MXPA99011019A - Fluorinated rare earth doped glass and glass-ceramic articles - Google Patents

Abstract

The present invention is directed to a fluorinated rare earth doped glass composition and method for making a glass-ceramic optical article therefrom, e.g. optical fiber waveguides, fiber lasers and active fiber amplifiers, having application in the 1300 nm and 1550 nm telecommunications windows. The inventive compositions include Pr3+ and/or Dy3+ in a concentration range of between 300 - 2,000 ppmw and Ag+in a concentration range of between 500 - 2,000 ppmw;or Er3+ in a concentration range of between 500 - 5, 000 ppmw and Ag+ in a concentration range of between 0 - 2,000 ppmw. The monovalent silver ion provides an ionic charge balanced glass-ceramic crystal. These compositions exhibit reduced or absent rare earth ion clustering and fluorescence quenching effects in the presence of high concentrations of rare earth ion dopants.

Description

IMPURIFIED GLASS WITH RARE FLOORED LANDS AND GLASS-CERAMIC ITEMS DESCRIPTIVE MEMORY The present application relates to the patents of E.U.A. Nos. 5,483,628 and 5,537,505 (hereinafter, the '628 and' 505 patents, respectively), which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION The invention relates to a doped glass composition with rarefied fluorinated earths showing reduced rare earth ion cluster and fluorescence quenching in the presence of relatively high concentrations of rare earth dopant, and for ultra-transparent glass-ceramic articles , particularly waveguides and particularly active fiber devices, i.e. amplifiers and fiber lasers, which use said waveguides. As used herein, the term "ultratransparent" refers to high optical clarity; that is, the transparency of the glass-ceramic of the invention is compared to the transparency of the glass in the spectrum of about 350 nm to 2.5 μ.

BACKGROUND OF THE INVENTION There is a general interest in, and industrial necessity for, the optical compositions of articles made therefrom which have potential applications in the telecommunication windows of 1300 nm and 1550 nm. Materials that can be an efficient 1300 nm fiber optic amplifier material, for example, have included the rare earth ions Pr3 + and Dy3 + doped with fluoride, mixed halide and sulfur glass host, although the amplification materials are 1500 nm they are adequately contaminated with Er3 +. A recent publication by Borrelli et al, Transparent glass ceramics for 1300 nm amplifier applications, J. Appl, Phys. 78 (11), (Sept. 1995), reported an alternative host for the Pr3 + ion that combines some of the advantages of the fluoride and oxide glasses. The new material is described in the '505 patent and consists of an oxyfluoride glass which has been adequately heat treated to form a transparent glass-ceramic. The glass-ceramic contains 5-40% by volume of fluoride nanocrystals having diameters ranging from about 6-15 nm, embedded in a glass matrix mainly of oxide. As described in detail in the '505 patent, optically active fluoride based on glass-ceramic articles was produced from Yb-free compositions that included between about 50 to 900 ppm of Pr3X Glass-ceramic was shown for carrying out an active device in the spectral window of 1300 nm in its concentration scale doping.

