112 research outputs found
A simulation method for determining the optical response of highly complex photonic structures of biological origin
We present a method based on a time domain simulation of wave propagation
that allows studying the optical response of a broad range of dielectric
photonic structures. This method is particularly suitable for dealing with
complex biological structures. One of the main features of the proposed
approach is the simple and intuitive way of defining the setup and the photonic
structure to be simulated, which can be done by feeding the simulation with a
digital image of the structure. We also develop a set of techniques to process
the behavior of the evolving waves within the simulation. These techniques
include a direction filter, that permits decoupling of waves travelling
simultaneously in different directions, a dynamic differential absorber, to
cancel the waves reflected at the edges of the simulation space, a
multi-frequency excitation scheme based on a filter that allows decoupling
waves of different wavelengths travelling simultaneously, and a
near-to-far-field approach to evaluate the resulting wavefield outside the
simulation domain. We validate the code and, as an example, apply it to the
complex structure found in a microorganism called Diachea leucopoda, which
exhibits a multicolor iridescent appearance.Comment: 43 pages, 19 figure
Eigenmodes of index-modulated layers with lateral PMLs
Maxwell equations are solved in a layer comprising a finite number of
homogeneous isotropic dielectric regions ended by anisotropic perfectly matched
layers (PMLs). The boundary-value problem is solved and the dispersion relation
inside the PML is derived. The general expression of the eigenvalues equation
for an arbitrary number of regions in each layer is obtained, and both
polarization modes are considered. The modal functions of a single layer ended
by PMLs are found, and their orthogonality relation is derived. The present
method is useful to simulate scattering problems from dielectric objects as
well as propagation in planar slab waveguides. Its potential to deal with more
complex problems such as the scattering from an object with arbitrary cross
section in open space using the multilayer modal method is briefly discussed.Comment: 17 pages, 4 figure
Shape resonances in nested diffraction gratings
The diffraction problem of a plane wave impinging on a grating formed by
nested cavities is solved by means of the modal method, for and
polarization modes. The cavities are formed by perfectly conducting sheets that
describe rectangular profiles. The electromagnetic response of the grating is
analyzed, paying particular attention to the generation of resonances within
the structure. The dependence of the resonances on the geometrical parameters
of the grating is studied, and results of far and near field are shown. The
results are checked and compared with those available in the literature for
certain limit cases.Comment: 18 pages, 8 figure
Bandwidth control of forbidden transmission gaps in compound structures with subwavelength slits
Phase resonances in transmission compound structures with subwavelength slits
produce sharp dips in the transmission response. For all equal slits, the
wavelengths of these sharp transmission minima can be varied by changing the
width or the length of all the slits. In this paper we show that the width of
the dip, i.e., the frequency range of minimum transmittance, can be controlled
by making at least one slit different from the rest within a compound unit
cell. In particular, we investigate the effect that a change in the dielectric
filling, or in the length of a single slit produces in the transmission
response. We also analyze the scan angle behavior of these structures by means
of band diagrams, and compare them with previous results for all-equal slit
structures.Comment: 16 pages, 5 figures, submitted to Phys. Rev.
