricated rods can or be carried out sintering later in the adulterated while of fluorine.Prefabricated rods maintains about 1 hour to 6 hours of the time of sintering temperature, and about 4 hours to 6 hours better.In sintering process, prefabricated rods is in a kind of rare gas element.Rare gas element can be by He, Ar, N ₂And composition thereof form.In order to form the tubular preform shown in Figure 4 and 5, as previously mentioned, hole 18 is not sealed.

Shown in Figure 4 and 5, the agglomerating prefabricated rods has a longitudinal length L, forms longitudinal cut 25 along this longitudinal length cutting prefabricated rods 12.In a preferred embodiment, prefabricated rods 12 has only a longitudinal cut 25 to make glass become a slice, similar tightly closed " C " shape in its cross section.With prefabricated rods 12 cuttings, flatten it then.

In an available embodiment, prefabricated rods 12 is cut twice at least along the longitudinal, be cut at least two otch that cut out separately and better equate along the circumference spacing of prefabricated rods 12.When the inner periphery of prefabricated rods 12 was 2 times, 3 times of the desired width of photomask or 4 times, prefabricated rods 12 just halved, the face of indulging of trisection and quartern cutting.When the inner periphery of prefabricated rods 12 during, preferably be cut to several parts significantly greater than the width of requirement photomask blank.

As shown in Figure 6, the C-shape part 23 of prefabricated rods 12 is passed through to hang, stretch, dangling becomes flat photomask blank with its flattening, is similar to have the flattening of the prefabricated rods 12 of single otch 25.As an alternate way, half prefabricated rods can directly overhang in the stove.Similarly, 1/3rd and four/part of prefabricated rods 12 directly can be overhang in the stove 31.In order to help flattening, these parts of prefabricated rods preferably place the position that is bent upwards.

Before cutting and flattening, the glass preform 12 of fixedization should have the internal diameter and the wall thickness of requirement.The core drill hole provides by for example pressurizeing to its cutting for these internal diameters and wall thickness.

The part 23 that flattens fixedization prefabricated rods 12 comprises this part 23 of heating, to deformation force of effect on the part 23 of heating.As shown in Figure 4, part 23 is flattened preferred step comprise: part 23 is hung in heat treated stove 31 of glass downward power of effect, for example weight of an additional traction on part 23.For part 23 is provided support, it is hung from the position near stove 31 tops with a suspension holdfast.Suspension holdfast 51 comprises that platinum filament is mounted on the place of part 23 near otch 25.Platinum filament can be articulated in the aperture that part 23 bored, and platinum filament passes this two apertures.Support 51 and platinum filament can directly or indirectly hang on the top of stove 31.

Can apply downward flattening reactive force to part 23, by hanging platinum filament and weight similarly, silicon-dioxide weight preferably is with the one side on the otch opposite of the part 23 that firmly is applied to prefabricated rods 21.Be applied to the part 23 that flattening reactive force 53 on the part 23 helps stretching heating.Stove 31 will be heated at least 1480 ℃, and the weight 53 that applies reactive force could play the flattening effect to part 23.Reach purpose stretching and that flatten by hanging and stretching, part 23 suitable Heating temperature scope in stove 31 is 1480 ℃ to 1580 ℃, is preferably lower than 1600 ℃, for example about 1500 ℃.

Except hanging weight, the temperature of can also hot spots 23 to dangling also applies a metamorphosis power on the part 23 of heating, reaches further the purpose to part 23 flattenings.Can be as shown in Figure 5 will have the part 23 of otch stretching by hanging weight as illustrated in fig. 4 after, by the further flattening of dangling glass treatment stove 31 in.A step preferably is that stove 31 is heated to sufficiently high temperature, makes the weight of raising that is not subjected to support section of otch of part 23 produce enough deformation forces, makes the pipe otch dangle and launches to become the glass workpiece of a flattening.

Stove 31 is heated to sufficiently high softening temperature and makes have the part 23 of otch to dangle, and temperature keeps below yield temperature, in order to avoid when part 23 flattens, flowing and attenuation of glass taken place.The scope of the temperature of dangling is more preferably at 1720 ℃ to 1760 ℃ at 1700 ℃ to 1800 ℃, is preferably in 1730 ℃.In order to reach flattening, except by applying deformation force on part 23, for example hang and/or dangle, another kind of deformation force is that pressure also can be applied on the part 23 that heats in the stove.