For glass-ceramic articles doped with Pr3 +, fluorescence lifetimes greater than 120 microseconds were observed in the base glasses of the '505 patent at Pr3 + concentrations and up to around 500 ppm. The removal of concentration was observed at Pr3 + concentrations slightly above 500 ppm, and it was observed that the fluorescence life periods were approximately linearly reduced from about 70 microseconds to 900 ppm. It was reported that a balance between the fluorescence life period and the Pr3 + concentration on the scale of around 200 to 550 ppm was achieved in the best case; however, functional active devices were reported with Pr3 + concentrations on the scale of around 50 to 650 ppm. Although both longer fluorescence lifetimes and higher doping concentrations are desirable for the production of active devices as described herein, the inventors recognize the need to improve the scales of the compositions of the new glass-ceramic material described in FIG. the '505 patent, and to create glass-ceramic compositions having similar advantages suitable for 1550 nm applications. Radioactive quantum efficiency is a key parameter in the evaluation of transparent glass-ceramics as a means of potential gain for lasers and fiber amplifiers. Quimby and Tick, in an article titled Quantum efficiency of Pr3 * doped transparent glass-ceramics (which is about to be published) reports the quantum efficiency of the emission of 1300 nm in transparent glass-ceramics doped with Pr3 + using a direct measurement technique based on measurements of relative fluorescence. Fluorescence was observed by stimulating the Pr3 + 1Ü2 level, reaching a peak of around 1400 nm (the "A" transition), and the fluorescence of the 1G4 level reached a peak of around 1300 nm (the "B" transition). ") when level 1Ü2 was directly stimulated with dye laser radiation of 595 nm. After the analysis described by Quimby et al., Opt. Lett., 20, 2021 (1995), the quantum efficiency of the 1300 nm emission of 1G4 was determined by taking the ratio of the total B transition rate to the total A transition rate. The data in Figure 1, which will be described in more detail below, shows the B / A ratio as measured for exemplary embodiments of the two glass-ceramic base composition of the '505 patent having Pr3 + concentrations that They vary from around 25 ppm to 1000 ppm. As expected by the inventors, the B / A ratio increases with the increase in concentration, which they believe is due to the effect of cross relaxation resulting from the increase of the Pr3 + ion cluster. It is known that when a trivalent impurified earth is incorporated into said ceramic-glass, the contaminated earth is segregated in the second phase, whose crystals are formed during the ceramization process. Said crystals have a cubic lattice structure and are believed to comprise the majority of the divalent cadmium and lead fluoride. The inventors believe that the agglutination arises from the local strains that are established in the lattice due to the substitution of trivalent dodecyl earth fluorides for the divalent fluorides. When the direct substitution of a contaminated earth occurs in the glass lattice, the charge balance can be maintained by the incorporation of an interstitial fluoride in the crystal structure near the contaminated earth. In the volume of the crystals, the above is the source of the local strain, which is observed to be reduced when said defects can accumulate. The inventors believe that a similar mechanism occurs in glass-ceramic nanocrystals. The foregoing, however, results in a reduction in quantum efficiency at higher concentrations of Pr, observed by the authors because they appear at concentrations of around 500 ppm. The inventors have therefore recognized the need for glass and glass-ceramic compositions doped with rare or transparent earths and articles made thereof in which the removal of agglomeration and concentrations of rare earth ions are reduced despite the high doping concentrations of rare earths, which have a relatively high quantum efficiency, and a wider spectrum gain band.

