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Proceedings Paper

Performances of the fractal iterative method with an internal model control law on the ESO end-to-end ELT adaptive optics simulator
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Paper Abstract

Adaptive Optics systems under study for the Extremely Large Telescopes gave rise to a new generation of algorithms for both wavefront reconstruction and the control law. In the first place, the large number of controlled actuators impose the use of computationally efficient methods. Secondly, the performance criterion is no longer solely based on nulling residual measurements. Priors on turbulence must be inserted. In order to satisfy these two requirements, we suggested to associate the Fractal Iterative Method for the estimation step with an Internal Model Control. This combination has now been tested on an end-to-end adaptive optics numerical simulator at ESO, named Octopus. Results are presented here and performance of our method is compared to the classical Matrix-Vector Multiplication combined with a pure integrator. In the light of a theoretical analysis of our control algorithm, we investigate the influence of several errors contributions on our simulations. The reconstruction error varies with the signal-to-noise ratio but is limited by the use of priors. The ratio between the system loop delay and the wavefront coherence time also impacts on the reachable Strehl ratio. Whereas no instabilities are observed, correction quality is obviously affected at low flux, when subapertures extinctions are frequent. Last but not least, the simulations have demonstrated the robustness of the method with respect to sensor modeling errors and actuators misalignments.

Paper Details

Date Published: 7 July 2008
PDF: 9 pages
Proc. SPIE 7015, Adaptive Optics Systems, 70151H (7 July 2008); doi: 10.1117/12.788805
Show Author Affiliations
C. Béchet, Univ. de Lyon (France)
M. Le Louarn, European Southern Observatory (Germany)
M. Tallon, Univ. de Lyon (France)
É. Thiébaut, Univ. de Lyon (France)

Published in SPIE Proceedings Vol. 7015:
Adaptive Optics Systems
Norbert Hubin; Claire E. Max; Peter L. Wizinowich, Editor(s)

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