Rare-earth Doped Tellurite Glasses And Tellurite Glass Fibers

With the rapid development of computer networks and other data-transmitting services, the demand for the increase of capacity of communication system is urgent. The conventional silica based Er³⁺-doped fiber amplifier (EDFA) can not meet this requirement because of its low rare earth ion solubility and intrinsic bandwidth limit (～30 nm). Therefore, wide bandwidth novel optical amplifier covering C-band, L-band and S-band for wavelength division multiplexing (WDM) system has been attracted a great deal of attention. The dissertation reports on research works in the subject of the Er³⁺-doped multi-component tellurtie glass active fiber for 1.53μm broadband optical amplifiers. The fundamental investigations on the properties and fluorescence characteristics of glass materials and fiber, the glass fiber fabrication technology and the pertinent theory of energy transfer have been carried out.Compared with conventional Er³⁺-doped silica glasses, Er³⁺-doped tellurite glasses combining the attribute of low melting temperature, wide bandwidth (⁷0 nm), wide transmission region (0.35-6μm), good glass stability, rare earth ion solubility, slow corrosion rate, lowest phonon energy spectrum among oxide glass formers, and high refractive index, are now promising candidates for use in fabricating novel optical amplifiers for WDM system. However, there are two important factors to be considered in developing efficient amplifiers using tellurite glasses. Firstly, the relatively poor thermal stability and low strength lead to crystallization processes at the moment of optical fiber drawing, as well as make the material easy damageable at high optical intensities. Secondly, due to their low phonon energy (～750 cm?1), under 980nm pump, up-conversion and excited state absorption (ESA) become two dominant loss mechanisms,significantly depleting the spectral gain of Er³⁺ ions.Herein, based on the requirement of the development of optical communication, the optimization on thermal stability and luminescence properties of the rare-earth-doped multi-component tellurite glasses have been the goal of this dissertation. The Raman spectra results indicate that the local ligand environment of Er³⁺ in glasses changed by different modifiers and mixed formers. The variations of maximum phonon energies in different glasses with vibrations of different kinds of structural group were discussed. And the influence of the structural characteristics on thermal stability and inhomogeneous broaden of Er³⁺emission spectrum were also pointed out. Moreover, the spectral properties of Er³⁺ ions in tellurite glasses have been improved by introducing donor ion and energy acceptor ions. And the possible energy transfer mechanisms involved have also been systemically analyzed and discussed. The cladding glasses and the core glasses were then selected considering their well match in refractive index, thermal properties and rheological properties. Finally, the rare- earth-doped optical fiber were fabricated and characterized optically with a single pass backward (SPB) configuration.The novel and main results of the research works are as follows:(1) The Raman spectra, XRD and DCS results indicate that the introducing network formers (Nb2O5,WO3 and GeO2) behaved better than other modifiers in improving the thermal stability of tellurite glasses. With appropriate phonon energy (900 cm-1), they are also helpful for lowering the up-conversion luminescence of Er³⁺-doped tellurite glass, via speeding up the nonradiative relaxation of Er³⁺:4I11/2→4I13/2 transition without influencing the 1.53μm emission.(2) The effect of energy acceptor RE³⁺ (RE³⁺ =Ce³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺ and Tm³⁺) ions on the fluorescence characteristics of tellurite glasses co-doped with Er³⁺/Yb³⁺ is reported. The energy transfer dominated by Dexter mechanism between Er³⁺ and RE³⁺ were explored based on their energy level diagrams, up-conversion and infrared emission properties. It is found that the incorporation of energy acceptor into Er³⁺/Yb³⁺-codoped tellurite glass could effectively reduce up-conversion emission. Moreover, co-doping Ce³⁺ could also enhanced the 1.53μm emission, which makes Er³⁺/Yb³⁺-codoped tellurite glass more attractive for using in 1.53μm optical fiber amplifiers.(3) A modified rod-in-tube technique is brought forward to prepared Er³⁺-doped and Tm³⁺-doped tellurite single-mode glass-fibers with the FWHM of 60 nm and 102 nm respectively. And broad emission spectra with bandwidth up to 128 nm (as 3 times of that in conventional Er³⁺-doped silica glasses), which coveres E-, S- and C-bands simultaneously, is obtained based on an tandem structure with Er³⁺-doped and Tm³⁺-doped tellurite glass-fibers.(4) A very broad erbium amplified spontaneous emission (60⁸0 nm) from erbium-doped single- mode tellurite glass-fiber is described in a single pass backward (SPB) configuration.The advantages of this EDTF are the short EDTF length and the small pumping power required in such an SPB configuration.The investigation results of this work provide theoretical foundation and technical support for the further research on rare-earth-doped tellurite glass fiber amplifier and laser.