BRIEF DESCRIPTION OF THE INVENTION Accordingly, the invention relates to a glass-ceramic optical article having a glass composition that provides such features, and to a method for manufacturing glass-ceramic optical fiber waveguide articles having core compositions and coating as described herein. One embodiment of the invention relates to a glass-ceramic optical article. The compositional structure of the glass-ceramic article is a second phase cubic lattice which substantially includes a divalent divalent cadmium fluorine or divalent lead fluoride having a trivalent doped earth ion incorporated herein, and including a monovalent or thallium monovalent silver for the crystal charge balance. Another embodiment of the present invention that is particularly suitable for applications in the 1300 nm telecom window describes a glass-ceramic optical article that includes an active core that is a transparent glass-ceramic having substantially only one crystal phase, consisting essentially, in terms of percent cation, of: SiO2 20-40; AIO -, 5 10-20; CdF2 19-34; PbF2 19-23; wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by the fluoride; and including at least one of the rare earth fluorides YF3 (3-7), GdF3 (3-7), and LuF3 (4-15), where the total amount of said rare earth fluorides is (3-15); including at least one of Pr3 + and Dy3 + at a concentration on the scale of about 300 to 2,000 ppm; and including Ag + at a concentration on the scale of around 500 to 2,000 ppm; and a coating that is a transparent glass, consisting essentially of a percent by weight of an oxide base, of: S¡O2 25-35; AI2O3 3-5; CdF2 12-16; PbF2 40-50; ZnF2 4-8; and Bi2O3 0-10. Another embodiment of the present invention that is particularly suitable for applications in the 1300 nm telecom window describes a glass-ceramic optical article that includes an active core that is a transparent glass-ceramic, having substantially only one crystal phase, consisting essentially, in terms of cation portions, of: SiO2 20-40; PbF2 15-25; AIO1.5 10-20; CdF2 21-31; ZzF2 3-7; wherein up to 5 mole% CdS or 3 mole% CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by fluorine; and including at least one of the rare earth fluorides YF3 (3-7), GdF3 (3-7), and LuF3 (4-15) where the total amount of said rare earth fluorides is (3-15); including at least one of Pr3 + and Dy3 + at a concentration on the scale of about 300 to 2,000 ppm, and including Ag + at a concentration on the scale of around 500 to 2,000 ppm; and a coating which is a transparent glass, consisting essentially of a percent by weight of an oxide base of: SiO2 25-35; AI2O3 3-5; CdF2 12-16; PbF240-50; ZnF24-8; and Bi2O3 0-10. In one aspect of the embodiments described above, the Ag + is at a concentration on the scale of about 700 to 1,000 ppm. Another embodiment of the invention that is particularly suitable for applications in the 1550 nm telecommunications window describes a glass-ceramic optical article that includes an active core that is a transparent glass-ceramic having substantially only one crystal phase, consisting of essentially, in terms of the percent cation, SiO2 20-40; AIO -? 5 10-20; CdF2 19-34; PbF2 19-23; wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by the fluoride; and including at least one of the rare earth fluorides YF3 (3-7), GdF3 (3-7), and LuF3 (4-15) where the total amount of said rare earth fluorides is (3-15); ErF3 at a concentration on the scale of around 500 to 5,000 ppm; and including Ag + at a concentration on the scale from 0 to 2,000 ppm; and a coating which is transparent glass, consisting essentially of a weight basis of an oxide base, of: SiO2 25-35; AI2O3 3-5; CdF2 12-16; PbF2 40-50; ZnF2 4-8; and Bi2O3 0-10. Another embodiment of the invention that is particularly suitable for applications in the 1550 nm telecommunications window describes an optical glass-ceramic article that includes an active core that is a transparent glass-ceramic having substantially only one crystal phase, consists essentially, in terms of percent cation, of: SiO2 20-40; PbF2 15-25; AIO -, 5 10-20; CdF2 21-31; ZnF2 3-7; wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by the fluoride; and including at least one of the rare earth fluorides YF3 (3-7), GdF3 (3-7), and LuF3 (4-15) where the total amount of said rare earth fluorides is (3-15); ErF3 at a concentration on the scale of around 500 to 5,000 ppm; and including Ag + at a concentration on the scale of zero to 2,000 ppm; and a coating that is a transparent glass, essentially consisting of about one percent by weight of an oxide base, of: SiO2 25-35; AI2O3 3-5; CdF2 12-16; PbF2 40-50; ZnF2 4-8; and Bi2O3 0-10. In one aspect of all the embodiments described above, the core is an elongated central member having a first and a second end, and the liner covers the surface of the elongated central member but leaves the first and second ends exposed. In another aspect of all the embodiments described above, the core composition contains up to 17% of the total cations of at least one component selected from the group consisting of (0-7%) BO1.5, (0-12%) GeO2 , (0-7%) PO2.5, (0.3%) TiO2, (0.2%) Nb2O5, (0-7%) GaF3, (0-7%) HfF4, (0-7%) lnF3, (0- 15%) BiF3, (0-1%) LaF3, (0-3%) CdCI2, and (0.5%) CdS. In one aspect of all the embodiments mentioned above, the silver is in the form of a monovalent cation provided by, for example, silver fluoride (AgF), silver oxide (Ag2O), silver nitrate (AgNO3), or any common silver salt. Another aspect of the invention pertains to a method for making a fiber optic waveguide comprising the steps of loading an inner crucible of a double crucible furnace with a finished core glass composition in a fluid state, preferably in the molten piece shape again, providing a coating glass having a stiffness sufficient to contain the fluid flow, preferably in the form of a tube, in an external crucible of the double crucible furnace, holding the core glasses and crucible at a temperature equal to or above their respective liquid temperatures, so that no portion of the core or coating glasses is contacted above their respective liquid temperatures with a platinum wall of the double crucible; extracting an elongated glass article from the oven, and cooling the glass article below its liquid temperature. In one aspect of the embodiment, the core member glass and the coating glass are heated to a temperature in the range of about 800-1300 ° C, and the elongated glass article is milled at a temperature below the temperature Crystallization peak in a time less than 1 minute. The elongated glass article, i.e. as an optical fiber, preferably has a first and a second end, and has a core and coating composition described in one of the aforementioned embodiments. The core of the glass article can be transformed into a transparent glass-ceramic having high optical clarity essentially containing only one crystal phase by heating the elongated glass article to a pre-selected temperature for a preselected period. Preferably, the ceramization step is carried out by heating the glass article close to the peak crystallization temperature of the core member glass of between about 1 / 2- 24 hours. The expression "substantially a crystal phase" refers to the fact that the glass-ceramic does not contain a sufficient amount of a second crystal phase to alter the chemical and / or physical characteristics of the glass-ceramic, more particularly, the optical clarity. More preferably, no amount of a second crystal phase will be present. Rare earth metal ions are present in the crystal phases. In an aspect of the invention in which the core glass composition contains up to 5 mole% CdS or 3 mole percent CdCI2 substituted with an equivalent amount of CdF2, or has an equivalent amount of fluoride-substituted oxides, the The glass core is transformed into a glass-ceramic by cooling as the article leaves the oven, and no additional or external ceramization step is required. Additional features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention will be achieved and will be achieved by the apparatus and method particularly indicated in the description and written claims of the present as well as the attached drawings. It will be understood that the foregoing general description and the following detailed description are exemplary and are intended to provide a further explanation of the invention as claimed. The accompanying drawings are included to provide further understanding of the invention and are incorporated and constitute a part of said specification; illustrate the embodiments of the invention; and together with the description serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS.

