Eight-channel 56-Gbit/s direct four-level pulse-ampli-tude modulation is demonstrated using a 1.3-μm wavelength-division-multiplexing (WDM) photonic integrated circuit (PIC) transmitter, consisting of membrane distributed-reflector lasers heterogeneously fabricated on Si and a SiN arrayed-waveguide-grating multiplexer. Direct bonding, epitaxial regrowth, and low-temperature SiN-waveguide fabrication technologies are employed for the integration on Si. Using a nonlinear equalizer, we operated the fabricated WDM PIC transmitter with a low power consumption of 403 fJ/bit for overall 448 Gbit/s signals. The total eight-channel bit-error rate was 2.7 × 10 -3 , which is less than the 7%-overhead hard-decision forward-error-correction limit.
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