Expand this Topic clickable element to expand a topic
OSA Publishing

Early Posting

Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Propagation of annular cos-Gaussian beams throughturbulence

wanjun wang and Zhen-Sen Wu

Doc ID: 321265 Received 01 Feb 2018; Accepted 22 May 2018; Posted 23 May 2018  View: PDF

Abstract: The propagation characteristics of annular cos-Gaussian beams and Bessel Gaussian beams in the turbulence havebeen widely investigated. However, the expression of the average intensity of Bessel Gaussian beams involves acomplex double integral, which requires large computational resources and is not easy to ensure accuracy. Underthis background, through the general cos-Gaussian beam rotation, a new annular cos-Gaussian beam is proposedwhich not only has some properties of the general cos-Gaussian beam, but also similar properties with the BesselGaussian beam. Moreover, the annular cos-Gaussian beam is simpler in form than the general one and much moretimesaving in calculation than the Bessel Gaussian beams. Based on the extended Huygens–Fresnel principle, thepolynomials and it is in good agreement with that of low order Bessel Gaussian beams. The average radius and thepower in the bucket are also derived. In summary, the annular cos-Gaussian beam has promising applications forits quick calculation and simple form among annular beams and hollow beams.

Second-order moments of a twisted Gaussian Schellmodelbeam in anisotropic turbulence

Jing Wang, Haiyan Wang, Shijun Zhu, and Zhen-hua Li

Doc ID: 327724 Received 12 Apr 2018; Accepted 22 May 2018; Posted 23 May 2018  View: PDF

Abstract: Analytical formulas for the Wigner distribution functions and the second-order moments (SOMs) of a twistGaussian Schell-model (TGSM) beam propagating through anisotropic turbulence have been derived by means of atensor method. It is found that the propagation law for the SOMs of a TGSM beam spreading in turbulence can bedescribed as a first-order optical systems propagation law with an additional turbulence-induced effect. Based onthe SOMs, second-order statistics in terms of the effective beam width, the M2-factor, the orbital angularmomentum flux, and the effective radius curvature are analyzed in detail. One finds that the anisotropic turbulenceleads to an anisotropic spreading of light beams, and a TGSM beam is less affected by turbulence than a GaussianSchell-model beam without twist phase. For short distance propagation, light beam is more sensitive to the initialbeam parameters than turbulence parameters. While for sufficiently long transmission distance, the beamcharacteristics are determined at most by turbulence statistics. The method can be extended to study thepropagation characteristics of various coherent and partially coherent complex Gaussian beams such as flattoppedbeams, dark hollow beams and array beams in turbulence, and promotes important supports in free-spaceoptical communications and remote sensing.

Pixel-Level Alignment of Facial Images for HighAccuracy Recognition Using Ensemble of Patches

Hoda Mohammadzade, Amirhossein Sayyafan, and Benyamin Ghojogh

Doc ID: 324495 Received 26 Feb 2018; Accepted 20 May 2018; Posted 21 May 2018  View: PDF

Abstract: The variation of pose, illumination and expression makes face recognition still a challenging problem.As a pre-processing in holistic approaches, faces are usually aligned by eyes. The proposed method triesto perform a pixel alignment rather than eye-alignment by mapping the geometry of faces to a referenceface while keeping their own textures. The proposed geometry alignment not only creates a meaningfulcorrespondence among every pixel of all faces, but also removes expression and pose variations effectively.The geometry alignment is performed pixel-wise, i.e., every pixel of the face is corresponded to apixel of the reference face. In the proposed method, the information of intensity and geometry of facesare separated properly, trained by separate classifiers, and finally fused together to recognize human faces.Experimental results show a great improvement using the proposed method in comparison to eye-alignedrecognition. For instance, at the false acceptance rate of 0.001, the recognition rates are respectively improvedby 24% and 33% in Yale and AT&T datasets. In LFW dataset, which is a challenging big dataset,improvement is 20% at FAR of 0.1.

