Beyond 1Tb/s Intra-Datacenter Interconnect Technology: IM-DD or Coherent Detection?

We discuss technology options and challenges for beyond 1Tb/s intra-datacenter interconnect bandwidth scaling, with a focus on pulse amplitude modulation (PAM)-based intensity modulation-direct detection (IM-DD) and baud-rate digital signal processing (DSP)-based coherent technology. We show that a flexible PAM (FlexPAM) technique with fine granularity of bandwidth/spectral efficiency (in terms of bits/symbol) could bring significant value for 200Gb/s per lane or per dimension bandwidth scaling. For baud-rate sampled coherent technology, we propose a much simplified DSP architecture which could bring down coherent DSP power close to that of IM-DD PAM technology. We also propose two new phase noise tolerant, 5 bits per symbol, 2D coherent modulation formats to lower the requirement on laser linewidth. To conclude, we present a comparative study of IM-DD PAM versus coherent PM-QAM (polarization multiplexed-quadrature amplitude modulation) for 200Gb/s per dimension throughput scaling in terms of achievable link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.

• Networking