PROCEEDINGS ARTICLE | August 21, 2009
Proc. SPIE. 7464, Free-Space Laser Communications IX
KEYWORDS: Photodetectors, Retroreflectors, Modulation, Sensors, Video, Free space, Telecommunications, Optical communications, Free space optics, Scintillation
Small robots are finding increasing use for operations in areas that may be dangerous to humans.
These robots often have needs for high bandwidth communications to return video and other data.
While radio frequency (RF) links can be used in may cases, in some circumstances they may be
impractical due to frequency congestion, reflections off surfaces, jamming or other RF noise. In
these cases an optical link may be advantageous, particularly when a clear line of sight exists.
However, a conventional optical link has limitations for this application. For example, a
conventional optical link operating at rates of megabits per second at ranges of 1 Km requires
about a 1 degree pointing accuracy. This implies a need for active pointing and tracking, which
maybe be unacceptable for a small platform. We explored an optical modulating retroreflector
(MRR) link for these cases. An array of 6 MRRs and photodetectors with a field of view of 180 degrees (azimuth)x 30 degrees (elevation) was constructed and mounted a small robot, the iRobot
PackbotTM. An Ethernet modem designed to work with MRR links was also part of the system.
Using a tracking laser interrogator at the other end of the link, a 1.5 Mbps free space optical
Ethernet link was established that completely replaced the normal RF Ethernet link. The link was
demonstrated out to ranges of 1 Km down a road, exceeding the range of the RF link. Design
issues and measurements of performance will be described.
