| Characterized by good beam quality,compactness,robustness,and heat dissipation,fiber lasers are widely applied in high-resolution spectroscopy,gravitational wave detection,nonlinear optics,and space communication.Rare-earth doped glass fiber is the core gain medium of fiber lasers.Traditional silica fibers have low rare earth（RE）solubility(1019ions/cm3)and gain coefficients.The working length of silica fiber laser reaches the meter level,which limits the device integration and performance improvement.Therefore,it is of great importance to explore new high-gain fibers.Fluoro-sulfo-phosphate（FSP）glass combines the excellent spectral properties of phosphate and fluoride glasses,and the enhancement of stability and glass-forming ability through sulfate addition,showing high potential as the gain medium of new fiber lasers.However,there are few reports on FSP glasses or fibers,and the insufficient basic data of physical,chemical,and spectral characteristics hinders the modification research and device applications.This work presents a systematic study of the glass forming region（GFR）,composition-structure-property relationship,fiber design,and device applications of FSP systems.This thesis is divided into five chapters.Chapter 1 reviews the research progress of phosphate-based（including phosphate,fluoro-phosphate（FP）and FSP）laser glasses and optical fibers,and presents the research objectives and contents.Chapter 2 uses the thermodynamic method to predict the GFR of FSP glasses and verify it.The composition-structure-property relationships and mechanism of modification in FSP glasses are discussed in Chapters 3 and 4.Chapter 5 focuses on the design and preparation of single-mode fibers and the construction of fiber lasers.The main results are as follows:（1）The GFR of various FSP systems was predicted through the thermodynamic methods,and the actual GFR was determined based on a small number of experiments with reference to the calculated GFR.The error of the calculated eutectic point composition is less than 9.3mol%,and the overlap area between the calculated and actual GFR is large.The results prove that the thermodynamic method is fast,effective,and accurate.The glass forming rule of FSP glasses with different compositions and melting conditions were studied in comparison,which laid the foundation for the subsequent compositional optimization.（2）The structural,mechanical,thermal,optical and spectral properties of aluminum metaphosphate-based Al-RFSP（R=Li,Na,K,composition:RF-R2SO4-Al（PO3）3）glasses were investigated.A mixed-ionic structure model was proposed based on Raman,X-ray photoelectron spectroscopy,nuclear magnetic resonance results and valence unit theory.The properties of FSP glasses depend on the mixed-ionic parameters including covalent and ionic interactions,such as packing density,average cross-linking,anion polarizability,etc.Al-RFSP glasses are characterized by a low non-linear refractive index of 1.2×10-13 esu,high anti-crystallization abilityΔT of 181°C and elastic modulus of 68.8 GPa.The mixed-ionic structure of FSP glass provides various ligands with electron density fluctuation,facilitating the enhancement of emission parameters.The emission cross-section,effective linewidth,lifetime,optical quality factor and gain bandwidth of Nd3+（1.5 wt.%）in Al-RFSP are 3.3×10-20 cm2,32.1 nm,372μs,1.2×10-23 s·cm2 and 105.9×10-27 cm3,respectively.The emission cross-section,optical quality factor and gain bandwidth of Er3+（1.5 wt.%）in Al-RFSP are1.1×10-20 cm2,5.8×10-23 s·cm2 and 73.8×10-27 cm3,respectively.The CDA for Yb3+:2F5/2→Er3+:4I11/2 in Al-RFSP is 51.87×10-39 cm6/s,which indicates effective energy transfer in the co-doping system.（3）The structure,physical and spectral properties of aluminum metaphosphate-based Al-Ba FSP（composition:Ba F2-Ba SO4-Al（PO3）3）glasses were investigated.The complex mixed anion structure of the FSP glass is conducive to their physicochemical stability and luminescent properties.Al-Ba FSP glasses have good anti-crystallization ability（ΔT>100°C）,high doping concentration(up to 6 mol%Nd3+),large emission cross section(2 mol%Nd3+:2.56×10-20 cm2),and high quantum efficiency（91.17%）.The effects of different melting conditions on the structure and properties of FSP glasses were also investigated in detail,which laid foundation for the optimization of FSP glass and fiber fabrication procedure.（4）Based on Al-Ba FSP glass,Er3+/Yb3+co-doped FSP fiber compositions were designed with high elastic modulus（>80 GPa）,anti-crystallization ability（>200°C）,chemical durability(DR<0.2×10-7 g cm-2 min-1),doping concentration(8 mol%RE3+),FOM(5.8×10-23s·cm2)and gain bandwidth(46.6×10-27 cm3).The 1.5μm single-mode fiber with a peak gain coefficient of 5.3 d B/cm@1540 nm was designed and fabricated.The mixed-ionic structure in the FSP glass results in spectral broadening.The full-width-at-half-maximum（FWHM）of the gain coefficient spectrum is 31 nm and the gain coefficient of 1600 nm is 2.4 d B/cm.1617 nm laser output could be achieved based on 1 cm-length FSP fiber.An all-fiber integrated mode-locked laser based on a 2 cm fiber was prepared with a fundamental repetition frequency of4.3 GHz at 1567 nm.The signal-to-noise ratio（SNR）is larger than 80 d B and the integrated RIN is 0.04%,showing high stability.This study demonstrates the great potential of FSP fibers for high-performance fiber lasers in the C+L band. |
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