Fiber nonlinearity mitigation using phase-conjugated OFDM subcarriers

Digital coherent superposition (DCS) provides an interesting approach to combat the fiber nonlinearity by trading off the spectrum efficiency. In this paper, we apply DCS of phase-conjugated OFDM subcarriers in two approaches. One is the DCS of OFDM subcarriers in the single polarization, denoted as SP-DCS-OFDM. The other is in the dual polarizations, or DP-DCS-OFDM. We show that both of them can cancel the fiber nonlinearity to the first order. We compare their performance in a simulation of long-distance nonlinear transmissions. With some difference, both approaches improve the Q-factor by much larger than 3 dB.