Multipoint phase calibration for improved compensation of inherent wavefront distortion in parallel aligned liquid crystal on silicon displays

Author(s): Joaquín Otón, Pierre Ambs, María S. Millán, and Elisabet Pérez-Cabré

Abstract:

“The inherent distortion of a reflective parallel aligned spatial light modulator (SLM) may need compensation not only for the backplane curvature but also for other possible nonuniformities caused by thickness variations of the liquid crystal layer across the aperture. First, we build a global look-up table (LUT) of phase modulation versus the addressed gray level for the whole device aperture. Second, when a lack of spatial uniformity is observed, we define a grid of cells onto the SLM aperture and develop a multipoint calibration. The relative phase variations between neighboring cells for a uniform gray level lead us to build a multi-LUT for improved compensation. Multipoint calibration can be done using either phase-shift interferometry or Fourier diffraction pattern analysis of binary phase gratings. Experimental results show the compensation progress in diffractive optical elements displayed on two SLMs.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 46, Issue 23, pp. 5667-5679, 2007
DOI: 10.1364/AO.46.005667

Twisted-nematic liquid-crystal-on-silicon adaptive optics aberrometer and wavefront corrector

Author(s): Seow-Hwang Eng, Douglas Chai, Fred Reinholz

Abstract:

“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.”

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Publication: Journal of Biomedical Optics
Issue/Year: J. Biomed. Opt. 14, 044014 (Jul 27, 2009)
DOI: 10.1117/1.3183814

Wavefront correction of spatial light modulators using an optical vortex image

Author(s): A. Jesacher, A. Schwaighofer, S. Fürhapter, C. Maurer, S. Bernet, and M. Ritsch-Marte

Abstract:

“We present a fast and flexible non-interferometric method for the correction of small surface deviations on spatial light modulators, based on the Gerchberg-Saxton algorithm. The surface distortion information is extracted from the shape of a single optical vortex, which is created by the light modulator. The method can be implemented in optical tweezers systems for an optimization of trapping fields, or in an imaging system for an optimization of the point-spread-function of the entire image path.”

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Publication:Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 9, pp. 5801-5808
DOI: 10.1364/OE.15.005801

Liquid Crystal based adaptive optics system to compensate both low and high order aberrations in a model eye

Author(s): Quanquan Mu, Zhaoliang Cao, Dayu Li, Lifa Hu, and Li Xuan

Abstract:

“Based on a simple eye model system, a high resolution adaptive optics retina imaging system was built to demonstrate the availability of using liquid crystal devices as a wave-front corrector for both low and high order aberrations. Myopia glass was used to introduce large low order aberrations. A fiber bundle was used to simulate the retina. After correction, its image at different diopters became very clear. We can get a root mean square (RMS) correction precision of lower than 0.049λ (λ=0.63μm) for over to 10 diopters and the modulation transfer function (MTF) retains 511p/mm, which is nearly the diffraction limited resolution for a 2.7mm pupil diameter. The closed loop bandwidth was nearly 4 Hz, which is capable to track most of the aberration dynamics in a real eye.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 4, pp. 1946-1953
DOI: 10.1364/OE.15.001946

Real-time digital holographic beam-shaping system with a genetic feedback tuning loop

Author(s): Joonku Hahn, Hwi Kim, Kyongsik Choi, and Byoungho Lee

Abstract:

“A novel implementation of a real-time digital holographic system with a genetic feedback tuning loop is proposed. The proposed genetic feedback tuning loop is effective in encoding optimal phase holograms on a liquid-crystal spatial light modulator in the system. Optimal calibration of the liquid-crystal spatial light modulator can be achieved via the genetic feedback tuning loop, and the optimal phase hologram can then overcome the aberration of the internal optics of the system.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 45, Issue 5, pp. 915-924, 2006
DOI: 10.1364/AO.45.000915

Dynamic closed-loop system for focus tracking using a spatial light modulator and a deformable membrane mirror

Author(s): Amanda J. Wright, Brett A. Patterson, Simon P. Poland, John M. Girkin, Graham M. Gibson, and Miles J. Padgett

Abstract:

“A dynamic closed-loop method for focus tracking using a spatial light modulator and a deformable membrane mirror within a confocal microscope is described. We report that it is possible to track defocus over a distance of up to 80 µm with an RMS precision of 57 nm. For demonstration purposes we concentrate on defocus, although in principle the method applies to any wavefront shape or aberration that can be successfully reproduced by the deformable membrane mirror and spatial light modulator, for example, spherical aberration.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 14, Issue 1, pp. 222-228, 2006
DOI: 10.1364/OPEX.14.000222

Spiral interferometry

Author(s): Severin Fürhapter, Alexander Jesacher, Stefan Bernet, and Monika Ritsch-Marte

Abstract:

“We present a surprising modification of optical interferometry. A so-called spiral phase element in the beam path of a standard microscope results in an interferogram of phase samples, for which the interference fringes have the shape of spirals instead of closed contour lines as in traditional interferograms. This configuration overrides the basic problem of interferometry, i.e., that elevations and depressions cannot be distinguished. Therefore a complete sample profile can be reconstructed from a single exposure, promising, e.g., high-speed metrology with a single laser pulse. The method is easy to implement, it does not require a spatially separated reference beam, and it is optimally stable against environmental noise.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 30, Issue 15, pp. 1953-1955 (2005)
DOI: 10.1364/OL.30.001953
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