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Mixed sensitivity H∞ control of magnetic fluid deformable mirrors

This paper presents experimental results on the H∞ control of a magnetic fluid deformable mirror (MFDM) used in retinal imaging adaptive optics (AO) systems. MFDMs are a recently proposed novel type of active optical elements called wavefront correctors, which constitute the central part of AO systems. They offer cost and performance advantages over existing wavefront correctors. They have been found particularly suitable for ophthalmic imaging systems where they can be used to compensate for the complex optical aberrations in the eye that blur the images of the internal parts of the eye. However, their practical implementation in clinical devices is hampered by the lack of effective methods to control the shape of their deformable surface. This paper presents a control algorithm that can be used to compensate for high-order, time-varying optical aberrations using a MFDM. The control algorithm is developed using the mixed-sensitivity H∞ design method which ensures optimal performance in tracking the desired wavefront shapes using MFDM and also limits the magnitude of the input control voltages. Experimental results showing the performance of a closed-loop system comprising the developed controller and a 19-channel prototype MFDM are presented.