MXPA99007216A - Method of having optical fiber having depressed index core region - Google Patents

Abstract

A tube (36) is connected to a different tube (27). A rod (22) is put in the different tube (27). Soot (28) is deposited on the outside of the different tube (27). A gas (55) is made to flow through the different tube (27). This structure (32) is then collapsed thereby creating an optical fiber preform.

Description

METHOD TO PRODUCE OPTIMAL FIBER THAT HAS THE CENTRAL REGION WITH REDUCED INDEX CROSS REFERENCE TO RELATED REQUESTS This is a continuation in part of the U.S. Patent Application. N.S. 08 / 359,392, filed on December 20, 1994.

BACKGROUND OF THE INVENTION This invention relates to a method for making a glass article by melting a rod and a tube in such a way that substantially no seeds are formed in the interspace between them. The method of this invention is useful for producing optical fibers with low dissipation, especially those fibers in which the center includes an annular region with reduced refractive index in relation to silicon. Optical fibers having refractive index profiles such as W profiles, segmented center profiles and the like possess desirable dispersion characteristics. See Patents E.U.A. 4,715,679 and 5,031,131 for teachings of various types of modified dispersion optical fibers. Frequently the fibers that have these types of refractive index profiles have been elaborated by chemical vapor deposition (CVD) procedures such as the CVD procedures of plasma that allow to form fibers in individual mode whose centers include layers with different refractive indexes (see figures 7 and 8, for example). Such procedures produce relatively small preforms. It is advantageous to form optical fiber preforms with modified dispersion by external vapor deposition (OVD) processes which produce relatively long preforms or stretched preforms to adequately decrease the cost of fiber processing. A typical OVD process for forming such fibers is described in US Pat. 4,629,485. In accordance with this patent, a silicon rod contaminated with germanium dioxide is formed and stretched to reduce its diameter. A piece of the rod is used as a mandrel on which silicon or soot glass particles are deposited. The resulting mixed material structure is heated in a consolidation (drying and concreting) furnace through which a fluorine-containing gas flows. The soot is therefore contaminated with fluorine and materializes in the rod. One or more additional layers of glass are formed on the outer surface of the fluorinated doped silicon layer to form a preform from which a fiber can be stretched. When the soot is made according to the aforementioned method, in which the fluorine is supplied to the porous preform solely by the muffle gas containing fluorine, the concentration of fluorine (as measured by the? Of the layer) which contains fluorine) is not sufficient to provide certain desirable optical characteristics. The Typical fluorine concentration achieved by impurifying the muffle gas provides -0.4%? when S¡F4 is the constituent that contains fluorine. The maximum delta value for SÍF4 that is produced by the procedure described above is -0.5% ?. One aspect of the invention relates to a method for making an optical fiber preform of which an annular region consists of doped silicon with a sufficient amount of fluorine such that the delta value of the annular region with respect to silicon is less than -0.5% ?. As used herein, the term? A-, which is the relative difference of refractive index between materials with refractive indexes na and nb, is defined as? Ab = (na2-nb2) / (2na2) . For simplicity of expression,? is expressed frequently in percent, that is, 100 times? In this discussion, na is the refractive index of the glass impurified with fluorine and nb is the refractive index of silicon. Another aspect of the invention relates to the crushing of a glass tube contaminated with fluorine and / or doped with boron in a central glass rod so that during the fusion resulting from the interlayer between these two elements, no seeds are formed substantially. When a tube of silicon doped with fluoride is crushed on a silicon rod contaminated with germanium dioxide, the The resultant between these two elements contains many seeds, and much of the resulting preform or preform produces optical fibers that can not be used. Such seed formation is less prevalent when the elements formed from other glass compositions such as a silicon rod doped with germanium dioxide and a pure silicon tube are melted to form a preform. The Patent E.U.A. No. 4,668,263 describes a method for crushing a silicon tube having an inner layer impurified with fluorine on the surface of a silicon rod. In accordance with that patent, the step of crushing is achieved by turning the tube and heating it with the flame coming from a burner traveling longitudinally. This technique could not be used to elaborate fiber designs with modified dispersion of the type that uses the fluoride-contaminated tube, including the external surface, as part of the central region or light-diffusing region of the fiber. The reason for this is that, because the flame moisturizes the glass, ie introduces