22 January 2002 Rayleigh link to overcome fog attenuation
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In case of fog ground to ground free space link with a laser is almost impossible because of the strong attenuation. In principle this event is relatively rare and the usual solution is to provide an alternate radio link in such a situation. However, in several practical cases, optical links for the 'last mile' are required in order to avoid to obtain licensing for a radio channel from local authorities. Usually, however, the fog has a vertical thickness that is very limited. It is not uncommon, for instance, that in foggy nights one can easily see 'stars' while a direct vision over the ground is completely forbidden. In this case one can send a modulated beam 'onto the sky' and recover it from its side by means of Rayleigh scattering. In order to achieve competitive data rate, however, one is forced to make on-ship fast tracking of the pulse train, in order to accumulate signal for a significant range of the Rayleigh beacon. A preliminary photon budget shows that such an approach can give interesting data rate with reasonable laser power and affordable optics. A preliminary discussion of potential drawbacks and circumventing possibilities is also reported.
© (2002) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Roberto Ragazzoni, Roberto Ragazzoni, Emiliano Diolaiti, Emiliano Diolaiti, "Rayleigh link to overcome fog attenuation", Proc. SPIE 4489, Free-Space Laser Communication and Laser Imaging, (22 January 2002); doi: 10.1117/12.453220; https://doi.org/10.1117/12.453220


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