The Study Of Adaptive Optical System Based On Shack-hartmann Wavefront Sensor

Adaptive Optics is a new technology that can measure and correct the distortedwavefront real-time. It has been widely used in many fields, such as astronomicalobservation, laser fusion and human eye retina imaging and become a focus in thesefields. Atmospheric turbulence is one of the main factors that prevent atmosphericlaser communication from practical application. For weakening the influence ofatmospheric turbulence, people utilize the fruits of adaptive optical technologyachieved in other fields, and begin to research how to improve the quality ofwavefront in laser communication using adaptive optical technology. On thebackground of laser communication’s application requirement, the theoretical analysisand experimental study on an aberrated wavefront corrected by adaptive opticalsystem were developed following the hotspot.The atmospheric turbulence’influence on laser transmission and optical imagingsystem was analyzed detailedly. Based on the adaptive optical fundamental, thesystem was investigated thoroughly in three main aspects including wavefrontdetection，wavefront reconstruction and wavefront control. Based on the theoryanalyzing, a numerical model of an adaptive optical system was expounded to correctthe aberrated wavefront.Then, in order to improve the correction precision of adaptive optical system，thehigher moment algorithm and the optimal reconstruction number’s selection methodwere proposed separately in wavefront detection and wavefront reconstruction, andtheir performance was validated by numerical simulation experiments. The resultsindicated that the higher moment algorithm can improve the precision of the centroid calculation and the appropriate reconstruction number can minimize thereconstruction error.In order to meet the real-time of adaptive optics system, the wavefront controllerwas designed according to the inner-frame pipeline and the parallel processing. Basedon the double pipeline method, the wavefront slope calculation was completed in theend of the output of CCD image, which could ensure the real-time of the system.Finally, according to the principle of wavefront compensation, a set ofexperimental adaptive optical system was established including a Shack-Hartmannwavefront sensor and a continuous surface deformable mirror. Its performance ofcorrecting abnormal wavefront was validated via two methods, self-correction methodand relative correction method. The experimental system couldn’t correct thewavefront real-time because of tha restriction of experimental conditions; itsbandwidth was limited by the control unit of a computer. But the static aberratedwavefront could be corrected. The improved iterative control algorithm was proposedin order to eliminate the impact of traditional control algorithm on the controlprecision, the wavefront’s rms acted as its estimation criterion, and the correctedoutput wavefront was converged to the expectant reference wavefront gradually. Theperformance of the improved algorithm was validated through open and closed loopexperiments. It indicated that the adaptive optics system used the new controlalgorithm, could mostly eliminate the aberration caused by the self, made thecorrected light beam close to the plane wavefront and could correct the aberratedwavefront in the correction range of the deformable mirror.