| This dissertation addresses systems/controls issues crucial for practical and dependable laser communication: accurate and agile beam positioning, rejection of vibration effects of satellite-based and airborne optical platforms, correction of atmospheric distortions, as well as performance enhancement of particular system devices. Major components of an acousto-optic beam steering system have been subjected to comprehensive laboratory testing and characterization. Mathematical and computer simulation models facilitating synthesis of advanced control laws have been developed. An optimal design problem of a Bragg cell is formulated on the basis of known equations of the underlying physical phenomena, and a genetic optimization scheme has been applied to solve the resultant formidable problem. The prowess of the proposed approach has been demonstrated by design optimization examples. An adaptive model reference controller intended for enhancing characteristics of a laser beam steering system containing a “Bragg cell-quadrant detector” combination has been designed and validated by computer simulations. A novel adaptive control technique utilizing Lyapunov methodology to assure global asymptotic stability of the system, resulting in highly robust and efficient controller design, has been developed and applied to a piezoelectric mirror beam steering setup. A mathematical model describing effects of turbulence on the optical wave propagating through the atmosphere has been developed. A wavefront correction scheme based on a spatially distributed gradient minimization procedure has been designed, implemented and tested. |
