.61-element Adaptive Optical System Real-time Wave Processing Technology

The adaptive optics (AO) system can measure and correct the static and dynamic wavefront error of an optics system in real time. For an AO system designed to compensate the atmosphere turbulence disturbed wavefront error, there must be up to several hundreds of actuators and up to several hundred Herz of control bandwidth. In modern AO system, high speed digital CCD camera is used generally in wavefront sensing, and the high speed digital wavefront processing computer (WPC)is used to do the imaging processing, the wavefront reconstruction and the wavefront control in real time. While the sampling frequency, the number of subapertures of Hartmann wavefront sensor and the number of actuators of deformable mirror is fixed, the control bandwidth of an AO system is limited by the time-delay of WPC. In order to improve the dynamic performance of an AO system, it is important to enhance the real-time characteristic of WPC, and reduce the time-delay of WPC.This paper analysed the tasks of WPC in AO system, the main calculation and calculation quantity of every task, the data flow relationship between tasks. The serial processing, inter-frame pipeline processing, inner-frame pipeline processing, double pipeline processing, parallel processing, inter-current processing and other different real-time processing methods are investigated. Both the advantage and the shortcoming, both the calculation delay and the time sequence of the WPC are discussed in detail. Based on the real time requirement, double pipeline and parallel processing method was proposed to build the WPC, a special real time digital WPC for 61 elements Adaptive Optics System operating with 2900Hz sampling frequency was designed. The WPC consists of 17 DSPs, with the peak speed of 850 million per second. This WPC is the largest scale and the fastest in china by now. The time delay of the WPC is only 330μs, which meets the real time requirement of the 61 elements AO system。Finally, shortcomings of this WPC are analysed, several research directions to improve the real time and flexibility of WPC in future are proposed too.