KR100819581B1 - Treating soot preforms with a reducing agent - Google Patents

Abstract

Silica soot preform 12 is inserted into furnace 30. The preform is then treated with heat and carbon monoxide gas to reduce impurities that may affect the final product.

Description

Processing method of soot preform using reducing agent {TREATING SOOT PREFORMS WITH A REDUCING AGENT}

The present invention relates to a method for producing soot preforms, and more particularly, to a method for treating soot preforms using a reducing agent.

In the manufacture of optical fibers (hereinafter referred to as 'fibres') and other products that can be produced from soot preforms, preforms with many impurities can cause various defects in the final product. The effect of these drawbacks can be seen in the attenuation of the signal propagating along the fiber, and in the transmission of light signals with arbitrary wavelengths through the resultant glass article. In manufacturing optical fibers, it is desirable to minimize the attenuation, so it is desirable to eliminate the defects causing the attenuation. The indication that the fiber contains impurities is that the attenuation exhibited by the fiber at any wavelength increases as the fiber operates longer. This increasing attenuation effect is most pronounced at wavelengths of at least 1200 nm.

Previous attempts to minimize the potential for the fiber to withstand this increase in damping include a method of drying the preform with chlorine gas. Conventionally, preforms are placed in a furnace prior to the consolidation process. The furnace is filled with a helium gas stream containing approximately 2% Cl ₂ and the furnace is heated to a temperature of approximately 1000 ° C. for about two hours. However, treating the soot pretreatment with chlorine gas does not satisfactorily reduce the increased attenuation exhibited by the fibers. Another limitation in treating soot preforms with chlorine gas is that it is limited to glass compositions that are relatively inert to chlorine treatment. Examples of glass compositions that are relatively inert to chlorine treatment include silica glass or silica glass doped with germanium. However, not all components of the silica glass composition can be inert to the chlorine treatment. Examples of silica glasses that are not inert to the chlorine treatment are compositions containing alumina, antimony, alkali oxides, boron oxides, phosphorus oxides or alkaline earth oxides. The chlorine treatment has been found to remove alumina, antimony, alkali or alkaline earth-containing compounds from preforms.

It has also been demonstrated that the chlorine treatment is inadequate for some glass articles added with fluorine after chlorine treatment because it will continue to carry some chlorine gas from the chlorine treatment even after the preform is doped with fluorine. Holding chlorine will affect the optical properties of the final glass article. One example of a glass article that is undesirable to contain chlorine is a lithography photomask plate. For example, the presence of chlorine in lithographic photomask plates reduces transmission at beneficial wavelengths. One of these wavelengths is 157 nm. It is proved that even if only about 79 ppm of chlorine is present in the lithographic photomask plate the transmission will be reduced by at least about 50% of the light having a wavelength of about 157 nm. For at least the same reason, there is a need for a new method for handling soot preforms.

In addition, fluorine-doped optical fibers exhibit increased attenuation at some wavelengths. The attenuation spectra of the fluorine doped optical fiber will exhibit absorption peaks at various wavelengths such as 1440 nm, 1546 nm, 1583 nm and 1610 nm. Because the 1583 nm wavelength is in the L band transmission window, it is necessary to make the optical fiber with a fluorine doped region that does not exhibit an absorption peak at the 1583 nm wavelength or other wavelengths mentioned.

1 is a cross-sectional view schematically showing the preform of the furnace according to the present invention.

2 is a partial cross-sectional view schematically showing a cured preform drawn into an optical fiber.

3 is a partial cross-sectional view schematically showing a soot coated with a core cane in a furnace according to the present invention.

4 is a perspective view of a tubular cured preform prepared in accordance with the present invention.

5 is a perspective view of a tubular cured preform with a longitudinal slice made in accordance with the present invention.

6 is a perspective view of stretching a section of a tubular cured preform.

7 is a perspective view sagging a cured preform section.                 

FIG. 8 is a bar graph of induced attenuation @ 1550 nm of control fibers and fibers made according to the invention after exposure of the fibers at 200 ° C. for 20 hours.

FIG. 9 shows fibers derived from hydrogen monoxide change at attenuation @ 1530 nm vs. preforms treated with halides followed by carbon monoxide-treated preforms, and preforms treated with halides and unprepared carbon monoxide preforms. It is a graph of draw tension for control fibers.

FIG. 10 is a graph of induction attenuation @ 1550 nm of control fibers and fibers made according to the invention after exposure of the fibers at 200 ° C. for 20 hours.

11 is an example of a spectrum of wavelengths exhibited by an optical fiber having attenuated versus fluorine doped sections. The optical fiber is manufactured by a conventional process.

12 is a schematic cross-sectional view of a preform in the furnace in accordance with one method of the present invention.

13 is a graph of the spectrum of attenuation versus the wavelength of three preforms and a control preform made according to at least one method according to the present invention.

FIG. 14 is the index of refraction of an optical fiber converted in delta percent as a radius function representing the area of reduced index of refraction.

The present invention relates to soot preforms and methods of processing soot preforms that can be used to make optical articles. One embodiment of the invention is a method of processing soot preforms. This method involves exposing the soot preform to an atmosphere substantially free of chlorine while containing at least one reducing agent to consume the excess oxygen present in the furnace. Preferred reducing agent is carbon monoxide.

An advantage of practicing the method of the present invention is that it can be used to cure the soot preforms in an environment that is not explicitly oxidizing. In addition, the process of the present invention can be practiced to remove excess oxygen from preforms and to produce optical fibers with a much longer period of attenuation. One particularly outstanding application of the present invention is to include the method described above in the manufacture of non-zero dispersion shifted optical fibers.

In a second method of practicing the invention, the preform is heated to a temperature below about 1000 ° C. and the preform is exposed to a reducing atmosphere. Preferred reducing atmospheres include carbon monoxide. One advantage of carrying out this embodiment according to the invention is that chlorine free glass can be formed from the preforms produced according to this embodiment. Chlorine free glass means at least preforms that have never been exposed to chlorine during the manufacturing process. Chlorine free glass has excellent applicability as a lithographic photomask plate. Chlorine-free photomasks can satisfactorily transmit light at wavelengths below about 160 nm. Another advantage of practicing this embodiment according to the invention is that it can be used to treat soot preforms comprising alumina, antimony, alkali oxides, alkaline earth oxides or other compounds which react with chlorine. Converted to crystalline chlorine. Another advantage of this embodiment according to the invention is that it can be carried out at low temperatures, such as temperatures below about 1000 ° C.                 

A third method of practicing the present invention is a method of making an optical fiber preform. The method comprises doping the soot body in an atmosphere comprising carbon monoxide and at least one fluorine-containing compound having the general formula of C _n F _{2n + 2} . Preferably in the general formula n is a positive integer. One advantage of incorporating the method according to the invention into a fiber manufacturing process with fluorine containing regions is that the optical fiber does not exhibit absorption peaks at wavelengths of about 1440 nm, 1546 nm, 1583 nm, or 1610 nm.

Additional features and advantages of the invention will be described in detail in the following, and the invention will be understood by practicing the invention as set forth in the description, claims, and drawings, and will be apparent to those skilled in the art to which the invention pertains. will be.

Reference is made in detail to the preferred embodiments of the invention and examples of the invention shown in the accompanying drawings. Like reference numerals will be used throughout the drawings to refer to the same or like parts. A representative embodiment of the process for treating soot preforms with a reducing agent according to the invention is shown in FIG. 1 and designated by reference numeral 10. The invention described herein relates to soot preforms and to advanced methods of treating soot preforms. The preform is treated with a reducing agent. Preferably the preform is treated with a chlorine free compound comprising carbon monoxide or sulfur dioxide.

Suit format

In FIG. 1, shown at 10, a soot preform 12 in a furnace 30 is shown. The soot preform 12 may be formed by any known technique to form a soot body. Such techniques include, but are not limited to, other known techniques such as outside vapor deposition (OVD), vapor axial deposition (VAD), modified chemical vapor deposition (MCVD), plasma chemical vapor deposition (PCVD), or solgel processes. It is not limited to the technologies. OVD, VAD, MCVD, and PCVD can be commonly referred to as chemical vapor deposition (CVD) techniques. Preferably, the soot may be deposited onto the initiation member to form the soot preform 12. Typical soot particles deposited on the initiating member are less than about 20 microns, preferably less than about 10 microns, more preferably about 0.1 to about 1.0 microns, and most preferably about 0.1 to 0.3 microns.

