Spatial filtering using dielectric photonic crystals at beam-type excitation

Cataloged from PDF version of article.Spatial filtering is demonstrated at beam-type excitations by utilizing finite thickness slabs of two-dimensional dielectric photonic crystals (PCs) showing exotic Fabry-Perot resonances that are preserved over a wide range of variation of the incidence angle. Bandstop and dual-bandpass filtering effects are illustrated theoretically and the corresponding filters are validated in the microwave experiments by using square-lattice PCs. It is shown that the basic transmission features that were observed earlier for a plane-wave illumination are also recognizable at beam-type excitations. The proposed spatial filtering mechanism exhibits directional beaming. The desired widths and the locations of the passbands and stopbands are attainable in the angle domain with a proper choice of the operating frequency for the given excitation characteristics. c 2010 American Institute of Physics. [doi:10.1063/1.3498810

Simultaneously opening transmission channels with negative and positive phase velocities for the stacked subwavelength apertures in fishnet metamaterials with hybrid unit lattices

Cataloged from PDF version of article.Hybridization of the unit lattice along the propagation direction was demonstrated to produce a negative-phase-velocity transmission band in the absence of the contributions from the higher diffraction orders for a stacked metallic fishnet grid with subwavelength apertures. This extraordinary transmission band is governed by the stacked resonators. The hybridized unit lattice configurations are not just slight modifications of the configurations with homogenous unit lattices. The volumetric proportions of different dielectric media are a key factor in the partitioned unit lattice for the estimation of the stacking and coupling effects between the resonators. The contribution of the coupling mechanisms enhances the transmission results almost by the same factor for the investigated lattice separations along the propagation direction in hybrid unit cells while the densely stacked resonators yield much higher transmission results, both around the regarding extraordinary transmission band that is associated with the negative phase velocity. A positive-phase-velocity transmission band was also exhibited by the hybridized unit lattice configuration when combined with a cavity resonator. Experimental transmission results of the hybrid configuration supported the theoretical predictions. The hybrid configurations are scalable to the near-infrared regime. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JNP.6.061608

Dispersion irrelevant wideband asymmetric transmission in dielectric photonic crystal gratings

Cataloged from PDF version of article.Wideband suppression of zero order and relevant strongly asymmetric transmission can be obtained in photonic crystal gratings that are made of linear isotropic materials and show the broken structural (axial) symmetry, even if zero diffraction order may be coupled to a Floquet-Bloch (FB) wave at the incidence and exit interfaces. The studied mechanism requires that the peculiar diffractions at the corrugated exit interface inspire strong energy transfer to higher orders, including those not coupled to an FB wave. At the opposite direction of incidence, transmission due to zero and some higher orders that may be coupled at the corrugated input interface can vanish. This leads to the alternative scenario of wideband unidirectional transmission, which itself does not need but can coexist with the other scenario based on the merging of asymmetric diffraction and dispersion of the FB mode. © 2012 Optical Society of America

Transmission enhancement through deep subwavelength apertures using connected split ring resonators

Cataloged from PDF version of article.We report astonishingly high transmission enhancement factors through a subwavelength aperture at microwave frequencies by placing connected split ring resonators in the vicinity of the aperture. We carried out numerical simulations that are consistent with our experimental conclusions. We experimentally show higher than 70,000-fold extraordinary transmission through a deep subwavelength aperture with an electrical size of lambda/31x lambda/12 (width x length), in terms of the operational wavelength. We discuss the physical origins of the phenomenon. Our numerical results predict that even more improvements of the enhancement factors are attainable. Theoretically, the approach opens up the possibility for achieving very large enhancement factors by overcoming the physical limitations and thereby minimizes the dependence on the aperture geometries. (C) 2010 Optical Society of Americ

Frequency dependent steering with backward leaky waves via photonic crystal interface layer

