Modeling of a Magnetic-Fluid Deformable Mirror for Retinal Imaging Adaptive Optics Systems

Abstract

Magnetic-fluid deformable mirrors (MFDMs) offer a simple alternative to the costly yet inefficient wavefront correctors currently in use in adaptive optics (AO) systems. They have been found particularly suitable for AO systems used in ophthalmic applications, such as retinal imaging. However, their practical implementation in clinical devices is contingent on the development of effective methods to model and control their surface-shape. This article presents a model of the dynamic response of the surface of a MFDM to the applied magnetic field. The resulting model allows the development of high-performance shape control algorithms for the mirror surface.

Linearization of the response of a 91-actuator magnetic liquid deformable mirror

“…This has the effect of linearizing the response of the actuators (h directly proportional to b) and also amplifies the maximum amplitude the mirror can produce (h directly proportional to B 0 ). This method was demonstrated experimentally by Iqbal and Amara [9,10] and later confirmed by Brousseau et al [8].…”

“…The technique to linearize the behavior of FDMs presented in [9,10] consists of superposing a strong and uniform magnetic field to that produced by the actuators. The deformation h on the liquid surface caused by one actuator is then given by,…”

“…However, there remained a major inconvenience with the early-generation of FDMs that came from the fact that the surface of the liquid is shaped by a magnetic vector field and that the induced deformations depends on the square of the magnetic field, requiring novel complicated control algorithms [7]. A major technical breakthrough that overcomes these problems was recently proposed by Iqbal and Amara [9,10]. The simple, yet powerful, technique described in [9,10] superposes a strong and uniform magnetic field to the magnetic field of the actuators, thereby linearizing the response of the FDM.…”

“…A major technical breakthrough that overcomes these problems was recently proposed by Iqbal and Amara [9,10]. The simple, yet powerful, technique described in [9,10] superposes a strong and uniform magnetic field to the magnetic field of the actuators, thereby linearizing the response of the FDM. The major advantage of this linearization is that one can use the same proven algorithms that are used with solid deformable mirrors.…”

Modeling and Experimental Evaluation of a Circular Magnetic-Fluid Deformable Mirror

“…Although MFDMs offer performance and cost advantages, their practical implementation in AO systems requires the development of effective methods of modeling and controlling the deformable surface of these mirrors (Laird et al 2006;Brousseau et al 2007). A comprehensive model of a MFDM with rectangular geometry was recently presented by (Iqbal and Ben Amara 2007). Given that almost all optical systems are designed and described in circular geometry, it is pertinent to extend the model to circular geometry.…”