An Iterative Model for Micro-Electro-Mechanical-Systems (MEMS) Deformable Mirrors
Célia Blain(1), Olivier Guyon(2), Colin Bradley(1), Frantz Martinache(2), Christophe Clergeon(2)
(1) University of Victoria Adaptive Optics Laboratory (2) Subaru Telescope, NAOJ
We present a high accuracy Micro-Electro-Mechanical-System (MEMS) deformable mirror (DM) control algorithm which was implemented in the real-time control interface of the Subaru Coronagraphic Extreme Adaptive Optics project (SCExAO) for the on-sky engineering run of July 2011. MEMS DMs are an attractive DM technology for ExAO because they offer unprecedented actuator density and actuator counts. The small size and low cost per actuator also make them attractive for Multi-Object AO (MOAO), where one DM is needed per science field. These applications both require a DM model capable of reproducing a phase map with a precision of few nm rms. The high accuracy DM control algorithm presented below is suitable for open-loop AO systems where DM calibration is essential. For SCExAO, the high accuracy wavefront sensing uses DM modulations to coherently mix light with slow/static speckles and precisely measure their complex amplitude. Therefore, wavefront sensing and correction both depend on precise DM control. The model (described in Blain et al., 2011) which relies (i) on a physical model of the actuators and the membrane and (ii) on the optimization of 8 coefficients, could be adopted as an open-loop control solution for future MOAO or ExAO ELTs instruments. During the initial test phase at the UVic AO Lab, the performance of the model reached an open-loop error equal to 7.3% of the rms of the desired phase (1.6% of the peak-to-valley(PV) of the desired phase) with Kolmogorov type wavefront (test performed over 10 phase screens with a mean PV of 1448.3 nm and a mean rms of 489.5 nm).