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Accepted papers to appear in an upcoming issue

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Broadband plasmon induced transparencymodulator in terahertz band based on multilayergraphene metamaterials

Zhenbin Zhang, Zhimin Liu, Fengqi Zhou, Jiawei Wang, Yuqing Wang, Xiao Zhang, Yipeng Qin, Shanshan Zhuo, xin luo, Enduo Gao, and Zao Yi

DOI: 10.1364/JOSAA.420743 Received 25 Jan 2021; Accepted 16 Apr 2021; Posted 16 Apr 2021  View: PDF

Abstract: In this study, multilayer graphene metamaterials comprising graphene-blocks and graphene-ribbon is proposed torealize the dynamic plasmon-induced transparence (PIT). By changing the position between the graphene blocks,PIT phenomenon will occur in different terahertz bands. Furthermore, PIT with a transparent window width of 1THzhas been realized. In addition, the PIT shows redshifts or blueshifts or disappears altogether upon changing theFermi level of graphene and hence a frequency selector from 3.91 THz to 7.84 THz and an electro optical switch canbe realized. Surprisingly, the group index of this structure can be increased to 469. Compared with the complex andfixed structure of previous studies, our proposed structure is simple and can be dynamically adjusted according todemands, which can provide a valuable platform and ideas to inspire the design of novel electro-optic devices.

Analytical Method for the Description of ImportantObstructed Optical Beams and the Poisson-Arago Spot

Juliano Carvalho Bento, Michel Zamboni-Rached, and Erasmo Recami

DOI: 10.1364/JOSAA.421670 Received 02 Feb 2021; Accepted 16 Apr 2021; Posted 16 Apr 2021  View: PDF

Abstract: In this work we describe analytically the diffractionof a plane wave due to a circular obstacle. In orderto obtain the desired results, we deal with the waveequation in paraxial approximation together with theDiffraction Fresnel Integral, and apply the analyticalmethod proposed by Zamboni et al [1]. As a by-productof our method, we noticed the formation of the PoissonArago Spot for ordinary beams (Plane Wave and Gaussian Beam) and a reconstruction of the beam for nondiffracting beams (Bessel Beam). Then, we pass to avectorial analysis, for better describing the electromagnetic beams.

Rapid Classification of Glaucomatous FundusImages

Hardit Singh, Simarjeet Saini, and Vasudevan Lakshminarayanan

DOI: 10.1364/JOSAA.415395 Received 23 Nov 2020; Accepted 13 Apr 2021; Posted 14 Apr 2021  View: PDF

Abstract: We propose a new method for training convolutional neural networks and use it toclassify glaucoma from fundus images. This method integrates reinforcement learning alongwith supervised learning and use it for transfer learning. The training method uses hillclimbing techniques via two different climber types namely, “random movement” and“random detection” integrated with a supervised learning model through stochastic gradientdescent with momentum (SGDM) model. The model was trained and tested using the DrishtiGS, and RIM-ONE-r2 datasets having glaucomatous and normal fundus images. Theperformance for prediction was tested by transfer learning on five CNN architectures namely,GoogLeNet, DenseNet-201, NASNet, VGG-19, and Inception-Resnet v2. A 5-foldclassification was used for evaluating the performance and high sensitivities whilemaintaining high accuracies were achieved. Of the models tested, the DenseNet-201architecture performed the best in terms of sensitivity and area under the curve (AUC). Thismethod of training allows transfer learning on small datasets and can be applied for teleophthalmology applications including training with local datasets.

An unambiguous derivation of the effective refractive indexof biological suspensions and an extension to dense tissuesuch as blood

Alexander Nahmad-Rohen and Augusto Garcia-Valenzuela

DOI: 10.1364/JOSAA.420136 Received 18 Jan 2021; Accepted 11 Apr 2021; Posted 12 Apr 2021  View: PDF

Abstract: The van de Hulst formula provides an expression for the effective refractive index or effective propagationconstant of a suspension of particles of arbitrary shape, size and refractive index in an optically homogeneous medium.However, its validity for biological matter, which often consists of very dense suspensions of cells, is unclear becauseexisting derivations of the formula or similar results rely on far-field scattering and/or on the suspension in questionbeing dilute. We present a derivation of the van de Hulst formula valid for suspensions of large, tenuous scatterers—the type biological suspensions are typically made of— which does not rely on these conditions, showing that theyare not strictly necessary for the formula to be valid. We apply these results specifically to blood and epithelial tissue.Furthermore, we determine the true condition for the formula to be valid for these types of tissues. We finally provide asimple way to estimate —and, more importantly, correct— the error incurred by the van de Hulst formula when thiscondition is not met.

