A Hartmann-Shack wavefront sensor (HSWS) has been proven to be a reliable tool for the quantitative analysis of human ocular aberrations. In an active adaptive optics (AO) system, it has the role to monitor wave aberrations. To ensure the exclusive retrieval of Zernike coefficients for the measured ocular wavefronts, we first nullify the AO system's aberrations. This is of particular importance in our setup with a twisted-nematic (TN) liquid-crystal-on-silicon (LCoS) chip as the wavefront manipulator due to its strong unwanted zero-order diffractive beam. We characterize the AO system's performance-before and after ocular corrections-by means of different parameters, including experimental and simulated point spread functions (PSFs). An iterative closed-loop algorithm reduces the residual wavefront error to typical values of 0.1 µm. This system constitutes a wavefront corrector that can possibly be used for high resolution retinal imaging purposes or for visual psychophysical experiments.
The ability of a liquid-crystal spatial light modulator (LC-SLM) to generate lens and lens arrays of variable focal lengths
and selectable fields of view (FOV) makes them excellent candidates for many adaptive optics applications including
free-space optical telecommunications, astronomy and retinal imaging. In this paper, we report a range of dynamic lens
and lens array designs and optimization using a LC-SLM as an adaptive Hartmann-Shack wavefront sensor. The
measured wavefront aberration is reconstructed using Zernike polynomials through the application of its conjugated
wavefront onto the LC-SLM to achieve dynamic wavefront detection and correction. Computer algorithms based on
Fourier transformation for lens synthesis have been developed to address the LC-SLM and to generate appropriate phase
holograms that emulate lens and/or lenslet arrays with programmable focal lengths, tilting angles and diameters. The
classic least-square (LS) method is used to determine the Zernike polynomial coefficients for the reconstruction of the
aberrated wavefront. Experimental results demonstrate the dynamic generation of lens arrays of variable focal lengths.
We also experimentally characterize the phase modulation performance and wavefront generation performance of the
LC-SLM through the application of Zernike functions and as diffractive optical elements (DOEs) for dynamic wavefront
generation.
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