42.8-Gb/s metro transmission using DPSK and joint-decision MLSE

Metropolitan Area Networks (MANs) are cost-sensitive environments. Such networks carry a large number of channels over short distances. Another key aspect is the ability to add or drop channels at each node. This scenario imposes the challenge of deploying cost-effective transceivers which are robust to strong linear filtering from several (reconfigurable) optical add-drop multiplexers (OADMs). Binary modulation formats are generally preferred in terms of cost, but are vulnerable to linear filtering due to their broad spectral content. Among all binary modulation formats with non-coherent detection, differential phase-shift keying (DPSK) exhibits the highest tolerance to noise. This paper investigates the potential use of DPSK combined with joint-decision maximum likelihood sequence estimation (JD-MLSE) in MANs. The performance of this alternative is evaluated in networks subject to strong optical filtering and residual dispersion. The results indicate that the relatively high noise-tolerance of DPSK is maintained in networks with strong optical filtering, when combined with JD-MLSE for the compensation of deterministic distortions. DPSK and JD-MLSE will be therefore an attractive alternative as the electronic evolves towards faster and more efficient MLSE implementations.