hydroxyl contamination, the resulting fiber could be rendered inappropiate for operation at wavelengths where the attenuation due to hydroxyl ions is large. An additional disadvantage of this method refers to the temperature of the flame, which is not less than 1900 ° C. At an elevated temperature, control of the process becomes difficult. The axis of the preform can become non-linear or arcuate. If the center rod is made of a soft glass such as a glass doped with germanium dioxide, the rod may become softer than the tube; this can result in a center not rounded or a center that is not concentric with the outer surface of the resulting fiber. The Patent E.U.A. No. 4,846,867 discloses a method for crushing a silicon tube doped with fluorine on the surface of a silicon wand. Prior to the crushing step of the tube, a reagent for gas phase attack is flowed through the space between the rod and the tube while the tube is heated by a flame. In the specific examples, where SF4 is the attack reagent, a gaseous mixture of SF4, Cl2 and oxygen (ratio 1: 1: 6 by volume) is introduced through the space between the rod and the tube. A gaseous mixture as such removes the glass from the treated surfaces of the rod and tube, thereby forming new surfaces in the rod-tube interface. The chlorine is present in an amount sufficient to remove the water generated by the fluorine-containing attack reagent. The outer surface of the resulting preform is hereinafter coated with particles of silicon soot which are dried, fluorinated and then concreted to form a preform from which an optical fiber can be stretched. The flame that was directed towards the tube during the gas attack step introduces water to the external surface of the tube. The attenuation of the resulting fiber from that water is high. The attenuation at 1380 nm as an example is 30 dB / km which is attributed to the contact of the oxyhydric flame with the preform.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the invention to provide a method for joining the first and second adjacent layers of a glass preform in such a way that the interlayer therebetween is substantially free of seeds. A further object is to provide an improved method of assembling a central region to an adjacent region in a glass preform. Another object is to provide a method for manufacturing a rod-in-tube preform by passing the adjacent surfaces of the rod and the tube in such a manner that the external surface is not contaminated with water. Even another object is to provide a method to form a seed-free interface between a rod and a tube in a fiber optic preform without removing glass from the adjacent surfaces of the rod and tube. Still another object is to provide a method for the manufacture of fluoride-contaminated silicon glass having a high delta negative by the OVD technique. The present invention relates to a method for making a glass article. The method consists of inserting a central rod of non-porous glass into a non-porous glass tube to form an assembly that is inserted into an oven. While the entire assembly is being heated, a chlorine-containing centerline gas is flowed into the first end of the tube and between the tube and the rod, and out of the second end of the tube. Hereinafter, the tube is crushed on the rod to form an assembly with which the glass article such as a fiber can be formed. optics. The crushing step of the tube can be carried out in the same furnace in which the cleaning step with chlorine is carried out. As the centerline gas cleans the adjacent surfaces of the rod and tube while the assembly is in the furnace, the outer surface of the tube is not contaminated with water that could be present if a flame were used to heat the tube. assemble during the cleaning step. This method is especially suitable for forming an optical fiber having a center that includes an annular region of reduced refractive index. The tube may be formed of silicon doped with fluorine or boron, of which both can be added to the silicon to lower its refractive index. Fluoride is the preferred impurifier since the attenuation due to B2O3 limits the use of the fiber to lengths less than 1200 nm. To provide a tube contaminated with fluorine, a fluorine-containing gas is flowed through the opening and out through the pores of a porous glass preform with cylindrical shape. The porous glass preform is heated to be concreted in a nonporous tube doped with fluorine. A further aspect of the invention relates to a method for making a glass article having an annular region with a high fluorine content. Initially a porous glass tubular preform is formed. The preform is heated, and a central line gas is flowed into the longitudinal opening of the preform and out through its pores. The centerline gas consists entirely of a fluorine-containing compound, from which a high concentration of fluorine is incorporated into the pores of the preform. The porous preform is heated to be concreted in a non-porous glass tube containing fluorine. A central rod with a cylindrical shape is inserted into the tube contaminated with fluoride. Then the tube is shrunk on the central rod, and the interpiece between the central preform and the tube is fused.

