Four-port coupled channel-guide device based on 2D photonic crystal structure

We have fabricated and measured a four-port coupled channel-waveguide device using W1 channel waveguides oriented along ΓK directions in a two-dimensional (2D) hole-based planar photonic crystal (PhC) based on silicon-on-insulator (SOI) waveguide material, at operation wavelengths around 1550 nm. 2D FDTD simulations and experimental results are shown and compared. The structure has been designed using a mode conversion approach, combined with coupled-mode concepts. The overall length of the photonic crystal structure is typically about 39 μm and the structure has been fabricated using a combination of direct-write electron-beam lithography (EBL) and dry-etch processing. Devices were measured using a tunable laser with end-fire coupling into the planar structure

Modelling of photonic wire Bragg Gratings

Some important properties of photonic wire Bragg grating structures have been investigate. The design, obtained as a generalisation of the full-width gap grating, has been modelled using 3D finite-difference time-domain simulations. Different types of stop-band have been observed. The impact of the grating geometry on the lowest order (longest wavelength) stop-band has been investigated - and has identified deeply indented configurations where reduction of the stop-bandwidth and of the reflectivity occurred. Our computational results have been substantially validated by an experimental demonstration of the fundamental stop-band of photonic wire Bragg gratings fabricated on silicon-on-insulator material. The accuracy of two distinct 2D computational models based on the effective index method has also been studied - because of their inherently much greater rapidity and consequent utility for approximate initial designs. A 2D plan-view model has been found to reproduce a large part of the essential features of the spectral response of full 3D models

Deterministic design of wavelength scale, ultra-high Q photonic crystal nanobeam cavities

Photonic crystal nanobeam cavities are versatile platforms of interest for optical communications, optomechanics, optofluidics, cavity QED, etc. In a previous work \cite{quan10}, we proposed a deterministic method to achieve ultrahigh \emph{Q} cavities. This follow-up work provides systematic analysis and verifications of the deterministic design recipe and further extends the discussion to air-mode cavities. We demonstrate designs of dielectric-mode and air-mode cavities with $Q>10^9$, as well as cavities with both high-\emph{Q} ($>10^7$) and high on-resonance transmissions ($T>95$)

The influence of the chelating/combustion agents on the structure and magnetic properties of zinc ferrite

AbstractThe present study is reporting the influence of the chelating/combustion agents on the magnetic properties of Zn ferrite. Six chelating/combustion agents, citric acid, egg white, tartaric acid, glycine, glucose and urea, were used to obtain monophase zinc nanoferrite via a sol-gel auto-combustion method. The samples were subjected to a comparative study of structural features and magnetic properties by means of infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Significant influence of fuel and combustion mode was observed in the magnetic behavior of as-obtained samples. Values of the structural parameters were discovered to vary as a function of fuel choice, and to obtain crystallite size between 38 and 62 nm, inversion degree between 0.239 and 0.807, lattice parameter between 8.4125 and 8.4432 Å. The optimization of sol-gel method synthesis of zinc ferrite nanoparticles by chosing the appropriate fuel is providing structural and magnetic properties of zinc nanoferrite as potential materials to be used in biomedical applications

Zinc levels, cognitive and personality features in children with different socioeconomic backgrounds

Zinc is an essential nutrient having a complex biological role, including neuropsychological aspects. The study aimed to compare zinc level and psychic features in two pupils groups from different socioeconomic backgrounds. It also ascertains the relationship between zinc levels and aspects of intellectual development (attention, memory, intelligence) and personality features (psychoticism, neuroticism and extraversion). 103 pupils from an orphanage and 100 pupils from a regular state school were investigated. They were 11-15 years old and apparently healthy. Serum and erythrocyte zinc mean values were higher in the regular state school group (p=0.001 in both cases). The distribution of subjects regarding intellectual development was different in the two groups (p=0.000 in all cases) and personality features differed regarding psychoticism and neuroticism tendencies (p=0.019 and p=0.012 respectively). The U-test showed a significant difference between the subjects with deficient serum zinc and those with normal serum zinc as regarding attention (p=0.024) and intelligence (p=0.035) and between the subjects with deficient erythrocyte zinc and those with normal erythrocyte zinc as regards extraversion (p=0.011) in the group from the orphanage. Subjects with normal zinc status obtained higher (better) scores for psychological traits in all these situations. In conclusion, zinc levels and psychological features were different in the two groups of pupils. Our study pointed out a positive connection between zinc level and some aspects of intellectual developmental and personality features, emphasizing the importance of this trace element for the normal psychological status of children

Extraordinary Optical Transmission and Extinction in a Terahertz Wire-Grid Polarizer

A THz wire grid polarizer is simulated and demonstrated consisting of 40-μm periodic aluminum strips mounted on a polycarbonate substrate with a variable metal-to-gap ratio. Full-wave numerical simulations were performed from 100 GHz to 550 GHz predicting that the transmission in perpendicular (parallel) polarization is much higher (lower) than that predicted by geometric optics, leading to a very high extinction ratio of ∼60 dB between 100 and 550 GHz when the gaps become very small (\u3c5 \u3eμm). This behavior is confirmed qualitatively in experiments between 100 and 530 GHz where extinction ratios exceeding 40 dB are achieved. These results are explained physically as an electromagnetic concentration effect in the gaps consistent with plasmonic-like behavior. The effect depends critically on gap width and weakly on frequency