FPGA-accelerated adaptive optics wavefront control

Abstract

The speed of real-time adaptive optical systems is primarily restricted by the data processing hardware and computational aspects. Furthermore, the application of mirror layouts with increasing numbers of actuators reduces the bandwidth (speed) of the system and, thus, the number of applicable control algorithms. This burden turns out a key-impediment for deformable mirrors with continuous mirror surface and highly coupled actuator influence functions. In this regard, specialized hardware is necessary for high performance real-time control applications. Our approach to overcome this challenge is an adaptive optics system based on a Shack-Hartmann wavefront sensor (SHWFS) with a CameraLink interface. The data processing is based on a high performance Intel Core i7 Quadcore hard real-time Linux system. Employing a Xilinx Kintex-7 FPGA, an own developed PCie card is outlined in order to accelerate the analysis of a Shack-Hartmann Wavefront Sensor. A recently developed real-time capable spot detection algorithm evaluates the wavefront. The main features of the presented system are the reduction of latency and the acceleration of computation For example, matrix multiplications which in general are of complexity O(n3 are accelerated by using the DSP48 slices of the field-programmable gate array (FPGA) as well as a novel hardware implementation of the SHWFS algorithm. Further benefits are the Streaming SIMD Extensions (SSE) which intensively use the parallelization capability of the processor for further reducing the latency and increasing the bandwidth of the closed-loop. Due to this approach, up to 64 actuators of a deformable mirror can be handled and controlled without noticeable restriction from computational burdens

Implementing a Hybrid Method for Shack–Hartmann Wavefront Spots Labeling on FPGA

“…Based on the ordered spots, the slopes and actuator values for an AO system can be calculated using the well-established methods described in refs. [5,40].…”

“…The holographic sensing method would allow direct measurements of wavefront modes with the readout speed of photodiodes, which could be up to the MHz range [4]. The Shack-Hartmann sensor can capture data in real time, which makes it suitable for real-time systems [5]. This method has been used for the successful demonstration of adaptive optics correction of atmospheric turbulence in breadboard and free-space experiments, e.g., classical laser [6][7][8] and quantum communications [9,10].…”

Real‐Time Adaptive Optic System Using FPGAs

“…The other interfaces are neglected in this context but are presented in detail in Refs. [9,21]. The integration of the FPGA card is realized via the PCIe interface.…”

FPGA Implementation of Shack–Hartmann Wavefront Sensing Using Stream-Based Center of Gravity Method for Centroid Estimation

“…In addition to the effort to improve the accuracy of centroid estimation algorithms, other researchers also tried to increase the wavefront sensing speed by utilizing special hardware such as GPU [22,23] or field-programmable gate array (FPGA) devices for implementation. For example, FPGA devices have been used both in complex AO systems to process data where the timing is crucial [24][25][26], or used to implement centroid estimation and reconstruction [27][28][29], or even to develop full AO application including driving the wavefront corrector [30,31]. In comparison with conventional CPU [32] or GPU-based solutions, FPGA devices provide a cost-effective way to achieve a high throughput, low latency and reconfigurable wavefront sensing, and AO system thanks to their parallel computation power.…”