Optical Basicity Bismuth-doped Germanate Glass Ultra-broadband Light-emitting

From the end of the 1980s, rare-earth doped fiber amplifiers (RDFA) have greatly promoted the development of optical communication, and RDFA have been extensively utilized in the long-distance optical communication. However, the gain bandwidth of RDFA cannot surpass 100 nm due to the nature of the inner shell transition of rare-earth ions, which limits the transmission capacity of optical fiber communications. Considerable efforts have been devoted to achieve wider bandwidth of optical fiber amplifiers, even all the developed optical fiber amplifiers are combined in parallel or in series, the low loss communication window of silicate glass fiber have not been utilized fully. Therefore, it will be a great breakthrough to develop a novel optical amplifier that can realize optical amplification covering the whole low loss communication window (1200 nm-1650 nm). In 2001, Fujimoto et al discovered broadband infrared luminescence from bismuth-doped glasses, since then bismuth-doped glasses have attracted much attention. Bismuth-doped glasses exist the characteristics of wider bandwidth and longer lifetime than RDFA, therefore, once bismuth-doped glasses are used as matrix materials for optical amplifier, the low loss communication window could be covered by a single fiber. However, at present, the mechanism of infrared luminescence is still unclear, and bismuth-doped glasses have some disadvantages, therefore, the effect of glass matrix on broadband luminescence of bismuth-doped glass should be investigated, as well as the mechanism of infrared luminescence. It is expected that the research results above will be useful to choose better glass matrix for broadband luminescence, overcome disadvantages of bismuth-doped glasses, so as to achieve more excellent broadband luminescence.In this paper, bismuth-doped germanate glasses were prepared as research object, and the effect of optical basicity on the broadband luminescence were investigated. In different alkali metal or alkali-earth metal oxides doped germanate glasses systems, broadband luminescence and long lifetime have been realized. Also, the mechanism for the infrared luminescence of bismuth ions was discussed. The research results will be a great help for the further study in the field. In Chapter 1, the purpose of the research on bismuth-doped glass was introduced at the first beginning, and then the history of optical fiber communication, basic structures and characteristics of kinds of optical fiber amplifiers were reviewed, as well as rare-earth doped optical fiber amplifiers. Subsequently, luminescent characteristics and limitation of transition metal ions doped glasses were introduced. Finally, research progress of bismuth-doped glasses in now days were presented.In Chapter 2, experimental method and related theories were simply introduced. The experimental method consisted of specification of materials, sample preparation and spectra measurement. The theories consisted of calculation method for absorption cross section, stimulated cross section as well as basicity theory.In Chapter 3, effects of optical basicity on broadband luminescence property of bismuth-doped glasses were investigated. It was reported that infrared luminescence of bismuth-doped glasses varied with optical basicity of glass matrix changing. The research studied the effects of optical basicity on the structure of glass matix, then the mechanism of infrared luminescence was discussed. In the experiment, bismuth-doped alkali metal or alkali-earth metal germanate glasses with different optical basicity were prepared, subsequently, relative spectra were measured and analyzed, and thereby the rules of optical basicity on broadband luminescence were obtained. Under 808 nm excitation, super broadband infrared luminescence centered at about 1.3μm covering the whole low loss communication window were observed with a full width at half maximum (FWHM) larger than 200 nm and lifetime longer than 400μs in the bismuth-doped germanate glasses. With optical basicity increasing in glass, the intensity of absorption and infrared fluorescence spectra decreased, which indicated that they might originate from the same valence state of bismuth doped ions; The infrared luminescence center shifted to longer wavelength, so did the visible luminescence, which implied the ligand field intensity changed in the glasses; The intensity of infrared luminescence decreased while the one of visible luminescence increased, the results indicated that two kinds of luminescence might originate from different mechanism. Although the valence state of bismuth ions resulting in infrared luminescence was still under discussion, it was suggested that the infrared luminescence might originate from bismuth ions with low valence state, according the experiment, the fluorescence might be ascribed to the Bi+ ions transitions between the ground state of 3P0 and the excited stated of 3P1. Besides, the stimulated cross section of bismuth-doped germanate glasses was calculated, and theστvalue was four times as big as Ti:Al2O3 laser. The results indicated that bismuth-doped germanate glasses showed great potential application in optical fiber amplifiers and tunable lasers.In Chapter 4, main research results were summarized.In the last chapter, the existed problems and further research direction were pointed out.