The soot preform 12 may have a core region 14 and a cladding region 16. Optionally, the soot preform 12 may have a near cladding region (not shown). The core region 14 has a central passage 18. The cladding region 16 is disposed around the core region 14. Core region 14 typically consists of silica or doped silica. Optionally, core region 14 may be doped with germanium to increase the refractive index of core region 14. Optionally, core region 14 may also include a second dopant, such as fluorine, or more preferably an annular fluorine doped region. Other potential soot dopants include alkali metal oxides, alkaline earth oxides, transition metals, alumina, antimony oxide, boron oxide, gallium oxide, indium oxide, tin oxide, lead oxide, phosphorus oxide, arsenic oxide, bismuth oxide, tellurium oxide, Selenium oxide, titanium oxide and mixtures thereof. Core region 14 may be comprised of a plurality of doped and undoped soot regions.

Cladding region 16 typically comprises at least silica. The cladding region 16 may have a refractive index lower than that of the core region 14. The present invention is not limited to the materials that make up the core region 14 and the cladding region 16. The soot preform 12 may be constructed from a glass based on any oxide.

As shown in FIG. 1, the suit preform 12 preferably has a handle 20 fused to a standard ball joint handle 22. Plug 24 with optional capillary tube 26 is located at the end of core region 14 opposite handle 20. The soot preform 12 is floated in the furnace 30 by the handle 20.

How to Handle Suit Forms

Treatment at a temperature of at least about 1000 ° C.

The first method of treating soot preforms is to eliminate the increase in attenuation at 1200 nm or larger wavelengths as the fiber becomes longer in operation. The increased attenuation is a post-fabrication defect that can contribute to the presence of at least one reduced germanium compound that approximates each other in excess oxygen and drawn fibers. Reduced germanium is an element of germanium in a fiber that does not have four bonds to an oxygen element in the fiber. Non-exhaustive lists of reduced germanium compounds that may be present in the fiber include Ge ⁺² , GeO ⁺¹ and Ge-Ge. Approximately, excess oxygen means within about 5 nm, more preferably within about 1 nm and most preferably within 0.5 nm of the reduced germanium compound. One potential source of excess oxygen in the drawn fibers is to cure the soot preforms in an environment containing excess oxygen. Curing is defined as heating the soot preform 12 at a temperature above about 800 ° C. to perform a variety of processes including, but not limited to, drying, doping, and sintering the soot preform. Excess oxygen is defined as the amount of oxygen present under an environment that exceeds the amount of essential oxygen that will be present for these curing steps to be performed. Some potential causes for excess oxygen include tramp oxgen, leakage into the consolidation furnace and oxygen produced during the curing process. In the method according to the invention, the soot preform 12 preferably comprises a region doped with at least one germanium, more preferably a region doped with at least two germaniums. The soot preform 12 is treated with a reducing agent in the furnace 30 to remove any excess oxygen from the atmosphere in the furnace 30. The reducing agent flows into contact with the soot preform 12 in the direction of arrow 32 to remove excess oxygen. An example of a preferred reducing agent is carbon monoxide. Preferably, the reducing agent will react with excess oxygen to form a stable reaction product and consume excess oxygen. For example, carbon monoxide will react with excess oxygen to form carbon dioxide. Another example of a suitable reducing agent is a buffered carbon monoxide such as a mixture of carbon monoxide / carbon dioxide gas. In addition to the reducing agent, the atmosphere in the furnace may optionally include an inert material such as helium, argon, nitrogen, or mixtures thereof. Inert materials are not limited to only those materials mentioned. Preferably, the atmosphere is substantially free of any chlorine containing compound. The treatment atmosphere comprises carbon monoxide and an inert material, and when the soot preform 12 is not doped with fluorine, the concentration of carbon monoxide is at least about 100 ppm and no greater than about 3000 ppm. The concentration of carbon monoxide is more preferably at least about 200 ppm, most preferably about 300 to about 600 ppm.

The reducing agent may be filled in the furnace 30 during the drying process of the soot preform 12 or during the sintering process. If the furnace 30 is filled with a reducing agent during the drying process, the soot preform 12 is heated to a drying temperature of about 1000 to 1200 ° C. Preferably, the soot preform 12 is heated to about 1100 to 1200 ° C. The soot preform 12 is maintained at a drying temperature for about 1 hour to about 6 hours. Preferably, it is maintained at the drying temperature for about 4 hours. Preferably, the atmosphere in the furnace 30 during the drying process is an atmosphere free of halides. The practice of the present invention will result in soot preforms with significantly reduced impurity concentrations and the production of fibers that do not exhibit this increase in attenuation.

Optionally, the soot preform 12 may be doped with fluorine during the drying process and the sintering process. Fluorine doping is accomplished by heating the soot preform 12 to a doping temperature in the range of about 1000 ° C to about 1600 ° C. Once the soot preform 12 is heated to an approximate doping temperature, the soot preform 12 is exposed to the doping gas. Preferably, the doping gas is composed of the following CF ₄ , SiF ₄ , C ₂ F ₆ , SF ₆ , F ₂ , C ₃ F ₈ , NF ₃ , ClF ₃ , BF ₃ , chlorine fluorine-carbon, and mixtures thereof At least one of the chlorine-containing gases that are configured. The soot preform 12 is exposed to the doping gas for about 1 hour to about 6 hours. Preferably, the reducing agent is present in the doping atmosphere. Another alternative process is to soot with a halide containing compound such as Cl ₂ , GeCl ₄ prior to fluorine doping of the soot preform 12, or prior to both fluorine doping of the soot preform 12 and reducing agent treatment of the soot preform 12. Processing the preform 12. Preferably, the halide containing compound is washed from the atmosphere in the furnace 30 prior to filling the furnace 30 with a reducing agent. Preferably, the halide containing gas is a metallic halide containing compound or a dihalide compound. In treating the soot preform 12 with the halide containing compound, the preferred temperature is about 800 ° C to about 1200 ° C, more preferably 1000 ° C to 1100 ° C. The halide treatment of the soot preform 12 preferably lasts for about 1 hour to 4 hours, more preferably about 2 hours. During the halide treatment process, the atmosphere in the furnace 30 may also include an inert material such as helium, argon or nitrogen mentioned previously. Preferably, the atmosphere of the furnace 30 after the halide treatment of the soot preform 12 is washed with inert gas for at least about 5 minutes to 2 hours.

After treating the soot preform 12 with a reducing agent, the central passage 18 can be closed and the soot preform 12 is sintered. One alternative technique for closing the central passage 18 is to apply a vacuum to the central passage 18. To sinter the soot preform 12, the reducing agent may optionally be removed from the furnace 30, the furnace 30 having a temperature of about 1200 ° C. to about 1600 ° C., more preferably about 1400 ° C. or more. Heated to Optionally, the atmosphere in the furnace 30 during the sintering process may contain a reducing agent. It is preferred that sintering takes place in an atmosphere containing at least an inert gas such as helium, argon or any other inert material mentioned previously. Suitable times for sintering the soot preform 12 are from about 30 minutes to about 6 hours. In a preferred embodiment, the sintering time is from about 4 hours to about 6 hours. However, the sintering time may vary depending on the sintering temperature, the size and density of the soot preform and the chemical composition of the soot preform. Sintering can take place in the same furnace or in another furnace as in the drying process. If the core region 14 contains a dopant such as germanium, the germanium is preferably excessively deposited as a cause for any side reaction between the reducing agent and the deposited germanium dioxide.

