Analysis of the resilience of 32-channels system to nonlinear impairments based on different modulation formats and bit rates

Designing a DWDM system for fiber optic transmissions requires optimizing some important parameters to enable the system to be more tolerant to nonlinear impairments. This paper proposes a simulation of a 32-channels system with different bit rates per channel, for different modulation formats (RZ, NRZ, 4-QAM, and DQPSK) then the Gaussian (Gauss) and Hyperbolic Secant (Sech) pulses. The main goal is to investigate the resilience of the designed system to nonlinear effects, taking into account the different modulation formats and bit rates used. Thus, several comparisons were taken into account in the different simulations carried out with the optisystem software. The results reveal that for a bit rate of 40 Gbps per channel, the order of performance is NRZ, Sech, 4-QAM, RZ, and DQPSK; whereas for a bit rate of 100 Gbps per channel, the order becomes NRZ, DQPSK, 4-QAM, Sech, and RZ. For a bit rate of 100 Gbps without nonlinear effects, the 4-QAM format would be more efficient than other modulation formats for the input powers considered (−10 dBm to 10 dBm). While this same 4-QAM format is more vulnerable to nonlinear effects beyond an input power of 5 dBm. At a bit rate of 100 Gbps, the DQPSK format would be more resilient to nonlinear effects for input powers between −10 dBm and 8 dBm for the simulated system.