[Laser] Researchers show-off high-speed laser communications device for space

[bernieS]

http://www.networkworld.com/community/node/84815

Researchers show-off high-speed laser communications device for space

(Photo) NIST and NASA's Jet Propulsion Laboratory demo tiny
array-on-a-chip for laser communications

By Layer 8 on Wed, 02/12/14 - 3:09pm.

Using lasers to communicate quickly through the long distances of
space has generally been the purview of science fiction.

But researchers at the National Institute of Standards and Technology
(NIST) and NASA's Jet Propulsion Laboratory (JPL) are out to change
that notion with a prototype array that can read more information -
and allow much higher data rates than conventional systems -- than
usual from single particles of light.  Lasers can transmit only very
low light levels across vast distances, so signals need to contain as
much information as possible, NASA said.

Specifically the 1.5 by 3 centimeters NIST/JPL array-on-a-chip easily
identifies the position of the exact detector in a multi-detector
system that absorbs an incoming infrared light particle, or photon,
the researchers stated.   That action may be the norm for digital
cameras but is a huge boost in these astonishingly sensitive detectors
that can register a single photon. The new device also records the
signal timing, as these particular single-photon detectors have always
done, the researchers said.

>From NIST:  In "pulse position modulation" in which a photon is
transmitted at different times and positions to encode more than the
usual one bit of information. If a light source transmitted photons
slightly to the left/right and up/down, for instance, then the new
NIST/JPL detector array circuit could decipher the two bits of
information encoded in the spatial position of the photon. Additional
bits of information could be encoded by using the arrival time of the
photon.  The new technology uses superconducting nanowire
single-photon detectors. The current design can count tens of millions
of photons per second but the researchers say it could be scaled up to
a system capable of counting of nearly a billion photons per second
with low dark (false) counts."

The NIST/JPL team has been working on this laser communications issue
for awhile and last year developed the detector arrays for the first
demonstration of two-way laser communications outside Earth's orbit.

In that test, NASA's Lunar Laser Communication Demonstration (LLCD)
made history, transmitting data from lunar orbit to Earth at a rate of
622 Megabits-per-second (Mbps). That download rate is more than six
times faster than previous state-of-the-art radio systems flown to the
moon. LLCD not only demonstrated a record-breaking download rate but
also an error-free data upload rate of 20 Mbps, NASA  stated.

The laser beam was transmitted the 239,000 miles from the primary
ground station at NASA's White Sands Complex in Las Cruces N.M., to
the LADEE spacecraft in lunar orbit. This breakthrough technology has
a laser-based space terminal that is half the weight of a comparable
radio-based terminal while using 25% less power, NASA said.  The space
agency also said that the laser communications between LLCD and Earth
ground stations was the longest two-way laser communication ever
demonstrated.

LLCD is on-board NASA's Lunar Atmosphere and Dust Environment Explorer
satellite or LADEE, currently orbiting the moon.

NIST/JPL research also shows how to make an even larger array of
detectors for future communications systems.