As shown in FIG. 2, designated 40, the sintered preform 42 may be drawn into the fiber 44. The sintered preform 42 is heated to a temperature of about 1800 ° C. or higher and drawn into the fiber 44. Preferably, the sintered preform 42 is transported to a drawing furnace 46 for drawing the sintered preform 42 into the fiber 44. The muffle is preferably arranged at the outlet of the drawway 46. The fiber 44 is pulled by the tractor 50 and stored in the spool 52. The tractor 50 rotates in the direction of the arrow 54. The spool 52 rotates about the axis A in the direction of the arrow 56. Typical drawing speeds are about 10 m / s or more, preferably about 20 m / s or more. Preferably, the fibers are drawn under a tension of about 75 to about 200 g, preferably about 90 to about 150 g. In yet another embodiment of this method, reducing agent treatment can only occur during the sintering process. Preferably, the soot is a fluorine-doped soot. In this embodiment, the reducing agent is filled into the furnace 30 and the furnace is heated to a sintering temperature of about 1200 ° C. to 1600 ° C., more preferably about 1400 ° C. or more. The time for the sintering process is at least about 30 minutes to about 6 hours. Preferably, the reducing agent concentration in the sintering atmosphere is about 300 to 600 ppm. Optionally, the sintering step may end with exposing the soot preform 12 to an inert gas for about 30 minutes. In a further embodiment of the above-mentioned method, the soot preform 12 shown in FIG. 1 is a core can preform, meaning that the soot preform can be drawn into the core can. Preferably, the refractive index of the additional soot is not higher than the refractive index of the core region with the highest refractive index. An example of a preferred material deposited on a core can is silica (SiO ₂ ). This silica may be doped with a refractive index dopant or a refractive index dopant. In addition, a suit coded with a core can is known as an overcladded preform or an overcladded core cane.

The overclad preform can be placed in the furnace 30 as shown in FIG. 3, designated 60, and treated with a reducing agent. The overclad preform 62 includes a core can 64 and at least one additional layer of soot 66 deposited over the core can 64. Preferably, the core can 64 is sintered into glass. The reducing agent is the same as previously described. The furnace is heated to the above-mentioned temperature range (about 800 ° C. to about 1200 ° C. or about 1200 ° C. to about 1600 ° C.) for the time mentioned above (about 30 minutes to about 6 hours). The overclad preform 62 is preferably exposed to a reducing agent during the sintering process.

The process of the invention mentioned above will minimize the potential for excess oxygen to be present in the furnace 30 during the curing process. Thus, fibers drawn from pretreatments treated as mentioned above will not exhibit this increased attenuation.

Submarine LEAF

섬유를 제조하는 데 있어서 뛰어난 적용력을 갖는다. 비영분산 천이 광섬유는 섬유이고, 바람직하게는 다음의 표의 다양한 정의와 함께 표 A에 기재된 다음의 성질을 갖는 단편 코어 섬유이다.The process for treating soot preforms with a reducing agent may comprise non-disperse transition optical fibers such as Corning's Corning

Submarine LEAF

Has excellent applicability in making fibers. The non-zero dispersion transition optical fiber is a fiber, preferably a fragment core fiber having the following properties as described in Table A, with various definitions in the following table.

Property If desired More desirable Most desirable Attenuation @ 1550 nm 0.28 dB / km or less About 0.23 dB / km or less                                      0.18 dB / km or less                                      Attenuation in the Wavelength Range of 1525-1575 nm 0.28 dB / km or less                                      About 0.23 dB / km or less                                      0.18 dB / km or less                                      Mode area diameter @ 1550 nm About 8.5 to about 10.0 μm About 8.95 to about 9.6 μm About 9.0 to about 9.55 μm Total dispersion @ 1560 nm About -4.0 to about -0.5 ps / nm-km About -3.4 to about -1.0 ps / nm-km About -3.4 to about -1.1 ps / nm-km Zero Dispersion λ (λ ₀ ) About 1560 to about 1595 nm About 1567 to about 1589 nm About 1580 nm Zero Dispersion Slope (S ₀ ) 0.15 ps / nm ² -km or less 0.12 ps / nm ² -km or less 0.11 ps / nm ² -km or less Effective Area (A _eff ) About 200 μm ² or less At least about 65 μm ² At least about 71 μm ² Band-induced attenuation for fibers wound once around a 32 mm diameter axis @ 1550 nm 0.50 dB or less Less than 0.50 dB Band-induced attenuation for fibers wound 100 times around a 75 mm diameter axis @ 1550 nm 0.05 dB or less Less than 0.50 dB

The following definitions are presented to help define these properties.

Justice

The following definitions are those commonly used in the art to which the present invention pertains.

The refractive index profile represents the relationship between the refractive index and the waveguide fiber radius. The fragment core is divided into at least first and second waveguide fiber core portions or fragments. Each portion or fragment is located along a certain radial length, is substantially symmetric about the waveguide fiber centerline, and has an associated refractive index profile. The effective area is A _eff = 2π (∫E ² r dr) ² / (∫E ⁴ r dr), where the integral range is 0 to ∞, E is the electric field associated with the light propagated into the waveguide. The effective diameter D _eff is defined as A _eff = π (D _eff / 2) ² . By large effective area, it is meant that the effective area of the fiber is larger than about 60 μm ² . More preferably, the effective area of the fiber is greater than about 65 μm ² and most preferably the effective area of the fiber is greater than about 70 μm ² . It is possible and desirable to have fibers with an effective area greater than about 80 μm ² to about 90 μm ² . Relative index of refraction , Δ% = 100 X (n _i ² -n _c ² ) / 2n _i ² , where n _i means the average refractive index of the cladding region unless otherwise specified.

Α -profile , expressed as Δ (b)%, refers to the refractive index profile, where b is the radius. Δ (b)% = Δ (b ₀ ) (1- [│bb ₀ │] / (b ₁ -b ₀ )] ^α ), where b ₀ is the point when Δ (b)% is maximum, b ₁ is the point when Δ (b)% is 0, b is b _{i ≤} b _≤ b _f , b _i is the initial point of the α-profile, b _f is the last point of the α- profile, and α is the exponent that is real. Initial and final points of the α-profile are selected and recorded in the computer model. If the α-profile is advanced by a step exponential profile or any next profile type, the starting point of the α-profile is the intersection of the α-profile with the step profile or another profile.

The attenuation was 1996.07. It may be measured according to US Patent No. 5,534,994, registered in 09, the specification of which is incorporated herein. Other operating processes that can be used to specify attenuation include FOTP-78, FOTP-67, FOTP-20A, or TIA 455-67.

This method according to the invention can be applied to fibers having at least one germanium doped region and at least one fluorine doped region. In an embodiment of the method, the soot preform 12 comprises at least one germanium doped region, and preferably a fluorine doped region formed during the soot deposition phase. Preferably, the soot preform 12 includes at least one fluorine doped region. The fluorine doped region may be formed during the fluorine doping step mentioned above or during the soot deposition process. The fluorine doping step may occur at a temperature of about 1100 ° C. or higher. The germanium doped region and the fluorine doped region may be distinct regions of the soot preform 12. These regions may overlap, and the at least one region in the soot preform 12 may contain both germanium and fluorine or a combination of the fluorine and germanium regions mentioned above.

In this embodiment, the soot preform 12 is preferably treated with a reducing agent during the sintering process. However, this embodiment according to the present invention is not limited to only treating the soot preform 2 during the sintering process. Optionally, the soot preform 12 may be treated during the sintering process and the fluorine doping step. Preferably, the temperature of the reducing agent atmosphere is at least about 1100 ° C, more preferably at least about 1300 ° C. As mentioned above, the reducing agent atmosphere is substantially free of chlorine containing compounds or urea.

For the fluorine doping preform, the reducing agent concentration in the atmosphere is preferably in the same order of magnitude as the fluorine doping agent concentration in the doping atmosphere. The same size order is used herein to mean that the reducing agent concentration in the reducing atmosphere is at least about 1/10 to about 3 times the concentration of fluorine in the fluorine doping atmosphere. For example, if the concentration of CF ₄ in the doping atmosphere is about 1% by weight, the preferred concentration of carbon monoxide reducing agent is at least about 0.5% by weight, more preferably at least about 1.0% by weight. The present invention is not limited to the following examples.

It is advantageous to treat the fluorine-doped preform with a reducing agent because the fluorine doping process will generate excess oxygen in the doping atmosphere. Fluorine is incorporated into the soot preform 12 according to the following chemical reaction.

The reducing agent will react with the oxygen generated from the fluorine doping reaction to form carbon dioxide. The amount of reducing agent in the atmosphere is greater than the stoichiometric amount of oxygen generated during the fluorine doping reaction, as a result of which further reducing agent is used to react with excess oxygen present in the curing process. Non-consumable lists of potential sources of excess oxygen include tramp oxygen, oxygen leakage into the curing process, oxygen generated during the curing process, and oxygen remaining in the curing gas. The reducing agent treatment described above will consume any excess oxygen present in the furnace.

