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Optical 64‐QAM transmitter using QPSK modulators in tandem driven by binary electrical signals is proposed. The proposed transmitter eliminates the need for complex electronics required for the generation of multiple‐level signals and provides a Gray‐coded constellation with high quality eye diagrams. The design could be scaled to higher‐order QAM based on the user needs. [ABSTRACT FROM AUTHOR]

Absolute added correlative coding with eight levels has been proposed and demonstrated numerically at bit rates of 30 and 60 Gbps back‐to‐back, and up to 75 Gbps over 2000 and 3000 m standard single‐mode fibre using a single‐drive multiple quantum‐well Mach–Zehnder modulator. The transmission performance is compared with the conventional eight‐level pulse amplitude modulation. [ABSTRACT FROM AUTHOR]