Flexible Coherent Optical Access: Architectures, Algorithms, and Demonstrations

To cope with the explosive bandwidth demand, significant progress has been made in the ITU-T standardization sector to define a higher-speed passive optical network (PON) with a 50 Gb/s line rate. Recently, 50 G PON has become mature gradually, which means it is time to discuss beyond 50 G PON. For ensuring an acceptable optical power budget, beyond 50 G PON will potentially use coherent technologies, which can simultaneously promote the applications of flexible multiple access such as time/frequency-domain multiple access (TFDMA). In this paper, we will introduce the architectures, algorithms, and demonstrations for TFDMA-based coherent PON. The system architectures based on an ultra-simple coherent transceiver and specific signal spectra are designed to reduce the cost of ONUs greatly. Meanwhile, continuous-mode and burst-mode digital signal processing (DSP) algorithms are proposed for dealing with downstream and upstream signals, respectively. Based on the architectures and algorithms, we experimentally demonstrate the first real-time TFDMA-based coherent PON where 50 Gb/(s x subcarrier) continuous downstream signal and 12.5 Gb/(s x subcarrier) burst upstream signal are processed in real time. Owing to the independent subcarrier processing, it has the potential to support peak line rates of downstream 200 Gb/s (i.e. four subcarriers) and upstream 100 Gb/s (i.e. eight subcarriers). Significantly, the proposed architectures and algorithms have been sufficiently verified by real-time demonstrations. In conclusion, the proposed technologies for the coherent PON make it more possible to be applied in the future beyond 50 G PON.