Figure 1 is a graph showing the B / A ratio (measurement of cross relaxation) as a function of the concentration Pr3 + in ppm for various exemplary compositional embodiments of the invention with and without Ag, which indicates reduced cross-relaxation to a concentration of Pr3 + for the composition containing Ag; Figure 2 shows a graph representing the spectral gain band of a standard ZBLAN glass and the corresponding wider spectral gain band of an article according to an embodiment of the invention; Figure 3 is a compositional map showing the compositional domains of various compositional embodiments of the invention; Figure 4 is a graph of viscosity versus temperature for an optical glass of fluorinated rare earth core (FROG) according to an embodiment of the invention which indicates the difference in viscosity between the glass and glass-ceramic composition; Figure 5 is a graph of viscosity against the temperature of a coating glass according to an embodiment of the invention; Figure 6 (a) shows the relative temperatures of the glass at different places in the double crucible furnace; Figure 6 (b) schematically shows the external crucible of a double crucible furnace according to one embodiment of the invention, including an inner crucible centering ring in the neck region thereof; Figure 6 (c) shows schematically the internal crucible of a double crucible furnace according to an embodiment of the invention; Figure 6 (d) schematically shows a two-zone oven with a cooling ring according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES OF THE INVENTION According to one embodiment of the invention, glass-ceramic optical articles such as single-mode and multi-mode optical waveguide fibers and optically active devices using such fibers, for example, amplifiers and optical lasers, are suitably manufactured from the inventive glass core compositions listed in tables I-IV and the coating or coating glass composition listed in Table V below.

