Polarization in Retracing Circuits for WDM-PON

Reflective semiconductor optical amplifier (RSOA)-based network-embedded self-tuning solutions for colorless optical network unit in wavelength-division-multiplexed passive optical network architecture suffer the device polarization-dependent gain (PDG). The Faraday-mirror-based topology proposed in the literature for low PDG RSOA is not suitable for high PDG RSOA. A polarization retracing circuit is proposed and discussed to comply with the high PDG RSOA. The polarization evolution is theoretically and experimentally analyzed in the presence of a high PDG RSOA comparing three cases: standard topology with standard mirror, the retracing circuit proposed in the literature with a Faraday rotator mirror (FRM), and the proposed retracing circuit, which includes both an FRM and a Faraday rotator.