T3B: Recent advancements in fiber optic transmission enabled by highly integrated mixed signal SoC and advanced digital signal processing

Mixed signal SoC has always played an important role in long haul, high capacity fiber optic transmission systems. In early days of 10Gbit NRZ transmission, the functions were simple, but implementing decision device, clock recovery and de-multiplexing functions at such high data rate was challenging at the time. In the span of 15 years, the single channel data rate and network capacities have increased 20x, owing to a fundamental change in the way data is modulated and demodulated over the fiber optic channel. Intensity modulation and direct detection has given way to coherent detection and advanced modulation formats such as Polarization-Multiplexed QPSK and higher order QAM. Today, commercial state-of-art single channel data rate have reached 100Gbit/s. 400Gbit/s data rates are being attempted in the laboratory. These astounding achievements are not possible without the parallel advancements in CMOS technology. High speed A/D and D/A converters implemented in CMOS side-by-side with massively parallel, highly dense digital circuits is a key enabler in delivering the network capacities demanded by network operators and consumers. In this tutorial, we first review the challenges of the fiber optic channel, and introduce the necessary digital signal processing functions that need to be implemented in the SOC. We provide some example implementations of clock recovery, carrier recovery and equalization algorithms. We will also review forward error correction methods adopted in the most state-of-art designs. We conclude by discussing the challenges in designing next generation transceiver ASICs.