Performance Enhancement of WDM Optical System with Coherent Detection

Abstract

Wavelength division multiplexed (WDM) optical communication is rapidly growing newlinewith deployment of multilevel modulation formats. Efficient utilization of optical fiber newlinebandwidth with high spectral efficiency is the key advantage of this technology for long newlinetransmission reach. However, fiber linear and nonlinear impairments are still the newlinechallenges which prevent the growth of WDM optical communication at high data rates. newlineCoherent detection technique with digital signal processing (DSP) at the receiver end newlinehas shown the capability to overcome these challenges. Further, multi-carrier newlinegeneration at transmitter and the use of polarization division multiplexed (PDM) multilevel newlinemodulation format are the solutions to enhance the spectral efficiency of the newlinesystem with narrow spacing between channels. newlineIn this thesis, multi-carrier generation concept is applied at transmitter side employing newlinecoherent detection technique with DSP at receiver end to enhance the performance of newlineWDM optical system. Polarization division multiplexed quadrature phase shift keying newline(PDM QPSK) and polarization division multiplexed 16- quadrature amplitude newlinemodulation (PDM 16-QAM) are used to realize the WDM optical system for long reach newlineat high transmission rates. Hybrid transmission approach has also been considered in newlinedesigning the system to represent the system performance in the dual modulation newlineenvironment. Q-factor, Log of Estimated symbol error (Log (ESE)) and error vector newlinemagnitude (EVM) are considered as a performance metrics. Simulation results are newlineobtained using optisystem software. newlineThe performance of 12 x 160 Gb/s (1.92 Tb/s) wavelength division multiplexed WDM newlineoptical system employing dual carrier and coherent detection with DSP is investigated newlinefor three different cases: gray coding, with differential coding and without any coding. newlineResults are compared for 100 km transmission using polarization division multiplexed newlinequadrature phase shift keying (PDM-QPSK) format. The results exhibit that system newlinewith differential coding performs better in comparison with gray coding and without newlineany coding technique. Improvement of 2 to 5 dB in Q factor is found for system using newlinedifferential coding. Moreover newline