Silicon photonics has shown great promise in overcoming communications
bottlenecks and providing low-cost components for the Internet—but can
it help “green” the industry as well? Harvesting the optical energy lost to
two-photon absorption in silicon devices may pave the way toward reduced
optical losses and the simultaneous generation of electrical power.
he global energy crisis looms large as a major challenge facing humanity. To prevent potentially
catastrophic environmental, economic and geopolitical consequences, green technologies are being
championed for the energy-hungry industrial sectors of the economy. In the area of lighting, for
instance, which currently consumes 20 percent of the world’s electricity, high-e ciency visible light-
emitting diodes now provide a green alternative to incandescent and fluorescent lamps.
e Internet represents one of the fastest-growing energy gobblers in modern society. Internet
transmission and switching equipment consume roughly 0.5 percent of the total electricity supply
in developed countries, and that figure is expected to rise to 5 to 10 percent as the data rate in the
access portion of the networks reaches 100 Mbps. Energy consumption is rising fast due to the
insatiable demand for bandwidth.
Moreover, the electricity bill of mega data centers—which are the backbone of companies like
Google—is currently 1. 2 percent of global electricity consumption, half of which is consumed
in information-technology equipment. ese data centers are experiencing a very high annual
growth rate of 16 percent worldwide, and they may consume 5 percent of the world’s electricity
in a few years.
e fast-growing Internet tra c has indeed resulted in a dramatic increase in power consumption, since the heat dissipated in data centers is nearing 20 kW per square foot of area,
with 28 percent annual growth for communication equipment as its main constituent. is
trend is creating formidable economic and logistical challenges for Internet companies, as
well as for utility companies that must meet their ever-increasing demand for electricity.
Meanwhile, to speed up communication links, electrical interconnects are being
replaced with optical counterparts for shorter and shorter distances. e battle-line
between metal and optical interconnects is currently at rack-to-rack communications—
that is, the lengths within data centers. is line is moving closer to the chip, and we
expect that optical interconnects will provide chip-to-chip communication and possibly
even intra-chip communication in the future. Wherever the final boundary winds up,
photonic components will undoubtedly become more widespread in computers and
consumer electronics. Given that computing-related power usage accounts for 15 percent of the United States’ electricity consumption, the energy e ciency of photonic
components will have paramount economic consequences.
18 | OPN June 2009