An Advance May Double the Capabilities of Fiber Optics
Credit University of California, San Diego, Photonics Systems Group |
Researchers
have announced an advance that could double the capacity of fiber-optic
circuits, potentially opening the way for networks to carry more data
over long distances while significantly reducing their cost.
Writing in the journal Science on
Thursday, electrical engineers at the University of California, San
Diego proposed a way to extend the range that beams of laser light in
fiber-optic glass wires can travel and, in theory, achieve that dramatic
improvement.
One
way to understand the challenge of sending data through fiber-optic
circuits is to imagine a person shouting to someone else down a long
corridor. As the listener moves farther away, the words become fainter
and more difficult to discern as they echo off the walls.
A
similar challenge confronts the designers of networks that carry data.
Beams of laser light packed densely in fiber-optic glass wires need to
be both amplified and recreated at regular intervals to send them
thousands of miles. The process of converting the optical ones from
light to electricity and then back again is a significant part of the
cost of these networks. The process also limits how much data they can
carry.
In
its report, the group described a way to “predistort” the data that is
transmitted via laser beams so that it can be deciphered easily over
great distances.
This
is done by creating, in effect, guardrails for the light beams with a
device known as a frequency comb — using very precise and evenly spaced
signals — to encode the information before it is transmitted.
That
has the effect of embedding a digital watermark in the original data,
making it possible to transmit data accurately over much longer
distances and dispense with the need to perform optical-to-electronic
conversions at relatively short intervals.
The
researchers said they had set a transmission record for a fiber-optic
message, sending it more than 7,400 miles in a laboratory experiment
without having to regenerate the signal. That experiment is not
discussed in the just-published paper.
The
research, which has been supported in part by Google and Sumitomo
Electric Industries, a maker of fiber-optic cables, is a step closer to
the vision of an “all-optical network,” according to Nikola Alic, one of
the authors of the paper and a research scientist in the Photonics
Laboratory of the California Institute for Telecommunications and
Information Technologies at the University of California, San Diego.
Such
a network would be significantly less expensive and could carry more
data. So far, the researchers have been able to increase the power of
the lasers twentyfold to achieve transmissions over far greater
distances, he said. Until now, increasing the power of the laser signal
in current fiber-optic networks has been analogous to moving in
quicksand — the more you increase the power, the greater the challenge
of interference and distortion.
“The more you struggle, the worse off you are,” Mr. Alic said.
Bart
Stuck, a venture capitalist at Signal Lake Management and a former Bell
Laboratories scientist who conducted research in signal processing,
said of the new paper, “This is great engineering.”
Similar
ideas were used in an earlier era of communications, he noted. Although
the concept was used in the world of analog voice communications, the
U.C. San Diego researchers have pushed the ideas into the optical
communications world.
“Their contribution is doing this at gigabits per second,” Mr. Stuck said.
Other optical scientists were more skeptical about the prospects for the new approach.
“This
is very interesting research, but there will be challenges applying
this approach in the real world,” said Alan Huang, a former researcher
at Bell Labs who has worked extensively with the “Kerr Effect,” a
physical phenomenon that distorts optical signals, which the San Diego
researchers are trying to overcome. “Their results will be more or less
effective depending on the type of data transmitted.”
Optical
networks emerged during the 1980s as a faster and higher-capacity
alternative to copper-wire-based communications. Their ability to carry
vast amounts of data has been further increased by encoding multiple
streams of data in different frequencies or “colors” in the same beam of
light.
Because
the signal needs to be both amplified and regenerated at regular
intervals over long distances, power for the computers that make the
conversion between light and electrical data is required. Each
conversion step also introduces a brief delay, or “latency.” The new
research suggests a path that effectively eliminates the regeneration
over long distances.
The
growth of the Internet, driven largely by the exploding consumption of
digital video, is continuing to expand at a significant rate. Last
month, Cisco reported that annual transmitted global Internet data would
pass a threshold of one zettabyte, or the equivalent of 250 billion
DVDs, by the end of 2016.
By
comparison, all of the information stored on the World Wide Web in 2013
was estimated to be four zettabytes. The amount transmitted annually —
to be sent across networks, not just stored — is expected to reach two
zettabytes a year by 2019.
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