. TABLE I (in% cation unless otherwise indicated) SiO2 20-40 wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by the fluoride: YF3 (3-7) and / or GdF3 (3-7) and / or LuF3 (4-15) [(3-15) total]] Pr3 + and / or Dy3 + (300 to 2,000 ppm); and Ag + (500 to 2,000 ppm); TABLE II (% cation unless otherwise indicated) SiO2 20-40 PdF2 15-25 AIOLS 10-20 CdF2 21-31 wherein up to 5 mole% CdS or 3 mole% CdCI2 can be replaced by an equivalent amount of CdF2 or an equivalent amount of an oxide can be replaced by the fluoride; YF3 (3-7) and / or GdF3 (3-7) and / or LuF3 (4-15) [(3-15) total]] Pr3 + and / or Dy3 + (300 to 2,000 ppm); and Ag + (500 to 2,000 ppm); TABLE III (in% cation unless otherwise indicated) S¡O2 20-40 Aid 5 10-20 CdF2 19-34 PdF2 19-23 wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by the fluoride: YF3 (3-7) and / or GdF3 (3-7) and / or LuF3 (4-15) [(3-15) total)] ErF3 (500 to 5,000 ppm); and Ag + (0 to 2,000 ppm); TABLE IV (% cation unless otherwise indicated) S¡O2 20-40 PbF2 15-25 AIO1.5 10-20 CdF2 21-31 ZnF2 3-7; wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by fluorine, or 3-7 mole% of substituted ZnO by ZnF2; YF3 (3-7) and / or GdF3 (3-7) and / or LuF3 (4-15), [(3-15) total]; ErF3 (500-5,000 ppm); and Ag + (0-2,000 ppm); TABLE V (% by weight in an oxide base) S0O2 25-35; AI2O3 3-5; CdF2 12-16; PbF2 40-50; ZnF2 4-8; and Bi2O3 0-10; A fiber optic waveguide article according to one embodiment of the invention comprises a member of the elongated central core consisting essentially of any of the base glass compositions in tables I-IV, and a coating or coating glass. compatible according to the compositions listed in Table V. The central member can also be made of metal oxide and metal fluoride selected from the group consisting of (0-7%) BO - ?, 5, (0-12%) GeO2, (0-7%) PO2) 5, (0-3%) TiO2, (0-2%) Nb2O5, (0-7%) GaF3, (0-7%) HfF4, (0-7%) lnF3, (0-15%) BiF3, (0-1%) LaF3, (0-3%) CdCI2, and (0-5%) CdS, which are replaced by the oxides and fluorides in the glass compositions of base listed in tables 1-IV. Up to 17% cation of the total substitution is acceptable. In general, oxides and fluorides are replaced by oxides and fluorides. The presence of at least 4% YF3 cation or at least 3% cation of GdF3 or LuF3 is required to ensure adequate crystallization in situ to produce a glass-ceramic material of high optical clarity. The inclusion of ZnF2 results in improved glass melting and crystallization behavior in some way; therefore, glasses containing ZnF2 are preferred. The base glass compositions contain a monovalent cation by the glass charge balance when a trivalent rare earth element is incorporated into the cadmium crystal or divalent lead fluoro. Ag + and Tl + have been identified as suitable monovalent cations; however, silver is preferred to thallium because of its reduced volatility, lower ionic size and lower toxicity. In an exemplary embodiment of the invention, the incorporation between about 500 to 2,000 ppm, and preferably between about 700-1,000 ppm, of AgF, Ag2O, AgNO3, or any common silver salt, into the glass compositions The bases listed in Tables I and II allow such compositions to accommodate the doping concentrations of Pr3 and Dy3 + in the range of between about 300 to 2,000 ppm without the damaging effects of crushing and cross-relaxation observed previously in the base compositions at concentrations impurifiers of around 500 ppm. The reduced agglomeration of the rare earth ions is consumed by the data shown in Figure 1, in which the sample containing Ag + has a significantly lower B / A ratio in Pr3 + concentrations to samples that do not contain any silver. The "B" value refers to the transition B that originates from the Pr3 + 1G4 level reaching a peak of 1300 nm, although the "A" value refers to the transition A that originates from the Pr3 + 1D2 level reaching a peak around of 1460 nm. The B / A ratio is an indirect measure of the degree of cross relaxation when an ion at the level 1Ü2 exchanges energy with a close ion in the ground state, one of the ions is left at the 1G4 level. The non-radioactive route for level 1G4 results in additional B fluorescence, thus increasing the B / A ratio. Cross relaxation becomes more important at higher Pr3 concentrations, where ion-ion separation is lower, for samples that do not contain a monovalent charge balance cation as indicated by higher B / A values for such samples . In Figure 1, the Y / Z samples refer to the doped Pr3 + / Dy3 + compositions of Table II (ie, those containing ZnF2) although the Y samples refer to the doped compositions Pr3 + / Dy3 + (Zn-free) of the Table I. The numbers associated with each composition sample in the form xxx / yy refer to the ceramization temperature and the ceramization time respectively for each sample. The inventors have also discovered that the core glass compositions listed in tables III and IV are about 500 to 5., 000 ppm Er3 + without significant agglomeration or fluorescence removal effects in the presence of 0-2,000 ppm AgX The fluorescence emission curve of Figure 2 compares the spectral gain band of a doped composition modality with Er3 + of the invention consisting of essentially, in% cation of 30 SiO2, 15 AIO?, 5, 3.5 YF3, 5 ZnF2, 17 PbF2, CdF2, and 0.5 ErF3, to a composition of ZBLAN doped with Er3 + and shows that the inventive compositions show longer life times longer and spectral gain bands wider than aluminosilicate doped with Er3 + or ZBLAN glass compositions. Preferred exemplary embodiments for core glass compositions are presented in Table VI (A, B, C, D, E, F, G and H) below.

TABLE IV (% cation unless otherwise indicated) A B c D E F G H Si02 30 30 30 30 30 30 30 30 AIOLS 15 15 15 15 15 15 15 15 CdF2 29 29 20 30 26.5 25 18 28 CdS / CdCI2 / CdO 0 0 0 0 1.5 * 3 ** 0 PbF2 22 17 25 20 17 17 17 17 ZnF2 0 5 0 0 5 5 5 0 ZnO 0 0 0 0 0 0 0 5 LuF3 0 0 10 0 0 0 0 0 YF3 4 4 0 0 4 4 4 4 GdF3 0 0 0 5 0 0 0 0 Pr3 + X 'X' 0 0 0 X '0 0 Er3 + 0 0 X "X" X "0 0 0 ErF3 0 0 0 0 0 0 1 1 Ag + (ppm) 500-2,000 500-2,000 0-2,000 0-2,000 < 2000 < 2000 where * = CdCI2, ** = Cds, *** = CdO, X '= 300-2,000 (ppm) and X "= 500-5,000 (ppm) The glass map of Figure 3 shows three scales of preferred composition of the core composition embodiments containing GdF3, YF3, and LuF3. The traced regions delimit the compositions that result in stable, ultratransparent glass-ceramic. The compositions outside said regions were unstable or nebulous after ceramization. A preferred exemplary embodiment for the coating glass composition is presented in the following Table VII.