An article such as an optical fiber can be formed from the resulting preform.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the formation of a porous glass preform on a mandrel. Figure 2 illustrates the concretion of a porous glass preform. Figure 3 illustrates the application of a coating of glass particles to a glass tube doped with fluorine. Figure 4 is a cross-sectional view of an apparatus for consolidating and fusing the assembly formed by the method of Figure 3. Figure 5 is a cross-sectional view taken along lines 5-5 of Figure 4 .

Fig. 6 is a cross-sectional view of the fused assembly resulting from the concreting / melting step illustrated in Fig. 4. Figs. 7 and 8 are examples of the refractive index profiles of optical fibers that can be produced by the method of this invention. Figure 9 is a cross-sectional view of a stretching oven in which a tube is stretched and crushed on a rod. Figure 10 is a cross-sectional view illustrating the closure of the tube 36.

DESCRIPTION OF THE PREFERRED MODALITY The method of this invention can be used to produce an optical fiber preform having at least one annular region containing a dopant that lowers the refractive index. Basically, this method consists of (a) making a solid non-porous glass tube containing a impuritant that lowers the refractive index through its entire radius, (b) inserting a solid non-porous core glass rod into the tube, (c) cleaning the adjacent surfaces of the rod and tube by flowing a gas containing at least 50% by volume of chlorine between the rod and the tube at an elevated temperature to no more than 1600 ° C, (d) crushing the tube on the rod, and (e) add to the resulting structure a sufficient amount of coating to form a glass article from which an optical fiber can be stretched. The center of the resulting optical fiber includes the inner central region and the region with reduced index and optionally includes other adjacent annular regions. Steps (a) through (e) are not necessarily performed in the established order. In one embodiment, the tube is covered with a soot coating, and steps (c) and (d) are carried out in the same oven, initially submitting the jacket preform to a temperature sufficient to achieve cleaning with chlorine, then increasing the temperature to concretize the soot and crush and fuse the tube to the rod. The attenuation of the fiber is low as a result of the low count of seeds in the entrecara between the inner center and the region with reduced index that results from step (c). The attenuation of the fiber in the water peak of approximately 1380 nm is low since the tube is not heated with a flame in steps (c) and (d). The fibers produced by the method of this invention exhibit approximately an excess of 1 dB / km loss at 1380 nm. The loss of Rayleigh scattering at 1380 nm depends on the delta center / coating. Yes, for example, a fiber has a Rayleigh scattering loss of approximately 0.4-0.5 dB / km at 1380 nm; its loss is approximately 1.5 dB / km at 1380 nm after the peak of water is added.

In one embodiment of the invention, the region of the annular preform of reduced refractive index is doped with fluorine. Figures 1 and 2 illustrate a method for making a glass tube doped with fluorine. The mandrel 10 is inserted through the tubular handle 1 1. The mandrel has a relatively large diameter to suitably produce a tube having an internal diameter large enough to be useful in the later steps of the method. As the mandrel 10 rotates, it also undergoes translational movement with respect to the burner 13 that generates the soot, whereby a porous glass preform 12 is formed on the mandrel. A standard ball joint 14 (see handle 44 of Figure 3 for further detail) is fused to the handle 11, and the preform 12 is suspended in the consolidation oven 15 by means of that handle. The concretion is carried out in an atmosphere including a fluorine-containing central line gas such as SiF 4, CF 4, C 2 F 6, or the like. SiF4 has the tendency to give higher levels of fluoridation (typically yielding -0.7%? And occasionally producing a delta of about -0.8%), but that doping produces high levels of water in the resulting glass. Such high levels of water in the fluorine-containing glass can be tolerated if the center of the fiber has a relatively high delta value with respect to the silicon coating, thereby propagating very little energy in the annular region of the fiber containing fluorine. CF4 results in a drier glass but does not give the high levels of impurities that can be obtained by using S¡F. The high fluoride concentrations can be used in this process because the porous preform 12 of soot is formed on pure silicon, ie there is no impurifier such as germanium dioxide that could diffuse disadvantageously into the preform. The resulting concreted tube contains a relatively high concentration of fluorine because the fluorine-containing gas is made to flow into the opening 18 of the tube (arrow 16) and out through the pores of the porous glass preform thereby it achieves maximum contact with the entire body of the porous glass, and because the center line gas may consist of a pure gaseous fluorine compound that does not contain diluent such as helium, chlorine or the like. In addition, the only impurifier introduced into the porous preform by the centerline gas is fluorine. The end of the porous preform that is first concretized preferably contains a capillary tube 19 to prevent muffle gases from entering the preform opening and causing most of the centerline gas to flow out through the interstices of the preform. the preform. A gas containing fluorine also flows through the muffle furnace 15, as indicated by the arrows 17. Where the muffle gas 17 preferably contains a diluent gas such as helium and a sufficient amount of chlorine to dry the preform, the central flow gas 16 preferably consists solely of the compound of gaseous fluorine. However, the central flow gas 16 may also contain one or more diluent gases such as helium and chlorine. The flow of chlorine can be stopped after the desired water content has been achieved and before the porous preform materializes. The tube 19 is separated from the tube doped with fluorine resulting. The resulting fluorinated doped tube can be stretched or re-stretched to reduce the internal diameter to the desired size. If the tube is stretched, it can be cut into appropriate lengths for the deposition of soot on it. A tube 27 doped with boron is easier to process than a tube doped with fluorine. For example, a porous preform of S¡O2-B2 ?3 can be formed on a mandrel as described in conjunction with Figure 1, feeding BCI3 to the burner along with SiC - The mandrel is removed, leaving a longitudinal opening, and the preform is placed in a consolidation furnace. A 40-liter standard muffle gas (slpm) of helium flows upward through the muffle furnace, and the center-line gases of 1 slpm of helium and 75 cm3 standard per minute (sccm) of chlorine flow into the opening. After the preform dries, it becomes concrete. The resulting tube can be stretched as described above. As shown in Figure 3, a standard frosted joint handle 44 (see Figure 4 for further details) is fused to one end of a length 27 of tube 27 doped with fluorine or doped with boron. A shorter length of the silicon tube 36 is preferably fused to the opposite end of the tube 27. The tube 27 is then mounted in a lathe where it is rotated and moved with respect to the burner 13 that generates the soot. The glass soot particles are deposited on the tube 27 to form the coating 28. The silicon tube 36 is used for the purpose of reducing the waste of fluorine tubing that may have been caused by the inability to deposit the soot coating 28 on the end of the tube 27 if it had been secured by the tool holder of the lathe. The liner 28 extends over that portion of the handle 44 adjacent the tube 27 for the following reason. During the subsequent concreting procedure, when that portion of the tube 27 adjacent the handle 44 is subjected to concreting temperature, its viscosity becomes low enough that if that portion of the tube 27 were not coated, it could not support the weight of the tube coated with soot, ie the structure would fall into the consolidation furnace, however, since the soot extends over the adjacent portion of the handle 44, the entire end of the tube 27 is coated adjacent to the handle 44. therefore, the silicon soot forms a sufficiently strong layer on the tube 37 to support the structure during the concreting process. While a single coating 28 is shown, a plurality of soot coatings could be deposited, the refractive indices of each coating depending on the profile of the desired refractive index of the resulting optical fiber. To form the refractive index profile between the spokes and r2 of Figure 7, the soot coating 28 could consist of pure SiO 2. To form the profile between the radii p and r3 of Figure 8, a first soot coating of SiO2 doped with GeO2 could be deposited on the tube 27 followed by a second soot coating consisting of pure SiO2.