Optionally, the soot preform 12 may be treated with a chlorine containing atmosphere prior to fluorine doping or reducing agent treatment. Preferred chlorine treatment steps are the same as described above. No chlorine treatment step is required to carry out the process of the present invention.

Fibers having a fluorine doped region produced according to the method will not show an increase in attenuation as the fiber lasts longer in the operating process. The fibers are drawn from the soot preform 12 in the same manner as mentioned above.

In addition, the present invention can be practiced to remove the absorption peak on the attenuation spectrum of the fluorine doped fiber. The absorption peak is the region along the spectrum where the attenuation deviates from the baseline attenuation. Deviation is typically an increase in attenuation. In Fig. 11, the attenuation spectrum of an optical fiber having a fluorine doped section prepared according to the conventional method is shown by reference numeral 110. The result of the spectrum is shown by line 112. Analysis 110 includes an absorption peak 114 at about 1440 nm, a second absorption peak 116 at about 1546 nm, a third absorption peak 118 at about 1580 nm, and a fourth absorption peak at about 1610 nm ( 119). Absorption peaks 114, 116, 118, 119 are shown in FIG. 11 as the deviation between the baseline of analysis 110 shown as dotted lines 120, 122, 124, 126 and the attenuation shown. Absorption is part of the attenuation resulting from the conversion of the optical power of the light signal into heat.

The attenuation spectrum of the optical fiber can be measured by various techniques. One source of known measurement techniques is fiber optic telecommunications issued by Steawart E. Miller and Alan G. Chynoweth. Pages 214-218 of this publication are incorporated herein by reference. An example of a device type that can be used to make the above mentioned measurements is the PK attenuation benches available from Hopkinton's GN Nettest. One example of a suitable PK bench is the PK-2500.

In analyzing various optical fibers having fluorine doped sections, it has been found that the fibers can have at least four different absorption peaks. The wavelength at which the absorption peak is present is nominally about 1440 nm (preferably at least about 1400 nm, more preferably at least about 1410 nm, most preferably at least about 1420 nm, and preferably about 1470 nm or less, more Preferably about 1460 nm or less, most preferably about 1450 nm or less, nominally about 1546 nm (preferably at least about 1520 nm, more preferably at least about 1530 nm, most preferably at least about 1540 nm) And preferably about 1560 nm or less, more preferably about 1555 nm or less, most preferably about 1550 nm or less, nominally 1583 nm (preferably at least about 1565 nm, more preferably at least about 1570) nm, most preferably at least about 1575 nm, and preferably about 1595 nm or less, more preferably about 1590 nm or less, most preferably about 1585 nm or less) and nominally 1610 nm (preferably at least about 1595 nm, more preferably at least about 1600 nm, most preferably at least about 1605 nm, and preferably about 1625 nm or less, more preferably about 1620 nm or less, most preferably Up to about 1615 nm). The inventors have found that the cause of the absorption peaks mentioned above is due to the doping of the soot preform 12 with a fluorine compound having the general formula C _n F _{2n + 2} (n is a positive integer) during the curing process. It was determined that the absorption peaks appear in the spectral analysis because at least one of the following compounds in the optical fiber is present: CO, CO ₂ , COF ₂ , COClF, C _n F _{2n + 2} and mixtures thereof. Examples of general formulas for how these compounds are formed are given below for CF ₄ (the formula below is not described in stoichiometric terms).

"x" is a number between about 1 and about 4, preferably between about 1 and about 3.

It has also been determined that the magnitude of the absorption peak can be greater for optical fibers having a delta percent (Δ%) of about -0.35% or less, preferably about -0.38% or less. Delta percent is relative refractive index percent, Δ% = 100 X (n _i ² -n _c ² ) / 2n _i ² , where n _i is the maximum refractive index in region i unless otherwise specified, and n _c is Unless otherwise specified, it is the average refractive index of the cladding region. The delta percent value described above is the maximum drop over the region of reduced refractive index of the fiber. An example of this is shown in FIG. 14, designated 140. 14 is a refractive index profile for an optical fiber in terms of delta percent as a function of radius. The refractive index profile 140 has a maximum delta percent of less than about −0.4, designated 142. One embodiment of the present method for removing the above-mentioned absorption peaks is generally a method of making an optical fiber preform. The method comprises doping the soot body in an atmosphere comprising carbon monoxide and at least one fluorine containing compound having the general formula C _n F _{2n + 2} (n is a positive integer). Preferably, the doping atmosphere comprises at least about 5 volume%, more preferably at least about 10 volume%, even more preferably at least about 15 volume%, most preferably at least about 20 volume% of the fluorine containing compound. . It is also preferred that the atmosphere does not contain more than about 50% by volume fluorine containing compound. The soot body may be any of the above embodiments of the soot body 12 shown in FIG. 1. An embodiment of this method according to the invention is shown in FIG. 12. FIG. 12 differs from FIG. 1 in that the carbon monoxide containing gas and the fluorine containing compound flow not only through the center of the soot preform 12 but in the direction of the arrow 32 along the outside of the soot preform 12. . However, the present invention is not limited to the embodiment shown in FIG. Non-consumable lists of preferred chlorine containing compounds include CF ₄ , C ₂ F ₆ or C ₃ F ₈ , more preferred compounds are CF ₄ . Preferably, the method may further comprise an additional step of exposing the soot body to an atmosphere comprising carbon monoxide substantially free of halides. Preferably, the exposing step is performed before the doping step. Optionally, the exposing step may be performed after the optional chlorine treatment step. Preferably the furnace is cleaned between the chlorine treatment step and the selective exposure step. The exposing step may also be performed during a ramping step of heating the soot preform from the final chlorine treatment temperature to the fluorine doping temperature. The temperature and time for the chlorine step and the doping step are the same as previously mentioned herein. In one embodiment of the process according to the invention, the atmosphere during the exposing step is a substantially chlorine free atmosphere. Preferably, the temperature of the preform during the exposure step is at least about 1000 ° C, more preferably at least about 1100 ° C, most preferably at least about 1200 ° C.

The exposing step comprises ramping the temperature, preferably from a temperature above 1000 ° C. in the furnace to a temperature above 1200 ° C., more preferably at least about 1000 ° C. to at least about 1200 ° C., most preferably Is increased to at least about 100 ° C to at least about 1300 ° C.

The exposure step takes time from about 15 minutes to about 60 minutes and preferred exposure steps include about 30 minutes, about 45 minutes, and about 60 minutes. The temperature in the furnace is increased at a rate of about 2 ° C to about 10 ° C per minute. The rate of temperature increase during the exposure phase can vary. In addition, the temperature during the heating process of the exposure step is not required to increase continuously through the entire time of the exposure step. However, the invention is not limited to increasing the temperature in the furnace during the exposure step. The exposure step may occur at isothermal conditions or part of the exposure step may occur at isothermal conditions.

The atmosphere in the furnace during the exposure step includes inert materials and carbon monoxide and the ratio of carbon monoxide to inert materials is at least about 0.0012. More preferably, the ratio comprises about 0.48 or less. The inert material may be, but is not limited to, any inert gas such as argon, nitrogen, helium and compounds thereof. In addition, the concentration of carbon monoxide in the furnace during any exposure step preferably includes at least about 300 ppm, more preferably at least about 600 ppm, most preferably at least about 1200 ppm. Moreover, preferably the concentration may comprise up to about 4800 ppm, more preferably up to about 4000 ppm, most preferably up to about 3000 ppm.

The concentration of carbon monoxide in the furnace during the doping step can be any one of the above mentioned concentrations with respect to the exposure step. The concentration of carbon monoxide in the furnace during the doping step is not required to be equal to the concentration of carbon monoxide in the furnace during the exposure step. The above ratio of carbon monoxide to inert material with respect to the exposure step can be applied in selectively carrying out the doping step but this ratio is not required to be the same as during the doping step.

The method may further comprise a step of sintering the preform as described above. Alternatively, the method may include a step of sintering the preform in an atmosphere comprising carbon monoxide. The preform is sintered in the same manner as described above except that carbon monoxide is added to the sintering atmosphere. The concentration of carbon monoxide may be the same as described for the exposure step, but the concentration of carbon monoxide in the sintering atmosphere is not required to be the same as the concentration of carbon monoxide in the furnace during any other step.

