4 Conclusion

The advantages and the disadvantages of use of a free-space optical link are summarised. Among the advantages we have quoted: high data rates (from 2 Mbps to 2500 Mbps and more), transparent protocol, interfaces diversity, absence of licence and regulation, simple, fast and reusable deployment, relatively protected transmission etc. Among the disadvantages we have quoted: no data guarantees by the manufacturers in term of availability and QoS, limited distances, line of sight technology, new technology, thus retreat and lack of information, parameters of ocular safety related to the laser class of the equipment.

In the search for equipment, one will choose the weakest laser class in order to limit the number of precautions and restrictions at the moment of deployment and maintenance.

It appears that the optimal establishment configuration of an equipment seems to be a short link, a high data rate and a point-to-point service.

We have also presented the various aspects of the propagation to be considered at the moment of the deployment of a free-space optical links ( geometrical attenuation, atmospheric effects, scintillations, beam misalignment).

We saw that the weather phenomena which bring the most important attenuation are in order, fog, dry snow, rainstorms ( generally short) and light rains. Fog constitutes the most important phenomenon . It is frequent in certain years and slow to be dissipated.

The installation of experimental links should make it possible to show that free-space optical links can constitute a reliable alternative broadband to the optical fiber installation and lead to a better acceptance of this technology in industry than the high data rate telecommunications networks necessary, between others, for the future deployment of many communicating objects.