Referring to Figure 4, the soot-coated tube is removed from the lathe, and a solid glass central rod 22 is inserted through the handle 44 and into the tube 27 to form the assembly 32. The rod 22 can not fall further of tube 36 since that tube has a relatively small hole. If tube 36 is not used, the tube 27 could be heated and tapered inwardly to form a region of sufficiently small internal diameter to retain the rod 22. Alternatively, a small deformation or enlargement could be made at the upper end of the rod 22 to cause it to be retained by the rod 22. high part of! tube 27. The rod 22 is preferably formed of a glass having a refractive index greater than that of the tube 27, for example pure silicon or silicon contaminated with GeO2, or the like. The rod 22 can be formed by any of various known techniques such as modified chemical vapor deposition (VAD), axial vapor deposition (MCVD) and external vapor deposition (VAD), depending on the desired refractive index profile. Two of the profiles that can be produced using the OVD technique are the central regions within the radii r? of Figures 7 and 8. The central region of Figure 7 is a region that is radially reduced while that of Figure 8 is a substantially inclined profile. To make optical fibers having various types of optical characteristics, such as a modified characteristic of specific dispersion, the central portion of the fiber may have a different refractive index profile such as a parabolic gradient or the like.

Any additional layers of radii greater than that of the tube doped with fluorine also affect the optical properties such as dispersion. The handle 44 is suspended in a support tube 46 for insertion into the consolidation oven 15. The handle 44 consists of a glass tube 45 having a gasket 48 enlarged at its upper end and an annular enlargement 49 separated from the gasket 48. The support tube 46 has a slotted handle formed at the end thereof. One side of the region 47 of the end of the tube 46 is removed to accept the upper end of the handle 44, the enlargement 49 resting on the slotted base 50 as the adjacent section of the tube 45 is inserted into the slot 51. At the end of the gas conduit tube 53 is a ball joint 52 which fits into the cavity 54 of the joint 48. While the assembly 32 is heated in the consolidation furnace 15, a drying gas flows upwards through the furnace (arrows 33). ). The drying gas conventionally consists of a mixture of chlorine and an inert gas such as helium. A stream of gas containing chlorine (arrow 55) is made to flow from tube 53 to tube 27. Although the jet 55 of gas could contain a diluent such as helium, 100% chlorine is preferred for cleaning purposes. The gas jets consist of dry gases, in which water is not present in the vicinity of the assembly 32 during the heat treatment. The gases can be acquired dry; in addition, the helium used for the muffle gas is also run through a dryer.