TABLE VII (% by weight in an oxide base) S02 32 AI2O3 3.5 CdF2 14 PbF2 45.6 ZnF2 4.9 B¡2O3 0-10 The double crucible technique is well known in the art and is described in several references, such as, "Fabrication of Long Single Mode and Multimode Fluoride Glass Fibers by the Double Crucible Technique", Tokiwa et al; Electronics Letters, # 24, V. 21, 1985. It is useful to make an optical fiber from a variety of core and coating compositions, but traditionally requires core and coating compositions having similar liquid viscosities. However, the oxyfluoride core composition of the present invention has high temperature properties which tend to be characteristic of fluoride fusions, the most difficult of these to be treated is that which has a low liquid viscosity. Although ceramization processes for one embodiment of the invention occur at viscosities of at least 100 million poises, as shown in Figure 4, the typical preform / stretch methods for the production of optical fiber are not viable because the material has the tendency to over-saturate at normal stretch viscosities. In normal stretching, the current viscosity should be about 2,000-1,000,000 poise, preferably between 10,000-1,000,000 poise, in order to control the root. However, the liquid viscosity of the core compositions of the invention is about four orders of magnitude more fluid than the lower viscosity limit. In light of these considerations, a modified double crucible technique is used to make the optical fiber from the compositions listed above wherein a fluid core composition is supplied in a coating glass that is rigid enough to contain the core current and eventually pull toward the fiber. A suitable coating glass composition as described herein was developed to utilize the double crucible stretching method described herein. The coating glass will preferably show a refractive index of between 1.64 and 1.75, more preferably on the scale of 1.65-1.74; a viscosity greater than 1500 poises at 800 ° C; a liquid temperature less than 800 ° C; a coefficient of thermal expansion of between about 65-1 10 x 10"7 / ° C of room temperature at 300 ° C, and not be chemically reactive with the core glass at 800 ° C The behavior of the viscosity of a The coating glass embodiment of the invention is shown in Figure 5. Although the coating glass compositions in the '628 and "505 patents involve a family of alkali lead silicate glass having physical and optical requirements for a composition of suitable coating, it is taken into account that the presence of the alkali in contact with the modalities of the core composition at 800 ° C resulted in a rapid devitrification of the core glass. further, the central member glasses described above will form large, undesirable crystals during the forming step if the glass remains for a long time at a temperature close to the liquid temperature, that is, around 800 ° C in one embodiment of the invention. In this way it was necessary to modify a standard double crucible furnace in order to make the optical fiber. Preferably, as shown schematically in Figure 6 (ad), a fluorinated rare earth glass (FROG) according to one embodiment of the invention, in a fluid state, and more preferably a fluid core of pieces 78 returned to melt, is supplied in a coating glass tube 64 which has sufficient rigidity to contain the core stream and subsequently pull onto the fiber. A key aspect of the method is to prevent the core 78 from coming into contact with any platinum wall of the double crucible furnace below liquid temperature and, likewise, to prevent the facing glass from coming into contact with the wall of the crucible. crucible below its liquid temperature to prevent the formation of undesirable glass. Because the core is always above the liquid temperature until it leaves the furnace, there is no inactive sublimid boundary layer and the residence time in the heat zone is short; however, the core current moves through the supply section 72 of the internal crucible suddenly, preferably as quickly as possible. After it leaves tip 74 of the supply section it is quickly crushed in the glass. Preferably, the glass is rapidly cooled to a temperature below the liquid temperature. Said temperature varies depending on the glass composition of the central member, but is easily determined by differential scanning calorimetry (DSC) or other methods well known in the art. The unwanted crystal growth is suppressed by cooling the elongated glass article formed in the double crucible at a temperature below the crystallization temperature scale is less than about 1 minute. In one embodiment of the invention in which up to 5 mole% of CdS or CdCI2 is replaced by an equivalent amount of CdF2, crystallization (ceramization) of the core occurs spontaneously as the fiber is cooled in the existing stretching oven; therefore, no external heating is required to ceramise the glass. In general, the peak crystallization temperature for ceramization, as shown in Figure 4, is based on the scale of about 400 to 500 ° C. Once the glassware has reached its final shape, it can be reheated (for those compositions that require additional heating, that is, an external ceramization step), to ceramise the core in an ultratransparent glass-ceramic. The crystallization process can be carried out at or near the peak crystallization temperature (the term crystallization as used herein is equivalent to the transformation of a glass into glass-ceramic). Said temperature is desirable due to the control that is had in determining the size, number and separation of the crystals. The preferred temperature is in the range of about 400 to 500 ° C and the time in said temperature range can vary from 1/2 to 24 hours. A temperature can be selected where the required crystallization is completed in 2-8 hours. The viscosity curve of Figure 4 is generally representative of a FROG according to a compositional embodiment of the invention. The curve between the two data sets was arbitrarily interpolated. The temperature of the liquid is around 800 ° C corresponding to a viscosity of around 25 poises, although the viscosity of ceramization is shown above 108 poise. Figures 6 (a-d) schematically illustrate the details of the design and method of the modified double crucible. An external crucible 60 is shown in Figure 6 (b). The outer crucible has a tubular supply section 62 that is about 5.08 cm in length and has an internal diameter of about 1.02 cm. A platinum rod having a covered end (not shown) is mountable for insertion at the lower end of the supply tube 62 to prevent the covering glass 64 from prematurely leaking from the outer crucible. The inner crucible 70 has a supply section 72 having a tubular tip 74 at the lower end thereof which is about 2.54 cm in length and preferably has an internal diameter of 0.076 cm + 0.013 cm for the compositional modalities of the invention. The inner crucible is mounted on a triaxial supporting bracket 76 independently movable to allow the tip 74 of the inner tube to be placed in any desired position within the supply section 62 of the outer crucible during a stroke. A platinum wire (not shown) having a sufficient external diameter for easy but tight adjustment and a removable position of the wire in the supply section 72 through the opening of the tip 74 was used to seal the inner crucible to prevent the flow of the fluid core 78 through the tip of the inner crucible until the system was ready to operate. A teflon plug 82 was optionally used to seal the inner crucible in an upper region thereof to pressurize the tube if desired. The internal diameter of the tip 74 of the internal crucible 70 is important to control the flow of the core glass. A tip too small D.l. can cause the fluid core to have a lot of surface tension to flow, although a D.l. large can cause the core / coating stream to be uncontrollable. As will be appreciated by one skilled in the art, the dimensions of the tip and flow rates will depend at least in part on the viscosities of the fluid core; therefore, the dimensions and the procedure of the modified double crucible must be adjusted. In an exemplary embodiment, the furnace 90, as shown schematically in Figure 6 (d), is separated into two zones 92 and 94, separated by an insulating plate 96. A load of glass pieces is introduced into an internal crucible in the upper zone 92 and re-melt, the temperature of the upper zone being maintained between about 1000-1200 ° C by thermocouple 98. There was a decrease of about 70 ° C from the control pair 98 to the center of the inner crucible , so although the piece of FROG must be re-melted above 1050 ° C, the upper zone is maintained at 1150 ° C for each route. A control pair 100 of lower dew temperature was placed in contact about 2.54 cm from the end of the supply tube 72 and was set to at least 800 ° C. The tip 74 of the inner supply tube 72 was placed at the same height of the thermocouple 100. A fiberfrax sheet 102 was placed between the supply tube and the lower damper 94 to prevent cooling of the supply section 72. A cooling ring of external air 104 having 20 circularly disposed holes 106, angled downwards, was placed just below the tip of the supply tube. The gas flow of the cooling ring effectively controlled the size of the root by cooling the glass as it exited the supply tube, thereby minimizing the possibility of devitrification. The described parameters provided a procedural window in which a structured optical waveguide / coating guide fiber was fabricated. It will be apparent to those skilled in the art that various modifications and variations may be made in the apparatus and method of the present invention without departing from the spirit or scope of the invention. In this way, it is intended that the present invention cover the modifications and variations of said invention considering that they are within the scope of the appended claims and their equivalents.

