Non-integer-oversampling digital signal processing for coherent passive optical networks

Beyond 100G passive optical networks (PONs) will be required to meet the ever-increasing traffic demand in the future. Coherent optical technologies are the competitive solutions for the future beyond 100G PON but also face challenges such as the high computational complexity of digital signal processing (DSP). A high oversampling rate in coherent optical technologies results in the high computational complexity of DSP. Therefore, DSP running in a non-integer-oversampling below 2 samples-per-symbol (sps) is preferred, which can not only reduce computational complexity but also obviously lower the requirement for the analog-to-digital converter. In this paper, we propose non-integer-oversampling DSP for meeting the requirements of coherent PON. Complexities of complex-valued multiplication of the proposed DSP working at 9/8-sps and 5/4-sps oversampling rates can be reduced by 44.04% and 40.78% compared to that working at the 2-sps oversampling rate, respectively. A 400-Gb/s-net-rate coherent PON based on digital subcarrier multiplexing was demonstrated to verify the feasibility of non-integer-oversampling DSP. There is almost no penalty on the receiver sensitivity when non-integer-oversampling DSP is adopted. In conclusion, non-integer-oversampling DSP shows great potential in the future coherent PON.