MXPA01002069A - Methods and apparatus for producing optical fiber - Google Patents

Abstract

Filament in tube and stick in tube processes of forming optical fiber are described. A solid or monolithic core feedstock (110) is disposed in a hollow cladding structure (112) to form a loosely filled cladding structure. The filled cladding structure is heated to a draw temperature approximately equal to the softening temperature of the cladding structure. The feedstock (110) melts and fills the heated portion of the cladding structure forming a filled core which can then be drawn into optical fiber or to an optical can which can then be further overclad consolidated and drawn into fiber. Feedstock (110) and cladding structures (112) having widely varying coefficients of expansion may be employed. The resulting fiber can be readily designed to be fused to existing installed fibers.

Description

METHODS AND APPARATUS FOR PRODUCING OPTICAL FIBER FIELD OF THE INVENTION The present invention relates generally to improvements in fiber optic waveguides and their manufacture. More particularly, the present invention relates to novel methods and apparatus for forming fiber optic waveguides by means of filament inside tube and rod inside tube in fiberization tube methods.

BACKGROUND OF THE INVENTION Fiber optic waveguides have come to play an increasingly important role in communications. A range of optical fiber types should be available with respect to size, index profiles, operating wavelengths, materials, etc., in order to meet many different system applications. In addition, there is a growing need for active devices such as amplifiers, lasers, switches and dispersion compensators. Additionally, fiber optic wires must be spliced together without excessive practical difficulties. It is important that these splicing techniques can be applied easily in field locations where the wire connection is made. It is particularly important in many applications that a new fiber can be spliced HÍÍL:, 7Í '. g ^ ^^^ H¡ ^ easily to a fiber already existing in the place. However, BS is often not an option to remove all existing fiber and replace it with new fiber that has different characteristics. Various techniques are used to make optical fibers. In one method (see US Patent No. 3,659,915), a bar of core material is placed within a tube of coating material of lower refractive index, forming a concentric and tight fit. The core material should be uniform in cross section and have a smooth surface. The temperature is then increased and the bar and tube stretched to the desired cross-sectional area. The optical fiber resulting from this procedure may not be ideal for communication due to dispersion and excessive losses. Another method (see U.S. Patent No. 5,651,083) involves inserting a core material into a molten coating material to create a preform. The core insert is made quickly so that the core is not softened or dissolved during the procedure. The resulting preform is then stretched as an optical fiber. Fluoride glasses, such as ZBLAN, manufactured in this way are not fusible to silica fibers, tend to devitrify and have poor durability. One of the most important methods used to make soot used in the manufacturing of low loss fiber optic is the chemical vapor deposition (DVQ) process. In a modality of ii. .1 . ? ' < ^ * ¡? ^ Ia * s.

DVQ process, relatively pure chemical compounds (such as silicon tetrachloride) are passed to the interior of a manifold with oxygen. They are then mixed and fed into a burner that moves under a bait bar or a high purity fused silica tube that rotates rapidly. The result is that the silicon is oxidized to silica in the bait bar or silica tube. Deposition can be impurified with a variety of materials. Typically a resulting preform is consolidated and then stretched as an optical fiber. This procedure is an external DVQ or DVO procedure. The internal procedure or MDVQ is also known as DVQ procedure. Current DVQ methods for the manufacture of optical fiber are limited to compositions consisting almost entirely of silica. Only modest amounts of rare earth elements can be incorporated without crowding or crystallization. Volatile components such as alkalis and halogens can not be easily introduced due to their tendency to evaporate during sedimentation. Other important glass modifiers such as alkaline earths can not be incorporated due to the lack of high vapor pressure DVQ precursors. Although glass soot can be deposited by DVQ, it must be consolidated subsequently, which leads to crystallization or loss of glass components with high vapor pressures. Recently another manufacturing technique known as the waste glass method has been developed inside a tube. This approach is described in U.S. Patent Application Serial No. 08 / 944,932. filed on October 2, 1997, which is assigned to the assignee of the present invention, and is hereby incorporated by reference in its entirety. In the waste glass process within the tube, the core waste glass material (having a particle size typically in the range of 100-5,000 μm) is introduced into a coating structure. The end of the core / sheath structure is heated in an oven to near the softening temperature of the sheath and drawn as an optical fiber. This method overcomes some of the disadvantages of typical DVQ procedures, allowing the coating composition to consist of pure SiO 2 and the core composition to consist of multi-component glasses. However, there is a need for methods and apparatus for making optical fiber from a variety of glass and vitreous ceramic compositions that overcomes the disadvantages of known methods, and which are more practical, efficient and economical than conventional methods. By way of example, the disadvantages of various prior art DVQ techniques include the very limited compositions that can be manufactured using the current DVQ methods. Only modest amounts of rare earth elements can be incorporated without crowding. Volatile components, such as alkalis and halogens, can not be introduced in significant quantities due to their tendency to evaporate during sedimentation. Other important glass modifiers such as alkaline earths are difficult to incorporate because they lack DVQ precursors high pressure steam. Although glass soot could be deposited by DVQ, subsequently it must be consolidated which also leads to a loss of glass components with high vapor pressures or crystallization. The disadvantages of typical in-pipe bar-d techniques include the requirement that the core and the liner be very similar. The profiles of the coefficient of expansion and of viscosity temperature need to be similar, otherwise, the end product will be subject to cracking or fracture upon cooling. The present invention also relates to an optical fiber having a numerical aperture greater than about .35. Fibers of this type comprising a core and a coated region that are glass, and are impurified with a rare earth element that is selected from the group consisting of ytterbium, neodymium, and erbium, can be used for fiber lasers. These fiber lasers can be manufactured by coupling a pump source coupled to the high AN fiber. Using the methods published here, numerical openings of approximately .40 or greater (for example, .45) can be achieved.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides methods and apparatus for producing a wide variety of optical fibers by means of fibrillation methods.

