Investigation on the spectral characteristics of bismuth doped silica fibers

We investigated the fluorescence characteristics of the bismuth doped silica fibers with and without Al co-dopant which are fabricated by means of modified chemical vapour deposition (MCVD) technique. It was found that the bismuth and germanium codoped silica fiber exhibited a strong broad infrared emission centring at 1450 nm and covering 1300 nm when excited by the laser diodes working at 808 nm and 976 nm respectively. It was also found that for the Al and bismuth codoped silica fiber, the red (centring around 750 nm) and the infrared fluorescence (centring around 1100 nm) may originate from different emission centers in the fiber. Furthermore, strong up-conversion luminescence was also observed in both Al codoped and non-Al codoped bismuth doped fibers when the fibers were excited by an acoustic-optic Q-switched Nd:YVO4 laser. It is thus concluded that the upper energy level absorption reported in the work of the bismuth doped silica fiber lasers may result from the fluorescence emission sites not responsible for the infrared emission.