Multi-Gigabits-per-second Optical Wireless Communications

Optical wireless is increasingly becoming an attractive option for multi-gigabit-per-second (multi-Gb/s) short range (up to 2 km) links where laying optical fiber is too expensive or impractical. For such links, a tracking scheme is essential to maintain proper pointing of the transceivers at each other to establish error-free communication. For the transmitter, the tracking ensures that a narrow beam is pointed at the receiver with minimal residual jitter in the presence of atmospheric beam-wander, building sway, and wind/temperature loading effects. For the receiver, the tracking ensures a tight focus on a relatively small detector (typically less than 100 μm) in the presence of atmospheric induced angle-of-arrival fluctuations, roof vibration caused by air-conditioning units, and wind loading effects. We present data on some of these angular noise sources as well as noise suppression capabilities of our tracking subsystem. Active tracking in our systems allows us to use sub-milliradian beams for communication. Error-free one-kilometer links at 1.25 Gb/s have been established with less than 1 mW of optical transmitter power.