Because the diameter of the rod 22 is slightly smaller than the internal diameter of the tube 27, the chlorine flows down around the entire periphery of the rod 22; it comes out through the tube 36. To facilitate the flow of chlorine beyond the lower end of the rod 22, that end may be provided with one or more grooves 23 in the periphery of the lower surface (Figures 4 and 5). Chlorine acts as a hot chemical cleaning agent. During this step of cleaning with hot chlorine, the temperature is below the setting temperature of the soot coating 28 so that the space between the rod 22 and the tube 27 remains open for a sufficient length of time to occur the cleaning required. The chlorine cleaning step is most effective at elevated temperatures. It is preferred that the temperature of the cleaning step be at least 1000 ° C, since at lower temperatures, the duration of the passage would be long enough so that the passage would be undesirable for commercial purposes. Obviously, lower temperatures could be used if the processing time is not important. The temperature should not be above 1600 ° C for the reasons given above and preferably not above 1500 ° C. The flow of hot chlorine between the fluorine tube and the rod 22 is very beneficial in the sense that it allows the surface of the two elements to come together without the formation of seeds in their interface. Seeds include defects such as bubbles and impurities that can cause attenuation in the fiber optic resulting. The flow of centerline gas 55 continues until the tube 36 begins to collapse as shown in Figure 10. As the soot coating 28 materializes, it exerts a radially inward force on the tube 27, thus forcing that tube inwardly against the rod 22 to form a fused assembly 38 (see Figure 6) in which the three regions 22, 27 and 28 'are fully fused. A soot of relatively low density provides a greater force directed inwards; however, the soot coating should be sufficiently dense to prevent cracking. It was previously stated that the tube 36 does not need to be used, whereby other means could be used to hold the rod 22 in the tube 27. For example, the rod 22 could be suspended by an elongated end as shown in Figure 9, or the lower end of the tube 27 could be subjected to heat treatment and its diameter made small enough to secure the rod 22. If the tube 22 was not present, the realization of the soot coating 28 could cause the lower end of the tube 27 to be squashed on the rod 27 and prevent further flow of the centerline gas 55. The fused assembly 38 could be re-stretched directly in an optical fiber in which the layer 28 'forms the outer region. Alternatively, the fused assembly 38 may be provided with additional coating before fiber optic restraint. For example, an additional coating of soot coating can be deposited on the assemble 38 in the manner shown in Figures 1 and 3; the additional coating can be dried and concreted, and the resulting preform can be stretched in an optical fiber. According to another aspect of the invention the soot coating 28 is not deposited in the tube 27, and the tube 27 is not crushed in the rod 22 in the oven 15. The assembly including the rod 22, the tube 27 and the tube 36 and the handle 44 with a ball joint is subjected to a high temperature in an oven while the chlorine flows between the rod 22 and the tube 27 as discussed above. Preferably the temperature remains within the range of about 1000 ° C to 1500 ° C to chemically clean the surface of the elements 22 and 27. After a sufficient period has elapsed to allow chemical cleaning, the clean assembly 63 is removed from the This oven is inserted into a conventional stretch oven (figure 9). The upper end of the rod 22 is provided with the enlarged end 65 which is suspended from a narrow region at or near the handle 44. In the illustrated embodiment, the inner diameter of the lower end of the handle 44 is larger than the internal diameter of the handle 44. upper part of the tube 27; this provides an edge for supporting the enlargement 65. A vacuum source (not shown) is connected to the handle 44. The lower tip of the assembly 63 is heated by a heater 62 of resistance. As the tip of the assembly 63 passes through the heater 62, the diameter of the assembly decreases, and the tube 27 collapses on the rod 22 and the space between these two members is emptied. The additional stretch in the assembly 63 causes the assembly to elongate in a central preform rod 66 in which the tube 27 is fused to the rod 22. The central preform rod is separated into appropriate lengths which are provided with coating and stretched in optical fibers as described above. Typical inclined index optical fibers that are designed to be used in lengths close to 1300 nm exhibit a positive dispersion in the 1550 nm window where the fiber exhibits the lowest attenuation. A system as such can be improved so that it works in the window of 1550 nm by placing in series with the inclined index fiber a dispersion compensating fiber (DC) having a relatively high negative dispersion value at 1550 nm. The following example describes the manufacture of a DC fiber as such. A DC optic fiber was individually fabricated having the refractive index profile illustrated in Figure 7 as follows. A 0.64 mm alumina rod was inserted through the center of an alumina tube having an outside diameter of 3.8 cm. Cork plugs were used at the ends of the alumina tube to center the alumina rod inside it. The handle was placed near one end of the alumina tube. Pure silicon soot was deposited on the alumina tube and on a portion of the handle. A detailed description of a method of forming a porous preform in an alumina tube can be found in US Patent No. 5,180,410.

