Energy-Efficient Reconfigurable 4|16|64|256-QAM Transmitter Based on PAM2|4-Driven Optical DACs

We propose, model and optimize an optical Digital to Analog Converter (oDAC) significantly improving the tradeoffs between spectral-, energy- and footprint- efficiencies, based on modifying our recently introduced multi-parallel oDAC, by adopting Multi-Level-Driven modulation for the individual Mach-Zehnder Modulators (MZM) in the parallelized paths. The most compact instance of this improved oDAC structure coherently combines two parallel optical paths, each comprising an MZM electrically driven by either PAM2 or PAM4. This oDAC is flexibly reprogrammable to generate ultra-high-speed, energy-efficient, optical bipolar PAM- $C$ with $C=2$ ,4,8,16. Two such oDAC units are IQ-nested to generate 4|16|64|256-QAM constellations.