We address the problem of how to exploit optics for ultrascale High Performance Computing interconnect fabrics. We show that for high port counts these fabrics require multistage topologies regardless of whether electronic or optical switch components are used. Also, per stage electronic buffers remain indispensable for maintaining throughput, lossless-ness and packet sequence. Although the notion of true all-optical packet switching is not yet viable, we show that appropriate use of optical switching technology offers power and scaling advantages that can be leveraged economically, and propose a hybrid opto-electronic HPC interconnect fabric architecture that combines the strength of electronics in processing and storing information with the strength of optics in switching and transporting high bandwidths. Using Semiconductor Optical Amplifier technology, we are building a prototype demonstrator switch that we believe solves all the technical challenges. Having reached this threshold now enables commercialization of this technology, which we are currently pursuing.

The authors describe the operating principle, design, and performance of an all-silicon light modulator at 1.3 mu m wavelength. The modulator is based on the plasma effect in silicon and the mode selectivity of single-mode optical fibers, resulting in low polarization dependence and the capability of handling high light intensities. Standard silicon IC technology is used in the fabrication process and the modulator has a vertical structure that takes up a small surface area (the active area matches the single-mode fiber core of 9 mu m diameter), simplifying integration with other circuitry on the same chip. The modulator can be directly coupled to a single-mode optical fiber, without using lenses or other bulk optical components. Typical performance of the fabricated modulators is 6 dB insertion loss, 24% modulation depth, and 60 MHz bandwidth with a current drive of 22 mA rms.>