Geometrical Ray Tracing in Uniaxial Crystals: DirectFormulas and the Equivalence between theElectromagnetic Wave Method and Huygens’ Principle

Pengqian Wang

Doc ID: 323481 Received 19 Feb 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: Using the electromagnetic wave method and Huygens’ principle, we have studied light refraction and reflectionon the boundary between two uniaxial crystals with arbitrary optic axis orientations. We providea set of direct formulas that calculate the directions of the refracted and reflected extraordinary rays andtheir associated waves, as well as the ray indices and refractive indices. The formulas use only the initialinput variables and do not require the calculation of intermediate quantities. Refraction and reflection arecombined in one formula. We also prove that the electromagnetic wave method and Huygens’ principleproduce analytically equivalent results for geometrical ray tracing.

Jacobi circle and annular polynomials : modalwavefront reconstruction from wavefront gradient

Wenhan Sun, Shuai Wang, Xing He, and Bing Xu

Doc ID: 325061 Received 27 Feb 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: Jacobi circle polynomials, which are orthogonal onthe unit circle with orthogonal radial derivatives, havebeen developed previously. As the classical Zernikemode can be represented as a linear combination ofJacobi modes, Zernike wavefront modes can be reconstructedusing Jacobi modes. Comparison of the Jacobiand Zernike modes for the modal approach indicatesthat a modal approach incorporating the Gram matrixwith the Jacobi modes has potential application in highsamplingwavefront gradient sensors. The Gram matrixmethod using the Jacobi modes can be extended to annularpupils.

Decomposition of a field with smooth wavefront intoset of Gaussian beams with non-zero curvatures

Norman Girma Worku, Ralf Hambach, and Herbert Gross

Doc ID: 327048 Received 28 Mar 2018; Accepted 14 May 2018; Posted 14 May 2018  View: PDF

Abstract: Decomposition of a general arbitrary field into set of Gaussian beams has been one of the challenges inthe Gaussian beam decomposition method for field propagation through optical systems. The most commonlyused method in this regard is the Gabor expansion, which decomposes initial fields into shiftedand rotated Gaussian beams in a plane. Since the Gaussian beams used have zero initial curvatures, theGabor expansion method does not utilize the ability of the Gaussian beams to represent the quadraticbehavior of the local wavefront. In this paper we describe an alternative method of decomposing anarbitrary field with smooth wavefront into set of Gaussian beams with non-zero initial curvatures. Theindividual Gaussian beams are used to represent up to the quadratic term in the Taylor expansion of thelocal wavefront. This significantly reduces the number of Gaussian beams required for the decompositionof the field with smooth wavefront and gives more accurate decomposition result. The proposedmethod directly gives the five ray sets representing the parabasal Gaussian beams, which can then bedirectly used for propagation of the Gaussian beams through optical systems. To demonstrate the applicationof the method, we have presented results for the decomposition of fields with strongly curvedspherical wavefronts, a cone shaped wavefront and a wavefront with large spherical aberration. The numericalcomparison of the input field with the field reconstructed after the decomposition show very goodagreement in both amplitude and phase profiles. We also show results for the far field intensity distributionsof the decomposed wavefronts by propagating in free space using the Gaussian beam propagationmethod.

Quantifying the effect of straylight on photopiccontrast sensitivity

Clemente Paz Filgueira and Elisa Colombo

Doc ID: 324616 Received 23 Feb 2018; Accepted 14 May 2018; Posted 15 May 2018  View: PDF

Abstract: The visual performance of a reference group (RG) using diffuser filters was compared to a cataract-diagnosed group (CatG).Measurements of straylight parameter (SL), photopic contrast sensitivity (CS) and visual acuity (VA) were carried out inboth groups. Before the analysis, the performance of the instruments used for this purpose was tested. The RG wascomprised of 3 healthy, young eyes (25 - 30 years old) while 59 subjects (aged 50 - 80 years old) with lens opacities wererecruited for the CatG. Six diffuser conditions were tested in the RG. To discriminate between light scattering levels,straylight measurements proved to be most sensitive, visual acuity did not discriminate at all, while CS showed intermediatesensitivity. VA was not correlated with SL, while the correlation between CS and SL was significant (p < 0.05) in both groups.Since the correlation in the RG was particularly strong, parameters of a linear regression model are presented. The behaviorof CS as a function of SL was comparable to some extent between RG and CatG.

