Coherent optical OFDM: has its time come? [Invited]

TLDR

Growing interest in coherent optical orthogonal frequency‑division multiplexing (CO‑OFDM) has emerged. The authors argue that CO‑OFDM is now ready for deployment, driven by network demand and available technologies. They describe CO‑OFDM signal processing, present a 2×2 MIMO OFDM model for single‑mode fiber, and demonstrate via simulation and experiment various MIMO‑OFDM systems—including CO‑SCFDE—highlighting polarization‑mode dispersion resilience. The 2×1 MIMO‑OFDM configuration with polarization‑time coding shows promise for optical access and broadcast networks.

Abstract

There has been growing interest in coherent optical orthogonal frequency-division multiplexing (CO-OFDM). We aim to present the case that the time for CO-OFDM has come, in terms of the demand from today's ever-advancing optical networks and the availability of its underlying technologies. We first lay out the signal processing aspect for CO-OFDM and then show a 2×2 multiple-input-multiple-output (MIMO) OFDM representation for the single-mode fiber optical channel. Through numerical simulation and experimental demonstration, we further present and discuss various MIMO-OFDM systems focusing on their polarization-mode dispersion resilience. Among those systems, the 2×1 MIMO-OFDM configuration incorporating polarization-time coding shows promise for optical access networks and broadcast networks. Finally, another class of the frequency-domain equalization techniques, namely, incoherent or coherent optical single-carrier frequency-domain equalization (CO-SCFDE) is discussed and experimentally demonstrated.