Recent developments on free space optical links and wavelength analysis

New results derived from the research in the field of Free Space Optics (FSO) for the qualification of different wavelengths with reference to space applications are presented. At the beginning, a brief introduction to the FSO technology and the explanation of some performance evaluation criteria is presented. The main part deals with a thorough discussion of the different optical wavelengths used either for terrestrial as well as for near-Earth and deep space FSO links. Some optical signal propagation experiments through the atmosphere (including the recent investigations in airborne and satellite application for FSO) are also shown. Practical results of COST Action IC-0802 are implemented in the modelling of the FSO channel under deteriorating conditions like rain, snow, dust, fog, clouds and other atmospheric effects. It is intended to interconnect well-proved technologies like 850 nm and 1,064 nm wavelength with new technologies under development like 10 μm wavelength. Quantum Cascade Lasers (QCLs) are currently experiencing a strong progression. Semiconductor quantum cascade lasers can operate at various wavelengths between 3 μm up to 17 μm what makes them attractive in view of the 10 μm technology. Finally, some recent major performance improvement results obtained by employing some specific modulation and coding schemes are presented.