Experimental and theoretical investigation of theco-occurrence of linear and circular dichroisms foroblique incidence of light on chiral sculptured thinfilms

Patrick McAtee and Akhlesh Lakhtakia

Doc ID: 324837 Received 26 Feb 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: Theory shows that a slab of a dielectric structurally chiral material (DSCM) exhibits both linear and circulardichroisms because of its anisotropy and structural chirality, for normal as well as oblique incidence.This conclusion was confirmed by fabricating a chiral sculptured thin film and measuring the spectra ofits reflectances and transmittances, both linear and circular. Signatures of the circular Bragg phenomenonare evident in the spectra of all reflectances, transmittances, absorptances, and dichroisms. Reversal ofthe structural handedness of a DSCM and rotation of the projection of the direction of propagation ofthe incident light clockwise instead of counterclockwise about the axis of helicoidal nonhomogeneitysimultaneously changes the sign of circular dichroism but has no effect on linear dichroism.

Full-Wave Optimization of Three-DimensionalPhotonic-Crystal Structures Involving Dielectric Rods

Bariscan Karaosmanoglu, Hamza Eray, and Ozgur Ergul

Doc ID: 313183 Received 09 Nov 2017; Accepted 06 May 2018; Posted 07 May 2018  View: PDF

Abstract: We present rigorous optimization and design of three-dimensional photonic-crystal (PhC) structures involvingfinite dielectric rods. These types of PhCs are known to be useful in diverse applications, suchas imaging, power focusing, filtering, and pattern shaping at optical frequencies. Without resorting totheir two-dimensional models, which are commonly used in the literature, we consider PhCs as threedimensionalstructures, whose electromagnetic characteristics are optimized via genetic algorithms integratedwith an efficient and accurate solver based on the multilevel fast multipole algorithm. In additionto the designs of PhCs that can provide desired output patterns, we present sensitivity tests to understandthe critical geometric parameters, as well as to test and evaluate the tolerance of the proposed designs topossible fabrication errors.

Frequency Subspace Amplitude Flow for Phase Retrieval

zhun wei, Wen Chen, and Xudong Chen

Doc ID: 325311 Received 02 Mar 2018; Accepted 06 May 2018; Posted 07 May 2018  View: PDF

Abstract: A novel approach, termed frequency subspace amplitude flow (FSAF), is proposed to reconstruct complex-valued signal from “phaseless” measurements. The proposed FSAF consists of two stages: The first stage approximates low-frequency coefficients of an unknown signal by spectral method, and the second stage refines the results by truncated conjugate gradient of amplitude-based nonconvex formulation. FSAF is easy to implement and applicable to natural images, where no additional constraint is needed. Extensive experiments with 1D signals, 2D images and natural images corroborate significant improvements by using the proposed FSAF method over the state of the art. Especially for sample complexity, FSAF pushes state-of-the-art for exactly reconstructing complex natural signals (with a size of n) from 3.2n to 2.2n under Gaussian model, and from 5n to 3n under coherent diffraction pattern (CDP) model without increasing computational complexity. More importantly, the proposed method is highly flexible and can be easily adapted to the existing algorithms under different noise models.

A fast and reliable method to estimate losses of single-mode waveguides with an arbitrary 2D trajectory

Fernando Negredo, Matthias Blaicher, Aleksandar Nesic, Pascal Kraft, Julian Ott, Willy Dörfler, Christian Koos, and Carsten Rockstuhl

Doc ID: 325381 Received 06 Mar 2018; Accepted 04 May 2018; Posted 07 May 2018  View: PDF

Abstract: Photonic wire bonds, i.e. freeform waveguides written by 3D direct laser writing, emerge as a technology to connect different optical chips in fully-integrated photonic devices. With the long-term vision of scaling up this technology to a large-scale fabrication process, the {\it in situ} optimization of the trajectory of photonic wire bonds is at stake. A prerequisite for the real-time optimization is the availability of a fast loss estimator for single-mode waveguides of arbitrary trajectory. Losses occur because of the bending of the waveguides and at transitions among sections of the waveguide with different curvatures. Here, we present an approach that resides on the fundamental mode approximation, i.e. the assumption that the photonic wire bonds carry predominantly its energy in a single mode. It allows to predict in a quick and reliable way the pertinent losses from pre-computed modal properties of the waveguide, enabling fast design of optimum paths.

