  Optics offers unique opportunities for reducing energy in information
processing and communications while resolving the problem of interconnect
bandwidth density inside machines. Such energy dissipation overall is now at
environmentally significant levels; the source of that dissipation is
progressively shifting from logic operations to interconnect energies. Without
the prospect of substantial reduction in energy per bit communicated, we cannot
continue the exponential growth of our use of information. The physics of
optics and optoelectronics fundamentally addresses both interconnect energy and
bandwidth density, and optics may be the only scalable solution to such
problems. Here we summarize the corresponding background, status,
opportunities, and research directions for optoelectronic technology and novel
optics, including sub-femtojoule devices in waveguide and novel 2D array
optical systems. We compare different approaches to low-energy optoelectronic
output devices and their scaling, including lasers, modulators and LEDs,
optical confinement approaches (such as resonators) to enhance effects, and the
benefits of different material choices, including 2D materials and other
quantum-confined structures. Beyond the elimination of line charging by the use
optical connections, the next major interconnect dissipations are in the
electronic circuits for receiver amplifiers, timing recovery and multiplexing.
We can address these through the integration of photodetectors to reduce or
eliminate receiver circuit energies, free-space optics to eliminate the need
for timing and multiplexing circuits (while solving bandwidth density
problems), and using optics generally to save power by running large
synchronous systems. One target concept is interconnects from ~ 1 cm to ~ 10 m
that have the same energy (~ 10fJ/bit) and simplicity as local electrical wires
on chip.
