Generation and transmission of a 400-Gb/s PDM/WDM signal using a monolithic 2×4 VCSEL array and coherent detection

We generate a 400-Gb/s polarization-division-multiplexed (PDM) and wavelength-division-multiplexed (WDM) 4-level pulse-amplitude-modulation signal using a 2×4 PDM/WDM monolithic VCSEL array and successfully transmit the signal over 400-km standard-single-mode-fiber using digital coherent detection.