Except the gravity of part itself, exert pressure when acting on part 23, can use lower texturing temperature.When pressure acted on the pipe, desired treatment temp was at 1550 to 1560 ℃, acted on part 23 with the dull and stereotyped spinning parts of a flattening.Be preferably in and cover the last layer platinum foil on the pressure surface of part 23 and separate the glass preform.What the dull and stereotyped press member of an alternate flattening was used is the high purity solid graphite.High purity solid graphite parts are in the present invention also as useful setter and furnace surface.

Except part 23 is flattened, part 23 is heated in the heating environment of no hydrogen, can guarantee that glass is not subjected to the pollution of hydrogen, and allow and enter H in the glass ₂Molecule is overflowed and is excluded.The result does not have the hydrogen of discernable quantity in the photomask blank.

Hot spots 23 is exactly the distortion softening temperature of hot spots 23 to glass, and this moment, the viscosity of glass reduced, so that the deformation force that applies can make the Glass tubing distortion.

Can consult following U.S. Patent application about other descriptions of being made photomask matrix technology by a fixedization preformed articles, they are all with reference to being incorporated into this: be filed in 12 days 60/119,805 February in 1999; Be filed in 60/123,861 of on March 12nd, 1999; Be filed in 60/135,270 of on May 21st, 1999; Be filed in 60/159,076 of on October 12nd, 1999; Be filed in 09/397,577 of on September 16th, 1999; Be filed in 09/397,573 of on September 16th, 1999; Be filed in 09/397,572 of on September 16th, 1999;

Aforesaid method of the present invention can be used in the technology of making no chlorine photomask.No chlorine photomask has can transmit the characteristics that at least 90% wavelength is the light of 157nm, better can transmit 100%.

Embodiment

The invention will be further described with some following embodiment.

Embodiment 1

The prefabricated rods assembly is made up of silica tube and quartz boat, is filling Iota-6 quartz sand (available from UNIMIN of New Canaan, CN) with the γ-Al of mean particle size less than 10 microns in silica tube ₂O ₃Soot (available from Alfa Aesar of Ward Hill, MA), with this prefabricated rods assembly in horizontal tube furnace 200 ℃ the heating 4 hours.In heat-processed, prefabricated rods contacts with CO reductive agent air-flow.CO gas charges into an end of boat continuously with the flow of 1L/min.CO gas purity 99.7%, available from Murray Hill, the BOC gas companies of NJ.Before handling and after handling with CO, γ-Al ₂O ₃Middle transition metal content is measured.Transition metal content is to adopt Shiva Technologies of Syracuse, and the inductance coupled plasma mass spectrograph (ICP-MS) that NY produces is analyzed.Analytical results sees Table 1-1.

Table 1.1

Element	Content (ppm) before CO handles	CO handles back content (ppm)
			Ti	10.0	1.0
V	1.4	＜0.05
			Cr	1.5	＜1.0
Mn	1.6	＜0.05
			Fe	60.0	＜2.0
CO	0.2	＜0.05
			Zn	2.0	1.0

The content of each element had reduced 1/3rd at least after CO handled.

Embodiment 2

For preparation optical fiber, measure the effect of handling prefabricated rods with reductive agent.NY is used for making the prefabricated rods of Submarine LEAF optical fiber available from CorningIncorporated of Corning with two, after handling in atmosphere containing chlorine, handles 2 hours with CO in sintering process.The concentration of CO changes in this reducing atmosphere.Prefabricated rods is handled in CO concentration is the atmosphere of 300ppm, and another root prefabricated rods is handled in CO concentration is the atmosphere of 600ppm.Prefabricated rods is drawn as Submarine LEAF optical fiber.As shown in Figure 8, a kind of is that another kind is under the high tensile situation of 180g, with two kinds of different drawing speed drawing optic fibre samples under the low-tension situation of 90g.The sample fiber that draws long 2 kms of each root that form according to certain drawing speed is measured its decay under the 1550nm wavelength.The optical fiber of long 2 kms placed subenvironment is indoor to be heated to 200 ℃ and be incubated 20 hours.This chamber of using is that Yamato DKN600 is (available from VWR of West Chester, PA).Measure the variation of decay.Also measured a control fiber.The difference of control fiber and test optical fiber is, is used for pulling out the prefabricated rods of control fiber, is to use Cl ₂Handle rather than handle with CO.The decay of each root sample (available from Photon Kinetics of Beavarton, OR) is upward measured according to the schedule of operation of PK-8 at PK-8 Spectral Attenuation Bench.

