Study Of The SPGD Controller Platform Of The AO System Based On FPGA

On the imaging observations of astronomical object, atmospheric turbulencecauses the wave phase distortion, and can lead to serious phase degradation, whichbrings great difficulties to the imaging. The adaptive optics system is correcting thestatic and dynamic wave front aberration, through the real-time and automaticimprovement of light wave front quality. The stochastic parallel gradient descent(Stochastic Parallel Gradient Descent: SPGD) algorithm is a new optimizationalgorithm developed in recent years, by applying the stochastic disturbance on allvariables to measure the estimates of gradient for each variables. It does not dependon the wave front aberration detection, but directly optimize system performanceevaluation function to realize the correction of the wave front aberration. Adaptiveoptical system based on the SPGD algorithm simplifies the structure of the systemand saves the cost. Also, because the SPGD algorithm has faster convergence speed,higher accuracy, the wave front correction technique based on the SPGD algorithmbecomes a hot research in the adaptive optics field.Firstly, the principles of adaptive optics, development status, SPGD AO(Adaptive Optics) system are expounded. Then, we introduces the basic principle ofthe stochastic parallel gradient descent algorithm, and analyses the factors thoseaffect the convergence speed of the SPGD algorithm. The method of the selection ofsystem performance evaluation function is given and the correction effect has beendiscussed based on different system performance evaluation function. Secondly, in virtue of the advantage of SPGD algorithm in the wave frontcorrection, the adaptive optical wave front control platform has been designed, basedon the field programmable gate array (FPGA). This design uses Altera FPGA as the core chip.The circuit design of the system functional modules and the principle of operation have beenexpounded in detail. Lastly, the program design and simulation has been finished.