Moreover, the present invention may include a process of drawing a preform into an optical fiber. In the process of drawing fibers from the furnace, it is preferred that the fibers exit the furnace and pass through a chamber filled with a gas having low thermal conductivity with respect to helium. The temperature of this gas is preferably lower than the temperature of the drawn fibers. More preferably, the temperature of this gas is at or about room temperature. Examples of low thermally conductive gases include nitrogen, argon, air and mixtures thereof. The chamber may be located adjacent the fiber outlet to the draw or may be located further downstream from the fiber outlet to the draw. This chamber may be referred to as a treatment furnace or lower extended muffle (LEM). For further description of the LEM, the contents of the US patent application "Fiber Optic Forming Method and Apparatus," filed on May 30, 2001, are incorporated herein by reference.

One embodiment of the present invention involves warming up the furnace with preform 12 already in the furnace for about 10 minutes, preferably for about 5 minutes, more preferably for 3 minutes. Preferably, the furnace has two zones: zone 1 (A.K.A. curing zone) and zone 2 (A.K.A. sintering zone), with independent temperatures controlled for each zone. Zone 1 of the furnace is heated to a temperature of about 1200 ° C or above, preferably about 1225 ° C or above. Zone 2 of the furnace is heated to a temperature of about 1300 ° C or above, preferably about 1325 ° C or above, more preferably 1350 ° C or above, most preferably 1380 ° C or above. During warming up, the furnace is filled with about 10 standard liters per minute (slpm) of inert gas, preferably about 15 slpm, more preferably about 20 slpm.

Preferably the preform is treated in zone 1 in the furnace under an atmosphere of about 2.2% chlorine for at least about 30 minutes, more preferably at least about 45 minutes, most preferably at least about 60 minutes. The temperature of the furnace is preferably the same as during the warm up phase. During the chlorine phase, about 20 slpm of helium and about 0.45 slpm of chlorine flow into the furnace. Preferably, the atmosphere in the furnace after the chlorine stage is released from the furnace.

Next, the soot preform 12 is exposed to the atmosphere of helium and carbon monoxide at the temperatures mentioned above. The exposure can last anywhere from about 15 minutes to about 45 minutes. The exposure atmosphere includes about 19.00 slpm of helium and carbon monoxide. Preferably about 19.24 slpm (more preferably about 19.48 slpm, most preferably at least about 19.76 slpm) and about 1.00 slpm carbon monoxide (more preferably about 0.76 slpm, most preferably at least about 0.52 slpm, Most preferably up to about 0.45 slpm) is filled into the furnace. Preferably the carbon monoxide was a 10% mixture of carbon monoxide and helium.

Embodiments further include doping the soot preform 12 in an atmosphere comprising helium, carbon monoxide, and CF ₄ . The flow rate of helium flowing into the furnace is about 14.00 slpm, preferably about 14.5 slpm, more preferably about 15.0 slpm and most preferably about 15.76 slpm. The flow rate of CF ₄ flowing into the furnace comprises at least about 2 slpm, preferably at least about 3 slpm, most preferably at least about 4 slpm. The flow rate of carbon monoxide flowing into the furnace is at least about 0.020 slpm, preferably at least about 0.024 slpm. The time of the doping step is at least about 30 minutes, preferably at least about 45 minutes, more preferably at least about 60 minutes, most preferably at least about 90 minutes.

Embodiments further include outpassing the doping atmosphere from the furnace. During the outpassing step, the temperature in zone 2 of the furnace is increased to at least about 1400 ° C, preferably at least about 1420 ° C, more preferably at least about 1440 ° C. The atmosphere of the furnace during the outfacing phase includes helium and carbon monoxide. Preferably at least about 19.0 slpm of helium is filled into the furnace, more preferably at least about 19.5 slpm, most preferably at least about 19.76 slpm. Preferably the flow rate of carbon monoxide flowing into the furnace is at least about 0.020 slpm, more preferably at least about 0.024 slpm. Preferably, the time for outpassing the doping atmosphere comprises at least about 10 minutes, more preferably at least about 20 minutes, most preferably at least about 30 minutes.

The preform is then sintered by moving the preform to zone 2 of the furnace at a rate of at least about 4 mm per minute. This speed can be as high as about 12 mm per minute, with a preferred degree of belonging being about 8 mm per minute. The temperature of zone 2 of the furnace is maintained at least about 1400 ° C., preferably at least about 1420 ° C., more preferably at least about 1440 ° C. The time for sintering the preform is at least about 120 minutes, preferably at least about 150 minutes, more preferably 170 minutes. During the sintering step, the atmosphere of carbon monoxide and helium is filled into the furnace. Preferably at least about 19.0 slpm, more preferably at least about 19.5 slpm, most preferably at least about 19.76 slpm is filled into the furnace. Preferably the flow rate of carbon monoxide flowing into the furnace is at least about 0.020 slpm, more preferably at least about 0.024 slpm.

Once the preform has been completely transferred to zone 2 of the furnace and the sintering step is complete, the preform is less than about 5 minutes, preferably less than about 3 minutes, more preferably less than about 2 minutes, most preferably about It is maintained in zone 2 of the furnace for a period of less than one minute. Preferably 20 slpm of helium is filled into the furnace during this step.

An embodiment of the invention leads to a termination step. During the termination step, the temperature in zone 2 of the furnace is lowered to less than about 1400 ° C., preferably less than about 1390 ° C., and most preferably less than about 1380 ° C. The atmosphere of the furnace during the terminating step preferably comprises argon. Preferably, argon is filled into the furnace at greater than about 10 slpm, more preferably greater than about 15 slpm, most preferably at least about 20 slpm. Preferably, the attenuation spectrum of the resulting fiber exhibits an attenuation not more than about 0.012 dB / km over a wavelength range of about 1565 nm to about 1595 nm. More preferably, the deviation is no greater than about 0.006 dB / km, even more preferably no greater than about 0.003 dB / km, most preferably about 0 dB / km. More preferably, the wavelength ranges from about 1570 nm to about 1590 nm, most preferably from about 1575 nm to about 1585 nm.

Preferably, the attenuation spectrum of the resulting fiber exhibits an attenuation not more than about 0.012 dB / km over a wavelength range of about 1400 nm to about 1470 nm. More preferably, the deviation is no greater than about 0.006 dB / km, even more preferably no greater than about 0.003 dB / km, most preferably about zero. More preferably, the range of wavelengths includes about 1410 nm to about 1460 nm, most preferably about 1420 nm to about 1450 nm.

Preferably, the attenuation spectrum of the resulting fiber exhibits an attenuation not more than about 0.010 dB / km over a wavelength range of about 1520 nm to about 1560 nm. More preferably, the deviation is no greater than about 0.006 dB / km, even more preferably no greater than about 0.003 dB / km, most preferably about zero. More preferably, the range of wavelengths includes about 1530 nm to about 1555 nm, most preferably about 1540 nm to about 1550 nm.

Preferably, the attenuation spectrum of the resulting fiber exhibits an attenuation not more than about 0.012 dB / km over a wavelength range of about 1595 nm to about 1625 nm. More preferably, the deviation is no greater than about 0.006 dB / km, even more preferably no greater than about 0.003 dB / km, most preferably about zero. More preferably, the range of wavelengths includes about 1600 nm to about 1620 nm, most preferably about 1605 nm to about 1615 nm.

Preferably, the spectrum of the drawn fiber will not exhibit at least one of the absorption peaks mentioned above (nominally about 1440 nm, about 1543 nm, about 1583 nm, about 1610 nm). More preferably the spectrum does not represent at least two of the above mentioned absorption peaks, and most preferably the spectrum does not represent any of the above mentioned peaks. In addition, the maximum deviation may be measured as root mean square (RMS). One way of calculating RMS is given by the following equation.

Where n is the number of sections in a given wavelength range, "λn" is the upper limit for the wavelength, "λl" is the lower limit for the wavelength, and attn _i is the fiber at any wavelength i between n and l Is the attenuation indicated by. For example, in the case of a 1583 absorption peak, the wavelength range may include about 1565 nm to about 1595 nm. The RMS is preferably about 0.0090 or less, more preferably about 0.0088 or less and most preferably about 0.0086 or less.

