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Journal of the Optical Society of America A

Journal of the Optical Society of America A



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Deflectometry for measuring inhomogeneous refractive index fields in two-dimensional gradient-index (GRIN) elements

  • Di Lin, James Leger, and Jeremy Teichman
  • received 02/05/2015; accepted 03/30/2015; posted 03/30/2015; Doc. ID 233764
  • [full text: PDF (484) KB)]
  • Abstract: We present a numerical method for calculating inhomogeneous refractive index fields in rectangular GRIN elements from measured boundary positions and slopes of a collection of rays that transit the medium. The inverse problem is reduced to a set of linear algebraic equations after approximating ray trajectories from measured boundary values and is solved using a pseudo-inverse algorithm for sparse linear equations. The ray trajectories are subsequently corrected using an iterative ray trace procedure to ensure consistency in the solution. We demonstrate our method in simulation by reconstructing a hypothetical rectangular GRIN element on a 15×15 discrete grid using 800 interrogating rays, in which RMS refractive index errors less than 0.5% of the index range (n_max-n_min) are achieved. Furthermore, we identify three primary sources of error and assess the importance of data redundancy and system conditioning in the reconstruction process.

Keywords (OCIS):

  • (080.2710) Geometric optics : Inhomogeneous optical media
  • (120.3940) Instrumentation, measurement, and metrology : Metrology
  • (080.5692) Geometric optics : Ray trajectories in inhomogeneous media

Omnidirectional absorption and off-resonance field enhancement in dielectric cylinders coated with graphene layers

  • Tiago Arruda, Alexandre Martinez, and F Pinheiro
  • received 03/04/2015; accepted 03/27/2015; posted 03/30/2015; Doc. ID 235688
  • [full text: PDF (388) KB)]
  • Abstract: We investigate electromagnetic scattering and absorption by dielectric cylinders coated with a concentric plasmonic shell at arbitrary incidence angles. Exploiting bulk and surface plasmon resonances in the long wavelength regime, we obtain an analytical condition to achieve wide-angle enhanced absorption for both TE- and TM-polarizations. We apply this result to investigate electromagnetic absorption in a silicon (Si) cylinder coated with a graphene monolayer epitaxially grown on silicon carbide (SiC). We demonstrate that enhanced absorption occurs for a broad frequency range in the terahertz, and that omnidirectional absorption exists at a frequency in between the bulk and localized surface plasmon resonances. By showing that omnidirectional absorption does not correspond to an extinction resonance, we associate this phenomenon with off-resonance field enhancement in this system, which in turn is explained in terms of Fano resonances in the graphene layer.

Keywords (OCIS):

  • (290.0290) Scattering : Scattering
  • (290.4020) Scattering : Mie theory
  • (290.5850) Scattering : Scattering, particles
  • (310.3915) Thin films : Metallic, opaque, and absorbing coatings
  • (290.5825) Scattering : Scattering theory

Light propagation analysis using a translated plane angular spectrum method with the oblique plane wave incidence

  • Hyeon-ho SON and Kyunghwan Oh
  • received 12/11/2014; accepted 03/25/2015; posted 03/25/2015; Doc. ID 230601
  • [full text: PDF (1098) KB)]
  • Abstract: A novel angular spectrum method was proposed to numerically analyze off-axis free-space light propagation on a translated plane to an arbitrary angle. Utilizing a shifted angular spectrum method based on an oblique incident plane wave assumption, a generalized light propagation formulation was obtained in a wide range of both tilt angles and sampling intervals, which overcame the limitations of prior attempts. A detailed comparison of the proposed angular spectrum method with prior methods is numerically presented for diffractive optics and computer generated holograms. The validity of the proposed method was confirmed experimentally by reconstructing a digital holographic image using a spatial light modulator.

Keywords (OCIS):

  • (050.1970) Diffraction and gratings : Diffractive optics
  • (070.0070) Fourier optics and signal processing : Fourier optics and signal processing
  • (090.1760) Holography : Computer holography
  • (090.1970) Holography : Diffractive optics
  • (070.7345) Fourier optics and signal processing : Wave propagation

Modal method for the 2D wave propagation in heterogeneous anisotropic media

  • Agnes Maurel, Jean François Mercier, and Simon Félix
  • received 12/10/2014; accepted 03/23/2015; posted 03/24/2015; Doc. ID 229012
  • [full text: PDF (4124) KB)]
  • Abstract: A multimodal method based on a generalization of the admittance matrix is used to analyze wave propagation in heterogeneous two dimensional anisotropic media. The heterogeneity of the medium can be due to the presence of anisotropic inclusions with arbitrary shapes, to a succession of anisotropic media with complex interface between them, or both. Using a modal expansion of the wavefield, the problem is reduced to a system of two sets of first-order differential equations for the modal components of the field, similar to the system obtained in the rigorous coupled wave analysis. The system is solved numerically, using the admittance matrix, which leads to a stable numerical method, the basic properties of which are discussed (energy conservation and convergence). The method is exemplified for the case of arrays of anisotropic inclusions with complex shapes (the effects of the inclusion shapes and of the direction of anisotropy are illustrated) and for a dielectric grating with slanted layered structures which gives rise to resonant guided waves (the validity of the homogenization of layered media is regarded).

