Perspectives on and road towards 100 Gb/s TDM PON with intensity-modulation and direct-detection

In this paper we assess the current status of PON technology, as 25G and 50G PONs leverage the Ethernet intra datacenter ecosystem. As a first step towards 100G PON, we predict the real-world impact of a flexible modulation enhancement to 50G PON, whereby PAM4 symbols can be transmitted at the same baud rate as 50G NRZ, but only where excess margins permit. We find that sufficient margins are likely to exist to allow for a majority of future 50G PON ONUs to operate at 100G PAM4. Next, we look at the options for a full 100G PON. There is no technical risk if coherent is adopted, but intensity-modulation direct-detection (IM-DD) will provide lower complexity, lower cost, and lower power dissipation. We evaluate this option and conclude that following IM-DD Ethernet to 100 GBd, single-wavelength IM-DD continues to be feasible for 100G PON and will be the irresistible choice for the next generation of PON after 50G.