The above methods can be incorporated into an optical fiber manufacturing process. For example, the methods may be incorporated into a process for manufacturing large effective area opticla fibers or dispersion managed optical fibers. Preferably, the dispersion management fiber has at least one region comprising a refractive index reduction dopant, the maximum delta percentage of the region being about -0.35% or less, more preferably about -0.38% or less, more More preferably about -0.40% or less, most preferably about -0.42% or less. For further description of distributed management fiber optics, see U.S. Patent Application Nos. 60/208342, filed May 31, 2000, 60/217967, filed May 31, 2000, and 30.2000. The contents of heading 60/193080 are incorporated herein.

Treatment at temperatures below about 1000 ° C

The method includes heating the soot preform 12 floating in the furnace 30 to a temperature below about 1000 ° C. The soot preform 12 is preferably heated to less than about 800 ° C., more preferably from about 25 ° C. to about 600 ° C., most preferably up to about 400 ° C.

As shown in FIG. 1, the furnace 30 is filled with a reducing agent. The reducing agent flows into contact with the soot preform 12 in the direction of the arrow 32. Preferably the reducing agent is at least one element selected from the group of elements on the periodic table consisting of general formula M _x O _y (M is 21-30, 39-47, 57-79, 89-107 and mixtures thereof, O is oxygen and x and y are integers greater than zero). More preferably, M is at least one element selected from the group consisting of Zr, Ni, Fe, Ti, V, Cr, Mn, Co, Cu, Zn and mixtures thereof.

Preferred reducing agent is carbon monoxide. The reducing agent is more preferably reacted with the M _x O _y compound to form a reaction product containing at least one carbonyl complex (-CO). For example, if the soot preform 12 includes nickel oxide, the nickel oxide will react with a carbon monoxide reducing agent to form Ni (CO) ₄ . Most preferably, the carbonyl complex reaction product will volatilize at a temperature below about 200 ° C. Another reducing agent is SO ₂ . In addition to the reducing agent, inert gases such as helium, nitrogen, argon, or mixtures thereof are preferably filled simultaneously into the furnace 30 with the reducing agent. The present invention is not limited to the above inert gas. Preferably, the soot preform 12 is exposed to a reducing agent for about 1 hour to about 4 hours.

Preferably, the soot preform 12 is a silicate body having at least one component selected from the group consisting of alkali metal oxides, alkaline earth oxides, aluminum oxides, antimony oxides, and mixtures thereof. More preferably, the soot preform 12 is selected from the group of elements consisting of Sb, Al, B, Ga, In, Ti, Ge, Sn, Pb, P, As, Bi, Te, Se, and mixtures thereof. Oxides with at least one element. Optionally, the soot preform 12 may be formed from a powder batch material for glass melting. Examples of suitable powder batch materials include silica, alumina, alkali oxides, and at least the other oxides mentioned above.

Optionally, after the soot preform 12 is exposed to a reducing agent, the soot preform 12 is doped with fluorine. Fluorine doping is achieved by heating the soot preform 12 to a doping temperature in the range of about 1000 ° C to about 1600 ° C. Once the soot preform 12 is heated to an appropriate doping temperature, the soot preform 12 is exposed to the doping gas. Preferably, the doping gas is selected from among fluorine-containing gases selected from CF ₄ , SiF ₄ , C ₂ F ₆ , SF ₆ , F ₂ , C ₃ F ₈ , NF ₃ , ClF ₃ , chlorine-fluorine carbon and mixtures thereof. At least one. The soot preform 12 is exposed to the doping gas for about 1 hour to about 6 hours. The soot preform 12 is heated to a sintering temperature of about 1200 ° C. to about 1600 ° C. to sinter the soot preform 12 into glass. In the case of fluorine doping preforms, the preform may be sintered during or after fluorine doping. The soot preform 12 is maintained at the sintering temperature for about 1 hour to about 6 hours, preferably about 4 hours to about 6 hours. During the sintering process, the preform may be exposed to an inert atmosphere. Preferred inert atmospheres may consist of He, Ar, N ₂ , or mixtures thereof. In order to form the tubular preform shown in FIGS. 4 and 5, the hole 18 is not closed as mentioned above.

As shown in FIGS. 4 and 5, the sintered preform 12 has a longitudinal length L, and cutting the preform 12 has a longitudinal length to form a longitudinal cut 25. Thus cutting. In a preferred embodiment, the soot preform 12 is cut once to provide a preform of cross section resembling a tightly closed "C" shape where the longitudinal cut 25 is only one piece of glass. The cut preform 12 is then flattened.

In another embodiment, the soot preform 12 is cut into at least two separate pieces with at least two longitudinal cuts, preferably with equally spaced cuts around the circumference of the soot preform 12. Cutting more than one-half piece, more than one-third piece, and more than one-quarter piece of the soot preform 12 is twice the width of the desired photomask in the circumference of the suit preform 12, 3 Preference is given to fold or quadruple. Cutting into pieces is preferred when the circumference of the soot preform 12 is substantially larger than the desired photomask blank width.

As shown in FIG. 6, the C-shaped section 23 of the suit preform 12 has a single cut 25 by hanging and stretching, followed by sagging. Similar to the flat soot preform 12, it may be flattened with a planar photomask blank member. Alternatively, half preforms can be sagged directly in the furnace. The third and fourth sections of the suit preform 12 may be directly sagged in the furnace. It is desirable for the preform pieces to be placed in a curved position for advantageous flatness.

The glass preforms 12 cured prior to cutting and plating are provided with the desired inner diameter and wall thickness. Such internal diameters and wall thicknesses are preferably provided by machining the tube, such as by core-drilling.

Flattening the section 23 of the cured preform 12 includes heating the section 23 and applying strain to the heated section 23. As shown in FIG. 4, a preferred step of flattening the section 23 is by hanging the section 23 in a heated glass manipulation furance and attaching a pulling weight to the section ( 23) to give downward force. Hanging suspenders 51 provide a support for floating section 23 from a position near the top of the furnace 31. The hanging suspender 51 preferably comprises a platinum wire member attached to the section 23 near the cut 25. The platinum wire is attachable by drilling a section 23 and inserting the wire into the hole. The hanging suspender 51 and the platinum wire are directly attachable to the top of the furnace 31, or indirectly attachable to the furnace 31.

Similarly, the downward downward force is applicable to the section 23 by a similar attachment of platinum wire and a hanging weight, preferably a silica hanging weight, to the opposite cut end of the section 23 of the preform 12. Do. The force applying member 53 exerts a flattening force on the section 23 so that the heated section 23 does not curl. Preferably, the furnace 31 is heated to at least about 1480 ° C., as a result of which the force application member 53 produces an appropriately flattened section 23. For flatness not to be dried by hanging and stretching, the preferred temperature range for heating the section 23 in the furnace 31 is from about 1480 ° C. to about 1580 ° C., and less than about 1600 ° C., such as about 1500 ° C. is preferred.

In addition to this hanging, further flattening of the section 23 is made possible by heating the section 23 to the sagging temperature and by applying strain to the heated section 23. As shown in FIG. 5, the uncut cut section 23 resulting from the hanging process mentioned in FIG. 4 can be flattened by sagging in the glass furnace 31. In a preferred step of sagging the section 23 into the flattened cut section, the furnace 31 is able to sag the cut pipe 23 of the raised and unsupported section weight into the flattened flat surface glass member. Heated to a high enough temperature for sufficient strain.

Preferably, the furnace 31 is heated to a softening temperature high enough to sag the cut section 23 and maintained at a temperature below the flowout temperature so that the section 23 is The flow out and thinning of the glass are flattened while being substantially prohibited. The sagging temperature is preferably in the range of about 1700 ° C. to about 1800 ° C., most preferably in the range of about 1720 ° C. to about 1760 ° C., and most preferably about 1730 ° C. In addition to being flattened by applying strain to the section 23, such as hanging and / or sagging, the strain can be applied to the heated section 23 by pressing.

