Ultrafast pulse-amplitude modulation with a femtojoule silicon photonic modulator

Ultrahigh-speed optical interconnects are essential to future cloud computing. Further increase in optical transmission speed has been hindered by power consumption and limited bandwidth resources, for which integrated optical transceivers using advanced modulation formats, such as pulse-amplitude modulation (PAM), are a promising solution. We report 80 Gb/s PAM operation of a silicon microring modulator (MRM) with an ultralow power consumption below 7 fJ/bit. We also report the first demonstration of PAM-8 modulation of MRMs in the Gb/s order, achieving error-free capability at 45 Gb/s, using 1 fJ/bit. To the best of our knowledge, these results feature the lowest power consumption, per transmitted bit, ever demonstrated at such high data rates. We further demonstrate PAM data transmission up to 64 Gb/s over 5 km. Simultaneous achievement of ultrafast modulation and ultralow power consumption is a critical step toward next-generation optical interconnects. (C) 2016 Optical Society of America