Performance Optimization of WDM Long-Haul Lightwave Systems using Optimum Modulation Schemes.


In this paper an optical communication system with N-Channel 40 Gb/s Wavelength Division Multiplexing (WDM) has been designed and optimized in the presence of Return-to-Zero Differential Phase Shift Keying (RZ-DPSK), Nonreturn-to-Zero (NRZ), Carrier Suppressed Return-to-Zero (CSRZ) and Modified Duo binary Return-to-Zero (MDRZ) modulation schemes. The system simulation is done using Optisystem simulator version-14 with multiple span Standard Single Mode Fiber (SSMF) transmission and the launched optical power range from (-10dBm to 10dBm). The effect of increase in launched power is studied in terms of Quality factor (Q-Factor), Bit Error Rate (BER), nonlinearity impairments and Eye Opening Penalty (EOP) for different modulation formats. The simulation results show that NRZ has highest Q-Factor of (38) and lowest BER with high nonlinear effects and system performance degradation with the increase of input optical power, while CS-RZ has the lowest Q-Factor of (6) with little nonlinear effect. On the other hand, RZ-DPSK offers high Q-Factor of (32) with high tolerant to nonlinear impairments and the system performance remains resilient to nonlinearity with the increase of input power. It is observed that RZ-DPSK has the lowest EOP that reaches only to 0.7 while NRZ has the highest EOP in which reaches to 4.5. Simulation results also show that RZ-DPSK has higher, wider and clearer eye diagram than other modulation formats. It is concluded that the light wave system with RZ-DPSK format offers the best performance, higher tolerance to nonlinearity and higher dispersion tolerance among other modulation formats.