Intra-PON communication based on DSCM coherent-PON for ultra-low latency 5G/6G X-haul services

Future passive optical networks (PONs) are expected to support the ultra-high bitrates and extremely low-latency requirements of X-haul networks. In parallel, many research groups and standardization bodies are investigating PON transmission solutions for 100+ Gbps per wavelength (very high speed PON or VHSP), considering also the introduction of coherent transmission technologies in PON. Building on these two trends, we propose and analytically investigate simple physical modifications to the standard PON infrastructures to enable direct all-optical ONU-to-ONU communications, showing their rationale for X-haul. We introduce both intra- and inter-PON ONU-to-ONU all-optical configurations and assess their impact on optical distribution network (ODN) loss, considering current and future-compliant transceivers. We focus in particular on coherent PON based on digital subcarrier multiplexing (DSCM), which is one of the solutions currently investigated by the ITU-T for VHSP. Our analysis shows that, under reasonable assumptions for future PON-complaint DSCM-based transceivers, the proposed architectures can support 40 km ONU-to-ONU links with an additional allowed loss margin of about 1.3 dB beyond the 29 dB N1 PON class limit, and one ONU to four ONU connections with only 2 dB of extra margin. Furthermore, the proposed architectures achieve significant latency reductions, making them suitable for future low-latency split- and service-based transport requirements.