Optical properties of bismuth-doped SiO2- or GeO2-based glass core optical fibers

A detailed study of optical properties of bismuth-doped fibers based on SiO2 and GeO2 glasses containing no other dopants has been carried out. To provide important information about spectroscopic properties of IR bismuth-related active centers (BAC) the excitation-emission fluorescence spectra for a spectral region of 220-2000 nm have been measured. The obtained three-dimensional spectra have been presented for different host glass compositions: silicate, germanate, aluminosilicate and phosphosilicate. Energy-level configuration and main radiative transitions associated with BACs in GeO2 and SiO2 glasses have been revealed. Fluorescence lifetime analysis of the basic radiative transitions of BAC have been carried out. It has been shown that the energy-level schemes of BAC-Si and BAC-Ge (BAC associated with silicon and germanium, respectively) are similar, corresponding BAC-Ge energy levels lying 10-16% lower than those of BAC-Si. It has been determined that BAC-Si, BAC-Ge and BAC-Si, BAC-P can exist simultaneously in bismuth-doped germanosilicate and phosphosilicate fibers, respectively. Optical amplification in the wavelength range 1410-1470 nm and lasing at 1460 nm in SiO2 glass fiber doped with bismuth have been demonstrated for the first time. The optical gain and lasing in this fiber were based on the radiative transition between the first excited and ground energy levels belonging to BAC-Si. Anti-stokes luminescence spectra of BAC-Si and BAC-Ge in optical fibers under the two-step excitation have been measured and analyzed in detail.