Evaluation of coarse- and fine-pointing methods for optical free space communication

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Free space optical communication provides a way to increase the data rate that is limited by the capabilities of current radio links. While also allowing saving of on-board power and shrinking of the size of the communication terminals, it presents more challenges in terms of the need of extremely precise pointing between the two partners involved in the link. Successful laser communication tests have been performed, e.g. between two satellites in space and between a satellite and a ground based fixed partner. A link through the atmosphere involving airborne moving terminals experiences disturbances like base-motion vibrations, fast relative motion and disturbances within the medium of propagation. These increase the requirements towards the pointing systems of the communication terminals. The traditional way to cope with misalignment is to operate two subsystems in parallel ? a coarse pointing and a fine pointing one. The current work researches on the possible technologies for the so-called fine pointing assemblies. It proposes the introduction of a medium pointing assembly as the stage between the coarse and fine pointing ones. A general design of the new approach is also present...