Statistical virtual eye model based on wavefront aberration

Wavefront aberration affects the quality of retinal image directly. This paper reviews the representation and reconstruction of wavefront aberration, as well as the construction of virtual eye model based on Zernike polynomial coefficients. In addition, the promising prospect of virtual eye model is emphasized.

Wavefront reconstruction algorithm for wavefront sensing based on binary aberration modes

We propose a new algorithm for wavefront sensing based on binary intensity modulation. The algorithm is based on the fact that a wavefront can be expended with a series of orthogonal and binary functions, the Walsh series. We use a spatial light modulator（SLM） to produce different binary-intensity-modulation patterns which are the simple linear transformation of the Walsh series. The optical fields under different binary-intensity-modulation patterns are detected with a photodiode.The relationships between the incident wavefront modulated with the patterns and their optical fields are built to determinate the coefficients of the Walsh series. More detailed and strict relationship equations are established with the algorithm by adding new modulation patterns according to the properties of the Walsh functions. An exact value can be acquired by solving the equations. Finally, with the help of phase unwrapping and smoothing, the wavefront can be reconstructed. The advantage of the algorithm is providing an analytical solution for the coefficients of the Walsh series to reconstruct the wavefront. The simulation experiments are presented and the effectiveness of the algorithm is demonstrated.

Configuration optimization of laser guide stars and wavefront correctors for multi-conjugation adaptive optics

Multi-conjugation adaptive optics（MCAOs） have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view（FOV）.The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors,such as deformable mirrors（DMs） or liquid crystal wavefront correctors（LCWCs）,is a very important step in the data processing of an MCAO＇s controller.In this paper,a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars（LGSs） and the reasonable conjugation heights of LCWCs.Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO.Several examples are given to demonstrate our LGSs configuration optimization method.Compared with traditional methods,our method has minimum wavefront tomographic error,which will be helpful to get higher imaging resolution at large FOV in MCAO.

A high precision phase reconstruction algorithm for multi-laser guide stars adaptive optics

Adaptive optics（AO） systems are widespread and considered as an essential part of any large aperture telescope for obtaining a high resolution imaging at present.To enlarge the imaging field of view（FOV）,multi-laser guide stars（LGSs） are currently being investigated and used for the large aperture optical telescopes.LGS measurement is necessary and pivotal to obtain the cumulative phase distortion along a target in the multi-LGSs AO system.We propose a high precision phase reconstruction algorithm to estimate the phase for a target with an uncertain turbulence profile based on the interpolation.By comparing with the conventional average method,the proposed method reduces the root mean square（RMS） error from 130 nm to 85 nm with a 30% reduction for narrow FOV.We confirm that such phase reconstruction algorithm is validated for both narrow field AO and wide field AO.

Pattern self-referenced single-pixel computational holographic imaging

We propose pattern self-referenced single-pixel common-path holography(PSSCH),which can be realized using either the digital-micromirror-device(DMD)based off-axis scheme or the DMD-based phaseshifting approach,sharing the same experimental setup,to do wavefront reconstructions.In this method,each modulation pattern is elaborately encoded to be utilized to not only sample the target wavefront but also to dynamically introduce the reference light for single-pixel common-path holographic detection.As such,it does not need to intentionally introduce a static reference light,resulting in it making full use of the pixel resolution of the modulation patterns and suppressing dynamically varying noises.Experimental demonstrations show that the proposed method can not only obtain a larger field of view than the peripheral-referenced approach but also achieve a higher imaging resolution than the checkerboardreferenced approach.The phase-shifting-based PSSCH performs better than the off-axis-based PSSCH on imaging fidelity,while the imaging speed of the latter is several times faster.Further,we demonstrate our method to do wavefront imaging of a biological sample as well as to do phase detection of a physical lens.The experimental results suggest its effectiveness in applications.

Acceleration for computer-generated hologram in head-mounted display with effective diffraction area recording method for eyes

Holographic head-mounted display（HHMD） is a specific application of holography. The previous conventional computer-generated hologram（CGH） generation method has a large redundancy and suffers from a heavy computing burden in the HHMD. A low redundancy and fast calculation method is presented for a CGH that is suitable for an HHMD with the effective diffraction area recording method. For the limited pupil size of an observing eye, the size of the area producing an effective wavefront is very small, and the calculated amount can be dramatically reduced. A numerical simulation and an augmented virtual reality experimental system are presented to verify the proposed method. 1.5% of the calculation consumption of the conventional CGH generation method is used, and good holographically reconstructed images can be observed.

Variable shearing holography with applications to phase imaging and metrology

We report variable shear interferometers employing liquid-crystal-based geometric-phase(GP)gratings.Conventional grating-based shear interferometers require two lateral shifts of the gratings to enable phase-shifting capabilities in x-and y-direction and two axial shifts of the gratings to adjust the shear amount in x-and ydirection,i.e.,these systems need control of four axes mechanically.Here we show that the GP gratings combined with a pixelated polarization camera give instantaneous-phase shifting so that no mechanical movement is necessary to obtain phase shifts.Furthermore,we show that a single fixed shear with a rotational shear axis provides a more robust selection of shears while requiring the control of only one mechanical axis.We verify this statement using spatial domain and frequency domain criteria.We further show that the resolution of the reconstructed wavefield depends not only on the numerical aperture of the imaging system,the pixel size of the detector,or the spatial coherence of the source but also on the ability to determine the shear amount accurately.To improve this,we report a methodology to accurately detect the shear amounts using the second derivative of the autocorrelation function of the measured holograms,which further relaxes the requirements on mechanical stability.

Digital holographic shape measurement using Fizeau microscopy

We present a Fizeau interferometer using a microscopic objective as a tool for surface contouring without the need for a numerical lens for reconstruction. The interferometer is associated with a telescope system to feature the object with collimated light. The experiment is conducted on two objects possessing different step heights.The phase maps from the captured off-axis holograms are calculated numerically, which allows us to deduce the contours of the objects. The great advantages of the presented technique are that it can be done in real time and there is no need for numerical lenses for micro-objects reconstruction.