National Academy of Engineering Symposium
March 22, 2012
The projections for energy consumption within exascale computers indicate that the energy required for communication to memory and other processors will be more than an order of magnitude larger than what is required to compute. Fiber optic communication has been successful at reducing the energy required to transmit a bit across the country by more than four orders of magnitude. Photonics has been less successful at reducing the energy required to transmit bits within a computer. We examine how to scale optical communications for microscale processors to macroscale data centers, supercomputers and telecommunications networks. High-bandwidth communication technologies that are cheap, low-power and small are required. Silicon photonics that utilize scalable CMOS technology may offer a highly integrated photonics transmission platform for such applications. Issues to be addressed include transmitters, receivers and the propagation medium. The typical propagation loss of ~0.3 dB/cm in an optical waveguide is five orders-of-magnitude larger than that in low loss optical fibers. This wide gap in loss performance has prevented planar waveguide technology from bringing potential improvements in stability, footprint, energy consumption, and fabrication cost to photonic applications requiring long propagation lengths or ultra-high-quality-factor resonators. Recent progress to reduce the propagation losses in planar waveguide technology by two orders of magnitude will be described. Integrated approaches to achieve energy efficient communication and computing will be described.