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

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.

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 $s$ and $p$ 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

Millimeter-wave phase resonances in compound reflection gratings with subwavelength grooves

Experimental evidence of phase resonances in a dual-period reflection structure comprising three subwavelength grooves in each period is provided in the millimeter-wave regime. We have analyzed and measured the response of these structures and show that phase resonances are characterized by a minimum in the reflected response, as predicted by numerical calculations. It is also shown that under oblique incidence these structures exhibit additional phase resonances not present for normal illumination because of the potentially permitted odd field distribution. A satisfactory agreement between the experimental and numerical reflectance curves is obtained. These results confirm the recent theoretical predictions of phase resonances in reflection gratings in the millimeter-wave regime, and encourage research in this subject due to the multiple potential applications, such as frequency selective surfaces, backscattering reduction and complex-surface-wave-based sensing. In addition, it is underlined here that the response becomes much more complex than the mere infinite analysis when one considers finite periodic structures as in the real experiment.D.S. gratefully acknowledges partial support from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET PIP 112-200801-01880), Universidad de Buenos Aires (UBA X208) and Agencia Nacional de Promocion Científica y Tecnológica (ANPCYT-BID1728 /OC-AR06-01785). This work was also supported by Consolider “ENGINEERING METAMATERIALS” CSD2008-00066

Experimental demonstration of phase resonances in metallic compound gratings with subwavelength slits in the millimeter wave regime

The following article appeared in Miguel Navarro-Cía, Diana C. Skigin, Miguel Beruete, and Mario Sorolla: Appl. Phys. Lett. 94, 091107 (2009) and may be found at http://dx.doi.org/10.1063/1.3086892We provide experimental evidence of phase resonances in metallic periodic structures in which each period comprises several subwavelength slits of the same width. We have analyzed and measured the response of these structures in the millimeter wave regime and show that phase resonances are characterized by a remarkable minimum in the transmission response, as predicted by numerical calculations. We compare experimental with numerical results, obtaining a very good agreement between them. This experimental confirmation encourages research in compound structures and their multiple potential applications, such as frequency selective surfaces.This work was also supported by Consolider “Engineering Metamaterials” Grant No. CSD2008-00066

Characterization of the iridescence-causing multilayer structure of the Ceroglossus suturalis beetle using bio-inspired optimization strategies

We investigate the iridescence exhibited by Ceroglossus suturalis beetles, which mostly live endemically in the southern end of South America. Two differently colored specimens have been studied. We observed and characterized the samples by different microscopy techniques, which revealed a multilayer structure within their cuticle. Using measured reflectance spectra as input data, we applied heuristic optimization techniques to estimate the refractive index values of the constituent materials, to be introduced within the theoretical model. The color of the samples was calculated for different incidence angles, showing that multilayer interference is the mechanism responsible for the observed iridescence.Centro de Investigaciones Óptica

Solution of Two Trascendental Complex Equations for the Scattering Problem By a Groove in a Metallic Plane

: We solve the complex trascendental equations that result from the application of the modal method to the problem of scattering from a metallic groove. The roots of these equations are fixed points of an entire function F c (z), where c and z are complex. Iterations are calculated with F c as: z j+1 = F c (z j ), or with an appropriate branch of its multiple-valued inverse function z j+1 = F \Gamma1 c (z j ). Since both methods fail to converge near the double roots of the trascendental equation, we give an insight to the problem and develop a method based on interpolation that solves the equations near the double roots with high precision. We give examples to illustrate the behaviour of the methods in different situations and show the connection to the theory of fractals. To obtain a copy of this report please fill in your name and address and return this page to: Infoteca Departamento de Computaci'on - FCEN Pabell'on 1 - Planta Baja - Ciudad Universitaria (1428) Buenos Aires - Ar..