Spectroscopic properties of bismuth/erbium co-doped fiber at room temperature and liquid nitrogen temperature

Since the first demonstration of broadband luminescence in bismuth doped material, the thermal effect has been found to play a significant role in modifying optical properties of bismuth active centers (BACs) not only in fabrication process but also when implementing post-treatment. Here, a comprehensive study on spectroscopic properties of bismuth/erbium co-doped fiber (BEDF) at room temperature (RT, 300 K) and liquid nitrogen temperature (LNT, 77 K) has been conducted regarding its ultra-broadband luminescence. The absorption bands of Er3+ blue shift due to the change of the thermal population distribution, but the absorption bands of BACs have less noticeable change. In addition, at LNT the emission of Er3+ at 1535 nm excited at 830 nm is significantly decreased due to the reduction of the absorption at 830 nm. Moreover, the emission intensities from BACs increase at LNT attributed to the re-distribution of pump power from Er3+ to BACs. Meanwhile, the emission at 1200 nm is broadened and the whole emission band of BACs redshifts due to the emission recombination of the different BACs. The on/off gain spectrum of BACs has less variation at LNT though the gain of Er3+ nearly disappears, which is consistent with the reduction of Er3+ emission.