Experimental result is listed in Fig. 8.As seen from the figure, handle optical fiber with reductive agent and reduced the decay that causes.The condition that is apparent that most drawing optical fibers is that speed and the low-tension of 10m/s at least is good.The optical fiber of manufacturing demonstration the significantly reducing decay that causes according to the present invention.

Embodiment 3

Measure the effect of handling the adulterated prefabricated rods of fluorine with aforesaid reductive agent.Three prefabricated rods are handled with a kind of chlorine-containing compound at 1000 ℃.The temperature of stove is warmed up to 1450 ℃ with the speed program of 4 ℃/min subsequently.Every prefabricated rods was handled 1 hour in fluorine-containing atmosphere, saw Table 3-1.By table 3-1 as seen, to test optical fiber, also comprise CO in the fluorine doping atmosphere.Prefabricated rods is drawn into a mandrel step-refraction index single-mode fiber that has ring-type fluorine doped region.Sample fiber draws with identical speed and tension force and forms.The sample fiber of every 2 km length (available from Photon Kinetics of Beavarton, OR) is upward measured according to the schedule of operation of PK-2500 at PK-2500 Spectral Attenuation Bench in the attenuation process of 1550nm wavelength.Sample fiber is placed on 200 ℃ temperature 20 hours.Measure the variation of decay.Control fiber is test according to this method also.The difference of control fiber and test optical fiber is control fiber Cl ₂Drying is used CF then ₄The reductive agent and the fluorochemicals that replace the invention described above to use are handled.

Table 3-1

Processing environment	The decay (dB/km) that causes at 1550nm
		1％CF 4(contrast) uses pre-dry Cl 2Handle	1.22
1％CF 4+ 1%CO uses pre-dry GeCl 4Handle	0.00
		1％CF 4+ 1%CO uses pre-dry Cl 2Handle	0.05

Make decay be reduced to minimum and even be zero with the optical fiber of reductive agent manufacturing of the present invention.In contrast be that control fiber has increased decay greatly.

Embodiment 4

In order to improve the performance of hydrogen in the opposing environment, further check the effect of in sintering process, handling prefabricated rods with CO.Two prefabricated rods contain helium and up to 4 weight %Cl at one ₂Atmosphere in dry, drying temperature is 1000 ℃ to 1150 ℃, about 4 hours of time of drying.A prefabricated rods in the helium that contains 200ppmCO at least, is carried out sintering 1100 ℃ to 1600 ℃ temperature.Another root prefabricated rods is sintering in inertia then.These two prefabricated rods all are drawn into SMF-28 ^TMOptical fiber can be from Corning, and Incorporated obtains.

The long sample fiber of each root 2 km was positioned in the environment that contains 1% hydrogen 144 hours under the room temperature condition of normal pressure.Measure the decay of optical fiber before placing hydrogen environment, and after placing 144 hours process of hydrogen, reached maximum attenuation.Decay is that the schedule of operation according to FOTP 61 is measured on Photon Kinetics PK-6.

Be used for the prefabricated rods of drawing optical fiber after the halogenide drying step, can reduce the susceptibility that hydrogen causes decay with the CO processing, and compare with control fiber (atmosphere of handling during its prefabricated rods sintering does not contain CO), attenuation change is much smaller under all fibre-optical drawing tension force, as shown in Figure 9.

Embodiment 5

Tested the effect of handling fluorine doping prefabricated rods with reductive agent in the present embodiment.Each root prefabricated rods has a Ge-doped mandrel zone, and a fluorine doped region contiguous with Ge-doped mandrel is by the germanium ring with the mandrel separation of this fluorine doped region at least.The ditch shape that the fluorine doped region surrounds depression makes prefabricated rods when being drawn into single-mode fiber, and the phase birefringence percentage of fluorine doped region is-5% or littler.