..? Mit? x + > . . . . J », A .. «Á w, * filament inside tube and rod inside tube. In one aspect, the present invention comprises the steps of filling a glass tube with a filament or glass rod of the desired material and subsequently stretching or lengthening the glass tube at elevated temperatures. The material inside the tube melts at the stretching temperature and fills the tube to form a continuous core. The loose fitting supply material can be automatically fed or automatically melted by gravity to maintain a constant depth of molten material, resulting in a homogeneous and reproducible product. The material may comprise a core material or a core / coating material. In the same way, the tube may comprise additional core material (eg, which may be used to form the outer core screed), core material / coating, or a coating material. The present invention can be used to stretch the optical fiber directly (filament into a tube) or it can be used to make a core shank or a core coating shank which is then overcoated with additional material before being stretched as an optical fiber. (rod inside tube). The present invention allows that almost any glass that can be produced by chemical (sol-gel, vapor deposition, etc.) or physical (batch and melt) techniques is economically manufactured in the form of a continuous coated filament. The rapid quenching that allows this technique makes it possible for glasses and previously unstable vitreous ceramics to form as stable fibers.

J. »jjL ¿M í * .. ^ Jt ^. , *****. J * ^ • * < ** A more complete understanding of the present invention, as well as additional features and advantages, may be obtained in the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional drawing of an apparatus suitable for performing the filament method within the fiber optic stretch tube according to the present invention; Figure 2 is a cross-sectional drawing of an apparatus suitable for performing the filament method within the fiber optic stretch tube according to the present invention; Figure 3 illustrates an apparatus suitable for coating an optical reed formed in accordance with the present invention which can then be stretched as an optical fiber according to the present invention; Fig. 4 is a graph showing the loss as a wavelength function for a 5 meter extension of optical fiber produced in accordance with an in-tube filament method of the present invention; Figure 5 is a graph showing the profile of the refractive index of a core-coated shank according to the present invention; Figure 6 is a graph showing loss as a function - * -. - < - * »- • ^" - - - - 'tA ^' - '' 1 * ^ - '- * - .--.. * ~ T * ~~ ... * rt- mt íi *.. »^ "Wavelength" for a 5-meter extension of fiber optic produced in accordance with a rod-in-tube method of the present invention, and Figure 7 is a graph showing the loss and diameter of the fiber. field as a function of the length of the fiber for an optical fiber produced in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method and apparatus for producing a wide variety of optical fibers by means of filament fiberization methods within a tube and rod within a tube, as explained in more detail below. Before explaining the present invention in detail in connection with the drawings, several general aspects and advantages will be explained in general. First, a crystal or glass rod of the desired core composition must be obtained. It does not matter if the rod has a square cross section, or triangular cross section, or some other one, you only have to fit inside a casing tube with which it is going to be used. Unlike the well-known rod-in-tube method, the inventive method does not require the core to fit tightly and concentrically within the cladding tube since the core filament melts to conform to the cladding walls. In the same way, the hole in the tube does not need to be circular but can be Rectangular, elliptical or any other non-circular shape that allows the formation of a fiber that has a non-circular core. Because in the present invention, the core glass or the rod conforms to the shapes to the inner diameter of the tube, when a rectangular shaped tube orifice is used the core glass will deform according to the shape of the tube, forming in this way a core region which, when solidified, will be rectangular in shape. A fiber having a generally rectangular core can be made using a tube having an internal diameter of rectangular shape. After stretching of the fiber, the core continues to have a substantially rectangular shape in cross section (with some rounding of the corners of the rectangle). Fibers having a rectangular shaped core have been made, using the methods of the present invention published herein, which exhibited a numerical aperture (AN) of more than about .35, in particular we have achieved numerical apertures of about .45. These high AN fibers can not generally be made using DVQ techniques, because the large amount of modifier needed for these changes in refractive index causes crystallization, cracking or buckling of core material during manufacturing. Having that fiber a rectangular shaped core that can be used to efficiently couple the light from a band laser diode. For example, a typical high power band laser diode emits a beam having essentially a rectangular geometry of 100 μm x 1 μm. In the same way, a beam that has this geometry is captured more ".l, **. . ? A..J »-" * • "'efficiently by a fiber formed in accordance with the present invention to have a core geometry substantially similar to that of the laser beam. Other tube orifices can also be used in a non-circular manner, including ellipticals, which can be used to form polarization while maintaining the fibers. In the same way, tubes having an outer periphery that is not circular in cross section can also be used to manufacture fibers whose outer perimeter is not circular. In each of these embodiments in which a non-circular ID or DE is to be maintained, a high stretch viscosity is preferable to facilitate the fiber or the core shank retaining at least substantially the shape of DI or DE, or both. In particular, in a preferred embodiment used to make a core fiber or rod having a non-circular core or a non-circular outer fiber diameter, or both, the stretch index and the temperature of the preform are maintained so that the fiber or the resulting core rod retains at least substantially the shape of the inside and outside of the tube. This result is facilitated by maintaining the stretching or re-stretching temperature (in the case of making a core rod) so that the tube viscosity is maintained above about 107 Poises. The inventive method also does not require that the core rod be uniform in cross section and have a smooth surface, unlike the previous in-tube bar technology.

