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.
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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.
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