  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 a
non-integer-oversampling DSP for meeting the requirements of coherent PON. The
proposed DSP working at 9/8-sps and 5/4-sps oversampling rates can be reduced
by 44.04% and 40.78% computational complexity compared to that working at the
2-sps oversampling rate, respectively. Moreover, a 400-Gb/s-net-rate coherent
PON based on digital subcarrier multiplexing was demonstrated to verify the
feasibility of the non-integer-oversampling DSP. There is almost no penalty on
the receiver sensitivity when the non-integer-oversampling DSP is adopted. In
conclusion, the non-integer-oversampling DSP shows great potential in the
future coherent PON.