The core rod can be manufactured by means of conventional trisol casting and casting, stretching, sol-gel, or other technique. The rod is then loaded into the casing tube. The composition of the tube that becomes the fiber liner is not limited and can range from pure SiO2 to multi-component glass. The only requirement is that the core glass melt at or below the smoothing point of the coating tube and that the difference in thermal expansion between the core between the core and the coating is not so great that the resulting fiber will crash when cooled. , as explained in more detail below. After the coating tube has been filled, it can be stretched into fibers or canes for overcoating. The filled tube is heated to soften the coating glass for elongation. When the coating tube is softened during stretching, the core rod will melt, clear (remove bubbles), and conform to the walls of the coating tube to form an interface determined by the inner surface of the coating tube. The ratio of the external diameter (OD) to the internal diameter (DI) of the tube will be approximately the same as the DO / DI ratio of the fiber or cane, although it can be controlled by the pressure (positive or negative) applied on the molten core in relationship with the exterior of the coating tube. The stretching temperature can also be used to control the diameter of the core since higher drawing temperatures will lead to smaller core diameters for the same OD of given fiber. This control represents a substantial advantage over the conventional preforms where this relationship is fixed once the preform has been manufactured. The higher temperatures used to stretch the coating tube (2000 ° C for the case of pure SiO2 coating) serve to homogenize the core casting and expel harmful water in the glass. In addition, a vacuum can be applied to a central line to increase water removal and clarification. The use of an open center line during the first stretch steps allows the atmospheric control of the casting at the stretching temperature. Oxidation as well as reduction of atmospheres can be introduced above the foundry to control the oxide-reduction state of the core material or to maintain reduced metal cores or superconductors in a dielectric coating. Multiple parallel or concentric cores can also be made by this method, where one core can conduct optical information and the other electrical information. For example, the stress bars (for example, glass bars of SIOO2 impure with B2O3) can be placed inside holes that are drilled in the walls of the tube. These stress bars can be made by means of DVQ and consolidated within the glass, then placed inside holes drilled in the side walls of the tube. Alternatively, the stress bars may comprise a glass not formed with DVQ (eg, a molten glass) and placed within the holes in the side walls of the tube. In any case, after the glass stress bars have been located within the holes in the side walls of the tube at opposite locations of the tube, the glass material of the core can be fed into the inner diameter of the tube as described herein. Additionally. The resulting preform can subsequently be stretched to make a polarization that maintains the fiber. Alternatively, two electrically conductive wires can be used in place of the stress bars (and likewise inserted into holes drilled in the side walls of the tube) to make a fiber that can be used as an electro-optical switch (for example, allow the application of a voltage between the two wires to change the refractive index of the core). The pressure inside the tube above the core can also be controlled to regulate the diameter of the core. This type of process control is not available with any of the current preform fibrillation methods, and in the present invention, this control greatly facilitates the formation of certain combinations of tube and core glasses. For example, with tubes with thicker walls, that vacuum assistance may not be important. However, with some thinner walled tubes, or in cases where the core glass has a larger casting depth, that vacuum application inside the tube can be used from above the core glass to compensate for the forces of the core. casting glass that push out on the walls of the tube, helping in this way to maintain the internal shape of the walls of the tube. The controlled glass composition and thermal history can also be used to generate graduated index profiles. Since it 'Jti? • »- jfc- - * melts the core and smoothes the coating, diffusion procedures are relatively fast, so index profiles can be created in situ. With an appropriate choice of coating material, the fibers produced can be spliced by fusion to conventional fibers that make them very practical in existing fiber networks and facilitate the manufacture of the device. The rod-in-tube method allows for complicated index profiles. For example, the first coating tube could have a refractive index between that of the core and that of the overcoated tube to control the numerical aperture of the fiber or it could contain circles and refractive index rings inserted to build the dispersion and diameter of the fiber. ! field of fiber mode. The first stretch reduces the radial dimensions of the index profile by a factor of 6-8, and the second stretch reduces them again by a factor of 400-500, so that very fine structures can be achieved. The present invention will now be described more fully below with reference to the accompanying drawings, in which many currently preferred embodiments of the invention are shown. However, this invention can be modalized in several ways and should not be interpreted as limited to the currently preferred modalities claimed here. Rather, the applicants provide these modalities so that this description is thorough and complete and will fully convey the scope of the invention to those skilled in the art who are very capable. to adapt these teachings to a wide range of modalities and applications. For exampleAlthough the present invention will be described primarily in terms of waveguide optical fiber, those skilled in the art will appreciate that the optical articles contemplated in the invention may also be included, but is not limited to flat amplifiers, couplers, fiber lasers. , Faraday rotators, filters, optical insulators and nonlinear waveguide fibers. In addition, the manufacture of continuous coated filaments for conductive conduits is contemplated, resulting in superconducting wire. Electro-optical and photonic crystal compositions are also contemplated. Figure 1 is a cross-sectional drawing of an apparatus 100 that may be suitable for use to implement the filament method within a tube for stretching the optical fiber according to the present invention. First, a coating tube 112, having a 57 mm OD and a 2 mm ID in a preferred embodiment, with an inner wall 118 is washed with a drying gas eg chlorine (CI2) or chlorine mixed with a inert gas, to remove unwanted moisture. A core or filament material 110, having a diameter of 1.5 mm in a preferred embodiment, is disposed within the coating tube 112. This material or filament 110 is preferably a bar of elongated monolithic material, however, a plurality of elongated bars can be stacked one on top of the other within the coating tube 112 to form the material.

