Free-Space Optics Wavelength Selection: 10 μ Versus Shorter Wavelengths

This paper is written in response to many inquiries about 10 μ Free-Space Optics (FSO) performance compared to shorter wavelengths. The increasing interest in better understanding FSO weather effects is the result of carrier requests as well as recent progress in analyzing fog effects on FSO signal propagation. Extensive studies in modeling fog and simulating FSO attenuations revealed the complexity behind estimating FSO link availability in a given geographical location. There are many different types of fog that are inhomogeneous along the propagation path. Each type is characterized by the water droplet sizes and their concentrations, which are used in Mie scattering theory to compute FSO signal attenuation. As a result, some vendors are augmenting their FSO links with a microwave backup link or simply investigating other wavelengths claimed to be more resistant to fog such as 10 μ. In this paper, we analyze ways to improve FSO link availability, 10 μ improvement compared to shorter wavelengths, and challenges behind successful microwave backup installation.