Date: Jan 15, 2010 Author: Joe Singleton Source: MDA (
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by Joe Singleton/jsingleton@nttc.edu
A free-space optical laser communications technology that can compensate for atmospheric distortions in real time might soon break the bandwidth bottleneck for cellular telephony networks and high-definition broadcast television transmissions.
AOptix Technologies, Inc. (Campbell, CA), has developed a laser communications system that uses deformable mirrors to send and receive signals transmitted through free space. Known as curvature adaptive optics, this technological approach relies on adjustable mirrors to compensate for the atmospheric interference that occurs as laser beams travel from point to point through the air. This wireless optical alternative helps to reduce network congestion bottlenecks caused by the spectral limitations common in radio-frequency (RF)-based systems.
MDA funded AOptix through a 2004 SBIR Phase II contract to develop an adaptive optics system capable of reducing the transmission challenges caused by the effects of atmospheric turbulence—the mixing of warm and cold air in the atmosphere.
The AOptix free-space laser-communications system focuses on controlling the optical paths used to transmit data through the atmosphere. When such data are transmitted in orbit, there is little problem because there is no atmosphere. But when the data are transmitted from Earth to a satellite or from a satellite to the Earth, the atmosphere does become an issue. The atmospheric disturbances distort the laser beam resulting in wavefront errors. These errors cause the beam itself to disperse, minimizing the light energy at the receiving location.
To minimize the effects of atmospheric disturbances, AOptix has developed a bi-directional, closed-loop-control system with its patented curvature adaptive optics. The system includes a specially designed deformable mirror that allows bi-directional optical data traffic, and a suite of sensors that collect, measure, and calculate the atmospheric distortions. As the system receives broadcast signal transmissions through free space, its sensor suite measures any wavefront errors. Then signals that have become distorted by atmospheric conditions are transmitted through the system's deformable mirror, ultimately becoming reformed and corrected onto an optical fiber or optical detector. The process also works in reverse, pre-correcting the transmission beam for atmospheric disturbances it will encounter on its outgoing journey. Once corrected, the signals are sent via optical fibers to a ground-based network node, from which devices capable of receiving the data can be reached. Such devices include computers, televisions or a cellular telephony infrastructure.
The main advantages of the AOptix laser communications system over traditional RF-based sys-tems are the technology's ability to deploy ultra-high bandwidths through reduced size, weight, power, and the fact that the optical spectrum does not require International Telecommunications Union allocation or licensing. To get the same transmission capabilities of a laser communications system, tens of RF systems would be required—but there would still be no guarantee against signal distortion, said David Abelson, AOptix vice president for business development.
Company tests show the adaptive optics technology is energy-efficient, operating on as little as 30 watts of power. Most RF technologies require several hundred watts to operate. AOptix's system is also faster, according to Abelson. Adaptive optics enable data transmission rates of more than 40 gigabytes per second, compared with the 274 megabytes common to comparable RF technologies.
AOptix's technology uses a very small-diameter laser beam capable of traveling tens of kilometers for line-of-sight transmissions. Such a system can reduce the chance of malicious eavesdropping or jamming of signals—a serious concern with military communications. RF transmissions do not have the same emission pattern, making communications security an ever-present concern.
The company, primarily funded by venture capital, is looking to further market its adaptive-optics technology to a wide array of potential users, including telecommunications companies, television broadcasters, intelligence agencies, law-enforcement agencies, or any organization needing long-distance, ultra-fast data transmission.
Beyond the commercial world, AOptix continues its quest to improve military communications, as first tested during the MDA SBIR project. The company now is teamed with Northrop Grumman, L3 Communications, and Johns Hopkins University to develop a fully functional Optical RF Communications Adjunct-networked communications system.