Converting an array of edge dislocations into a multivortex beam

Victor Kotlyar and Alexey Kovalev

DOI: 10.1364/JOSAA.420963 Received 26 Jan 2021; Accepted 05 Apr 2021; Posted 06 Apr 2021  View: PDF

Abstract: We theoretically show how, using a cylindrical lens, a Gaussian beam with a finite number of parallel zero-intensity lines(edge dislocations) is transformed into a vortex beam that carries orbital angular momentum (OAM) and topologicalcharge (TC). Remarkably, while the original beam is assumed to carry a non-zero OAM and have no TC, the latter isshown to appear during free-space propagation. Considering two parallel center-symmetric zero-intensity lines locatedas an example, we look into the dynamics of generating two intensity nulls at the double focal length: with increasingdistance between the vertical zero-intensity lines, two optical vortices are first generated on the horizontal axis, beforeconverging at the origin and then diverging along the vertical axis. Irrespective of the between-line distance, such anoptical vortex has TC = –2 at any distance from the optical axis, except for the original plane. With changing distancebetween the zero-intensity lines, the OAM that the beam carries is changing, taking positive and negative values, or azero value at a certain between-line distance. We also show that if the number of zero-intensity lines is infinite, a vortexbeam with finite OAM and infinite TC is generated.

Reproducing Kernel Hilbert Spaces for wave optics: tutorial

Franco Gori and Rosario Martinez-Herrero

DOI: 10.1364/JOSAA.422738 Received 16 Feb 2021; Accepted 04 Apr 2021; Posted 06 Apr 2021  View: PDF

Abstract: An introduction to the Hilbert Spaces that are endowed with a Reproducing Kernel is presented on using the mathematical tools of Fourier Optics and coherence theory. After giving the basic definition of such spaces some examples are worked out to show how the inner product can take different forms depending on the particular function space one works with. The basic rule to build a RKHS is then presented together with the basic properties of those spaces. Eigenfunctions and eigenvalues of the reproducing kernel are then illustrated and lead to the important integral representation of the RK. The latter is used to present pseudomodal expansions and generalized forms of sampling. The concluding section offers some thoughts on the applications of RKHSs in wave optics. An appendix presents an introduction to treatments using more advanced concepts of functional analysis.

Airy beam propagation: autofocusing, quasi-adiffractional propagation and self healing

Jorge Anaya-Contreras, Arturo Zúñiga-Segundo, and Hector Moya-Cessa

DOI: 10.1364/JOSAA.418533 Received 24 Dec 2020; Accepted 04 Apr 2021; Posted 06 Apr 2021  View: PDF

Abstract: We study the propagation of superpositions of Airy beams and show that effectssuch as autofocusing and quasi adiffractional beams may be generated. We also give a simple analytical expression for free-propagation of any initial field, based on so-called number states, which allows us to study their self-healing properties.

Spatial coherence in two-dimensional holography

Aaron Diebold, John Pendry, Alberto Favaro, Mohammadreza Imani, and David Smith

DOI: 10.1364/JOSAA.419420 Received 12 Jan 2021; Accepted 31 Mar 2021; Posted 02 Apr 2021  View: PDF

Abstract: Holography is a long established technique for encoding an object's spatial information into a lower-dimensionalrepresentation. We investigate the role of the illumination's spatial coherence properties in the success of such an imaging system through point spread function and Fourier domain analysis. Incoherent illumination is shown to result in more robust imaging performance free of diffraction artifacts at the cost of incurring background noise and sacrificing phase retrieval. Numerical studies confirm that this background noise reduces image sensitivity as the image size increases, in agreement with other similar systems. Following this analysis, we demonstrate a 2D holographic imaging system realized with lensless, 1D measurements of microwave fields generated by dynamic metasurface apertures.

Analytical phase optical transfer function for Gaussian illumination and the optimized profiles

Thomas Gaylord, Jianhui Huang, and Yijun Bao

DOI: 10.1364/JOSAA.417407 Received 11 Dec 2020; Accepted 31 Mar 2021; Posted 02 Apr 2021  View: PDF

Abstract: The imaging performance of tomographic deconvolution phase microscopy can be described in terms of the phase optical transfer function (POTF) which, in turn, depends on the illumination profile. To facilitate the optimization of the illumination profile, an analytical calculation method based on polynomial fitting is developed to describe the POTF for general non-uniform axially-symmetric illumination. This is then applied to Gaussian and related profiles. Compared to numerical integration methods that integrate over a series of annuli, the present analytical method is much faster and is equally accurate. Further, a “balanced distribution” criterion for the POTF and a least-squares minimization are presented to optimize the uniformity of the POTF. An optimum general profile is found analytically by “relaxed optimal search” and an optimum Gaussian profile is found through a tree search. Numerical simulations confirm the performance of these optimum profiles and support the “balanced distribution” criterion introduced.