^^ ¡^^,. ^ *? A Using a plurality of bars is particularly appropriate for the production of manipulated dispersion fiber. The casing tube 112 and the filament 110 of the core form a casing tube filled with an open centerline 122 which is heated by an oven 114, as described further below. The furnace 114 is operated at a stretching temperature that is at or above the melting temperature of the core filament 110, but only causes the coating tube 112 to soften. As the coating tube 112 is softened, the filament 110 of the core will melt at the stretching temperature to form a melt 120 of the core contained within the coating tube 112. It is currently preferred that the stretching temperature be at or above the liquid temperature of the core filament to remove the crystals in the casting 120 of the core. As used herein, casting means that filament 110 of the core flows and fills or deforms to the interior of casing tube 112 so as to result in a filled casing structure. According to a preferred embodiment of the present invention during the step in which the core is melted and deformed into the tube, the core preferably exhibits a viscosity of 10 poise, more preferably 10 poise, more preferably 1000 pols or less , and the coating structure maintains a sufficient viscosity so that the coating substantially retains its internal shape. More preferably, the coating tube 112 exhibits a higher viscosity of 10 ^ -6 poises at this temperature. This distinguishes the present invention from more conventional methods (eg rod and tube or DVQ) of the prior art, in which the viscosity of the core and the coating are typically matched so that the rod and the tube had a viscosity that was different in less than a factor of about 10 at the temperature at which the fiber is stretched or the cane is stretched. An optical fiber 116 is then stretched. While melting, the filament 110 of the core will preferably be rinsed and will conform to the interior wall of the casing tube 112, forming an interface determined by the inner surface 118, and completely filling the interior of the casing tube 112. At its softening point, a glass coating material 112 has a viscosity of about 10 ^ -6 poises. For some types of SIO2, this occurs at a temperature of approximately 2000 ° C. The coating material should be selected so that at the temperature at which the core material fills the interior of the coating tube has a viscosity greater than 10 pols, and preferably greater than 10 ^ -6, and more preferably greater than 10 ^. . However, at this same temperature a core 120 as of 69.86 moles% silica (S1O2), 18.63 moles% aluminum oxide (AI2O3), 4.66 moles% sodium oxide (Na2?), And 6.85 moles% fluoride of lanthanum (I ^ F?) will have a viscosity of about 10 poises, seven orders of magnitude lower than that of coating 112. Core 120 may appropriately have a viscosity less than or equal to approximately 10 ^ -5 poises. In contrast, a typical bar in the tube process will typically employ core and facing material having substantially the same viscosity. A significant advantage of the present invention is that the core filament 110 can be produced in any shape (round, square, triangular, etc.) and by any method (conventional crucible casting and casting, stretching, sol-gel, etc.). The only physical requirement is that the filament 110 of the core fit within the inner walls of the coating tube 112. Therefore, less rigid process controls are required during the manufacture of core filament 110. further, the filament 110 of the loose fitting core can be fed down or dripped as its bottom melts to maintain a constant depth of molten core 120, resulting in a homogeneous and reproducible optical fiber 116. The filament 110 of the core has a melting temperature, as defined above, which is below the softening temperature of the coating 112, and the difference in thermal expansion between the filament 110 of the core and the coating 112 is not so great as to crash fiber 116 when it cools. The composition of the coating 112 is preferably silicate glass, but it can be appreciated by those skilled in the art that the coating composition 112 is essentially not limited and can range from pure SiO2 to multi-component glasses. Figure 2 is a cross-sectional drawing of an apparatus 200 ..s ata, «8a At ^. ^. -TO, . , s «.» - ^ 4, ^ á ^^ < * ¿? * "JM MJMG which can be appropriately employed to carry out the rod method within fiber optic stretch tube in accordance with the present invention. A coating tube 212 with SI02 one meter long (55 mm outer diameter and 6 mm inner diameter) is