Optical free-space communication is one of the most promising technologies for solving future communication challenges. By using optical frequencies, the beam divergence used can be greatly reduced, which significantly improves the efficiency of these systems. However, the large distances between the communication terminals inevitably widen the beam. The atmosphere and vibrations of the terminals also inevitably cause an error in the alignment. This results in a loss of efficiency.
In this project, a laser ranger was implemented for use in the auto-focusing of a laser as well as a system for beam stabilisation. For this purpose, the deviation of the beam is measured in real time using a four-quadrant detector (4-QD) and compensated for using a tip-tilt mirror. This achieves active alignment and the laser beam is dynamically focussed on the received terminal.