Claims (19)

NOVELTY OF THE INVENTION CLAIMS

1. - An optical article comprising: a transparent glass-ceramic core, said glass-ceramic core having substantially only one crystal phase, consisting essentially, in terms of percent cation, of: SiO2 20-40; AIO1.5 10-20; CdF2 19-34; PbF2 15-25; ZnF2 0-7; REF 3-10; RE 300-5,000 ppm; Ag + 0-2,000 ppm; wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by the fluoride; wherein REF is at least one of YF3 (3-7), GdF3 (3-7), and LuF3 (4-15) and RE is at least one of Pr3 +, Dy3 +, and Er3 +; and a transparent glass coating, consisting essentially of a weight basis of an oxide base of: SiO2 25-35; AI2O3 3-5; CdF2 12-16; PbF2 40-50; ZnF2 4-8; and Bi2O3 0-10.

2. The article according to claim 1, wherein: PbF2 19-23; ZnF2 0; Er3 + 0; at least one of Pr3 + and Dy3 + (300-2,000 ppm); and Ag + 1, 000-2,000 ppmw.

3. The article according to claim 1, wherein: CdF2 21-31; ZnF2 3-7; Er3 + 0; at least one of Pr3 + and Dy3 + on the scale (300-2,000 ppm); and Ag + 1, 000-2,000 ppm.

