Rare earth doped oxyhalide laser glass

Abstract: The oxyhalide rare earth doped laser glass of the present invention comprises the substitution of fluorine for oxygen in glasses having the general molar batch composition of 50% SiO 2 , 25% CaO, 25% Al 2 O 3 to improve the distribution of rare earth dopants in the glass. The general molar batch composition of the invention ranges from approximately 45-70% SiO 2 , 15-35% CaO , 10-25% Al 2 O 3 , 4-15% Al 2 F 6 , and .001-2% Er 2 O 3 . This substitution of fluorine into the 2SiO 2 ·Al 2 O 3 ·CaO glass system provides erbium doped laser glasses having a Er 2 O 3 batch content of .01 mole% Er 2 O 3 to 1.2 mole% Er 2 O 3 (500 ppm Er 2 O 3 to 5.68 wt.% Er 2 O 3 ) which show little to no concentration quenching and exhibit useful fluorescence lifetimes of approximately 6 milliseconds (ms) or greater.

Description: FIELD OF THE INVENTION This invention relates to oxyhalide laser glasses doped with rare earth elements. BACKGROUND OF THE INVENTION It is known in the prior art that laser glasses may be produced by doping silica glass with rare earth elements. The laser property of such rare earth doped laser glasses is derived from the light amplification achieved by stimulated emission of the excited rare earth element ions doped in the glass and is dependent on the fluorescence lifetime of the doped ions. It is further known that the laser output of a laser glass is dependent on the number of rare earth ions present in the glass. The problem in the prior art has been that a maximum usable concentration of rare earth ions in a laser glass is quickly reached due to the phenomenon of concentration quenching. Concentration quenching is due to the non-radiative decay of excited rare earth ions which are too close to their neighboring unexcited rare earth ions. Excited rare earth ions will transfer energy to closely neighboring non-excited rare earth ions through dipole-dipole coupling, resulting in no net output of light. As the concentration of rare earth ions in a laser glass is increased, the rare earth ions tend to cluster close together with neighboring rare earth ions, consequently an increase in actual excitable rare earth ions responsible for the laser output is not achieved, and the fluorescence lifetime of the rare earth ions is reduced. The problem faced by the prior art has been to provide a glass composition which may be doped to a relatively high rare earth ion concentration without ion clustering reducing the fluorescence lifetime of the rare earth ions. Presently erbium is a popular rare earth element used in doping laser glasses, since erbium doped laser glasses can effectively amplify the 1.55 µm wavelength of light used in optical telecommunication systems. Neodymium is also used as a rare earth dopant in laser glasses. Accordingly, it is the object of the present invention to provide a laser glass that overcomes the problems of the prior art. Rare earth doped fluorophosphate and fluoride glasses are described in Glastechnische Berichte, vol. 66, no.g. 1993, pages 235-244; Journal of Non-Crystalline Solids, vol.143, no.1, 1992, pages 40-45 ; Materials Letters, vol. 13, no.6, pages 299-355 and Physics and Chemistry of Glasses, vol.37, no 1, 1 Febr.1996, pages 41-43. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a glass composition having a relatively high concentration of excitable erbium ions resistant to clustering which can be advantageously used in laser applications such as planar optical amplifiers and other compact laser products which require a high concentration of excitable ions over a short path length. Briefly, the present invention relates to an oxyhalide glass composition which allows for an increased rare earth dopant concentration without the detrimental effects of concentration quenching. More particularly, the present invention provides an oxyhalide laser glass doped with a plurality of rare earth ions, said glass having a fluorescence lifetime of at least approximately 6 msec, wherein said glass is an alumina silicate oxyfluoride glass which has a fluorine concentration sufficient to inhibit concentration quenching of said rare earth ions. According to one aspect, the invention relates to an oxyhalide laser glass composition which advantageously disperses erbium ions to prevent dipole-dipole coupling and provide long fluorescence lifetimes. The present invention allows an oxyhalide glass with an increased erbium ion concentration to be produced without the detrimental effects of concentration quenching. The oxyhalide glass composition provides a glass chemistry structure which advantageously disperses erbium ions away from neighbouring erbium ions so as to prevent the dipole-dipole coupling of concentration quenching which