Laser beam wander monitoring with large aperture for terrestrial free space optical communication

A prototype of large aperture laser beam wander monitor was presented for terrestrial free space optical communication, which was in order to meet the increasing demand of understanding beam propagation characteristic in the turbulent atmosphere. Compared with traditional method based on a scatter board, this equipment adopted a large aperture imaging optics to receive the whole propagation beam. Thereby the received power density was higher than traditional method and the test distance could be farer. Some design details and calibration technique were discussed. The experiment was conducted over 1.5 kilometers for 24 hours. The result showed that this device could be used for monitoring the whole beam wander and its daily changes. Furthermore, inspired by the experiment, an important phenomenon for FSO initialization was presented. It indicated that the daily variety of beam shape should be considered when the FSO began to point to each other. If the FSO device started at noon and receive aperture was located in the central beam of another terminal, the receive power might be weaken at night because of beam wander and intensity distribution change.