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Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

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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.

<< Previous Page Articles 21 to 31 of 31

February


Poynting Theorem Constraints on the Signs of the Imaginary Parts of the Electromagnetic Constitutive Parameters

  • Omar Ramahi, Ali Kabiri, and Babak Alavikia
  • received 12/22/2014; accepted 02/02/2015; posted 02/04/2015; Doc. ID 231185
  • [full text: PDF (1227) KB)]
  • Abstract: In time-harmonic analysis, media composed of sub-wavelength metallic or dielectric inclusions are described by complex and dispersive effective constitutive parameters. A study of such parameters based on the conservation law of energy and causality is presented. We derive a set of general constraints on the real and imaginary parts of the constitutive parameters for lossy and lossless media in terms of electric and magnetic loss tangents. It is shown that a passive medium can indeed have negative imaginary part of either the permeability or permittivity over a range of frequencies. These findings are consistent with the principles of causality and energy conservation.

Keywords (OCIS):

  • (160.0160) Materials : Materials
  • (160.4670) Materials : Optical materials
  • (160.4760) Materials : Optical properties
  • (160.3918) Materials : Metamaterials

Performance analysis of cone detection algorithms

  • Letizia Mariotti and Martin Devaney
  • received 10/09/2014; accepted 02/01/2015; posted 02/04/2015; Doc. ID 224577
  • [full text: PDF (4383) KB)]
  • Abstract: Many algorithms have been proposed to help clinicians evaluate cone density and spacing, as these may be related to the onset of retinal diseases. However, there has been no rigorous comparison of the performance of these algorithms. In addition, the performance of such algorithms is typically determined by comparison with human observers. Here we propose a technique to simulate realistic images of the cone mosaic. We use the simulated images to test the performance of two popular cone detection algorithms and we introduce an algorithm which is used by astronomers to detect stars in astronomical images. We use Free Response Operating Characteristic (FROC) curves to evaluate and compare the performance of the three algorithms. This allows us to optimize the performance of each algorithm. We observe that performance is significantly enhanced by up-sampling the images. We investigate the effect of noise and image quality on cone mosaic parameters estimated using the different algorithms, finding that the estimated regularity is the most sensitive parameter.

Keywords (OCIS):

  • (010.1080) Atmospheric and oceanic optics : Active or adaptive optics
  • (100.0100) Image processing : Image processing
  • (170.4470) Medical optics and biotechnology : Ophthalmology

January


Manifold regularized semi-supervised Gaussian mixture model

  • Haitao Gan, Nong Sang, and Rui Huang
  • received 09/25/2014; accepted 01/30/2015; posted 02/09/2015; Doc. ID 223863
  • [full text: PDF (882) KB)]
  • Abstract: In the last decades, Gaussian Mixture Models (GMMs) have attracted considerable interest in data mining and pattern recognition. A GMM-based clustering algorithm models a dataset with a mixture of multiple Gaussian components and estimates the model parameters using the Expectation-Maximization (EM) algorithm. Recently, a new Locally Consistent GMM (LCGMM) has been proposed to improve the clustering performance by exploiting the local manifold structure of the data using a p nearest neighbor graph. Besides the underlying manifold structure, many other forms of prior knowledge may guide the clustering process and improve the performance. In this paper, we introduce a Semi-supervised LCGMM (Semi-LCGMM), where the prior knowledge is provided in the form of class labels of partial data. In particular, the new Semi-LCGMM incorporates the prior knowledge into the maximum likelihood function of the original LCGMM and the model parameters are estimated using the EM algorithm. It is worth noting that in our algorithm each class may be modeled by multiple Gaussian components while in the unsupervised setting each class is modeled by a single Gaussian component. Our algorithm has shown promising results in many different applications, including clustering breast cancer data, heart disease data, handwritten digit images, human face images, and image segmentation.

Keywords (OCIS):

  • (100.5010) Image processing : Pattern recognition
  • (150.1135) Machine vision : Algorithms
  • (100.3008) Image processing : Image recognition, algorithms and filters

Photospectroscopically observed pore-space correlations of a wetting fluid during the drying process in nanoporous Vycor glass

  • Shigeo Ogawa and Jiro Nakamura
  • received 12/04/2014; accepted 01/29/2015; posted 02/06/2015; Doc. ID 228791
  • [full text: PDF (368) KB)]
  • Abstract: We use light scattering to study spatial correlations in the pore space of Vycor glass on draining a wetting fluid. We analyze the transmission spectrum of forward-scattered light on the basis of the theory of dielectric constant fluctuation, whereas the conventional light scattering analyzes the scattered light at small angles of monochromatic incident light. Assuming that the drained pores, which are surrounded by filled pores, exhibit long-range correlations of a fractal dimension of 2.5, we analytically derive the corresponding turbidity. The slight deviation from the 1/λ⁴-Rayleigh wavelength dependence directly provides the correlation length of the interconnected network of drained pores. The estimated length, ranging from 0.5 nm to 18 nm at most, is almost the same order of that indirectly estimated from our previous simple effective Rayleigh scatterer model.

