Fiber Nonlinearity Tolerance of APSK Modulated DFT-S OFDM Systems

Discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) was proposed in coherent optical OFDM (CO-OFDM) to improve the fiber nonlinearity tolerance in CO-OFDM transmission systems. In this letter, we propose to apply amplitude phase shift keying (APSK) modulation in DFT-S OFDM to further improve the fiber nonlinearity tolerance. We investigate the effects of several parameters on the transmission performance to determine the optimal values of these parameters. Compared with 16 quadrature amplitude modulation modulated DFT-S OFDM and 16-APSK (4 and 12 constellation points in the respective first and second rings) modulated CO-OFDM, the optimized 16-APSK (6 and 10 constellation points in the respective first and second rings) modulated DFT-S OFDM extends the maximum transmission reach by ~ 12% and ~ 19% for both nondispersion managed and dispersion managed links, respectively.