Abstract
We study a carrier-synchronization scheme for coherent optical communications that uses a feedforward
architecture that can be implemented in digital hardware without a phase-locked loop. We derive the equations for
maximum a posteriori joint detection of the transmitted symbols and the
carrier phase. The result is a multidimensional optimization problem that we approximate with a two-stage iterative
algorithm: The first stage is a symbol-by-symbol soft detector of the carrier phase, and the second stage is a
hard-decision phase estimator that uses prior and subsequent soft-phase decisions to obtain a minimum
mean-square-error phase estimate by exploiting the temporal correlation in the phase-noise process. The received
symbols are then derotated by the hard-decision phase estimates, and maximum-likelihood sequence detection of the
symbols follows. As each component in the carrier-recovery unit can be separately optimized, the resulting system is
highly flexible. We show that the optimum hard-decision phase estimator is a linear filter whose impulse response
consists of a causal and an anticausal exponential sequence, which we can truncate and implement as an
finite-impulse-response filter. We derive equations for the phase-error variance and the system bit-error ratio
(BER). Our results show that 4, 8, and 16 quadrature-amplitude-modulation (QAM) transmissions at 1 dB above sensitivity for BER=10<sup>-3</sup> is possible with laser
beat linewidths of ΔνT<sub>b</sub>=1.3×10<sup>-4</sup>,
1.3 x 10<sup>-4</sup>, and 1.5
x 10<sup>-5</sup> when a decision-directed soft-decision phase estimator is employed.
© 2007 IEEE
PDF Article
More Like This
Chip-based Brillouin processing for carrier recovery in self-coherent optical communications
Elias Giacoumidis, Amol Choudhary, Eric Magi, David Marpaung, Khu Vu, Pan Ma, Duk-Yong Choi, Steve Madden, Bill Corcoran, Mark Pelusi, and Benjamin J. Eggleton
Optica 5(10) 1191-1199 (2018)
Cited By
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Contact your librarian or system administrator
or
Login to access Optica Member Subscription