Variational Scaling Law for Atmospheric Propagation

Sophia Potoczak Bragdon, D Cargill, and Jacob Grosek

DOI: 10.1364/JOSAA.417705 Received 16 Dec 2020; Accepted 29 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: A new scaling law model for propagation of optical beams through atmospheric turbulence is presented and compared to a common scalar stochastic waveoptics technique. This methodology tracks the evolution of the important beam wavefront and phasefront parameters of a propagating Gaussian-shaped laser field as it moves through atmospheric turbulence, assuming a conservation of power. As with other scaling laws, this variational technique makes multiple simplifying assumptions about the optical beam in order to capture the essential features of interest, while significantly reducing the computational cost of calculation. This variational scaling law is shown to reliably work with moderately high turbulence strengths, producing at least a ~2x computational speed-up per individual propagation of the beam and >100x memory reduction (depending on the chosen resolution).

Individual design of aberration-free intraocular lenses

Bruno Chassagne and Lionel Canioni

DOI: 10.1364/JOSAA.420066 Received 15 Jan 2021; Accepted 29 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: An analytical tool, capable of calculating easily a new aspheric intraocular lens (shape factor, aspherization) chosen to be designed as “aberration free” in terms of spherical aberration and/or coma, is reported. In terms of retinal image quality, the theoretical performances given by the new proposed intraocular lenses compare well with commercial IOL.

Color Appearance Shift in Augmented Reality Metameric Matching

Lili Zhang, Mike Murdoch, and Romain Bachy

DOI: 10.1364/JOSAA.420395 Received 21 Jan 2021; Accepted 29 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: The physical additivity of optical-see-through (OST) augmented reality (AR), where display and real world overlay with each other, impacts its color appearance. We explored this unique dynamic by looking at the effect of background correlated color temperature (CCT) on AR color appearance with a color matching experiment between a prototype OST-AR RGB system and daylight spectrum reproduction. Different background CCT, luminance levels, and two stimulus types (simulated 2D disk and 3D cube) were examined. We found that when the background color is inconsistent with the stimulus providing conflicted cues, matched colors in AR shifted towards the background. The luminance matched on the 3D cube is higher than the 2D disk, suggesting the impact of context on the AR appearance. A controlled metameric matching group between daylight reproduction, and LCD or CRT did not show the shift, indicating the appearance shift is not due to the RGB-spectrum metameric matching, but due to RGB foreground-spectral background interaction beyond simple additivity. How perceptual weighting on foreground and background is modified to predict the appearance as a function of additivity is discussed.

Deep Image Enhancement for Ill Light Imaging

Rizwan Khan, You Yang, Qiong Liu, Jialie Shen, and Bing Li

DOI: 10.1364/JOSAA.410316 Received 21 Sep 2020; Accepted 16 Mar 2021; Posted 07 Apr 2021  View: PDF

Abstract: Imaging in the natural scene under ill lighting conditions (e.g., low light, back-lit, over-exposed front-lit, andany combinations of them) suffers from both over-and under-exposure at the same time, whereas processing ofsuch images often results in over and under enhancement. A single small image sensor can hardly provide asatisfactory quality for ill lighting conditions with ordinary optical lenses in capturing devices. Challenges arisein the maintenance of a visual smoothness between those regions while color and contrast should be well preserved. The problem has been tried by various methods, including multiple sensors and handcrafted parameters,but extant models capacity is limited to only some specific scenes (i.e., lighting conditions). Motivated by thesechallenges, in this paper, we propose a deep image enhancement method for color images captured under illlighting conditions. In this method, input images are first decomposed into reflection and illumination maps withthe proposed Layer Distribution Loss Net, where illumination blindness and structure degradation problem canbe subsequently solved via these two components, respectively. The hidden degradation in reflection and illumination are tuned with a knowledge-based adaptive enhancement constraint designed for ill illuminated images.The model can maintain a balance of smoothness and contribute to solving the problem of noise besides overand under enhancement. The local consistency in illumination is achieved via repairing operation performedin the proposed Repair-Net. The total variation operator is optimized to acquire local consistency, and the image gradient is guided with the proposed enhancement constraint. Finally, a product of updated reflection andillumination maps reconstructs an enhanced image. Experiments are organized under both very low exposureand ill-illumination conditions, where a new dataset is also proposed. Results on both experiments show thatour method has superior performance in preserving structural and textural details compared to other state-ofthe-arts, which suggests that our method is more practical in future visual applications.

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