Wavelength diversity in free-space optics to alleviate fog effects

Free-space optical communication systems are adversely affected by weather conditions, especially fog. The objective of this paper is to examine the use of wavelength diversity in free-space optics to mitigate the effect of fog on the received optical signal strength. The source information was encoded and transmitted onto three carrier wavelengths obtained from different parts of the infrared spectrum: 0.85 mu m, 1.55 mu m, and 10 mu m. The transmitted carriers traveled through two different simulated fog conditions, radiation and advection, before being detected and decoded by the receiver. Then, the multiple carriers were combined and processed using two diversity schemes: equal gain and selective diversity. The study was conducted using simulation software PcModWin by onTar Corporation. The results show an average power reception improvement in tens of percent, by comparison to the use of a single carrier. Hence, the increase of the received power translates into a distance improvement of at least fifteen percent.