Control bandwidth analysis of adaptive optical systems

For wavefront disturbance to be corrected, an adaptive optics system acts as a low pass filter, for noise of wavefront sensor-as high pass filter. For most of AO systems there is a time delay in wavefront sensing and processing, and the bandwidths will be limited by the time delay. In this paper, three kinds of transfer functions (close-loop, open-loop and error transfer functions) for an AO system with time delay are analyzed. The four criteria of bandwidths are defined and compared between a simple proportional-integral (PI) control algorithm and a Smith control algorithm. By using the Smith algorithm, the bandwidths are improved. The experimental results of the transfer functions and bandwidths with our newly developed 61 elements system are also presented.