Coherent technology for access networks

We review the recent progresses in the coherent detection techniques developed for the use in the optical access network. To enhance the cost-effectiveness, we implement the coherent receiver by utilizing a portion of the seed light as a local oscillator and a 3×3 coupler as a 120° optical hybrid. In addition, instead of using the complicated polarization-diversity receiver, we achieve the polarization stability simply by placing a Faraday rotator in front of the reflective semiconductor optical amplifier (RSOA) located at the optical network unit (ONU).