occurs when erbium ions are located too close together. The composition maximizes total erbium concentration in the glass while also maximizing the distance between neighbouring erbium ions. The composition allows for relatively high erbium concentrations while providing useful fluorescence lifetimes. The oxyfluoride laser glass according to the invention involves the substitution of fluorine for oxygen in alumina silicate glasses. According to a preferred embodiment, the distribution of erbium dopant in the glass is improved by replacing a percentage of the Al 2 O 3 in the general molar batch composition of 2SiO 2 ·Al 2 O 3 ·CaO with Al 2 F 6 . The general molar batch composition used to make the glasses of the invention ranges from approximately 45-70% SiO 2 , 15-35% CaO, 10-25% Al 2 O 3 , 4-15% Al 2 F 6 , and 0.001-2% Er 2 O 3 . The batch compositions are melted and formed under conditions to provide an oxyfluoride glass having at least 6 wt % F. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plot of fluorescence lifetime versus Erbium ion concentration. FIG. 2 is a plot of fluorescence lifetime versus the analyzed Fluorine weight percent of glasses doped with 0.01 mole percent of Er 2 O 3 . FIG. 3 is a compositional weight percent diagram of the invention. DESCRIPTION OF THE INVENTION According to one embodiment, the oxyhalide glass comprises the substitution of fluorine for oxygen in glasses being made from the general molar batch composition of 50% SiO 2 , 25% CaO, 25% Al 2 O 3 with approximately 11 mole % of the Al 2 O 3 batched as Al 2 F 6 to improve the distribution of erbium doped in the glass. The general molar batch composition for making glasses of the invention ranges from approximately 45-70% SiO 2 , 15-35% CaO, 10-25% Al 2 O 3 4-15% Al 2 F 6 , and 0.001-2% Er 2 O 3 . With this substitution of fluorine into the 2SiO 2 ·Al 2 O 3 ·CaO glass system, erbium doped laser glasses have been produced having a Er 2 O 3 batch content of 0.01 mole % Er 2 O 3 to 1.2 mole % Er 2 O 3 (500 ppm Er 2 O 3 to 5.68 wt % Er 2 O 3 ) which show little to no concentration quenching and exhibit useful fluorescence lifetimes of approximately 6 milliseconds (ms) or greater. The batch compositions used to make the glasses of the invention and comparison samples were melted in covered platinum crucibles for approximately 6 hours at approximately 1600°C and then poured onto steel plates to form glass bricks measuring 10.2 x 10.2 x 1,3 cms (4" x 4" x ½"), which were subsequently annealed at 550°C. Glass testing samples were taken from these glass bricks by scoring and breaking, and then the fluorescence lifetime of the samples were measured in milliseconds (ms) to determine the laser properties of the glass. Fluorine batch composition ranges of 5 to 11 mole% of Al 2 F 6 (7-15 wt.% F) are particularly preferred for such glass forming conditions. Fluorine retention rates for the melts of the invention vary from 50 to 80% depending on the initial fluorine concentration and melting temperature. For example, if 30 wt.% F is batched, about 15 wt.% F is actually analyzed in the glass after melting. If 10 wt.% F is batched, about 7 wt.% F is analyzed in the glass after melting. The percentage of F retained in the glass increases with a decreased melt temperature. The general weight percentage batch compositions for making glasses of the invention are: 30-45 wt.% SiO 2 , 25-45 wt.% Al 2 O 3 , 10-25 wt.% CaO , 0.005-10 wt.% Er 2 O 3 , and 7-35 wt.% F (batched as Al 2 F 6 ) with an analyzed fluorine weight percent after melting of 6.2-20 wt.% F. The preferred weight percentage batch compositions for making glasses of the invention are: 37-40 wt.% SiO 2 , 30-40 wt.% Al 2 O 3 , 15-19 wt.% CaO , 0.005-6 wt.% Er 2 O 3 , and 9-30 wt.% F (batched as Al 2 F 6 ) with an analyzed fluorine weight percent after melting of 6.5-15 wt.% F. Table 1 discloses batched weight % compositions for making glasses of the invention as embodied in samples 1-10. Table 1 also discloses the analyzed weight % of fluorine (F) present in the glass after melting and formation of samples 2, 4, 5, 6, 7, 8, 9 and 10. Table 1 includes the batched weight % compositions of non-fluorine comparison samples 11, 12, 13, 14, 15, 16, 17, and 19 which were manufactured and compared to the fluorine containing glasses of the invention. The fluorescence lifetimes of samples 1-19 were measured by exciting the samples with an Argon ion laser beam (514 nm). Fluorescent radiation from the samples was detected with a Ge photodiode and fluorescent lifetimes were computed therefrom. FIG. 1 presents the fluorescence lifetimes of the erbium ions of samples 1-19 in milliseconds (ms) versus the erbium dopant density of samples 1-19 in erbium ions per cm 3 . FIG. 1 clearly shows the superior fluorescence lifetime performance of the invention as compared to the non-fluorine containing samples outlined by the curve from sample 11 to sample 19. As shown in FIG. 1, as the erbium weight % is increased from 0.0055 wt.