Bismuth-doped fiber amplifier for full S-band amplification

We report the first single-stage/single-pass bismuth-doped fiber amplifier (BDFA) achieving > 10 dB gain across the full S-band (1465-1530 nm), a critical step toward extending capacity in multi-band optical transmission systems. The proposed amplifier employs a 400 m-long germanosilicate fiber, bi-directionally pumped at 1425 nm, delivering 11.3-35.6 dB small-signal gain and a noise figure of 5.6-7.7 dB. Compared to thulium- and Raman-based S-band solutions, our BDFA offers a compact, efficient, and silica-compatible platform with improved performance in the lower S-band, where other technologies struggle. This demonstration paves the way for practical S-band amplification in future high-capacity, power-efficient optical networks without reliance on fluoride fibers or kilometer-scale nonlinear media.