Improved phase noise tolerance using phase-conjugated OFDM subcarriers

We have recently demonstrated the improved phase noise tolerance in coherent optical OFDM by digital coherent superposition of optical OFDM subcarriers, which are phase-conjugated pairs with Hermitan symmetry. In this approach, we realized DCS of OFDM subcarriers in single polarization (or channel), denoted as SP-DCS-OFDM. In this paper, we show that another approach is in dual polarizations, or DP-DCS-OFDM. We prove that both approaches can reduce the ICI due to phase noise, including laser phase noise and nonlinear phase noise. We discuss their improved phase noise tolerance in simulation. We also discuss their difference in terms of complexity and performance.