Increased tolerance toward fiber nonlinearity with star L quadrature amplitude modulation modulated coherent optical orthogonal frequency division multiplexing system

Abstract

Star L quadrature amplitude modulation (SLQAM, L representing the number of constellation points) modulated orthogonal frequency division multiplexing (OFDM) is applied to the optical domain for the first time. Numerical simulations are conducted between an S16QAM and a square 16QAM modulated optical OFDM system to compare the tolerance toward various transmission penalties in a 30.2-Gbit /s coherent optical OFDM (CO-OFDM) system over 640, 720, and 800 km. After 640-km transmission, the optimal launch power and corresponding Q 2 factor of an S16QAM modulated optical OFDM signal are 2 and 0.6 dB higher, respectively, than the square 16QAM modulated OFDM signal in a 30.2-Gbit /s single-channel single-polarization CO-OFDM system, while in a 5×30.2-Gbit /s wavelength-division multiplexing single-polarization CO-OFDM system, the optimal launch power and corresponding Q 2 factor of an S16QAM modulated optical OFDM signal are 1 and 0.7 dB higher than with a square 16QAM modulated OFDM signal, showing increased tolerance toward nonlinearity such as SPM and XPM.