Focal-plane image and beam quality sensors for adaptive optics

Control of adaptive optical elements for real-time wavefront phase distortion compensation is a rapidly growing field of research and technology development. Wavefront correction is essential for reliable long distance, near-ground laser communication as well as for imaging extended objects over large distances. Crucial to adaptively correcting the wavefront is a performance metric that can be directly evaluated from the acquired image or received laser beam, to provide real-time feedback to the controller adapting the wavefront. Custom VLSI controllers and sensors are a good match to the requirements of high resolution, real-time adaptive optical systems. In this paper we introduce two VLSI focal plane sensors that supply image and beam quality metrics to an adaptive controller that performs parallel perturbative stochastic gradient descent on a spatial phase modulator in the control loop. For imaging applications, we designed an image quality metric chip that reports the high spatial frequency energy content of the received image. For laser communications applications, we designed a beam variance metric chip that calculates the compactness of the transmitted or received beam as well as its centroid location. We present experimental results from both sensor chips and demonstrate the beam variance metric chip in the feedback loop of an adaptive optics laser receiver.