Electronic Signal Processing for Cancelation of Optical Systems Impairments


Abstract –In this paper 40 Gb/s DP-QPSK system with coherent reception and DSPunit for optical fiber impairments compensation is proposed . The DSP unit processesthe detected coherent DP-QPSK signal. The Chromatic Dispersion (CD) is compensatedusing a simple transversal digital filter and Polarization Mode Dispersion (PMD) iscompensated using adaptive butterfly equalizer which is realized by applying theconstant-modulus algorithm (CMA). A nonlinear compensator (NLC) is used forcompensating the nonlinear effects based on the technique of multi-span backpropagation.A modified Viterbi-and-Viterbi phase estimation algorithm (workingjointly on both polarizations) is then used to compensate for phase and frequencymismatch between the transmitter and local oscillator (LO). After the digital signalprocessing is complete, the signal is sent to the detector and decoder, and then to theBER test set for direct-error-counting. The presented system is designed and simulatedusing OptiSystem (2011) software interfaced with MATLAB software R2011a forimplementing the DSP unit algorithms. The performance of each part of the system isanalyzed by showing the optical spectrum, RF spectrum, electrical constellationdiagrams, eye diagram and BER performance for different sampling rates and differentbit rates.