Before fixedization, a prefabricated rods is handled with CO under 1000 ℃.Second prefabricated rods is following to containing CO and Cl at 1125 ℃ ₂Gas processing; The 3rd prefabricated rods Cl ₂Handle.Each root prefabricated rods is drawn into single-mode fiber with the speed of minimum 10m/s.

The sample fiber of long 2 kms of each root that are drawn into according to certain drawing speed is measured its decay at the 1550nm wavelength.This optical fiber of long 2 kms is heated to 200 ℃ and be incubated 20 hours in a subenvironment chamber.This environmental chamber is that Yamato DKN600 is (available from VWR of West Chester, PA).The decay measure of the change it.Control fiber is also tested.The difference of control fiber and measuring fiber is that the prefabricated rods that pulls into control fiber is to use Cl ₂Handle rather than handle with CO.The decay of each root sample (available from Photon Kinetics of Beavarton, OR) is upward measured according to the schedule of operation of PK-8 at PK-8 SpectralAttenuation Bench.

Experimental result is shown in Figure 10.As seen from the figure, handle optical fiber with reductive agent and significantly reduced the decay that causes.Only use Cl ₂Handle or use simultaneously Cl ₂Showed the higher decay that causes with the optical fiber that reductive agent is handled.Use Cl ₂The optical fiber that the prefabricated rods of handling draws, along with the increase of fibre-optical drawing speed, the decay that causes in the optical fiber also increases.Optical fiber constructed in accordance, its decay that causes significantly reduces.

Embodiment 6

Prefabricated rods is handled the effect of eliminating aforementioned absorption peak with CO test, used prefabricated rods is to be used for optical fiber such as the Vascule that the production chromatic dispersion handles ^TMOptical fiber, this prefabricated rods is from ConingIncorporated of Corning, and NY obtains.Four prefabricated rods have been tested.Except following explanation separately, all processing steps of each root prefabricated rods all is identical.The preparation process condition of contrast prefabricated rods is as follows:

1. the contrast prefabricated rods is at 1150 ℃, and is chloride and contain in the helium-atmosphere and handled 90 minutes, and the flow that chlorine flows in the stove is 0.825slpm, and the flow that helium flows in the stove is 20slpm.

2. in 30 minutes, be raised in 1225 ℃ from 1150 ℃ when the temperature of stove, will contrast prefabricated rods and contact with this inert atmosphere of helium.

3. will contrast prefabricated rods 1225 ℃ of temperature, contain 15%CF ₄Helium atmosphere in mixed CF 120 minutes ₄The flow that feeds stove with helium is respectively 3slpm (CF ₄) and 17slpm (He).

4. will contrast prefabricated rods at 1490 ℃ of sintering.With extra soot deposit on the agglomerating prefabricated rods.The prefabricated rods that soot coats is carried out sintering, is drawn into optical fiber, uses the speed of 200g tension force and 9 meter per seconds during drawing.

Except the contrast prefabricated rods, also prepare three test prefabricated rods.The difference of test prefabricated rods is, uses CO in preparation prefabricated rods process.In each step the working concentration of CO all constant be 1200ppm.The difference that CO uses is: in the stage stove that heats up and mix CO is arranged when No. 1 prefabricated rods prepares; And No. 2 prefabricated rods are heating up, and in doping and the sintering stage stove CO are arranged; Heat up at stove as for last a kind of i.e. No. 3 prefabricated rods, the gas removal stage after mixing and mixing is used CO.Each root proof stick is in drying, and the intensification and the controlled condition in the stage of doping are as follows:

1. the test prefabricated rods is at 1150 ℃, and is chloride and contain in the atmosphere of helium and handled 90 minutes, and the flow that chlorine flows in the stove is 1slpm, and the flow that helium flows in the stove is 40slpm.

2. in 30 minutes, be raised in 1225 ℃ from 1150 ℃ when the temperature of stove, make the test prefabricated rods and contain helium and CO ₂Inert atmosphere contact.

3. the test prefabricated rods is 1225 ℃ in temperature, is containing 15%CF ₄With mixed 120 minutes CF in the atmosphere of helium ₄The flow that feeds in the stove with helium is respectively 3slpm (CF ₄) and 17slpm (He).