4. - The article according to claim 1 wherein: PbF2 19-23; ZnF2 0; Er3 + 500-5,000 ppm; Pr3 + 0; and Dy3 + 0.

5. The article according to claim 1, wherein: CdF2 21-31; ZnF2 3-7; Er3 + 500-5,000 ppm; Pr3 + 0; and Dy3 + 0.

6. The article according to claim 1, having a first and a second end, further characterized in that the coating covers the surface of the core but leaves the first and second ends exposed.

7. The article according to claim 2, wherein the Ag + is on the scale (700-1,000 ppm).

8. The article according to claim 3, wherein the Ag + is on the scale (700-1,000 ppm).

9. The article according to claim 1, wherein the core contains up to 17% total cation of at least one component selected from the group consisting of: (0-7%) BO1.5, (0-12 %) GeO2, (0-7%) PO2.5, (0-3%) TiO2, (0-2%) Nb2O5, (0-7%) GaF3, (0-7%) HfF4, (0-7%) lnF3, (0- 15%) BF3, (0-1%) LaF3, (0-3%) CdCI2, and (0-5%) CdS.

10. The article according to claim 1, wherein the Ag + is provided by at least one silver fluoride (AgF), silver oxide (Ag2O) and silver nitrate (AsNO3).

11. The article according to claim 1, further characterized in that said article is an optical waveguide fiber.

12. - The article according to claim 1 1, further characterized in that said optical waveguide is a single mode fiber.

13. An optical article having a composition that is balanced in its ionic charge, comprising: a second phase of substantially cubic lattice crystal comprising at least one divalent cadmium fluoride and divalent lead fluoride; a divalent rare earth ion incorporated in said crystal; and at least one of a monovalent silver and monovalent thallium form for the charge balance of said crystal.

14. The article according to claim 13, wherein said trivalent rare earth ion is at least one of Pr3 +, Dy3 +, and Er3X

15. A method of manufacturing a fiber optic waveguide comprising the steps of: loading an inner crucible comprising a supply section, of a double crucible furnace, with a finished core glass composition in a fluid state, said core glass composition having a liquid temperature; providing a coating glass having a liquid temperature in an external crucible of the double crucible furnace in which the coating glass has sufficient rigidity to contain said fluid core; maintaining a portion of said core glass and said coating glass at a temperature above its respective liquid temperature in said double crucible furnace so that no portion of said core or coating guide is contacted with a surface of platinum of said double crucible below said core or liquid coating temperatures, respectively; maintaining said fluid core in a region of Rayleigh instability thereof at an outlet of said supply section to provide a flow by dripping said core from said supply section; extracting a fiber comprising said coating containing said core from an outlet of said furnace; cooling said fiber to a temperature below its liquid temperature.

16. The method according to claim 15, further comprising the ceramization of said fiber after it has cooled below its liquid temperature.

17. A method of manufacturing a fiber optic waveguide comprising a core and a coating, comprising the steps of: a) forming an elongated glass body having first and second ends, comprising a center member which consists of a transparent glass consisting essentially, in terms of percent cation of: S¡O2 20-40; AIO1.5 10-20; CdF2 19-34; PbF2 19-23; wherein up to 5 mole% of CdS or 3 mole% of CdCI2 can be replaced by an equivalent amount of CdF2, or an equivalent amount of an oxide can be replaced by fluoride; at least one of the rare earth fluorides YF3 (3-7), GdF3 (3-7), and LuF3 (4-15) where the total amount of said rare earth fluorides is (3-15); at least one of Pr3 + and Dy3 + at a concentration on the scale of about 300 to 2,000 ppm; Ag + at a concentration on the scale of around 500 to 2,000 ppm; and a transparent glass covering the surface of said elongated central member but leaving the first and second ends exposed, consisting essentially of a weight of an oxide base, of: SiO2 25-35; AI2O3 3-5; CdF2 12-16; PbF2 40-50; ZnF2 4-8; and Bi2O3 0-10; and b) heating the elongated glass body to a pre-selected temperature for a preselected time, to transform said center glass member into a transparent, optically clear glass-ceramic containing essentially only one crystal phase.

18. The method according to claim 17, further characterized in that the forming step is carried out using a double crucible technique, wherein in addition said center member glass and said transparent coating glass are heated each to a temperature on the scale of about 1, 000-1, 200 ° C during the formation and the glass formed, having a peak crystallization temperature, is crushed at a temperature below the peak crystallization temperature at a time less than 1 minute.

19. The method according to claim 17, further characterized in that the heating step is carried out using a preselected temperature close to the peak crystallization temperature of said center member glass and the preselected time is on the scale about 1 / 2-24 hours.