A standard patella handle 14 was fused to the 1 1 silicon handle before consolion. The consolion was performed in the manner described in conjunction with Figure 2. The central flow gas 16 consisted of 1.5 slpm of SiF4. The muffle gas 17 consisted of 20 slpm He, 0.5 slpm Cl and 1.0 slpm SiF4. The fluorinated doped concrete tube contained near 2. 4% by weight of fluorine (the? Value of the tube with respect to silicon was approximately -0.7%?). The tube was re-stretched to form an elongated tube with an outer diameter of approximately 12 mm and an inner diameter of 6.1 mm. A 76 cm fluorinated tube 27 was separated from this concreted tube. A handle 44 of standard ground joint was fused to a first end of tube 27. A tube 36 of silicon 10 cm long having internal and external diameters of approximately 3 mm and 12 mm was fused to the second end of the tube 27. The resulting tubular structure ends were mounted on a lathe where they were rotated and moved with respect to the burner of flame hydrolysis 13 (figure 3). The SiO 2 soot particles that entered the burner flame were deposited on the tube 27 to form a coating 28 having a length of 70 cm and an external diameter of 90 mm. The coating 28 was extended over the entire length of the tube 27, and this extended a longitudinal distance of approximately 50 mm along the handle 44. The coated structure 30 was then removed from the lathe.

The following method was used to elaborate the central rod 22.

The larger diameter end of an alumina mandrel was inserted into a tubular glass handle. The outer diameter of the mandrel was used from 5.5 mm to 6.5 mm on its 107 cm length. The ends of the mandrel were mounted on a lathe where they were rotated and moved. Soot from SiO2 doped with GeO2 was deposited on the mandrel and a portion of the handle. The reagents GeCI4 and SiCU were flowed initially to the burner in sufficient quantities to form a soot formed of doped SiO2 with 37% by weight of GeO2. With each step of the burner with respect to the mandrel, the flow of GeCI4 decreased and in the last step, pure silicon soot was deposited. The flow of GeCU to the burner decreased in accordance with said recipe so that the radial decrease in the concentration of GeO2 in the resulting fiber was substantially parabolic. After the deposition of a soot preform to a thickness of 100 mm, the mandrel was removed by pulling it through the handle, thereby leaving a longitudinal opening. A capillary tube was inserted into the end of the opening of the porous preform opposite the handle. The porous preform was suspended in the consolidation furnace, and a central line drying gas consisting of 1.0 slpm of helium and 50 sccm of chlorine was flowed through the handle to the preform opening, and out through the interstices of the preform. A muffle gas consisting of 40 slpm of helium was flowed up through the furnace. The maximum temperature of the oven consolidation was 1460 ° C. The opening of the cap of the capillary tube was closed during the concreting process. The concreted preform was inserted into a stretching apparatus where its tip was heated to 21 OOX while a vacuum connection was fixed at its upper end in the manner described in FIG.

U.S. Patent 4,486,212, which is incorporated herein by reference.

After the end of the preform was stretched so that its opening was either too narrow or completely closed, the opening was evacuated. As the lower end of the preform was stretched down at a speed of approximately 15 cm / min, and its internal diameter was reduced, the evacuated opening was crushed. The diameter of the resulting rod was approximately 6 mm. The refractive index profile of the resulting drawn rod was similar to that between the axis and the radius and of Figure 7. A rod 22 having a length of 70 cm was separated from the drawn rod. Two slots 23 were marked on the periphery of this end 24 of the rod 22 so that the lower end was formed in the subsequent consolidation process. The rod 22 was inserted through the handle 44 and into the tube 27 doped with fluoride until the end 24 thereof was brought into contact with the tube 36, thereby forming the assembly 32 coated with soot of figure 4. handle 44 of assembly 32 was suspended from a support tube 46 for insertion into the consolidation furnace. While the assembly 32 was rotated at 1 rpm, it was lowered towards the consolidation muffle furnace at a speed of 5 mm per minute. A gas mixture composed of 50 sccm of chlorine and 40 slpm of helium flowed up through the muffle. The central line gas flow 55 consisted of 0.5 slpm of chlorine. The chlorine flowed down around the rod 22 and exited through the tube 36. The maximum temperature in the consolidation furnace was 1500 ° C. As the assembly 32 moved down in the furnace, the assembly temperature became high enough so that the central line chlorine flow cleaned the adjacent surfaces of the rod 22 and the tube 27. As the assembly 32 was subsequently moved to the furnace, first its tip and then the remnant of the assembly was subjected to a temperature of 1460 ° C which was sufficient to concretize the coating 28. During the concretion of the soot coating 28, the tube 27 was forced inward against the section 22, and the surfaces that were in contact were fused, thus forming the fused assembly 38. In assembly 38 it was removed from the consolidation furnace and inserted into a stretching furnace. The lower end of the preform was heated to approximately 2100 ° C, and stretched to form a rod having a diameter of 5.5 mm. A 90 cm section was separated from the resulting rod, and was supported on a lathe where it worked as a mandrel for the deposition of an additional coating of coating glass soot. The deposition was continued in the manner described in conjunction with Figure 1, until a layer of SiO2 particles that had an outside diameter of 100 mm was deposited to form a preform of mixed material. The resulting mixed material preform was gradually inserted into a consolidation furnace having a maximum temperature of 1450 ° where it concreted while a mixture of 99.5% by volume of helium and 0. 5% by volume of chlorine flowed up through the muffle furnace. The resulting concreted stretched preform, whose diameter was about 50 mm, was inserted into a stretching oven where the tip thereof was subjected to a temperature of about 2100 ° C. The stretched preform was stretched to form a dispersion compensating optical fiber having an outer diameter of 125 μm. The cutoff value of the fiber individually was 750 nm. At a wavelength of 1550 nm, the attenuation was 0.5 dB / km and the dispersion was more negative at -90 psec / km nm. The lowest dispersion value for the figures elaborated by this method was -105 psec / km nm. Prior to the present invention, seeds were formed at the interface between the fluorine tube and the germanium dioxide rod when these two elements were put together. This procedure essentially completely eliminates the tai seeds and as evidenced by the fact that the preforms supplying 50 km of fiber were consistently stretched unimpeded, ie the fiber attenuation at 1550 nm was consistently around 0.5 dB / km .

