A graded-index confined bismuth-doped fiber for cladding-pumped E+S-band high-power amplifiers

Amultimode double-clad graded-index fiber with the confined Bi -doped $\mathrm{GeO}_{2}-\mathrm{SiO}_{2}$ glass core was fabricated by all-gas-phase MCVD technology. The bismuth-doped fiber as an active medium exhibited good performance characteristics in the developed E+S-band power amplifier, which provided a maximum output power of about 1 W at an input signal of 150 mW under pumping by multimode laser diodes at 808 nm.