Generation and Transmission of 21.4-Gbaud PDM 64-QAM Using a Novel High-Power DAC Driving a Single I/Q Modulator

We generate a single-carrier 21.4-Gbaud polarization-division-multiplexed (PDM) 64-ary quadrature-amplitude- modulated (QAM) signal (256.8-Gb/s line rate) using a single in-phase/quadrature (I/Q) optical modulator driven by 8-level electrical waveforms from a novel high-power digital-to-analog converter (DAC). We measure a required optical signal-to-noise ratio of 29.5 dB (0.1-nm reference bandwidth; bit-error rate), 4.6-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 400-km single-channel transmission. The DAC was also used to obtain excellent results with quadrature-phase-shift-keyed and 16-QAM signals at 21.4 Gbaud.