Electrical constant envelope signals for nonlinearity mitigation in coherent-detection orthogonal frequency-division multiplexing systems

A theoretical analysis and a numerical investigation of 3-dB peak-to-average power ratio electrical constant envelope over orthogonal frequency-division multiplexing (OFDM) signals in coherent-detection optical (CO) systems are proposed. A 100 - Gb / s optical system is studied to increase the nonlinear tolerance (NLT) to both Mach–Zehnder modulation and optical propagation impairments. Simulation results show that, with 16- and 64-QAM subcarrier modulations, the proposed system outperforms a conventional CO-OFDM system, if an optical modulation index OMI = 2.5 and an electrical phase modulation index 2 π h = 3 are simultaneously adopted. The achieved NLT denoted by a performance gain of 24 dB is attractive after propagation through 1200 km of dispersion-uncompensated standard single-mode fiber, especially for 10-dBm fiber input power and despite the intrinsic bandwidth enlargement of PMs.