Claims (32)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for making a glass article consisting of the steps of: inserting a solid non-porous glass core rod into a solid non-porous glass tube to form an assembly, said tube having an outer surface, first and second ends and a radius, characterized in that said tube contains a doping agent throughout its radius, inserting the assembly in an oven, heating the complete assembly, flowing a central line gas at the first end of said tube, between said tube and said rod, and outside the second end of said tube, said center line gas being selected from the group consisting of 100% chlorine and chlorine mixed with a diluent gas, crushing said tube on said rod to produce an assembly, continuing the line gas flow central until it is stopped by crushing a softened glass element, and forming a glass article with said assembly.

2. The method according to claim 1, further characterized in that an extension tube is fused to the second end of said tube and, during the step in which said tube is crushed in said rod, the step of flowing the gas from the center line continues until it is stopped by the crushing of said extension tube.

3. - The method according to claim 1, further characterized in that before the step of heating the assembly, a coating of glass particles is deposited on the external surface of said tube, and further characterized in that the step of crushing consists of heating the assembly which consists of the coated tube and the rod for concreting said lining, thereby generating a radially inwardly directed force which causes said tube to be crushed on said rod and fused thereto.

4. The method according to claim 3, further characterized in that a handle tube is fused to the first end of said non-porous glass tube, and said coating of glass particles extends over said handle tube.

5. The method according to claim 1, further characterized in that a source of said central line gas is connected continuously to the first end of the tube, and the step of crushing said tube on the rod consists of subjecting regions by increments of said tube at a higher temperature, starting with the second end of said tube and ending with the first end of said tube, whereby said regions by increments of said tube are crushed on said rod, starting at the second end of said tube. tube and continuing to the first end of said tube.

6. - The method according to claim 1 further characterized in that during the step of flowing, said assembly is heated to a temperature of less than 1600 ° C.

7. The method according to claim 1, further characterized in that said glass tube is formed by the steps of forming a tubular porous glass preform having a longitudinal opening from one side to another thereof, flowing a gas that contains fluorine in said opening and out through the pores of said porous preform, and heat treating the porous glass preform to concretion it in a nonporous tube doped with fluorine.

8. The method according to claim 7, further characterized in that said fluorine-containing gas does not contain diluent.

9. The method according to claim 1, further characterized in that the step of crushing said tube is performed in said oven.

10. The method according to claim 1, further characterized in that during the step of crushing said tube on said rod, the region between the rod and the tube is evacuated.

11. The method according to claim 1, further characterized in that said center line gas consists of 100% chlorine.

12. - The method according to claim 1, further characterized in that said central line gas consists of more than 50% by volume of chlorine, the remaining one being a diluent gas.

13. The method according to claim 1, further characterized in that the source of said central line gas is connected continuously to the first end of the tube, and further characterized in that the second end of said tube is subjected to a temperature of sufficiently high so that the second end of said tube is flattened and prevents the subsequent flow of said central line gas,

14. The method according to claim 1, further characterized in that the steps of heating and flowing clean the surfaces adjacent said rod and said tube without removing glass from the adjacent surfaces.

15. The method according to claim 1, further characterized in that said assembly rests vertically during the heating and flow steps, whereby said central line gas flows around the entire periphery of said central rod during the passage flow.

16. The method according to claim 15, further characterized in that said rod has an elongate end that is supported by the first end of said tube.

17. - The method according to claim 14, further characterized in that said assembly is suspended by a handle that is fused to the first end of said tube.

