Drawing-induced improvement of amplification in bismuth-doped phosphosilicate fibers

This study investigates drawing-induced effects on bismuth active centers (BACs) and optical amplification in Bi-doped phosphosilicate fibers operating in E and S bands. A twofold increase in BAC-related active absorption was observed, while the unsaturable loss remained nearly constant over a 100 °C drawing temperature. Unitary gain (dB/m) was found to increase linearly with drawing temperature, reaching ∼0.4 dB/m under bi-directional pumping when using 390 mW. With this pumping configuration, the amplifier's unsaturated peak gain was close to 35 dB using an optimum fiber length less than 100 m, demonstrating efficient amplification with high Bi concentration in those fibers.