Three decades of experiment by the authors have shown that the combination of high intensity light emitting diodes, silicon photodiodes, and large aperture moulded Fresnel lens collimators of moderate focal length provide effective and economical long distance atmospheric optical communications. While the use of larger transmitter and receiver lenses increases optical flux at the detector, their greatest advantage is in dramatically reducing the depth of the scintillation or rapid signal fading. This is caused by differential phase distortion, beam steering, focusing/defocusing by air turbulence cells along the transmission path, and the effects of local coherence. It has been observed that scintillation effects diminish rapidly when the transmitter and receiver apertures are larger than the central diffraction peak of the distant aperture, or about 30-cm diameter for red light over a 160-km path.

Date Published: 15 February 2008
PDF: 12 pages
Proc. SPIE 6878, Atmospheric Propagation of Electromagnetic Waves II, 68780C (15 February 2008); doi: 10.1117/12.768227

Published in SPIE Proceedings Vol. 6878:
Atmospheric Propagation of Electromagnetic Waves II
Olga Korotkova, Editor(s)