Scientists at Lawrence Livermore National Laboratory in Livermore, Calif., have successfully established a 28-km-long air-optics link between the laboratory and nearby Mount Diablo.One of the longest such high-capacity laser communications links in existence, the system is being tested as part of the lab's Secure Air-Optic Transport and Routing Network (SATRN) as a means of communicating strategic information in situations where radio-frequency or microwave wireless communication lacks sufficient bandwidth and where laying fiber optic cable is impractical.The system used a 1550-nm diode laser amplified with wavelength-division-multiplexed, erbium-doped fiber to send information at 10 Gb/s over four channels (2.5 Gb/s per channel). To receive the signal, the researchers used a system based on a modified fiber-coupled 16-in. telescope and a fiber-coupled 6-in. transmitter. Initial trials have shown that bit error rates for uncoded single channels are typically on the scale of 10-4 to 10-5 -- although these vary with atmospheric conditions.