washed with drying gas to remove unwanted moisture. A 5 mm diameter core rod 210 is disposed or placed within the casing tube 212 to form a filled casing tube. The full casing tube is heated by an oven 214 to 1700 ° C to soften the casing tube 212 in preparation for elongation. As the coating tube 212 is softened, the core rod 210 is melted, and then a shank 216 of the optical core of 6 mm outer diameter is stretched in a standard manner. With "cane" or "core cane" as used herein, it is meant an optical fiber precursor element comprising a core glass material, to which additional coating must be added to the core shank before being stretched as optical fiber. That additional coating can be applied, for example, by inserting the shank into a glass liner sleeve, or by depositing core glass and / or additional coating by means of exterior vapor deposition or other methods. While melting, the core rod 210 will become lighter and conform to the inner walls of the casing tube 212 forming an interface determined by the inner surface of the casing tube 212. In this embodiment, in which the core rod and tube are first re-stretched within a core rod, the material 212 of The coating preferably has a viscosity of about 10 ^ pols at the stretching temperature (for example, about 1700 ° C for some forms of silica) and the core rod 210 will have a viscosity of about 10 ^ pols or less at the stretching temperature. . In one embodiment of the present invention shown in Figure 2, the shank 212 of the resultant core is then placed inside a coating tube 220. The filled liner tube 220 is fired in an oven 222 to soften the liner tube 220 in preparation for elongation. When the coating tube 220 is softened, the shaft 216 will be smoothed, and the optical fiber 224 stretched. In an illustrative method for forming fiber using the rod-in-tube method of the present invention, a core glass of molar composition 70.0 of SIO2-11.25 of AI2O3-7.5 of Ta2? -10 of CaF2 was batch-splitted. - .05 of Er2? 3 from high purity powders, mixed, calcined at 400 ° C for 12 hours to dry the batch and then melted in a high purity silica crucible covered at 1650 ° C for 4 hours. hours. The melt was stirred with a fused silica bar to promote homogeneity, then cooled to 1500 ° C and stretched to a rod 4-5 mm in diameter from the casting. The 5 mm diameter core glass rod was then inserted into a consolidated SiO2 preform, one meter long and 55 mm outside diameter (OD), previously manufactured using the external vapor deposition procedure with a internal diameter (DI) of 6 mm. The dry He gas pipe was washed to remove unwanted moisture and heated to 1800 ° C to soften the SiO2 preform and extract it as a 6mm diameter core / cladding rod that was flared into pieces of one meter long. A one meter long piece was then mounted on a DVQ lathe and overcoated with soot from SIÜ2 to obtain the desired casing diameter / core diameter ratio of 32: 1. The overcoated shank was then consolidated between 1440 and 1500 ° C to form a monolithic SIOO2 preform with a nucleus This preform was then heated to 1950-2000 ° C in a graphite resistance furnace and stretched as a standard fiber of 125 microns in diameter at a speed of 2 m / s. The resulting fiber having an impure core with Er is suitable for use as an optical amplifier. Figure 3 is a drawing of an apparatus 300 used to coat an optical shank by means of an alternative DVQ method and then stretch an optical fiber according to the present invention. A cane is cut 216, produced by the embodiment of the present invention shown in figure 2, in pieces of one meter long. Next, the shank 216 cut on a DVQ lathe 332 is mounted and overriding with S02 to obtain the desired ratio between the coating diameter and the diameter of the core, forming an over-coated optical shank 330. The overbore 330 is then consolidated at a temperature between 1400 ° C and 1500 ° C to form a preform 336 of monolithic SI02. TO then one end of the monolithic preform 336 is furnace in a furnace 338 at a stretching temperature of 1950-2000 ° C and stretched as a standard optical fiber 340 of 125 microns in diameter. Figure 4 is a graph 400 showing the loss as a function of the wavelength by a 5 meter extension of an optical fiber produced in accordance with the present invention. The low loss optical fiber (0.07 dB / m at 1310 nm) exhibits the same loss per meter, starting at the end, in an extension of 2000 meters. The core of the optical fiber was successfully impure with erbium ions, Er3 +, as evidenced by the adsorption bands at 980 and 1500 nm.

