Analysis and experimental demonstration of possible architectures for future coherent metro+PON converged networks [Invited]

We present in this paper a detailed brainstorming on the future option of merging the metro and the passive optical network (PON) access network segments, enabled by the introduction of end-to-end coherent transmission. We begin by reporting the experimental results presented by our group at OFC2024 (for which this paper is an invited extension). Starting from these preliminary but very promising results, we elaborate on two different possible schematics for metro+PON convergence using edge reconfigurable optical add-drop multiplexers (ROADMs) at the boundary of the two segments, and then we study their physical layer scalability by a mix of experimental characterization and numerical modeling. We show that coherent transceivers enable excellent performance in this scenario, allowing at least 200G per wavelength and even 400G in most cases when traversing all-optically two ROADMs before being routed towards a high splitting ratio PON in the access part of the network. We study several realistic conditions analyzing different bit rates, modulation formats, and network architectures, showing the physical layer conditions that would enable the PON optical distribution network loss to be in the range from 29 to 35 dB, as required by current international standards. The scalability analysis is first based on link budget and optical signal-to-noise ratio (OSNR) fundamental limitations, and it is then extended considering other physical layer issues, such as tight optical filtering in the ROADMs.