With an infrared rainbow, IBM optical chip outpaces copper wires
Big Blue's researchers have demonstrated fiber-optic technology that
could help computers break through today's speed limits by transferring
data faster.
by Stephen Shankland
CNET News
May 12, 2015 9:59 AM PDT
A stack of IBM's silicon photonics demonstration chips, each able to
send 100 gigabits of data per second, underneath a quarter. IBM Research
IBM Research engineers have pushed a step ahead with a technology called
silicon photonics designed to loosen up bottlenecks in the computing
industry.
Silicon photonics marries conventional chip technology with the
superfast data-transfer abilities of fiber optics. Sending data as light
over optical links instead of electrons over copper wires offers big
advantages in both speed and transmission distance, but because it's
expensive, it's mostly limited to long-haul uses like connecting
computers in different buildings, cities and continents.
But IBM's researchers demonstrated a computer chip that can
simultaneously transmit and receive four different colors of infrared
light over a single fiber-optic line -- a technology called
multiplexing. Each link can transmit 25 gigabits of data per second, for
a total of 100Gbps. That's enough to transfer a Blu-ray disc's
full-resolution 25 gigabyte movie every 2 seconds.
This multiplexing-based speed, combined with the chip's all-in-one
design, is an industry first, IBM said in an announcement Tuesday.
It's only a demonstration chip from a research lab at this stage, but
silicon photonics work from companies like IBM, Intel and Luxtera could
play a crucial role in advancing services like Google search, Microsoft
Office Online and Facebook social networking that are housed in mammoth
data centers packed with thousands of servers. Those servers today are
often linked with copper lines, but more economical fiber-optic links
could help unify those servers into a larger, more powerful block of
computing power. That means more sophisticated online services.
"People would love to have a way to do inexpensive silicon-compatible
photonics," said Linley Group analyst David Kanter. But the technology
hasn't been easy to develop, he said.
Silicon photonics dovetails with a number of technologies like
spintronics, exotic carbon materials and quantum computing that are in
development to ensure the computing industry can keep up its steady pace
of progress even after conventional silicon runs out of steam. The
steady progress is embodied in a 50-year-old observation called Moore's
Law named after Intel co-founder Gordon Moore.
A photograph of IBM's chip shown between records of its ability to
transmit and receive with four frequencies of light over the same
fiber-optic link. IBM Research
Commercial use later
IBM Research typically works a step ahead of what's commercially
feasible, but Big Blue expects the work will pay off for the company later.
"Making silicon photonics technology ready for widespread commercial use
will help the semiconductor industry keep pace with ever-growing demands
in computing power driven by big data and cloud services," said Arvind
Krishna, senior vice president and director of IBM Research. So-called
big-data services rely on computationally intense analysis that reveals
patterns in things like shopping, traffic or product demand.
The four-link technique could cut data-center fiber-optic costs roughly
in half, said Will Green, manager of IBM Research's Silicon Photonics Group.
"Multiplexing four wavelengths into one optical fiber means that you can
carry four times as much data per fiber, and therefore will need four
times less fiber in your interconnect system," Green said. "This fact
translates into an additional system-level cost savings for the
data-center application on the order of two times on the cost of
installed fiber."
Longer-term future
In the longer run, fiber-optic links could tie together components
within a computer, too.
Power-consumption limits have capped the speed of processors -- few
chips ever make it past 4GHz these days, meaning that their internal
clock speed ticks 4 billion times per second. As a result, computing
engineers have been looking for other ways to improve overall system
performance, and silicon photonics could play a role in keeping
processors fed with the data they need to work at maximum efficiency
instead of spending large fractions of their time idle.
Key to silicon photonics will be bringing the optical transmitters and
receivers -- transceivers -- closer to the processors that need to send
and receive data. Those components eventually will be stacked one atop
another, linked with a technology called a through-silicon via (TSV),
said An Steegen, senior vice president of process technology at Imec, a
large Belgian-based chip research group. It'll take years to bring that
idea to fruition, she predicted.
Intel has had a long-running interest in silicon photonics and with a
technology called Light Peak hoped to build an inexpensive fiber-optic
link for computers. It never commercialized that project, though,
instead partnering with Apple on the Thunderbolt technology that uses
either copper or fiber-optic links that today reach up to 40Gbps.
That's pretty fast, but copper has significant length limits. Copper
Thunderbolt cables can reach 3 meters, but fiber-optical alternatives
from Corning are available in lengths up to 60 meters.
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