Adaptive optics based on analog parallel stochastic optimization: analysis and experimental demonstration

Abstract

Wave-front distortion compensation using direct system performance metric optimization is studied both theoretically and experimentally. It is shown how different requirements for wave-front control can be incorporated, and how information from different wave-front sensor types can be fused, within a generalized gradient descent optimization paradigm. In our experiments a very-large-scale integration (VLSI) system implementing a simultaneous perturbation stochastic approximation optimization algorithm was applied for real-time adaptive control of multielement wave-front correctors. The custom-chip controller is used in two adaptive laser beam focusing systems, one with a 127-element liquid-crystal phase modulator and the other with beam steering and 37-control channel micromachined deformable mirrors. The submillisecond response time of the micromachined deformable mirror and the parallel nature of the analog VLSI control architecture provide for high-speed adaptive compensation of dynamical phase aberrations of a laser beam under conditions of strong intensity scintillations. Experimental results demonstrate improvement of laser beam quality at the receiver plane in the spectral band up to 60 Hz.

Simulated Annealing for Control of Adaptive Optics System

“…This independence, as well as being a simple straightforward algorithm to implementation, allows a great deal of latitude in system design. The reason why we compare these algorithms with the simulated annealing is that these algorithms has ever been used to control the adaptive optics system and obtained some valuable research results, such as GA (Yang et al 2007), Alopex (Zakynthinaki & Saridakis, 2003), SA (Zommer et al 2006 ), SPGD (Vorontsov & Carhart, 2000).…”

“…SPGD (Vorontsov & Carhart, 2000) control is a "hill-climbing" technique implemented by the direct optimization of a system performance metric applied through an active optical component. Control is based on the maximization (or, with equal complexity minimization) of a system performance metric by small adjustments in actuator displacement in the mirror array.…”

Integrated multi-dithering controller for adaptive optics

“…The need for high-speed adaptive controllers for phase correction is therefore apparent, and significant efforts in the optical engineering community have been directed towards increasing bandwidth and precision of adaptive optics control systems, e.g. [6], [7].…”

“…Effective compensation of scintillation caused by atmospheric turbulence has been demonstrated [7], [8] by using analog VLSI chips implementing the stochastic parallel gradient descent (SPGD) optimization technique for bandwidths up to several hundreds of Hz. A challenging task has been to opt the adaptation speeds of such controllers, by possibly implementing different algorithms in VLSI, in order to be able to compensate higher bandwidth sources of phase distortion.…”

Design of surface shape control for large two-dimensional arrays

“…Decentralized localized control approaches will significantly improve computational performance, and for MEMS technology, they could be implemented on the same silicon substrate as the actuator. A description of an experimenal MEMS adaptive optics system with distributed local computing can be found in [12].…”