Progress in Low-Power Switched Optical Interconnects

摘要

Optical links have successfully displaced electrical links when their aggregated bandwidth–distance product exceeds ∼100 Gb/s-m because their link energy per bit per unit distance is lower. Optical links will continue to be adopted at distances of 1 m and below if link power falls below 1 pJ/bit/m. Providing optical links directly to a switching/routing chip can significantly improve the switched energy/bit. We present an early experimental switched CMOS-vertical-cavity surface-emitting laser (VCSEL) system operating at Gigabit Ethernet line rates that achieves a switched interconnect energy of less than 19 pJ/bit for a fully nonblocking network with 16 ports and an aggregate capacity of 20 Gb/s/port. The CMOS-VCSEL switch achieves an optical bandwidth density of 37 Gb/s/mm$^2$ even when operating at a modest line rate of 1.25 Gb/s and is capable of scaling to much higher peak bandwidth densities (∼350 Gb/s/mm $^2$) with 5–10 pJ/switched bit. We also review a silicon photonic system design that will lower link energies to 300 fJ/bit, while providing multiterabits per second per square millimeter bandwidth densities. This system will ultimately provide switched optical interconnect at less than a picojoule per switched bit and computer/router system energies of tens of picojoule per bit. We review progress made to date on the silicon photonic components and analyze an energy and bandwidth–density roadmap for future advances toward these goals.