APSK Modulated CO-OFDM System With Increased Tolerance Toward Fiber Nonlinearity

An amplitude and phase-shift keying (APSK) modulated coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) system is proposed, with increased tolerance toward fiber nonlinearity. Numerical simulation results, based on 30.2-Gb/s single-channel and 5×30.2-Gb/s wavelength-division-multiplexing (WDM) single-polarization CO-OFDM systems, show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, the 16 APSK modulated optical OFDM signal has a higher tolerance toward fiber nonlinearity, such as self-phase modulation and cross-phase modulation. The optimal launch power and the corresponding Q
²
factor are, respectively, 2 and 0.5 dB higher than 16 QAM modulated optical OFDM signal after 640-km transmission, both in single-channel and WDM CO-OFDM systems.