Heterogeneous transmission of analog radio and digital coherent signals over multispan metro and PON for bandwidth-efficient fronthaul in mmWave centralized RANs [Invited]

We experimentally investigate the transparent coexistence of heterogeneous analog radio-over-fiber (ARoF) and digital coherent optical (DCO) signals in a converged metro network/passive optical network (PON). Our streamlined setup employs RF generation via optical heterodyning so that both carrier and modulated signals can be generated centrally and transmitted to the antenna site across a metro network and a PON. The experiment includes the transmission of 8.8 Gbps mmWave signals and 400 Gbps coherent optical signals within a 68.75 GHz reconfigurable optical add/drop multiplexer (ROADM) channel bandwidth and a 1:32–1:128 split PON. We also analyze the impact of varying ROADM channel bandwidth, PON split ratios, metro network distance, and number of ROADMs traversed on the performance of DCO and ARoF signals. The results reveal that the error vector magnitude (EVM) of the ARoF signal is significantly influenced by the allocated bandwidth, the number of ROADMs, and the overall network loss, providing insights into optimizations necessary to achieve target EVM levels.