Authors
Abstract
Abstract –In this paper 40 Gb/s DP-QPSK system with coherent reception and DSP
unit for optical fiber impairments compensation is proposed . The DSP unit processes
the detected coherent DP-QPSK signal. The Chromatic Dispersion (CD) is compensated
using a simple transversal digital filter and Polarization Mode Dispersion (PMD) is
compensated using adaptive butterfly equalizer which is realized by applying the
constant-modulus algorithm (CMA). A nonlinear compensator (NLC) is used for
compensating the nonlinear effects based on the technique of multi-span backpropagation.
A modified Viterbi-and-Viterbi phase estimation algorithm (working
jointly on both polarizations) is then used to compensate for phase and frequency
mismatch between the transmitter and local oscillator (LO). After the digital signal
processing is complete, the signal is sent to the detector and decoder, and then to the
BER test set for direct-error-counting. The presented system is designed and simulated
using OptiSystem (2011) software interfaced with MATLAB software R2011a for
implementing the DSP unit algorithms. The performance of each part of the system is
analyzed by showing the optical spectrum, RF spectrum, electrical constellation
diagrams, eye diagram and BER performance for different sampling rates and different
bit rates.
Keywords
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