Lower-order adaptive beam steering system in terrestrial free space point-to-point laser communication using fine tracking sensor

The Terrestrial Free Space Point to Point Laser Communication (TFSPPLC) offers an attractive alternatives for transferring high -bandwidth data. The wave propagation takes place in optically inhomogeneous atmospheric channel. Various deleterious effects of the atmospheric channel leads the optical wave to serious signal fading, misalignments of fixed position and even complete loss of signal altogether. Therefore, understanding the atmospheric behavior to the optical wave propagation with the real time experimental data collected over long duration become significant. A TFSPPLC opto-electronic architecture is established for the range of 500m and 28.5m altitude above the surface of the earth. An Adaptive Optics (AO) based steering technique is incorporated in the experimental test-bed to mitigate the lower order temporal and spatial distortions measured at the receiver aperture. The technique of incorporating 2 Dimensional - 4 Quadrant fine tracking sensor (2D-4QS) and Fast Steering Tip-Tilt Mirror (FSTTM) in the adaptive receiver in a closed loop control configuration is presented. An Adaptive Fuzzy Logic Controller (AFLC) is developed in the Field Programmable Gate Array (FPGA) and its performance is tested in real time with generating the control signal to drive the piezoelectric actuators of FSTTM. The method of compensating the atmospheric effects using FSTTM is described. The statistical analyses of the experimental data are also presented.