Advanced DSP for 400Gb/s and beyond Optical Networks

This paper presents a systematic review of several
digital signal processing (DSP)-enabled technologies recently
proposed and demonstrated for high spectral efficiency (SE)
400Gb/s – class and beyond optical networks. These include 1) a
newly proposed SE-adaptable optical modulation technology ⎯
time-domain hybrid quadrature amplitude modulation (QAM),
2) two advanced transmitter side digital spectral shaping
technologies ⎯ Nyquist signaling (for spectrally-efficient
multiplexing) and digital pre-equalization (for improving
tolerance toward channel narrowing effects), and 3) a newly
proposed training-assisted two-stage carrier phase recovery
algorithm that is designed to address the detrimental cyclic phase
slipping problem with minimal training overhead. Additionally,
this paper presents a novel DSP-based method for mitigation of
equalizer-enhanced phase noise impairments. It is shown that
performance degradation caused by the interaction between the
long-memory chromatic dispersion (CD) compensating
filter/equalizer and local oscillator (LO) laser phase noise can be
effectively mitigated by replacing the commonly used fast
single-tap phase-rotation-based equalizer (for typical carrier
phase recovery) with a fast multi-tap linear equalizer. Finally,
brief reviews of two high-SE 400Gb/s-class WDM transmission
experiments employing these advanced DSP algorithms are
presented.

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