% Er 2 O 3 in sample 11 to 4.21 wt.% Er 2 O 3 in sample 19 (less than 10 18 to greater than 10 20 Er ions/cm 3 ), the fluorescence lifetime declines exponentially from 7.5 ms to 3 ms. Over this same range of erbium concentration, the fluorine containing samples of the invention have markedly improved lifetimes. The inventive composition allows for erbium dopant densities greater than 10 20 ions/cm 3 while maintaining useful fluorescence lifetimes of 6 ms and greater. With the inventive composition, as the erbium concentration is increased from sample 1 (0.005 wt.% Er 2 O 3 batched) to sample 6 (0.995 wt.% Er 2 O 3 batched), the fluorescence lifetime continues to climb. As the erbium dopant increases beyond 10 20 ion/cm 3 , the fluorescence lifetime levels off in the 8 to 9 msec range and then declines to 6 msec with sample 10. The 6 msec lifetime of sample 10 is a utilizable level, especially considering the high erbium concentration. A comparison of sample 18 (4.05 wt.% Er 2 O 3 batched, 6.7 wt.% F batched, and 4.9 wt.% F analyzed) with samples 8, 9, and 10 discloses that the 4.9 wt.% F analyzed in sample 18 is not sufficient to inhibit concentration quenching at such high erbium densities. Table 2 and the plot of FIG. 2 show the relationship of fluorine content analyzed in the glass after formation to the increased fluorescence lifetimes of the invention and the invention's ability to inhibit concentration quenching. Table 2 presents the weight % batch compositions of samples 20-24 along with samples 15 and 5 from Table 1, all of which have a 0.01 mole% Er 2 O 3 batch composition. FIG. 2 clearly shows the relationship of the fluorine content of the glass to their fluorescence lifetime. Weight % Compositions Having 0.01 Mole % Er 2 O 3 15 20 21 22 5 23 24 SiO 2 43.1 42.0 41.4 39.7 39.4 36.8 35.6 Al 2 O 3 36.6 35.7 35.1 39.1 33.5 31.3 30.2 CaO 20.1 19.6 19.3 15.6 18.4 17.2 16.6 Er 2 O 3 0.0549 0.0535 0.0527 0.0506 0.0502 0.0469 0.0453 F (Batch) 0 4.26 6.98 9.38 14.6 24.9 30 F (Anal.) 3.61 6.17 7.04 10.2 12.8 14.2 As the analyzed wt.% F of the 0.01 mole% Er 2 O 3 batch compositions are raised from sample 15 which has no F to sample 21 with 6.17 wt.% F the fluorescence lifetime remains stable and in the 6.8-7 ms range. Then with an increase of approximately 1 wt.% F, the fluorescence lifetime of sample 22 jumps up to 8 ms. Increased lifetimes are further achieved with the increased wt.% F of samples 5, 23, and 24. This threshold wt.% F between 6 and 7% correlates with the fluorine content threshold between sample 18's 4.9 wt.% F and sample 8's 6.7 wt.% F. The inventive composition inhibits concentration quenching of the erbium ions by providing a glass chemistry structure wherein the erbium ions are advantageously distributed apart from one another. The fluorine content of the inventive composition allows for an increased concentration of erbium ion while providing useful fluorescence lifetimes. As illustrated in the Compositional Weight Percent Diagram of FIG. 3, the general oxide glass composition area 101 of the invention correlates with the general stoichiometry of the anorthite (CaO·Al 2 O 3 ·2SiO 2 ) and gehlenite (2CaO·Al 2 O 3 ·SiO 2 ) crystalline phases, with the addition of erbium and fluorine to provide laser characteristics having adequate fluorescent lifetimes. The inventor has produced erbium doped oxyfluoride alumina silicate glasses by the substitution of CaO in the batch compositions with ZnO, alkaline and alkaline earth oxides such as MgO, BaO and Na 2 O. Such glass compositions incorporating the benefits of the invention's fluorine content to suppress concentration quenching of the rare earth ions should exhibit similar laser properties. The inventive glass compositions further include those made by the substitution of Al 2 O 3 in the batch compositions with Ga 2 O 3 . Al 2 O 3 can be totally substituted in the batch composition with gallium. The glass batch composition used can include from 0-25 mole percent Ga 2 O 3 . The inventive glass compositions further include those made by the substitution of SiO 2 in the batch compositions with GeO 2 . SiO 2 can be totally substituted in the batch composition with germanium. The glass batch composition used can include from 0-50 mole percent GeO 2 . The inventive glass composition further includes those made by the substitution of Al 2 O 3 in the batch composition with B 2 O 3 . Aluminum can be substituted in the batch composition with boron. The glass batch composition used can include from 0-15 mole percent B 2 O 3 .