Additionally. Fluorescence of Er3 + was observed from the optical fiber when 980 nm laser light was pumped into the fiber. In Figure 4 it is illustrated that, using the methods of the present invention, fiber having a rare earth impurity can be made therein that exhibits a background attenuation of less than 2 dB / m. Figure 5 is a graph 500 showing the profile of the refractive index of a core rod produced in accordance with the present invention employing the core glass composition described above with respect to Figure 2. The core rod has a diameter stretched of 2.74 mm, the core of the shaft having a diameter of .21 mm, for a core / coating thickness ratio of approximately .077. As can be seen in Figure 5, the core exhibited a refractive index delta of approximately .11 (with respect to the silica core), or a - ^ ... aat, - * .... * A - - - - »- - ^ - - cent delta of approximately 6.76 percent (again with respect to the non-impure silica coating) The maximum delta The 6.76 percent observed is significantly higher than the one seen for the fibers produced by typical DVQs.The cane was subsequently coated and stretched as 10,000 m of homogenous optical fiber.The variance of the total core diameter during the 10,000 m extension it was ± 0.25 μm, compared to the waste glass in the tube method which could have a variance of ± 4 μm, whereby the fiber manufactured according to the present invention shows an improvement of at least one order In addition, using Si? 2 as the cladding material allowed the resulting optical fiber to be spliced by fusion using conventional fusion splicers.Slice losses of less than 0.5 dB have been achieved when joining the fibr This is done in accordance with the invention to the optical fiber SMF-28, and splice losses of less than 0.2 dB have been made when the fibers according to the invention were spliced to the optical fiber CS-980. Figure 6 is a graph 600 showing loss as a function of wavelength by a 5 meter extension of optical fiber produced in accordance with the present invention. A tube was made by depositing pure silica, followed by impure silica with germanium, followed by a region of pure silica coating. The resulting soot preform was consolidated to form a tube. Then the same type of glass core bar described above with respect to Figure 2, was inserted inside _ ^ ^ - ^ U of the glass tube and stretched like a fiber. The resulting multi-component core in this case comprised a central region of high index surrounded by a circle of silica, which in turn was surrounded by a ring of impure SIOO2 with germanium oxide (Ge? 2). This shows that the refractive profiles of the complex index can be made with a background attenuation of less than 0.5 dB / m. Figure 7 is a graph 700 showing the loss and diameter of the field so as a function of the length of the fiber for an optical fiber produced in accordance with the present invention. Figure 7 shows that the diameters of the mode field can be expanded by using an increased index ring external to the region of! core high core index, to expand the field diameter in this way beyond what could be achieved by using a single incremented index core. Minimal variations in the loss and diameter of the mode field can be achieved to vary the lengths, as illustrated in Figure 7. The method of the present invention has a variety of advantages. The method of the invention discovers a wide range of compositions for fiberization that were previously not achieved by conventional DVQ techniques that had been used to manufacture optical fiber. New compositions with high rare earth solubility, improved gain flatness and improved optical properties can be easily manufactured in the form of fiber. The method also accommodates large differences in thermal expansion between the filament 110 of the core or the rod 210 of the core, and the cladding material 112 or the cladding material 212, since the core 110, 210 is not rigidly bonded to the cladding 112, 212 until the core filament 110 or the core rod 210 is in the form of fiber or