In applying the pressing force to the section 23, a lower deformation temperature in addition to the weight of the section itself is usable. In applying the pressing force, the tube can be treated to a temperature of about 1550 ° C. to about 1650 ° C., and the pressing force can be applied to the section 23 using a flat flat pressing member and supplied. The surface of the pressed section 23 is preferably covered with platinum foil to liberate the glass preform. Another flat planar flashing member is a high purity dense graphite slab, and the high purity graphite slab member can also be used as an advantageous setter and furnace surface in the practice of the present invention.

In addition to flattening section 23, in order to derive a photomask blank that does not have a detectable amount of hydrogen, section 23 heating is performed to ensure that the glass does not hybridize with hydrogen and to any It is preferred to be treated in a hydrogen-free heated environment to allow the H ₂ molecules to escape.

Heating section 23 includes heating the section to a glass strain softening point temperature, where the viscosity of the glass is lowered and consequently the glass tube is deformed by the application of strain.

For further disclosure regarding the process of forming a cured preform into a photomask substrate, the following U.S. patent application specification is incorporated herein by reference: 60 / 119,805 (filed Feb. 12, 1999), 60 / 123,861 (filed March 12, 1999), 60 / 135,270 (filed May 21, 1999), 60 / 159,076 (filed Oct. 12, 1999), 09 / 397,577 (filed Sep. 16, 1999) ), 09 / 397,573 (filed Sep. 16, 1999), 09 / 397,572 (filed Sep. 16, 1999).

The method of the present invention can be incorporated into a process for making chlorine free photomasks. Chlorine-free photomasks have the advantage of being able to transmit at least about 90% of light with a wavelength of about 157 nm, more preferably at least about 100% of light with a wavelength of about 157 nm.

The invention will be further clarified by the following examples which are intended as representative examples of the invention.

Example 1

The preform assembly consisting of quartz tube and quartz boat was heated in a horizontal tube furnace at about 200 ° C. for about 4 hours, inside the tube containing silica sand Iota-6 (UNMIN, CN in New Canaan) and less than 10 microns. Γ-Al ₂ O ₃ powder (Alfa Aesar, Ward Hill, MA) with average particle size is filled. During the heating process, the preform was exposed to a carbon monoxide reducing agent. A continuous stream of about one liter of carbon monoxide gas per minute was filled into one end of the boat. The carbon monoxide gas has a purity of 99.7%, which is available from Murray Hill's BOC gas. The transition metal content of γ-Al ₂ O ₃ was tested before and after carbon monoxide treatment. The transition metal content was tested according to Inductively Coupled Plasma Mass Spectrometry (ICP-MS) performed by Shiva Technology of Syracuse. The test results are shown in Table 1-1 below.

Table 1-1

element Concentration before carbon monoxide treatment (ppm) Concentration after carbon monoxide treatment (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

Carbon monoxide treatment reduced the concentration of each relative element by at least 1/3.

Example 2

섬유(Corning) 제조용 두 개의 예형이 염소 함유 분위기에서 처리된 후에 소결 공정동안 약 2시간동안 일산화탄소로 처리되었다. 환원 분위기에서의 일산화탄소의 농도는 다양하였다. 일 예형은 약 300 ppm 의 일산화탄소를 포함하는 분위기에서 처리되었고, 다른 예형은 약 600 ppm 의 일산화탄소를 포함하는 분위기에서 처리되었다. 이 예형들은 Submarine LEAF

섬유로 인발되었다. 섬유의 샘플들은 약 90 g의 낮은 텐션 또는 150 g의 높은 텐션하에서 도 8에 도시된 것처럼 두 개의 다른 인발속도에서 인발되었다. 특정 인발속도에서 인발된 각 섬유에 의해 나타나는 감쇠는 2 km 샘플의 각 섬유에 대하여 약 1550 nm 의 파장에서 측정되었다. 2 km의 섬유는 환경 챔버내에서 약 20 시간동안 약 200 ℃의 온도까지 가열된 후 유지되었다. 사용된 환경 챔버는 Yamato DKN 600(West Chester의 VWR)였다. 감쇠에서의 변화가 측정되었다. 제어 섬유가 또한 시험되었다. 제어 섬유는 제어 섬유가 인발된 예형이 Cl₂ 로 처리되었고, 일산화탄소로 처리되지 않았 다는 점에서 시험 섬유들과 달랐다. 각 샘플의 감쇠는 PK-8 Spectral Attenuation Bench(Beavarton 의 Photon Kinetics)상에서 PK-Bench 에 대한 작동 공정에 따라서 측정되었다.The effect of treating preforms with a reducing agent to test the fibers was tested. Submarine LEAF

Two preforms for making the corn were treated in a chlorine containing atmosphere and then treated with carbon monoxide for about 2 hours during the sintering process. The concentration of carbon monoxide in the reducing atmosphere varied. One preform was processed in an atmosphere containing about 300 ppm of carbon monoxide and another preform was processed in an atmosphere containing about 600 ppm of carbon monoxide. These examples are Submarine LEAF

Drawn into fibers. Samples of the fiber were drawn at two different drawing speeds as shown in FIG. 8 under a low tension of about 90 g or a high tension of 150 g. The attenuation exhibited by each fiber drawn at a specific drawing speed was measured at a wavelength of about 1550 nm for each fiber of the 2 km sample. The 2 km fiber was maintained after being heated to a temperature of about 200 ° C. for about 20 hours in an environmental chamber. The environmental chamber used was Yamato DKN 600 (VWR from West Chester). The change in attenuation was measured. Control fibers were also tested. The control fibers differed from the test fibers in that the preforms from which the control fibers were drawn were treated with Cl ₂ and not with carbon monoxide. The attenuation of each sample was measured according to the operating process for PK-Bench on the PK-8 Spectral Attenuation Bench (Photon Kinetics, Beavarton).

The results of the example are shown in FIG. 8. As shown in FIG. 8, the process of treating the fibers with a reducing agent reduces induced attenuation. This is most evident for fibers drawn at a speed of at least about 10 m / s under low tension. Fibers made in accordance with the present invention showed a marked reduction in induced attenuation.

Example 3

The effect of treating the fluorine-doped preform with the above reducing agent was tested. Three preforms were treated with chlorine containing compounds at a temperature of about 1000 ° C. The furnace temperature then rose to about 1450 ° C. at a rate of 4 ° C./min. Each preform was treated in a fluorine containing atmosphere for about 1 hour as shown in Table 3-1. As described in Table 3-1, the fluorine doping atmosphere also included carbon monoxide for the test fibers. The preform was drawn with a central core step index single mode fiber with annular fluorine doped regions. Samples of the fiber were drawn at the same speed and tension. The attenuation for each 2 km long sample represented by each fiber was measured according to the operating process for the PK-2500 Bench on the PK-2500 Spectral Attenuation Bench (Photon Kinetics, Beavarton) at a wavelength of about 1550 nm. The fiber sample was maintained at a temperature of about 200 ° C. for about 20 hours. The environmental chamber used was a Yamato DKN 600 (VWR from West Chester). The change in attenuation was measured. Control fibers were also tested in this manner. The control fibers differed from the test fibers in that the control fibers were dried with Cl ₂ and then treated with CF ₄ and a fluorine containing compound instead of the reducing agent above.

Table 3-1

Processing environment Induced Attenuation @ 1550 nm (dB / km) Previous Cl ₂ Drying and 1% CF ₄ (Control) 1.22 Previous GeCl ₄ Drying and 1% CF ₄ + 1% CO 0.00 Previous Cl ₂ Drying and 1% CF ₄ + 1% CO 0.05

Fibers made using the disclosed reducing agents showed minimal for unincreased attenuation. In comparison, control fibers showed a marked increase in attenuation.

Example 4

The effect of pretreatment with carbon monoxide has been further tested for improved resistance to hydrogen environments. Both preforms were dried to 4% by weight of Cl ₂ in an atmosphere of helium. The preforms were dried for about 4 hours at a temperature of about 1000 ° C to about 1150 ° C. One of the preforms was sintered at a temperature of about 1100 ° C. to 1600 ° C. in an atmosphere of at least about 200 ppm carbon monoxide and helium. Another preform was sintered in an inert atmosphere. Preforms were drawn with Corning's SMF-28 ^™ .

Each fiber of the 2 km sample was exposed to a 1% hydrogen environment for about 144 at atmospheric pressure and room temperature. Fiber attenuation was measured prior to hydrogen exposure and peak attenuation was reached during 144 hours of exposure. Attenuation was measured on the Photon Kinetics PK-6 Attenuation Bench according to FOTP 61.

