Study On Tm³⁺ /Ho³⁺-doped Special Germanate Glasses And Optical Fiber

Recent decades , people have been paying more and more attention to near two micron fiber lasers for their wide application in military, remote sensing and other fields, Tm³⁺ and Ho³⁺ are better rare earth ions which can generate two micron laser.For the cross-relaxation effect of Tm³⁺ and the energy transfer between Tm³⁺ and Ho³⁺ ,it is possible that we obtain the ideal quantum efficiency 200% form Tm³⁺ doped and Tm³⁺/Ho³⁺ co-doped materials,so scholars in different countries pay more attention to Tm³⁺ and Ho³⁺.Though Tm³⁺/Ho³⁺ co-doped mid-infrared fiver laser at².0μm has the attraction of continuous wave powers of several hundred watts,some properties such as the optical and optical parameters,output powers,laser threshold and so on,can still be improved.If improved,we can obtain cheap and practical laser device,then use these device in industrial and agricultural production.In this article,we explore and study glasse material which has better spectra parameters,good materialize properties and high doping capacity for Tm³⁺ and Ho³⁺,and then fabricate practical fiber material.Germanate glass has many advantages,such as lower phonon energy, materialize properties ,high doping capacity and so on.We studied germanate glass mainly in this article,the research includes:First,the effect of chemical composition on the optical and spectra properties of Tm³⁺ and Ho³⁺ in germanate glasses;Second,the study on thermal stability of glasses;Third,the solubility of Tm³⁺ and Ho³⁺ in germanate glasses;Fourth,we studied the effect of the doping concentration of rare earth ions on the mid-infrared spectra and its reasons;Fifth,we studied the fabrication of perform and the drawn of optical fiber.In chapter one,we presented the characters and the research progress and features of optical fiber and fiber lasers,then we summarized the characters of germanate glasses. The principle of absorbtion spectra,fluorescenc spectra and raman spectra were prensted,and the basic theories such as J-O theory were obtained,too.In chapter two, glasses with the compositions of GeO₂-AlF₃-Na₂O doped with different Tm³⁺ concentration were fabricated by conventional melting method, the procedure and method were introduced in details. We measured the DTA curve of glass samples. According to the Judd-Ofelt theory, the J-O strength parameters (O₂,O₄,O₆) of Tm³⁺ were calculated, by which the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. According to McCumber theory, the absorption and emission cross-sections, gain cross section spectra of Tm³⁺ were obtained. The infrared emission spectra (with 808nm LD excitation) at ¹.47μm and ¹.8μm of various concentration Tm³⁺-doped glasses were studied.The fluorescence strength at ¹.8μm reaches the maximum when the Tm₂O₃ doping concentration is 3wt%.In chapter three, glasses with the compositions of 86GeO₂-4Nb₂O₅-10Na₂O co-doped with Tm³⁺ and Ho³⁺ ions were fabricated by conventional melting method. According to the Judd-Ofelt theory, the J-O strength parameters (Ω₂,Ω₄,Ω₆) of Tm³⁺ were calculated. According to McCumber theory, the absorption and emission cross-sections, gain cross section spectra of Tm³⁺ and Ho³⁺ have been obtained.With 808nm LD excitation, the cross-relaxation process of Tm³⁺ and infrared emission spectra of Tm³⁺ sensitized Ho³⁺ ions were studied. The results indicated that the energy transfer efficiency of Tm³⁺(3F4)→Ho³⁺(5I7)ions was enhanced and the infrared fluorescence intensity at ².0μm was increased as the Ho³⁺ co-doped into glass .In chapter four, glasses with the compositions of (90-?)GeO2-?Nb₂O₅-10Na₂O(?=1,2,4,6,8 molar ratio)doped with the same Tm₂O₃ concentration (4wt%) and 86GeO₂-4Nb₂O₅-10Na₂O were fabricated respectively by conventional melting method. The effects of Nb₂O₅ on glass stability, fluorescence strength and J-O strength parameters were studied. According to the Judd-Ofelt theory, the J-O strength parameters (O₂, O₄,O₆) of Tm³⁺ in different Nb₂O₅ concentration were calculated, with which the radiative transition probabilities, branching ratios and radiative lifetime were obtained. Meanwhile, according to McCumber theory, the absorption and emission cross-sections corresponding to the ³F₄? ³H₆ transitions of Tm³⁺ at 1.8μm were obtained. The gain cross section was calculated by using the emission cross-section, absorbtion cross section and Tm³⁺ concentration.The fluorescence features (with 808 nm LD excitation) at ¹.47 and ¹.8μm of various concentrations of Tm³⁺-doped glasses were studied. The fluorescence intensity at ¹.8μm reached to the maximum when the Tm₂O₃-doping concentration was near to be³ wt.% , and then decreased as doping concentration increased further. The fluorescence intensity at ¹.8μm reached to the maximum when the Nb₂O₅ content in glass composition was near to be ² mol%. The effects of Nb₂O₅ content on the glass structure and the spectra properties were also discussed.On the basis of experiments done before,we choose germante-niobate glasses to fabricate fiber in chapter five,we designed the components of the cladding and fiber core.some important paraments were measured. We obtained good fiber samples successfully at last and some important paraments were also measured.