cane when the tension due to the non-coincidence of the thermal expansion are much lower than in a rigid monolithic preform of greater size, since these tensile forces vary inversely with the square of the radius of the fiber, preform or similar. Accordingly, many large numerical aperture fibers can be produced for use as efficient couplers and lasers by the method of the present invention. The method also allows atmospheric control of the molten material 120, 220 of the core at the stretching temperature. Oxidation, reduction or chemically reactive atmospheres can be introduced using the open center line to control the redox state. The pressure above the filament 110 of the core or of the core rod 210 can be controlled to regulate the diameter of the core, as can the stretching temperature. Higher stretching temperatures lead to smaller core diameters for the same given outer diameter of fiber (DE), in contrast to conventional preforms in which this ratio is fixed once the preform is manufactured. For example, these factors can be used to modulate the core diameter by plus or minus 50% using the present invention. The ratio of the OD to the internal diameter (DI) of the tube will be approximately the same as the OD to DI ratio of the optical fiber although, as stated, it can be controlled by positive or negative pressure applied to the molten core 120, 220 in with the exterior of the casing tube 112 or casing tube 212, respectively. Additionally, the high temperatures used to stretch the optical fiber 116, 216 serve to homogenize the molten material 120, 220 of the core and expel the noxious water present in the melt 120, 220 of the core. While the foregoing description includes details that allow those skilled in the art to practice the invention, it should be recognized that the description is illustrative in nature and that modifications and variations will be apparent to those skilled in the art having the benefit of these teachings. By way of example, while it is currently preferred that a core material, such as the core feed material 110, be a solid bar, the core feed material could be conceivably hollow, or be divided into several large blocks. In addition, the term "supply material" is intended to comprise a thin filament, a thicker rod, a plurality of elongated filaments packaged for insertion into the tube, or elongated filaments or rods stacked axially one on top of the other for insertion into the tube. , or in the same way, that will be properly fed upon melting. On the other hand, as defined herein, the supply material is preferably not powder or waste glass. In addition, the supply material can be formed from core materials «•« • "•" * - - - "a * t, .M a¿ ^.". "^? *? *. X,. IC-i. ', - ,, • > frf jfr * - alone or of a core material having a coating material disposed thereon, Either of these embodiments may then be disposed within a tube formed of coating material. core material or coating material Therefore, it is conceivable to manufacture a preform having a plurality of concentric rings of core material and coating material, each ring having the same or different optical characteristics as other rings within the preform. In addition, a preform can be formed, cooled, stored and then reheated and stretched although today this is not preferred. In addition, as is appropriate, the term optical fiber is intended to encompass any fihra or fiber component used in applications that include but not limit optical waveguides, single-mode fibers, multi-mode fibers, amplifiers, electro-optical fibers, couplers, lasers or similar. It is obvious to those skilled in the art that many modifications and variations may be made in the present invention without deviating from the spirit or scope of the invention. Therefore, it is the intention that the present invention cover the modification and variations of this invention as long as they fall within the scope of the appended claims and their equivalents. r ii irni f * - - - ^ - ^. L **** ^^ "" • - - »- ..t *? *. A ^ A, jkJ aJL,. .maut-. *