Cataloged from PDF version of article.A Photonic Crystal (PC) with a surface defect layer (made of dimers) is studied in the microwave regime. The dispersion diagram is obtained with the Plane Wave Expansion Method. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Two facts are noted: First, a guided (bounded) wave is present, propagating along the surface of the dimer-layer. Second, above the light line, the fast traveling mode couple to the propagating spectra and as a result a directive (narrow beam) radiation with backward characteristics is observed and measured. In this leaky mode regime, symmetrical radiation patterns with respect to the normal to the PC surface are attained. Beam steering is observed and measured in a 70 degrees angular range when frequency ranges in the 11.88-13.69GHz interval. Thus, a PC based surface wave structure that acts as a frequency dependent leaky wave antenna is presented. Angular radiation pattern measurements are in agreement with those obtained via numerical simulations that employ the Finite Difference Time Domain Method (FDTD). Finally, the backward radiation characteristics that in turn suggest the existence of a backward leaky mode in the dimer-layer are experimentally verified using a halved dimer-layer structure. (C) 2009 Optical Society of Americ

High efficiency of graded index photonic crystal as an input coupler

Cataloged from PDF version of article.A graded index photonic crystal (GRIN PC) configuration was placed at the input side of a photonic crystal waveguide (PCW) in order to efficiently couple the light waves into the waveguide. We compared the transmission efficiencies of light in the absence and presence of the GRIN PC structure. We report a significant improvement in coupling when the GRIN PC is incorporated with the PCW. The intensity profiles were obtained by carrying out the experiments at microwave frequencies. Finite difference time domain based simulations were found to be in good agreement with our experimental results

The focusing effect of graded index photonic crystals

Cataloged from PDF version of article.We describe an approach to implement graded index (GRIN) structures using two- dimensional photonic crystals (PCs). The lattice spacing along the transverse direction to propagation is altered and we show, both theoretically and experimentally, that such a spatial perturbation is an effective way to obtain GRIN PC. The response of the structure to spatially wide incident beams is investigated and strong focusing behavior is observed. The large spot size conversion ratio can be attainable and is mainly limited by the finite size of the structure. The designed GRIN PC shows promise for use in optical systems that require compact and powerful focusing elements compared to the traditional bulky lenses. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3009965

Coupling effect between two adjacent chiral structure layers

Cataloged from PDF version of article.A pair of mutually twisted metallic cross-wires can produce giant optical activity. When this single chiral layer is stacked layer by layer in order to build a thick chiral metamaterial, strong coupling effects are found between the two adjacent chiral layers. We studied these coupling effects numerically and experimentally. The results show that the existing coupling between chiral layers can make the chiral properties of a two-layered chiral metamaterial different from the constituting single chiral layers. It is explained qualitatively that the coupling effects are generated from the coupling of metallic cross-wires belonging to different chiral layers. Our experimental results are in good agreement with the simulation results. ©2010 Optical Society of Americ

Volumen de madera muerta en rodales gestionados de Haya Oriental (Fagus orientalis Lipsky) en Turquía

