Impact of Backreflections on Single-Fiber Bidirectional Transmission in WDM-PONs

We analyze the system impairment due to beat noises between backreflections and the upstream signal in bidirectional single-fiber wavelength-division-multiplexing passive optical networks (WDM-PONs). The relative intensity noise (RIN), the power penalty caused by the beat noises and the optimum optical network unit (ONU) gain that minimizes this penalty are investigated. In addition to the transmission line loss (TLL), we find that these parameters are also dependent on the linewidth of the seed light, the chirp effect at the ONU and the receiver bandwidth. Different types of laser sources at the optical line terminal (OLT) and various wavelength-independent ONU configurations are intensively investigated to explore those dependencies. It is also found that the systems with remodulation configurations are more tolerant to the backreflections.