Keywords (OCIS):

  • (160.1190) Materials : Anisotropic optical materials
  • (230.1950) Optical devices : Diffraction gratings
  • (260.2110) Physical optics : Electromagnetic optics
  • (160.3918) Materials : Metamaterials

Ultrasound modulated optical tomography: Direct recovery of elasticity distribution from experimentally measured intensity autocorrelation

  • R. Vasu, K Mohanan, A. Nandakumaran, and Debasish Roy
  • received 12/04/2014; accepted 03/23/2015; posted 03/24/2015; Doc. ID 229022
  • [full text: PDF (609) KB)]
  • Abstract: Based on an ultrasound modulated optical tomography (UMOT) experiment, a direct, quantitative recovery of Young's modulus (E) is achieved from the modulation depth $(M)$ in the intensity autocorrelation. The number of detector locations is limited to two in orthogonal directions, reducing the complexity of the data gathering step whilst ensuring against an impoverishment of the measurement, by employing ultrasound frequency as a parameter to vary during data collection. The modulation depth $M$ and Young's modulus (E) are related via two partial differential equations. The first one connects M to the amplitude of vibration of the scattering centres in the focal volume and the other, this amplitude to E. A (composite) sensitivity matrix is arrived at mapping the variation of M with that of E and used in a (barely regularized) Gauss-Newton algorithm to iteratively recover E. The reconstruction results showing the variation of E are presented.

Keywords (OCIS):

  • (110.0110) Imaging systems : Imaging systems
  • (170.3880) Medical optics and biotechnology : Medical and biological imaging
  • (110.0113) Imaging systems : Imaging through turbid media
  • (110.6955) Imaging systems : Tomographic imaging
  • (110.3010) Imaging systems : Image reconstruction techniques

Origins of Radiative Transport Theory: Diagrammatic and Multiscale Approaches

  • John Schotland and Alexandre Caze
  • received 01/16/2015; accepted 03/14/2015; posted 03/17/2015; Doc. ID 232297
  • [full text: PDF (449) KB)]
  • Abstract: The radiative transport equation (RTE) is widely used to describe the propagation of multiply- scattered light in disordered media. In this tutorial, we present two derivations of the RTE for scalar wave fields. The first derivation is based on diagrammatic perturbation theory, while the second stems from an asymptotic multiscale expansion. Although the two approaches are quite distinct mathematically, some common ground can be found and is discussed.

Keywords (OCIS):

  • (030.5620) Coherence and statistical optics : Radiative transfer
  • (290.4210) Scattering : Multiple scattering

Easy approach to assembling a biomimetic color film with tunable structure colors

  • Wentao Wang, Bingtao Tang, Wei Ma, Jian Zhang, Benzhi Ju, and Shufen Zhang
  • received 10/09/2014; accepted 03/13/2015; posted 04/10/2015; Doc. ID 224722
  • [full text: PDF (2557) KB)]
  • Abstract: The self–assembly of silica microspheres into a close–packed array is a simple method of fabricating three–dimensional photonic crystal structure color films. However, the color is very dull because of the interferences of scattering and background light. In this study, we added a small quantity of surface–modified carbon black (CB) to the system of colloidal silica in n–propanol. The use of n–propanol as dispersant is beneficial to the rapid development of photonic crystal films during the process of dip–coating. The doping of CB into silica microspheres can absorb background and scattered light, resulting in vivid structure colors.

Keywords (OCIS):

  • (160.6030) Materials : Silica
  • (330.1690) Vision, color, and visual optics : Color
  • (160.5298) Materials : Photonic crystals


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

Bit error rate of focused Gaussian beams in weak oceanic turbulence: Comment

  • Mikhail Charnotskii
  • received 12/11/2014; accepted 01/08/2015; posted 03/20/2015; Doc. ID 229256
  • [full text: PDF (460) KB)]
  • Abstract: Recent calculations [1] of the scintillation index of focused beams did not take into account the second order of the perturbation theory, and therefore led the author to erroneous conclusions regarding dependence of the scintillation index for the focused beams on the aperture size. The log-normal intensity probability distribution used for the Bit Error Rate (BER) calculations in [1] is also invalid for the wide focused beams. As a result, most of conclusions of [1] are incorrect.

Keywords (OCIS):

  • (010.4450) Atmospheric and oceanic optics : Oceanic optics
  • (010.7060) Atmospheric and oceanic optics : Turbulence
  • (030.7060) Coherence and statistical optics : Turbulence
  • (350.5500) Other areas of optics : Propagation
  • (060.2605) Fiber optics and optical communications : Free-space optical communication
  • (010.4455) Atmospheric and oceanic optics : Oceanic propagation


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


(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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