Waveguide coupling gratings for high-sensitivity biochemical sensors

Grating coupling is now currently used in evanescent-wave biochemical sensors as a waveguide coupling element or as the sensing element. In most coupling cases of practical interest, the Rayleigh-Fourier method is valid, and leads to physically meaningful analytical solutions allowing grating coupling to be designed in simple terms. In the present paper the emphasis is placed on the grating as a waveguide coupling element

Reciprocity Violation for Mie Scatterers at the Interface and a Scattering Solar Concentrator

It is shown that reciprocity of the optical path can be violated through asymmetric strength coupling via near-field from resonant Mie scatterers to total internal reflection modes in a dielectric slab. Numerical simulations for silicon nanospheres separated by a nanogap from the glass substrate reveal that at least two orders of magnitude rectification ratio can be realized for such an optical diode configuration. Implementation to a solar light harvesting device, a scattering solar concentrator, is discussed, indicating a similar efficiency is achievable as for the state-of-the-art devices based on luminescence.Comment: 4 pages, 4 figure

Enhancement of optical switching parameter and third-order optical nonlinearities in embedded Si nanocrystals: a theoretical assessment

Third-order bound-charge electronic nonlinearities of Si nanocrystals (NCs) embedded in a wide band-gap matrix representing silica are theoretically studied using an atomistic pseudopotential approach. Nonlinear refractive index, two-photon absorption and optical switching parameter are examined from small clusters to NCs up to a size of 3 nm. Compared to bulk values, Si NCs show higher third-order optical nonlinearities and much wider two-photon absorption threshold which gives rise to enhancement in the optical switching parameter.Comment: 8 pages, 3 figures, to be published in Optics Communication

Effect of substrate proximity on luminescence yield from Si nanocrystals

The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.Support for this work was provided by the Swedish Research Council VR and the Australian Research Council ARC

X-ray radiation hardness and influence on blinking in Si and CdSe quantum dots

We study the effect of X-ray irradiation on the photoluminescence (PL) efficiency and intermittency (blinking) of single Si/SiO2 and CdSe/CdZnS quantum dots (QDs). Our results show that the PL efficiency of Si nanocrystals is not significantly altered up to a cumulative fluence of 1020 photons/m2 (corresponding to $300 kGy of absorbed dose in SiO2), while CdSe particles become completely dark already after a 17 times lower fluence. In both types of QDs, the statistical nature of blinking ON-and OFF-times remains unaltered: mono-exponential for Si and power-law for CdSe QDs. However, the evolution of the blinking parameters with absorbed dose depends on the choice of material. On average, both ON-and OFF-time constants do not vary in Si nanocrystals, highlighting their radiation hardness. Instead, the ON-time exponent increases while the OFF-time exponent decreases with the increasing dose for CdSe

Creative laboratory works on disciplene «Microwaves and antennas»

Представлены лабораторные работы по высокочастотной схемотехнике «Проектирование полосно-пропускающего микрополоскового фильтра» и «Согласование нагрузки с линией питания» дисциплины «Устройства СВЧ и антенны» направления подготовки «Радиотехника». Методика выполнения работ предусматривает расчет, изготовление и измерение характеристик разработанных устройств.Laboratory works on microwave design discipline "Microwaves and antennas" devoted to the analysis of microstrip filters and matching are presented. The technique of suggested works is based on microwave calculations, design and measurement of characteristics of developed devices

CdSe/CdS dot-in-rods nanocrystals fast blinking dynamics

The blinking dynamics of colloidal core-shell CdSe/CdS dot-in-rods is studied in detail at the single particle level. Analyzing the autocorrelation function of the fluorescence intensity, we demonstrate that these nanoemitters are characterized by a short value of the mean duration of bright periods (ten to a few hundreds of microseconds). The comparison of the results obtained for samples with different geometries shows that not only the shell thickness is crucial but also the shape of the dot- in-rods. Increasing the shell aspect ratio results in shorter bright periods suggesting that surface traps impact the stability of the fluorescence intensity