Dr. Azhar Iqbal Profile

Dr. Azhar Iqbal

at Univ of Toronto

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Proceedings Article | 16 October 2019 Paper

Model-based wavefront sensorless control with magnetic fluid deformable mirror for large aberration corrections

Xiang Wei, Yuanyuan Wang, Zhan Cao, Dziki Mbemba, Zhu Zhang, Azhar Iqbal, Zhizheng Wu

Proceedings Volume 11205, 112051V (2019) https://doi.org/10.1117/12.2541639

KEYWORDS: Wavefronts, Adaptive optics, Magnetism, Model-based design, Control systems, Deformable mirrors, Systems modeling, Actuators

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Adaptive optics (AO) systems are used to enhance the performance of optical systems. A classical AO system consists of the wavefront corrector with the wavefront sensor (WFS). Wavefront correctors are able to compensate for aberrations in real-time with the measured aberrations. Compared with traditional wavefront correctors, the major advantage of the magnetic fluid deformable mirror (MFDM) features large deformation strokes that can be easily up to more than 100μm both for the single actuator or inter-actuators. However, the measuring range of WFS is normally small, which could limit its usage in the applications with large aberrations. Considering the idea of taking full advantages of the MFDM’s stroke strengths and the limitations of the AO system with the WFS, this paper proposes a model-based wavefront sensorless control algorithm for the adaptive optics systems with magnetic fluid deformable mirror. Compared with the model-free wavefront sensorless AO systems, the model-based control algorithm for the wavefront sensorless AO systems features faster convergence without dropping into the local optima. The model-based control approach is developed based on a relationship between the second moments of the wavefront gradients and the far-field intensity distribution by taking Zernike polynomials as the predetermined bias functions, therefore, the unknown aberrations can be corrected without the wavefront measurement in the closed-loop AO control system. The control algorithm is evaluated in a wavefront sensorless AO system setup with a prototype MFDM, where a parallel laser beam with unknown aberrations is supposed to produce a focused spot on the CCD. Experimental results show that the model-based control method can effectively make the MFDM to compensate for unknown aberrations in an imaging system

Proceedings Article | 5 August 2009 Paper

Closed-loop control of magnetic fluid deformable mirrors

Azhar Iqbal, Zhizheng Wu, Foued Ben Amara

Proceedings Volume 7386, 738628 (2009) https://doi.org/10.1117/12.839872

KEYWORDS: Wavefronts, Adaptive optics, Magnetism, Control systems, Mirrors, Deformable mirrors, Imaging systems, Actuators, Reflectivity, Prototyping

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Adaptive optics (AO) systems make use of active optical elements, namely wavefront correctors (WFC), to improve the resolution of imaging systems by compensating for complex optical aberrations. Recently, magnetic fluid deformable mirrors (MFDM) were proposed as a promising new type of WFCs. These mirrors are developed by coating the free surface of a magnetic fluid with a thin reflective film of nano-particles. The reflective surface of the mirrors can be deformed using a locally applied magnetic field and thus serves as a WFC. MFDMs have been found particularly suitable for ophthalmic imaging systems where they can be used to compensate for the complex 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 facilitated the first-ever use of a MFDM in a closed-loop AO system. The algorithm utilizes the influence function technique to decouple the multi-input multi-output system and features a proportional-integral controller structure. Experimental results showing the performance of the closed-loop system comprising the presented controller and a 19-channel prototype MFDM are presented.

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