We propose a stable multi-longitudinal Brillouin/semiconductor fiber laser （BSFL） as the upstream source in a bidirectional single-fiber wavelength-division multiplexing-passive optical network （WDM-PON）. The downstream wavelength serves as the pump of the BSFL. Brillouin-frequency-shifted （-10.8 GHz） upstream carrier is generated to suppress the Rayleigh backscattering and back reflection-induced crosstalk. The stable multi-longitudinal operation of the BSFL, attributed to the four-wave mixing （FWM） effect in the semiconductor optical amplifier （SOA） reduces the difficulty of generating a stable single-longitudinal fiber laser-based upstream carrier. Bidirectional symmetric transmission at 10 Gb/s over a 12.5-km single mode fiber with less than 2-dB power penalty is demonstrated.