4. the test prefabricated rods is carried out sintering at 1490 ℃.With extra soot deposit on the agglomerating prefabricated rods.The prefabricated rods that soot coats is carried out sintering, is drawn into optical fiber, uses the speed of 200g tension force and 9 meter per seconds during drawing.

Four prefabricated rods all are drawn into optical fiber respectively.Wavelength be 1420nm to the 1620nm scope, each root optical fiber is all measured its decay spectra, is shown in 130 among Figure 13.Optical fiber is measured on Photon Kinetics (PK) platform attenuation meter.Suitable device is Model 2500 optical fiber analytical systems, comes from GN Nettestof Hopkinton, MA.The instruction manual of this model instrument is with reference to being incorporated into this.In this guide, introduced the method for using Model 2500 test prefabricated rods decay.The step size of Shi Yonging is 1nm in the present embodiment.The length of each root sample fiber of test is about 2 kms, and it is loose around roll form that sample is.

As shown in figure 13, control fiber is at 1440nm, 1543nm, and aforesaid absorption peak has appearred in 1580nm and 1610nm, sees the line 132 among the figure.Each absorption peak of control fiber is all greater than 0.012Db/km.And the aforesaid absorption peak that any one can be measured does not all appear in each test optical fiber, sees the line 134,136 and 138 among the figure.

Under situation without departing from the spirit and scope of the present invention, various changes and modifications are conspicuous to those of ordinary skill in the art.Therefore need only this changes and improvements in the scope of appended claims and equivalents thereof, the present invention just comprises these changes and improvements.

Claims (13)

1. the preparation method of a preform, described method comprises the following steps:

The heating soot preforms,

Soot preforms is contained 100ppm at least with halide not, and must not be higher than the atmosphere contact of 3000ppmCO,

Soot preforms is in 1000 ℃ to 1600 ℃ temperature range and containing in the atmosphere of CO and at least a fluorochemicals and mix, and the general formula of described fluorochemicals is C _nF _2n+2, " n " is positive integer in the formula,

The sintering soot preforms forms preform.

2. preparation method as claimed in claim 1 is characterized in that described method also is included in before the described contact procedure, dry described soot preforms in dry atmosphere, and described atmosphere comprises at least a chlorine-containing compound.

3. preparation method as claimed in claim 1 is characterized in that in the atmosphere of described contact procedure fluorine concentration is in identical quantity grade in the CO concentration and described atmosphere.

4. preparation method as claimed in claim 1 is characterized in that, also comprises rare gas element, the ratio at least 0.0012 of described CO and rare gas element in the atmosphere of described contact procedure.

5. preparation method as claimed in claim 1 is characterized in that sintering soot preforms in containing the atmosphere of CO.

6. preparation method as claimed in claim 1 is characterized in that described method also comprises the step that preform is drawn into optical fiber, and the decay spectra of gained optical fiber is presented at wavelength 1565nm in the 1595nm scope, and decaying offset is not more than 0.012dB/km.

7. preparation method as claimed in claim 6, it is characterized in that described wavelength region at 1570nm between the 1590nm.

8. preparation method as claimed in claim 6 is characterized in that described decaying offset is not more than 0.006dB/km.

9. preparation method as claimed in claim 1 is characterized in that described method also comprises the step that preform is drawn into optical fiber, and the decay spectra of gained optical fiber is presented at 1400nm and is not more than 0.012dB/km to the interior decaying offset of the wavelength region of 1470nm.

10. preparation method as claimed in claim 9 is characterized in that described decaying offset is not more than 0.006dB/km.

11. preparation method as claimed in claim 1 is characterized in that described method also comprises the step that preform is drawn into optical fiber, the decay spectra that this optical fiber is showed at wavelength 1565nm in the 1595nm scope promising 0.009 or littler rootmean-square.

12. preparation method as claimed in claim 11 is characterized in that described rootmean-square is less than 0.0088.

13. preparation method as claimed in claim 1 is characterized in that described method also comprises the step that preform is drawn into optical fiber, the decay spectra of gained optical fiber is presented at 1595nm and is not more than 0.012dB/km to the interior decaying offset of the wavelength region of 1625nm.

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