Bismuth-Doped Bidirectional Fiber Amplifier for High-Speed Passive Optical Networks

We experimentally demonstrate a bidirectional, cross-gain-modulation-free, bismuth-doped fiber amplifier (BDFA) for O-band high-speed passive optical networks. Based on the spatially and spectrally resolved gain profiles of the bidirectional BDFA characterized via Rayleigh backscattering measured by a coherent swept wavelength interferometer, an optimization scheme for bidirectonal amplification is introduced. The BDFA is located at the optical line terminal and acts as both a downstream (DS) signal booster and a pre-amplifier for the upstream (US) burst mode signal, with an equal bidirectional saturated gain of 21.3 dB and noise figure of 5.7 dB, which offers 20.8-dB DS and 17-dB US power budget improvement. Our experimental results also indicate that the transient impact of the BDFA is negligible, as it is saturated by the DS signal, resulting in an US power budget penalty of only 0.5 dB in burst mode.