Claims (34)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for producing an optical fiber, said method comprising the steps of: placing a solid and elongated supply material inside a hollow tube; and heating at least a portion of said tube and supply material at a temperature sufficient to cause said supply material to deform to the shape of said tube, and reduce the external diameter of the tube; wherein the supply material comprises a softening p that is less than the softening p of said tube.

2. The method according to claim 1, further characterized in that said tube comprises a coating structure.

3. The method according to claim 1, further characterized in that said hollow tube comprises a core material.

4. The method according to claim 1, further characterized in that said supply material comprises a substantially continuous supply material that is a core material. ._. - ... .. -i ^ U ^ U .. **. * -_.-, ^ .. ^^^^ ..._ ^^^ ^. ^ ^. ^ ¿T &Jt ^

5. - The method according to claim 4, further characterized in that said supply material comprises a plurality of supply materials.

6. The method according to claim 3, further characterized in that said step of reducing the external diameter comprises forming a core shank, and said method additionally comprises the step of coating said core shank with coating material to form a preform of core-coating, and stretching said core-coating preform as an optical fiber.

7. The method according to claim 1, further characterized in that said supply material comprises a core supply material and wherein said tube comprises a coating structure.

8. The method according to claim 1, further characterized in that said step of reducing the outer diameter comprises stretching said tube and supply material directly as an optical fiber.

9. The method according to claim 1, further characterized in that a difference in the softening p of said core supply material and the softening p of said coating structure is at least 100 ° C.

10. The method according to claim 8, further characterized in that said supply material exhibits a f.,? viscosity of less than 10 ^ poises at a temperature at which said tube exhibits a viscosity of 10 ^ -poises.

11. The method according to claim 1, further characterized in that said supply material exhibits a viscosity of less than 10 ^ poises at a temperature at which said tube exhibits a viscosity of 107-6 poises.

12. The method according to claim 11, further characterized in that said supply material exhibits a viscosity of less than 10 ^ poises when said tube exhibits a viscosity of 10 ^ -6 poises.

13. The method according to claim 12, further characterized in that said supply material exhibits a viscosity of less than 1000 poises when said tube exhibits a viscosity of 10 ^ -6 poises.

14. The method according to claim 1, further characterized in that the coefficient of thermal expansion of said core supply material is greater than the coefficient of thermal expansion of said tube.

15. The method according to claim 7, further characterized in that said coating structure is essentially only silica. Aüfa A t.A. * JL .. .. »A J -J _ ^^ yg £

16. - The method according to claim 7, further characterized in that said coating structure is at least 90 weight percent of silica manufactured by a chemical vapor deposition process.

17. The method according to claim 16, further characterized in that said chemical vapor deposition process comprises an external chemical vapor deposition process.

18. The method according to claim 8, further characterized in that said supply material is fed at a faster speed than said tube.

19. The method according to claim 7, further characterized in that said coating structure comprises a plurality of holes that runs through it longitudinally, wherein the method additionally comprises the steps of: placing a metal inside at least one of the plurality of holes defined by said coating structure; and stretching said preform into an electro-optical fiber.

20. The method according to claim 7, further characterized in that said coating structure comprises a plurality of holes that run through it longitudinally, wherein the method additionally comprises the steps of: positioning a glass rod having a composition that differs of the coating within at least one of the plurality of holes defined by said coating structure; and stretching said preform as a fiber that maintains polarization.

21. The method according to claim 8, further comprising additionally comprising the step of rendering said supply material impure with a rare earth element.

22. The method according to claim 21, further characterized in that said rare earth element is selected from the group consisting of ytterbium, erbium, praseodlmium and neodymium.

23. A method for manufacturing an amplifier using the fiber manufactured in accordance with the method of claim 22, further characterized in that it comprises the step of coupling said optical fiber to a wavelength division multiplexer in optical communication with a laser of pump and a signal source to form a fiber amplifier.

24. The method according to claim 21, further characterized in that said rare earth element is selected from the group consisting of ytterbium, neodymium and erbium.

25. A method for manufacturing a fiber laser using the fiber manufactured in accordance with the method of claim 24, further characterized in that it comprises the step of coupling said optical fiber to a pump source to form the fiber laser. 26.- An optical fiber formed by the method of: placing a substantially elongated continuous supply material inside a hollow tube; and heating at least a portion of said tube to A temperature sufficient to cause said supply material to deform to the shape of said tube, thereby forming a preform. 27. The method according to claim 1, further characterized in that the internal orifice of said tube is not circular. 28. The method according to claim 27, further characterized in that the internal orifice of said tube is rectangular. 29. The method according to claim 27, further characterized in that the internal orifice of said tube is elliptical. 30.- An optical fiber that comprises a numerical aperture of approximately .35 or greater. 31. The optical fiber according to claim 30, further characterized in that said fiber comprises a core and a coating region comprising glass. 32. The optical fiber according to claim 31, further characterized in that the core of said fiber is impure with a rare earth element that is selected from the group consisting of ytterbium, neodymium and erbium. 33.- A fiber laser comprising a pump source coupled to the fiber according to claim 32. 34. The optical fiber according to claim 32, further characterized in that said fiber comprises a numerical aperture of approximately .40. or older. gJi * üts * ~? ¡tk. ... . «I -I,«. -: «> . »AjsiSi