Photonics investigates how optical technology could replace
electrical signals sent through copper cables, which are used in
today's computers. Not only would it mean faster computers it would
also enable power usage to be cut by up to 40%.
Imagine a computer that can run thousands of times faster than
today's state of the art hardware. This is the goal of photonics,
where data is transferred literally at the speed of light.
Copper is one of the fundamental building blocks in computer
systems. The cables that enable data transfer between servers, the
cables inside the box, and the wires imprinted on the circuit
boards are all made from copper. It is considered a great conductor
of electricity. But copper wires have some significant
disadvantages. Researchers say copper has unstable electrical
properties, high noise levels and high power consumption, which
limit how fast a copper circuit can run and how far a copper cable
can stretch.
Today's computer system design has evolved from more than four
decades of engineering and development in electronics and
microelectronics. Although the size may have shrunk and the
performance increased exponentially in this time, all computers are
made up of the same fundamental elements - electrically optimised
silicon in electrically optimised packages, attached to
electrically optimised printed circuit boards that plug into
electrically optimised backplanes.
While the level of integration and density has continued to
evolve, physical system implementations have remained relatively
constant. Terry Morris, who works at HP's Enterprise Storage and
Servers Group, says computers have had to be designed to take into
account the fundamental limitations of electrical signalling using
copper wires, including loss, delay and signal/noise ratio.
What's more, whilst the simplest computer architecture only
needs a data bus to connect the processor to memory and peripheral
devices, user demand for higher performance has changed this
architecture radically. The physical bus architectures in today's
computers are supplanted by collections of switched point-to-point
circuits. These require additional power and introduce latency into
the circuit design.
Optical fibre is being used to overcome the limitation of
copper. It is already used in networking and storage area networks
to support faster interconnects between datacentres. The next
threshold in performance is the connectivity between chips and
processors. Researchers believe an optical link between systems
could lift the performance of future generations of computers
significantly.
Photonics is the area of research that investigates how optical
interconnect technology can replace electrical binary "on" and
"off" signals in copper cables with a bitstream of light supplied
by a bank of minute lasers.
In a recent presentation at HP Labs, HP senior fellow Stan
Williams predicted that light transmitted through optical fibre
would eventually replace electrical signals sent through copper
cables. "The future of communication inside a datacentre, inside a
computer rack, inside a blade and eventually even between and on
chips belongs to the photon."
While HP has been researching a variety of potential
technologies to enable photonic interconnects, from component-level
connections to interconnects that are metres in length, to succeed,
photonics needs to be adopted industry-wide. "It is clear that
creating a multi-scale optical fabric for computation will be a
community effort," says Williams.
Unlike industry photonics initiatives of the past, which were
dependent upon eventual trickle-down from low-volume, high-cost
proprietary systems, Morris says HP is trying to bring the
fundamental advantages of photonic signalling technology to the
mass market.
Intel sees the importance of mass producing photonics devices
and made a breakthrough last year, announcing it had built the
world's first
40gbps Silicon Laser Modulator. Given that Intel and other
companies in the semiconductor industry are fully tooled up in the
fabrication of silicon chips, this device from Intel shows it may
be possible one day to mass produce silicon-based optical
devices.
The microprocessor giant has a strategy as part of its
multi-core roadmap to provide end users with tera-scale computing,
where thousands of processor cores combine to boost desktop and
server computing. Intel knows how to put multiple processor cores
on silicon chips. And over time its fabrication process will be
fine-turned to enable it to embed greater numbers of processor
cores on a single chip. But to achieve tera-scale computing, Intel
needs an electrically efficient mechanism to link thousands of
processors together. Copper is unsuitable, and photonics may be its
only option.
Justin Rattner, Intel chief technology officer, says, "We see
silicon photonics at the heart of future, low cost optical
interconnects for tera-scale computing."
Tera-scale computing may seem a long way off, but photonics has
some short-term benefits that could improve datacentre computing.
One of the most exciting is in the area of green IT. HP is
investigating how photonics could be used to replace the copper
connections in
blade servers. Copper is not energy-efficient it is
increasingly scarce and expensive and mining it can create
environmental problems. According to HP, photonic interconnects can
improve performance, solve bandwidth problems, and operate at much
lower power than conventional electrical switches in copper
cicuits. Morris says building servers using optical connections
could cut power use annually by 40% worldwide, so the potential
benefits of photonics are significant.
Copper could save on fibre as boffins aim for 100gbps
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