18. The method according to claim 1, further characterized in that said rod is a rod of silicon doped with germanium dioxide and said tube is a tube of silicon doped with fluorine.

19. The method according to claim 1, further characterized in that said glass article is an optical fiber.

20. A method for preparing a fiber optic preform consisting of the steps of: fusing an extension tube to the second end of a glass tube, inserting a central glass rod into said glass tube to form an assembly, having said tube an outer surface, first and second ends, and a radius, further characterized in that said tube contains a doping agent throughout its radius, heating the complete assembly, flowing a central line gas at the first end of said tube, between said tube and rod, and outside the second end of said tube, with the centerline gas selected from the group consisting of 100% chlorine and chlorine mixed with a diluent gas, crushing said tube on said rod to produce an assembly, continuing the step of flowing the central line gas until it is stopped by the crushing of said extension tube, and, providing the assembly with a coating glass layer.

21. A method for producing a glass article consisting of the steps of: providing a solid non-porous glass tube having an external surface, first and second ends, and a radius, characterized in that said tube contains a contaminant throughout its radius, deposit a coating of glass particles on the external surface of said glass tube, characterized in that the glass particles have a concreting temperature, insert a central rod of solid non-porous glass into said glass tube to form an assembly coated, inserting said coated assembly into a muffle furnace, flowing a muffle gas containing chlorine through said muffle furnace, flowing a central line gas at the first end of the tube, between the tube and said rod, and outside the second end of said tube, the center line gas being selected from the group consisting of 100% chlorine and chlorine mixed with a diluent gas, r the coated assembly at a temperature lower than the concreting temperature of said glass particles, thereafter, heating the coated assembly to a temperature sufficient to concretize said coating, thereby generating a radially inwardly directed force causing said The tube is crushed on said rod and fused thereto, whereby a specific assembly is formed, and a glass article of said assembly is formed.

22. The method according to claim 21, further characterized in that said glass article is an optical fiber.

23. The method according to claim 21, further characterized in that the step of forming a glass article consists in providing said concreted assembly with a coating layer to produce a stretched preform, and stretching the stretched preform to form an optical fiber.

24. The method according to claim 21, further characterized in that a source of said central line gas is connected continuously to the first end of said tube, and characterized in that the step of heating the coated assembly to a temperature sufficient to specifying said coating comprises subjecting regions to increments of said coated assembly at a high temperature, beginning with the second end of said tube and ending with the first end of said tube, whereupon, as the glass particles become concreted , the regions by increase of said tube are crushed on said rod, starting at the second end of said tube and continuing to the first end of said tube, and characterized in that said central line gas stops flowing when said second end of said tube crushes on said rod.

25. The method according to claim 21, further characterized in that said glass tube contains a doping agent selected from the group consisting of fluorine and boron.

26. The method according to claim 25, further characterized in that said glass tube is formed by the steps of forming a tubular porous glass preform having a longitudinal opening from one side to the other thereof, flowing a fluorine-containing gas in said opening and out through the pores of said porous preform, and heat treating the porous glass preform to be concreted in a non-porous tube doped with fluorine.

27. The method according to claim 26, further characterized in that the amount of fluorine in said tube is sufficient to give said tube a delta value of less than -0.5% with respect to silicon, where? Ab = (na2 -nb2) / (2na2), where na is the refractive index of the glass impurified with fluorine and nb being the refractive index of silicon.

28. The method according to claim 21 further characterized in that said center line gas consists of 100% chlorine.

29. The method according to claim 21, further characterized in that said assembly is supported vertically during the heating and flow steps, whereof said central line gas flows around the entire periphery of said central rod during the passage of flow.

30. A method for preparing a fiber optic preform comprising the steps of: forming a tubular porous glass preform having a longitudinal opening from one side to the other thereof, heating said preform, making it flow in said opening and towards out through the pores of said porous preform a central line gas consisting entirely of a fluorine-containing compound, whereby a high concentration of fluorine is incorporated in the pores of said preform, heating said porous preform to be concreted in a non-porous tube containing fluorine, inserting a central rod of cylindrical shape in said tube fluorinated doped, shrinking said tube on said central rod, and melting the interface between said central preform and said tube.

31. The method according to claim 30, further characterized in that the amount of fluorine in said fluorine-containing glass tube is sufficient to give said tube a delta value of less than -0.5% with respect to silicon, wherein ? ab = (na2-nb2) / (2na2), where na is the refractive index of the glass impurified with fluorine and nb being the refractive index of silicon.

32. The method according to claim 30, further characterized in that the amount of fluorine in said fluorine-containing glass tube is sufficient to give said tube a delta value of less than -0.7% with respect to silicon, wherein ,? ab = (na2-nb2) / (2na2), where na is the refractive index of the glass contaminated with fluorine and n the refractive index of silicon.