Keywords (OCIS):

  • (160.4760) Materials : Optical properties
  • (290.7050) Scattering : Turbid media
  • (290.2558) Scattering : Forward scattering
  • (290.5825) Scattering : Scattering theory
  • (160.2710) Materials : Inhomogeneous optical media
  • (260.2710) Physical optics : Inhomogeneous optical media

Internal energy flows of coma affected singular beams in low Numerical Aperture systems

  • Monika Bahl, Paramasivam Senthilkumaran, Brijesh Singh, and Rakesh Singh
  • received 10/29/2014; accepted 01/22/2015; posted 01/29/2015; Doc. ID 225824
  • [full text: PDF (12179) KB)]
  • Abstract: The circulating phase gradient component of a singular beam gets modified when focused by a low NA system suffering from coma aberration. The gradient due to this coma aberration splits the higher charge vortex, into elementary vortices and distributes them spatially. This splitting depends on the charge and polarity of the incident singular beam as well as the sign and magnitude of the aberration coefficient. The transverse component of the Poynting vector field distribution at the focal plane is decomposed into the curl or solenoidal component and divergence or irrotational component using the Helmholtz Hodge Decomposition technique. The solenoidal component that relates to the Orbital Angular Momentum carries the circulating energy while the irrotational component shows the sources and sinks of energy. Intriguing results on the study of energy flow around the edge dislocations apart from the point phase defects in the irrotational components are also presented.

Keywords (OCIS):

  • (050.1940) Diffraction and gratings : Diffraction
  • (080.1010) Geometric optics : Aberrations (global)
  • (120.3940) Instrumentation, measurement, and metrology : Metrology
  • (050.4865) Diffraction and gratings : Optical vortices
  • (080.4865) Geometric optics : Optical vortices

Metric for the Measurement of the Quality of Complex Beams. Theoretical Study

  • Boris Zeldovich, Sergiy Kaim, Julien Lumeau, Vadim Smirnov, and Leonid Glebov
  • received 11/10/2014; accepted 01/22/2015; posted 01/29/2015; Doc. ID 226551
  • [full text: PDF (490) KB)]
  • Abstract: We study theoretically various definitions of laser beam width in a given cross-section. Quality of the beam is characterized by dimensionless Beam Propagation Products BPPs (∆x∙∆θ_x)⁄λ , which are different for 21 definitions, but are close to 1. Six particular beams are studied. In the process we had to review the properties of Fourier transform of various modifications: Physical Fourier Transform (PFT), Mathematical Fourier Transform (MFT), Discrete Fourier Transform (DFT), and relationships between them. We found axially-symmetric self-MFT function, which may be useful for description of diffraction-quality beams. In Appendices we illustrate the thesis “Fourier lives on the singularities of original”.

Keywords (OCIS):

  • (120.4800) Instrumentation, measurement, and metrology : Optical standards and testing
  • (070.2465) Fourier optics and signal processing : Finite analogs of Fourier transforms
  • (070.7345) Fourier optics and signal processing : Wave propagation

Electromagnetic Wave Transmission Through a Subwavelength Nano-hole in a Two-dimensional Plasmonic Layer

  • Norman Horing, DESIRE MIESSEIN, and Godfrey Gumbs
  • received 10/30/2014; accepted 01/22/2015; posted 02/25/2015; Doc. ID 226040
  • [full text: PDF (5940) KB)]
  • Abstract: An integral equation is formulated to describe electromagnetic wave transmission through a subwavelength nano-hole in a thin plasmonic sheet in terms of the dyadic Green's function for the associated Helmholtz problem. Taking the subwavelength radius of the nano-hole to be the smallest length of the system, we have obtained an exact solution of the integral equation for the dyadic Green's function analytically and in closed form. This dyadic Green's function is then employed in the numerical analysis of electromagnetic wave transmission through the nano-hole for normal incidence of the incoming wave train. The electromagnetic transmission involves two distinct contributions, one emanating from the nano-hole and the other is directly transmitted through the thin plasmonic layer itself (which would not occur in the case of a perfect metal screen). The transmitted radiation exhibits interference fringes in the vicinity of the nano-hole, and they tend to flatten as a function of increasing lateral separation from the hole, reaching the uniform value of transmission through the sheet alone at large separations.

Keywords (OCIS):

  • (050.0050) Diffraction and gratings : Diffraction and gratings
  • (050.1960) Diffraction and gratings : Diffraction theory
  • (350.5400) Other areas of optics : Plasmas
  • (350.5500) Other areas of optics : Propagation
  • (050.6624) Diffraction and gratings : Subwavelength structures
  • (310.6628) Thin films : Subwavelength structures, nanostructures

Analytical Models for Electrically Thin Flat Lenses and Reflector

  • Omar Ramahi and Miguel Ruphuy
  • received 01/13/2015; accepted 01/21/2015; posted 01/29/2015; Doc. ID 232081
  • [full text: PDF (1247) KB)]
  • Abstract: This work presents analytical models for two-dimensional (2D) and three- dimensional (3D) electrically thin lenses and reflectors. The 2D formulation is based on infinite current line sources, whereas the 3D formulation is based on electrically-small dipoles. These models emulate the energy convergence of an electrically thin flat lens and reflector when illuminated by a plane wave with specific polarization. The advantages of these models are twofold: first, prediction of the performance of electrically-thin flat lenses and reflectors can be made significantly faster than full-wave simulators, and second, providing insight on the performance of these electrically-thin devices. The analytic models were validated by comparison with full-wave simulation for several interesting examples. The validation results show that the focal point of the electrically thin flat lenses and reflectors can be accurately predicted through a design that assumes low coupling between different layers of an inhomogeneous media.

