Quantum cascade lasers and the Kruse model in free space optical communication

Mid-infrared (MIR) free space optical communication has seen renewed interest in recent years due to advances in quantum cascade lasers. We present data from a multi-wavelength test-bed operated in the New York metropolitan area under realistic weather conditions. We show that a mid-infrared source (8.1 mu m) provides enhanced link stability with 2x to 3x greater transmission over near infrared wavelengths (1.3 mu m & 1.5 mu m) during fog formation and up to 10x after a short scavenging rain event where fog developed and visibility reduced to similar to 1 km. We attribute the improvement to less Mie scattering at longer wavelengths. We confirm that this result is generally consistent with the empirical benchmark Kruse model at visibilities above 2.5 km, but towards the 1 km eye-seeing limit we measured the equivalent MIR visibility to be > 10 km. (C) 2008 Optical Society of America