As a result of " clean management " systems in forests, many species are lost or reduced to the point of being endangered. This is a broad term which refers to the pursuit of a tidy, system of intensively productive forest in which dead and dying wood, standing and fallen, is rigorously removed or cleansed from the system. This is because foresters believed that such wood harboured diseases and pests. The consequence of such policies applied over decades or in some cases centuries has been a massive depletion of the resource and serious declines of removal of biodiversity. This study assesses the amount of coarse dead wood in oriental beech forests in Turkey. The total volume of dead wood was revealed as 22.87 +/- 4.34 cubic m/ha; made up of 3.37 +/- 1.41 cubic m/ha (15%) as snag1 (standing dead wood with dried tips and intact top), 9.87 +/- 2.2 cubic m/ha (43%) as snag2 (standing dead wood with bark loosened and broken top), 4.13 +/- 1.9 cubic m/ha (18%) as log1 (newly fallen dead wood), and 5.51 +/- 1.99 cubic m/ha (24%) as log2 (rotted fallen dead wood). From this research the managed oriental beech stands in Turkey can be described as relatively dead wood-rich. The proportion of the total dead wood volume (%) of oriental beech stands investigated 4.81 +/- 4.72 percent of the total living wood volume. There were significant differences (F sub(14;65)= 4.109***, and SNK -Student-Newman-Keuls- = 3.99) in dead wood volume between the main study areas (min.: 4.46 cubic m/ha; max.: 46.11 cubic m/ha). This was due to the topography and particularly the steep slopes, and the road network infrastructure which influences the situation through local timber production. It is hoped that this study of oriental beech forests, may guide managers in considering dead wood and processes of decomposition in managing forests in Turkey, Southeastern Europe, the Northern Caucasus, Northern Iran and Syria.Muchas especies forestales se pierden o ven reducida su distribución hasta el punto de estar amenazadas, como resultado de sistemas de "gestión limpia" de los sistemas forestales. Este es un término amplio que se refiere a conseguir un sistema de bosques productivos de forma intensiva en los que la madera muerta, tanto en pie como caída, se extrae del sistema. Esto es debido a que los forestales creen que esta madera alberga a plagas y enfermedades. La consecuencia de estas políticas, aplicadas durante décadas o siglos, ha sido una disminución de los recursos y la perdida de biodiversidad. Este estudio evalúa la cantidad de madera muerta en bosques de haya oriental en Turquía. El volumen total extraído fue de 22,87 +/- 4,34 m cúbicos/ha; siendo de 3,37 +/- 1,41 m cúbicos/ha (15%) la madera muerta en pie de árboles puntisecos, 9,87 +/- 2,2 m cúbicos/ha (43%) de madera muerta en pie con corteza desprendida y parte superior rota, 4,13 +/- 1,9 m cúbicos/ha (18%) de madera muerta caída reciente, y 5,51 +/- 1,99 m cúbicos/ha (24%) de madera caída podrida. A partir de esta investigación, la gestión de los rodales de haya oriental en Turquía puede describirse como relativamente rico en madera muerta. La proporción del volumen total de madera muerta (%) de los rodales de haya oriental representan el 4,81 +/- 4,72% del volumen total de madera viva. Existen diferencias significativas (F sub(14;65)= 4,109***, y SNK -Student-Newman-Keuls- = 3,99) en el volumen de madera muerta entre las áreas principales de estudio (min.: 4,46 m cúbicos/ha; max.: 46,11 m cúbicos/ha). Esto se debe a la topografía y particularmente a las pendientes pronunciadas, y la red de caminos que influyen la situación de la producción local de madera. Se espera que este estudio sobre los bosques de haya oriental puedan servir de guía a los gestores para considerar la madera muerta y su proceso de descomposición en la gestión de los bosques de Turquía

Application of extracts from the poisonous plant, Nerium Oleander L., as a wood preservative

The antifungal properties of poisonous plant extracts from oleanders (Nerium oleander L.) were determined when used as a wood preservative. The extract was prepared from oleanders leaves andflowers in 96% ethyl alcohol. The wood blocks of Turkish oriental beech (Fagus orientalis L.) and Scots pine (Pinus sylvestris L.) were impregnated with the extracts. The abilities of the extract to suppressattack by Postia placenta (Fr.) (brown rot) and Trametes versicolor (L: Fr.) Quel. (a white-rot) was investigated. Treated blocks were exposed to P. placenta and T. versicolor attacks for 12 weeks by following the soil-block method. While untreated wood specimens have weight loss ranging between 27.37 and 30.66% for P. placenta and 8.64 and 24.06% for T. versicolor, the wood treated with theextracts is of weight loss between 5.54 and 10.98% for P. placenta, and between 5.02 and 28.25% for T. versicolor. The lowest weight loss was found to be for beech wood (5.02%) impregnated with the extractof oleander at a concentration level of 0.25% against T. versicolor. While the highest weight loss was also on the beech wood (28.25%) treated with the same extract at the level of 0.50% concentrationagainst T. versicolor. In conclusion, the extracts could be used as effective wood preservative