Abstract
Blind equalization and carrier phase recovery in a simulated 14 Gbaud
16-QAM optical coherent system are investigated. Equalization techniques to
compensate for linear transmission impairments are presented using the
constant modulus algorithm (CMA), the recursive least-squares (RLS)-CMA, and
the radius directed equalization (RDE). With 7 T/2-spaced taps, the RDE and
the RLS-CMA can compensate up to 1000
ps/nm of CD in the 16-QAM coherent system with
performances comparable to the decision-directed (DD) equalizer. We show
that the RDE is a promising technique for blind equalization in a 16-QAM
coherent system with lower complexity than the RLS-CMA. Blind carrier phase
recovery is investigated in a decision-directed-mode. We show that the blind
carrier phase recovery algorithm can recover the Square-16-QAM constellation
for laser beat linewidths of $\Delta \nu T_{s} \sim 10^{-4}$ in a polarization-multiplexed (POLMUX) 16-QAM coherent system
with the RDE algorithm giving better overall performance than the CMA when
compensating for CD and differential group delay (DGD). Finally, the
dynamical characteristics of the equalizers to track endless polarization
rotations are discussed. With the adaptation parameters optimized, the
equalizers can track angular rate of rotation ${\sim 10}^{5}~$ rad/s.
© 2009 IEEE
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