Keywords (OCIS):

  • (080.3620) Geometric optics : Lens system design
  • (080.3630) Geometric optics : Lenses
  • (080.4225) Geometric optics : Nonspherical lens design

A New Method for Optimizing Channelized Quadratic Observers for Binary Classification of Large-Dimensional Image Datasets

  • MEREDITH KUPINSKI and Eric Clarkson
  • received 09/05/2014; accepted 01/04/2015; posted 02/05/2015; Doc. ID 222489
  • [full text: PDF (1295) KB)]
  • Abstract: We present a new method for computing optimized channels for channelized quadratic observers (CQO) that is feasible for high-dimensional image data. The method for calculating channels is applicable in general and optimal for Gaussian distributed image data. Gradient-based algorithms for determining the channels are presented for five different information-based figures of merit (FOM). Analytic solutions for the optimum channels for each of the five FOMs are derived for the case of equal mean data for both classes. The optimum channels for three of the FOM under the equal mean condition are shown to be the same. This result is critical since some of the FOMs are much easier to compute. Implementing the CQO requires a set of channels and the first- and second- order statistics of channelized image data from both classes. The dimensionality reduction from $M$ measurements to $L$ channels is a critical advantage of CQO since estimating image statistics from channelized data requires smaller sample sizes and inverting a smaller covariance matrix is easier. In a simulation study we compare the performance of Ideal and Hotelling observers to CQO. The optimal CQO channels are calculated using both eigenanalysis and a new gradient-based algorithm for maximizing Jeffrey's divergence (J). Optimal channel selection without eigenanalysis makes the J-CQO on large-dimensional image data feasible.

Keywords (OCIS):

  • (100.5010) Image processing : Pattern recognition
  • (110.2970) Imaging systems : Image detection systems
  • (110.3000) Imaging systems : Image quality assessment
  • (150.1135) Machine vision : Algorithms
  • (100.4994) Image processing : Pattern recognition, image transforms

December


Creation of a 50,000λ long needle-like field with 0.36λ width: comment

  • Sabino Chavez-Cerda and Jixiong Pu
  • received 09/15/2014; accepted 12/08/2014; posted 12/09/2014; Doc. ID 223032
  • [full text: PDF (563) KB)]
  • Abstract: In a recent paper, a method for the generation of a long, narrow needle of light was proposed [J. Opt. Soc. Am. A 31, 500 (2014)]. The authors missed some fundamental aspects of the mathematical physics of cylindrical electromagnetic waves described by Bessel functions that are essential to obtain the desired result. Also, their solution of the wave field lacks the component of longitudinal energy flow that is needed for most of the applications they suggest. We show that a minor modification solves this absence with practically negligible increase of the needle width.

Keywords (OCIS):

  • (000.3860) General : Mathematical methods in physics
  • (030.1670) Coherence and statistical optics : Coherent optical effects
  • (260.1960) Physical optics : Diffraction theory
  • (260.2110) Physical optics : Electromagnetic optics
  • (070.3185) Fourier optics and signal processing : Invariant optical fields
  • (070.7345) Fourier optics and signal processing : Wave propagation

February


(CV) Independence and interaction of luminance and chromatic contributions to spatial hyperacuity performance

  • Bonnie Cooper and Barry Lee
  • received 09/30/2013; accepted 02/02/2014; posted 02/03/2014; Doc. ID 198653
  • [full text: PDF (1336) KB)]
  • Abstract: Here we test interactions of luminance and chromatic input to spatial hyperacuity mechanisms. First, we tested alignment with matching or mismatching (contrast polarity or modality) grating pairs that were adjusted to detection threshold. Thresholds with mismatched pairs were significantly elevated. Second, we determined alignment acuity as a function of luminance or chromatic contrast alone or in the presence of contrast pedestals. For in-phase pedestal conditions, performance followed the envelope of the more sensitive mechanism. However, polarity reversals revealed an asymmetric effect for luminance and chromatic conditions. This suggests that luminance can overrule chromatic mechanisms in hyperacuity; we interpret these findings in the context of spatial mechanisms.

Keywords (OCIS):

  • (330.1720) Vision, color, and visual optics : Color vision
  • (330.5510) Vision, color, and visual optics : Psychophysics
  • (330.6100) Vision, color, and visual optics : Spatial discrimination

<< Previous Page Articles 21 to 31 of 31





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