Cost-effective and flexible coherent passive optical networks [Invited]

Driven by the continuous growth of bandwidth-intensive services, optical access networks are required to support ever-increasing data rates. Benefiting from high receiver sensitivity, expanded modulation dimensions, and wavelength selectivity, coherent optics is emerging as a promising solution for next-generation 200G or even 400G optical access networks. Accordingly, coherent PON has been included by ITU-T Q2/SG15 as a candidate solution for very high-speed PON. As a point-to-multipoint system, cost is a critical factor in CPON deployment, making cost optimization particularly important, especially at the optical network unit side. In addition, enabling flexible rate allocation in CPON systems is essential to fully exploit heterogeneous channel conditions among users and to improve overall system efficiency. In this paper, building upon our recent work published in ECOC 2025, we review key enabling technologies for next-generation CPON from the perspectives of cost simplification and flexibility. Furthermore, the main challenges associated with cost-effective and flexible CPON systems are analyzed, and potential solution directions are discussed.