High Order Dual Polarization Modulation Formats for Coherent Optical Systems

The present high capacity, speedy and spectral efficient optical access networks face immense challenges to deal with ever-increasing bandwidth demand which arises from common use of high bandwidth-hungry applications, such as video-on-demand, online gaming, and other multimedia applications. Present research trends encourage the use of higher order modulation formats for further improvement in the spectral efficiency and overall capacity of the network. In this paper, we investigated the comparison of a single-channel coherent-optical-system (CO-OS) with dual polarization (i) Quadrature phase shift keying Modulation (DP-QPSK) and (ii) Quadrature amplitude modulation (DP-QAM) methods with the use of single mode fiber by considering digital-signal-processing (DSP) at the data rate of 112 Gb/s. The evaluation metrics include fiber nonlinearities, the power of the continuous wave (CW) laser and the range of the distance. We displayed the relation between error-vector-magnitude in percentage (% EVM), transmitted power and transmission distance to indicate the efficiency and robustness of the modulation schemes. Results analyzed from the comparison of higher order modulation techniques conclude that modulation schemes are more vulnerable to nonlinearities, channel dispersion and thus are less spectral efficient. The results help in selecting appropriate dual polarization higher modulation technique keeping in mind the fiber nonlinearities of optical networks.