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Digital Coherence Enhancement Enabling 6-GBd DP-64QAM Using a 1.4-MHz Linewidth Laser

Paper by ONG Research Associate Dr Domanic Lavery et al. published in IEEE Photonics Technology Letters

Laser linewidth adds noise to the phase of a received signal, restricting the number of phase levels which can be used for modulation and, in turn, reducing the total data rate of the network.  This work uses an interferometric technique to independently measure the phase noise from a high linewidth local oscillator laser in a coherent receiver and, subsequently, undo this phase noise digitally.  This enables the reception of the modulation format polarisation multiplexed 64-QAM, encoding 64 amplitude and phase levels in each polarization where, previously, only four (QPSK) would have been possible.

DOI: 10.1109/LPT.2013.2283744