Claims: An oxyhalide laser glass doped with a plurality of rare earth ions, said glass having a fluorescence lifetime of at least approximately 6 msec, wherein said glass is an alumina silicate oxyfluoride glass which has a fluorine concentration sufficient to inhibit concentration quenching of said rare earth ions. A laser glass as claimed in claim 1, which contains at least 6.2 wt % F. A laser glass as claimed in claim 1 or 2 wherein said rare earth ions are erbium. A laser glass as claimed in claim 3, wherein said laser glass amplifies the 1.55 µm wavelength of light of an optical telecommunication system. A laser glass as claimed in claim 3 or 4, wherein said erbium ions are contained in a concentration of at least 1x10 17 ions/cm 3 , said glass having an analyzed fluorine wt % content of at least 6.2 wt % fluorine, and wherein said glass exhibits a fluorescence lifetime of at least 7.6 ms. A laser glass as claimed in claim 5, wherein said erbium ion concentration is at least 1x10 20 ions/cm 3 . A laser glass as claimed in any of claims 3 to 6, said laser glass being made from a batch composition comprised of: at least 13 wt % F, and at least 2 wt % Er 2 O 3 . A laser glass as claimed in claim 7, wherein said laser glass has a stoichiometry of the anorthite crystalline phase. A laser glass as claimed in claim 7, wherein said laser glass has a stoichiometry of the gehlenite crystalline phase. A rare earth doped laser glass as claimed in any of claims 1 to 9, said laser glass being made from a molar batch composition comprised of: 45-70 mole % SiO 2 15-35 mole % X; 15-35 mole % Y; wherein X is a metal oxide selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, and ZnO; and Y is an aluminum compound selected from the group consisting of aluminum oxide and aluminum fluoride, wherein at least 10 mole % of Y is aluminum fluoride. A laser glass as claimed in claim 10 wherein X is CaO. A laser glass as claimed in claim 10 or 11 wherein said aluminum fluoride is Al 2 F 6 . A laser glass as claimed in any of claims 1 to 9, being made from a weight % batch composition comprising: 30-45 wt % SiO 2 ; 25-45 wt % Al 2 O 3 ; 10-25 wt % CaO; 0.005-10 wt % Er 2 O 3 ; and 7-35 wt % F, wherein said glass has an analyzed content of at least 6.2 wt % F. A laser glass as claimed in any of claims 1 to 9 being made from a weight % batch composition consisting essentially of: 37-40 wt % SiO 2 ; 30-40 wt % Al 2 O 3 ; 0.005-6 wt % Er 2 O 3 ; and 9-30 wt % F, wherein said glass has an analyzed content of at least 6.5 wt % F. A laser glass as claimed in claim 13 or 14, wherein F is batched as Al 2 F 6 . Use of the laser glass of any one of the preceding claims in an optical amplifier.

Inventors: DICKINSON JAMES EDWARD JR, DICKINSON, JAMES EDWARD, JR.
Applicants: CORNING INC, CORNING INCORPORATED
Application year: 1997
Main classification: C03C3
IPC codes: H01S3, C03C3, C03C4