Free-space optical (FSO) communication is fast emerging as a viable option for the "last mile" wireless network extension to the existing optical fiber infrastructure. An FSO communication system provides data rates compatible with those of optical fiber but higher than those of radio frequency systems. FSO deployment is inexpensive and does not require digging up ground as is the case with fiber, or obtaining FCC licensing as is the case with RF system. Unlike fiber or RF installations, a new FSO installation can be accomplished in hours or days. However, one major disadvantage that hinders the widespread deployment of FSO systems is the degradation effect that adverse weather conditions have on optical signals traveling in the free space. Fog is one such condition.
The objective of this thesis is to apply wavelength diversity techniques in free-space optics to enhance the received optical signal power under different fog conditions. The same information was encoded and transmitted onto three carrier wavelengths obtained from different parts of the infrared spectrum: 850 nanometer, 1,550 nanometer, and 10 microns. The transmitted carriers travel 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 results of this work show an average power reception improvement in tens of percent, by comparison to the use of a single carrier. The increase of power translates to a distance improvement of at least fifteen percent.