As shown in FIG. 9, the fibers drawn from the carbon monoxide treated preform after the halide drying step became less sensitive to hydrogen induced attenuation and showed much lower changes than control fibers at all fiber pull tensions.

Example 5

The effect of treating fluorine-doped preforms with a reducing agent was tested in this example. Each preform has a germanium doped center core region, a fluorine doped region adjacent to the germanium center core and a germanium ring isolated from the center core by at least the fluorine doped region. Settling of the fluorine doped region is such that the preform can be drawn into a single mode fiber having a fluorine doped region with a delta percent of about -0.5 or less.

Prior to curing one preform was treated with carbon monoxide at about 1000 ° C. The second preform was treated with an atmosphere of CO and Cl ₂ at a temperature of about 1125 ° C., and the third preform was treated with an atmosphere of Cl ₂ . Each preform was drawn into a single mode fiber at a drawing speed of at least about 10 m / s.

The attenuation exhibited by each fiber drawn at a specific drawing speed was measured at a wavelength of about 1550 nm for each fiber of the 2 km sample. 2 km of fiber was heated and maintained at a temperature of about 200 ° C. for about 20 hours in an environmental chamber. The environmental chamber used was Yamato DKN 600 (VWR from West Chester). The change in attenuation was measured. Control fibers were also tested. The control fibers differed from the test fibers in that the preforms from which the control fibers were drawn were treated with Cl ₂ and not with carbon monoxide. The attenuation of each sample was measured according to the operating process for the PK-8 Bench on the PK-8 Spectral Attenuation Bench (Photon Kinetics, Beavarton).

 The results of the example are shown in FIG. 10. As shown in FIG. 10, the process of treating the fibers with a reducing agent significantly reduces the induced attenuation. Fibers treated only with chlorine or with reducing agents showed higher induced attenuation. This increased induced damping of the fibers drawn from the chlorinated preforms was more noticeable as the drawing speed of the fibers increased. Fibers made in accordance with the present invention showed a marked reduction in induced attenuation.

Example 6

The effect of treating the preformation that would be used to form a dispersion-controlled fiber such as Vascule ^™ fiber (Corning) with carbon monoxide to remove these absorption peaks was tested. Four preforms were tested. All of the processes in the steps of forming each preform were not specifically defined below and they were all the same. Process conditions for producing the controlled preforms are as follows.

1. The control preform was treated at a temperature of about 1150 ° C. for about 90 minutes in an atmosphere of chlorine and helium, the flow rate of chlorine into the furnace was about 0.825 slpm, and the flow rate of helium into the furnace was about 20 slpm.                 

2. The control preform was exposed to helium atmosphere while the temperature in the furnace increased from about 1150 ° C to about 1225 ° C and the lamp time was about 30 minutes.

3. The controlled preform was doped in an atmosphere containing 15% CF ₄ and helium at about 1225 ° C. for about 120 minutes, and the flow rates of CF ₄ and helium into the furnace were 3slpm (CF ₄ ) and 17slpm (helium), respectively.

4. The controlled preform was sintered at about 1490 ° C. Additional soot was deposited on the sintered preform. The soot coated preform was sintered and drawn into fibers. The fibers were drawn at a drawing speed of about 9 m / s under a tension of about 200 g.

In addition to the control preforms, three test preforms were formed. Test prototypes differed for certain process steps involving the use of carbon monoxide during the preform formation process. The concentration of carbon monoxide was kept constant at 1200 ppm for each process step involving the use of carbon monoxide. The use of carbon monoxide varied in that one preform was formed from carbon monoxide present in the furnace during the ramping and doping steps. For the second preform, carbon monoxide was present in the furnace during the ramping, doping, and sintering steps. For the last test preform, carbon monoxide was present during the ramping, doping, and post doping outgassing steps. The constant conditions for the drying, ramping, and doping steps for each of the test prototypes are as follows.                 

1. Test prototypes were treated at a temperature of about 1150 ° C. for about 90 minutes in an atmosphere of chlorine and helium, the flow rate of chlorine into the furnace was about 1 slpm, and the flow rate of helium into the furnace was about 40 slpm.

2. Test prototypes were exposed to an atmosphere of helium and carbon monoxide while the temperature in the furnace increased from about 1150 ° C. to about 1225 ° C. and the lamp time was about 30 minutes.

3. Test preforms were doped in an atmosphere containing 15% CF ₄ and helium at about 1225 ° C. for about 90 minutes, and the flow rates of CF ₄ and helium into the furnace were 3slpm (CF ₄ ) and 17slpm (helium), respectively. .

4. Test preforms were sintered at about 1490 ° C. Additional soot was deposited on each sintered preform. The soot coated preforms were sintered and drawn into fibers. The fibers were drawn at a drawing speed of about 9 m / s under a tension of about 200 g.

Each of the four preforms was drawn with an optical fiber. The attenuation spectrum of each fiber over the wavelength range from about 1420 nm to about 1620 nm was determined and shown in FIG. 13, designated 130. The fibers were tested on a Photon Kinetics ("PK) bend attenuation measuring device. A suitable device is Model 2500, an optical fiber analysis device (GN Nettest, Hopkinton). User operations on this model are incorporated herein by reference. The use of Model 2500 to perform attenuation measurements is described here: A step size of 1 nm was used in the Examples Each sample length of the fiber tested was about 2 km and each sample was a loose coil. Was arranged.

As shown in FIG. 13, the control fiber exhibits absorption peaks of about 1440 nm, about 1543 nm, about 1580 nm, and about 1610 nm as described above. See line 132. Each absorption peak represented by the control fiber is greater than 0.012 dB / km. Each of the test prototypes did not show any of the above absorption peaks. See lines 134, 136, and 138.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without changing the scope of the invention. Accordingly, the invention may include variations and modifications of the invention provided that such variations and modifications are within the scope of the claims and equivalents thereof.

Claims (41)

delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete Heating the soot preform; And Exposing the soot preform to an atmosphere comprising a reducing agent substantially free of halides; Method of producing a soot preform, characterized in that it comprises a. The method of claim 25, wherein the reducing agent comprises carbon monoxide. 27. The method of claim 26, wherein the amount of carbon monoxide is at least 100 ppm. 27. The method of claim 25, further comprising forming a soot preform by depositing soot on the initiating member, wherein the soot comprises silica and alkali metal oxides, alkaline earth oxides, transition metals, aluminas, antimony oxides. At least one component selected from the group consisting of boron oxide, gallium oxide, indium oxide, germanium oxide, tin oxide, lead oxide, phosphorus oxide, arsenic oxide, bismuth oxide, tellurium oxide, selenium oxide, titanium oxide and mixtures thereof Method comprising a. The method of claim 25, wherein said heating is performed at a temperature of 1000 ° C. or less. The method of claim 25, wherein said heating is performed at a temperature of 800 ° C. or less. delete delete delete 29. The method according to any one of claims 25 to 28, wherein the reducing agent is M _x O _y (Where M is composed of elements having 21-30 atoms, elements having 39-48 atoms, elements having 57-79 atoms, elements having 89-107 atoms, and mixtures thereof At least one element selected from the group of elements, O is oxygen, and x and y are integers greater than zero). 35. The method of claim 34, wherein the exposing step comprises a reaction between an oxide having a reaction product comprising a carbonyl complex and a reducing agent. The method of claim 34, wherein M is at least one element selected from the group consisting of Zr, Ni, Fe, Ti, V, Cr, Mn, Co, Cu, Zn and mixtures thereof. 27. The method of claim 25, further comprising doping the soot preform with fluorine prior to the exposing step. The method of claim 25, wherein the atmosphere of the exposing step comprises at least one fluorine-containing compound having the general formula C _n F _{2n + 2} (n is a positive integer). The method of claim 38 further comprising, prior to said exposing, drying the preform in a dry atmosphere comprising at least one chlorine containing compound. 27. The method of claim 26, wherein the concentration of carbon monoxide in the atmosphere of the exposing step is 1/10 to 3 times the concentration of fluorine in the atmosphere. 27. The method of claim 26, wherein the atmosphere of the exposing step further comprises an inert material, wherein the ratio of carbon monoxide concentration to concentration of inert material is greater than 0.0012.

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