¿Cómo nominan los partidos políticos? Divisiones internas, difusión de primarias y acuerdos de élites en la selección de candidatos
Una de las herramientas más poderosas que tienen las elites partidarias es el control de las candidaturas para cargos ejecutivos y legislativos. Entonces, ¿por qué algunos partidos pierden ese control a través de primarias en lugar de seleccionar a sus candidatos por otros mecanismos más cerrados
Analytical modeling of compound metallic reflection gratings
The transmission and reflection of electromagnetic waves impinging on metallic surfaces with periodically distributed slits (diffraction gratings) have been the subject of thorough studies using numerical and experimental approaches. Of special interest are the properties of the so-called compound gratings, which are periodic arrays of slits whose unit cell contains several of them. The transmission properties of such diffraction gratings have been studied along the last few years both theoretically (D.C. Skigin and R.A. Depine, Phys. Rev. Lett., 95, 217402, 2005) and experimentally (A.P. Hibbins et al., Phys. Rev. Lett., 96, 257402, 2006; M. Navarro-Ca et al., App. Phys. Lett., 94, 091107, 2009). However, analytical models are very useful for design purposes and, moreover, they provide physical insight that is not obvious from numerical approaches. For compound transmission gratings, the authors of this contribution recently developed a circuit-model-based analytical approach (F. Medina, F. Mesa and D.C. Skigin, IEEE Trans. on Mic. Theory Tech., 58, 105-115, 2010) that captures the essential physics of these optical systems. Thus, compound transmission gratings are now well understood, and numerical or analytical design tools are available
Color optimization of a core–shell nanoparticles layer using machine learning techniques
Neural networks were recently introduced in the field of nanophotonics as an alternative and powerful way to obtain the non-linear mapping between the geometry and composition of arbitrary nanophotonic structures on one hand, and their associated properties and functions on the other. Taking into account the recent advances in the application of the machine learning concept to the design of nanophotonic devices, we employ this tool for the optimization of photonic materials with specific color properties. We train a deep neural network (DNN) to solve the inverse problem, i.e., to obtain the geometrical parameters of the structure that best produce a desired reflected color. The analyzed system is a single layer of core–shell spheres composed of melanin and silica embedded in air, arranged in a hexagonal matrix. The network is trained using a dataset of the three CIE 1976 (L*a*b*) color coordinates obtained from the simulated reflectance spectra of a large set of structures. The direct problem is solved using the Korringa–Kohn–Rostoker method (KKR), widely applied to calculate the optical properties of sphere composites. The color optimization approach used in this work opens up new alternatives for the design of artificial photonic structures with tunable color effects.Fil: Urquia, Gonzalo Martin. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Grupo de Electromagnetismo Aplicado; ArgentinaFil: Inchaussandague, Marina Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Skigin, Diana Carina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Analysis of the optical response of reptile tissues in the visible and UV applying the KKR method
Extraordinary transmission through arrays of slits: A circuit theory model
Extraordinary transmission and other interesting related phenomena for 1-D periodic arrays of slits (compound diffraction gratings) have recently been the object of intense research in the optics and solid state physics communities. This case should be differentiated from the extraordinary transmission through arrays of small apertures on metal screens since small holes only support below-cutoff modes, whereas slits can also support transverse electromagnetic modes without cutoff frequency. In this paper, an equivalent-circuit approach is proposed to account for the most relevant details of the behavior of slit-based periodic structures: extraordinary transmission peaks, FabryProt resonances, and transmission dips observed in compound structures. The proposed equivalent-circuit model, based on well-established concepts of waveguide and circuit theory, provides a simple and accurate description of the phenomenon that is appropriate for educational purposes, as well as for the design of potential devices based on the behavior of the structures under study.Ministerio de Educación y Ciencia TEC2007-65376, CSD2008-00066Junta de Andalucía TIC-25
Multifunctional blazed gratings for multiband spatial filtering, retroreflection, splitting, and demultiplexing based on C 2symmetric photonic crystals
The concept of multifunctional reflection-mode gratings that are based on rod-type photonic crystals (PhCs) with C 2 symmetry is introduced. The specific modal properties lead to the vanishing dependence of the first-negative-order maximum on the angle of incidence and the nearly sinusoidal redistribution of the incident-wave energy between zero order (specular reflection) and first negative diffraction order (deflection) at frequency variation. These features are key enablers of diverse functionalities and the merging of different functionalities into one structure. The elementary functionalities, of which multifunctional scenarios can be designed, include but are not restricted to multiband spatial filtering, multiband splitting, retroreflection, and demultiplexing. The proposed structures are capable of multifunctional operation in the case of a single polychromatic incident wave or multiple mono-/polychromatic waves incident at different angles. The generalized demultiplexing is possible in the case of several polychromatic waves. The aforementioned deflection properties yield merging demultiplexing with splitting in one functionality. In turn, it may contribute to more complex multifunctional scenarios. Finally, the proposed PhC gratings are studied in transmissive configuration, in which they show some unusual properties.Fil: Serebryannikov, Andriy E.. Adam Mickiewicz University; PoloniaFil: Skigin, Diana Carina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Vandenbosch, Guy A. E.. Katholikie Universiteit Leuven; BélgicaFil: Ozbay, Ekmel. Bilkent University; Turquí
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