Purchase this article with an account.
K. Y. Li, P. Tiruveedhula, A. Roorda; Assessment of a Linearized Controller on a MEMS Adaptive Optics System for Correcting Static and Dynamic Aberrations. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4197. doi: https://doi.org/.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Performance of adaptive optics (AO) controllers can be improved with better modeling and wavefront reconstructor design1. Our goal is to implement a control system on an AO testbed for real-time testing of control algorithms and reconstructors on model and real eyes.
An integrator with Smith-predictor type controller was implemented on an AO testbed consisting of a 12 by 12 MEMS deformable mirror (DM) (3.5 µm stroke, Boston Micromachines Corporation) and a Shack-Hartmann (SH) wavefront sensor. Integral and Smith-predictor gains were set at 1.0 and 0.05 respectively and tuned online when necessary. The controller is designed such that the computation unit of choice aims to linearize the response of the DM, and that either zonal or modal (Zernike polynomials up to 10th order) reconstruction can be used. The controller was tested on 2 real eyes that had pre AO correction root-mean-squared (rms) wavefront errors of 0.73 and 0.58 µm and 4 model eyes using phase plates2 with uncorrected rms of 0.97, 1.17, 0.81 and 0.47 µm. The control update rate was 20 Hz for the model eyes and approximately 13 Hz for the real eyes. Wavefront error after AO correction was estimated from SH sensor data using a geometric zonal reconstructor3.
Using the proposed design, a correction of 74 to 83 percent of the initial wavefront error for the model eyes and 65 and 70 percent for the two real eyes can be achieved within 2 control steps according to the rms of the estimated residual wavefront. For the model eyes, residual rms values below 0.08 µm was achieved for the 2 aberration profiles with lower initial levels of aberrations. Comparable levels of correction (0.06 ± 0.003 and 0.116 ± 0.012 µm rms) were observed for the real eyes since they had similar amounts of aberrations prior to correction. Residual rms values for the other 2 static aberration profiles settled at 0.17 and 0.22 µm respectively due to stroke limitations imposed by the DM.
Fast and stable correction of the eye’s aberrations to or close to levels desired for retinal imaging has been demonstrated using the proposed control strategy.1. L. H. Lee, "Loopshaped wavefront control using open-loop reconstructors," OE 14(17), 7477-7486 (2006).2. G. Yoon, T. M. Jeong, I. G. Cox, and D. R. Williams, "Vision improvement by correcting higher-order aberrations with phase plates in normal eyes," J. of Ref. Surg. 20(5), S523-S527 (2004).3. J. Herrmann, "Least-Squares Wave-Front Errors of Minimum Norm," JOSA 70(1), 28-35 (1980).
This PDF is available to Subscribers Only