Image authentication using vector beam with sparsephase information

Areeba Fatima and Naveen Nishchal

Doc ID: 322586 Received 06 Feb 2018; Accepted 02 May 2018; Posted 03 May 2018  View: PDF

Abstract: We propose a novel optical information authentication scheme that uses Stokes polarimetry of vector beams.Phase-only functions of the plaintext are generated using modified Gerchberg-Saxton algorithm. Partialinformation of these phase functions are used to tailor the phase of a vector beam. The Stokes parametersrecording of the vector beam generates the ciphertext which contains sparse information of the input image. Incontrast to most authentication schemes, the proposed scheme can authenticate two images from a single realciphertext. Computer simulation results prove the feasibility of the proposed scheme.

Multipurpose S-shaped solvable profiles of the refractive index: application to modeling of antireflection layers and quasicrystals

Jean-Claude Krapez

Doc ID: 318039 Received 18 Dec 2017; Accepted 01 May 2018; Posted 02 May 2018  View: PDF

Abstract: A class of four-parameter solvable profiles of the electromagnetic admittance has recently been discovered by applying the newly developed Property & Field Darboux Transformation method (PROFIDT). These profiles are highly flexible. In addition, the related electromagnetic-field solutions are exact, in closed-form and involve only elementary functions. In this paper, we focus on those who are S-shaped and we provide all the tools needed for easy implementation. These analytical bricks can be used for high-level modeling of lightwave propagation in photonic devices presenting a piecewise-sigmoidal refractive-index profile such as, for example, antireflection layers, rugate filters, chirped filters and photonic crystals. For small amplitude of the index modulation, these elementary profiles are very close to a cosine profile. They can therefore be considered as valuable surrogates for computing the scattering properties of components like Bragg filters and reflectors as well. In this paper we present an application for antireflection layers and another for 1D quasicrystals. The proposed S-shaped profiles can be easily manipulated for exploring the optical properties of smooth quasicrystals, a class of photonic devices that adds to the classical binary-level quasicrystals.

A Discrete Spherical Harmonics Method for RadiativeTransfer in Scalar Planar Inhomogeneous Atmosphere

Romuald Tapimo, Herve Thierry Kamdem, and David Yemele

Doc ID: 293022 Received 21 Feb 2018; Accepted 29 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: The radiative transfer problems in participating inhomogeneous scalar planar atmosphere, subjected to diffuse orcollimated incidence is investigated using the discrete spherical harmonics method. In developing the method, theradiative intensity is expanded in a finite series of Legendre polynomials and the resulting first-order coupleddifferential equations of radiance moments are expressed in a set of discrete polar directions. The method isapplied to homogeneous/inhomogeneous atmospheres of various anisotropic scattering degrees and thicknesses,and reflective boundary conditions. The discrete spherical harmonics method albedo, transmittance and radiativeintensity predictions agree well with benchmark literature results. Additionally, numerical predictions shown that thediscrete spherical harmonics method using Mark boundary conditions are more efficient than using Marshak boundaryconditions.

Experimental demonstration of ray-rotation sheets

Johannes Courtial, Nong Chen, Sean Ogilvie, Blair Kirkpatrick, Alasdair Hamilton, Graham Gibson, Tomas Tyc, Eric Logean, and Toralf Scharf

Doc ID: 325977 Received 13 Mar 2018; Accepted 18 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: We have built micro-structured sheets that rotate, on transmission, the direction of light rays by an arbitrary, but fixed, angle around the sheet normal. These ray-rotation (RR) sheets comprise two pairs of confocal lenticular arrays. In addition to rotate the direction of transmitted light rays, our sheets also offset ray position, but only on the scale of the scale of the diameter of the lenticules. If this ray offset is sufficiently small so that it cannot be resolved, our RR sheets appear to perform generalised refraction.

Select as filters


    Select Topics Cancel
    © Copyright 2018 | The Optical Society. All Rights Reserved