Effect of noise on constellation diagram of 100 Gbps DP-QPSK systems under influence of different digital filters

In this paper a DP-QPSK modulation scheme has been used at 100 Gbps for the propagation length 500 km. To mitigate effects of Chromatic dispersion (CD) and Polarization mode dispersion (PMD), constant modulus algorithm (CMA) is used, while to compensate carrier phase estimation (CPE) a modified Viterbi-Viterbi algorithm is used by means of DSP at the receiver end. The comparison of constellation diagrams has been performed by using different digital low pass filters such as Gaussian, Bessel, Butterworth and Chebyshev filters, for order 1st to 6th. It is observed that Bessel filter 6th order is superior, while Gaussian filter 4th order gives second best performance.