Design, Testing and Performance Evaluation of Beam Positioning System for Free Space Optical Communication System

Abstract

Beam wandering and the wavefront distortion are the significant sources for the power loss in Wireless Optical Communication (WOC). In this paper Full Factorial Design (FFD) and Back Propagation Neural Network (BPNN) controller based autonomous beam monitoring, positioning and recovery system for fine steering of the laser beam at the focal point of the FSOC receiver is proposed. The proposed controllers process the intensity information of the received optical beam as inputs and produce the control signals as outputs. These control signals bring the beam at the focal point of the receiver and avoid the power loss of the optical link. The work describes, performance analysis of Field Programmable Gate Array (FPGA) based novel digital architecture of FFD and BPNN controller. Real time experimental verification of the stability and suitability of the developed adaptive controllers are tested for percentage of prediction error, Bit Error Rate (BER) and beam wander reduction ability and the same is demonstrated with suitable results. The experimental result shows that the BPNN controller gives high accurate approximation towards the control for the control signals Cx and Cy with the minimum and maximum values of 99.29% and 99.86% respectively. With the chosen parameters, the neuro-controller exhibits fast response for the error changes. The proposed BPNN controller provides prediction error very close to -0.5 to +1.0%, the values lie in the range of -0.06781% and 0.9862% which shows that the BPNN controller is efficient for the real time tracking and control for FSOC, LIDAR imaging, micro/nano positioning, atomic force microscopes, scanning tunnelling microscopes, etc.