Trends in microdisk laser research and linear optical modelling

Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules made of several microdisks as “photonic atoms” show lasing at several closely spaced frequencies. A microdisk with a single quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently for “warm-cavity” linear modelling, that are able to bring a new vision of the physics of lasing.     

Theoretical prediction of a dramatic Q-factor enhancement and degeneracy removal of whispering gallery modes in symmetrical photonic molecules

Coupled-microdisk photonic molecules with high-symmetry geometries that support nondegenerate whispering gallery modes with high quality factors are numerically designed, based on a two-dimensional model. Dramatic enhancement of calculated Q factors of nondegenerate modes as compared with single-microdisk whispering gallery modes of the same radial order is achieved by tuning the intercavity coupling distances. Potential applications of this work to the design of single-mode coupled-microdisk structures with large spontaneous emission factors and low threshold lasing operation and to random laser simulations are discussed.     

Deterministic aperiodic nanostructures for photonics and plasmonics applications

This review focuses on the optical properties and device applications of deterministic aperiodic media generated by mathematical rules with spectral features that interpolate in a tunable fashion between periodic crystals and disordered random media. These structures are called Deterministic Aperiodic Nano Structures (DANS) and can be implemented in different materials (linear and nonlinear) and physical systems as diverse as dielectric multilayers, optical gratings, photonic waveguides and nanoparticle arrays. Among their distinctive optical properties are the formation of multi‐fractal bandgaps and characteristic optical resonances, called critical modes, with unusual localization, scaling and transport properties. The goal of the paper is to provide a detailed review of the conceptual foundation and the physical mechanisms governing the complex optical response of DANS in relation to the engineering of novel devices and functionalities. The discussion will mostly focus on passive and active planar structures with enhanced light‐matter coupling for photonics and plasmonics technologies.     

Enhancement of the magnetorefractive effect in magnetophotonic crystals

The magnetorefractive effect in a one-dimensional magnetophotonic crystal, more specifically, a photonic crystal (SiO₂/Ta₂O₅) containing a built-in defect in the form of a thin layer of the Co-(Al-O) magnetic nanocomposite, is studied in a computer simulation experiment. The structure of the unit cell of the photonic crystal in which most of the field energy is concentrated in cells nearest to the defect is determined. This makes it possible to increase the defect-mode Q factor and, owing to the multiple passage of light along the defect, to enhance the magnetorefractive effect by more than one order of magnitude as compared to a thin film on a substrate and by two orders of magnitude as compared to thick films. The reflectance of these structures in an applied magnetic field can be as high as 60%.     

Tuning of elliptic whispering-gallery-mode microdisk waveguide filters

High-Q semiconductor microdisk resonators laterally coupled to optical waveguides serve as compact and robust components in wavelength-division-multiplexing systems. We present an efficient algorithm for the two-dimensional design of wavelength-selective filters based on waveguide-coupled whispering-gallery-mode (WGM) microresonators of arbitrary cross-sectional shape. A full-wave integral equation formulation enables us to accurately account for the coupling between the resonator and bus waveguide as well as for radiation and material losses. Furthermore, we apply this approach to the analysis of elliptic-resonator filters. Filter tuning by changing the resonator shape from circular to elliptic reduces the dependence of the coupling efficiency on the width of the air gap. Two alternative coupling designs are suggested for monolithic and hybrid integration technologies. One is based on increasing the coupling length, while the other exploits the field concentration at the increased-curvature portion of the deformed WGM resonator.     

Magnetorefractive effect in manganites

The magnetotrans mittance and magnetoreflectance of manganite films and one-dimensional magnetophotonic crystals containing a manganite film as a defect are calculated. The calculations demonstrate that the magnetotransmittance and magnetoreflectance of manganites with a colossal magnetoresistance can be treated as a manifestation of the magnetorefractive effect. The magnitude of the magnetorefractive effect in transmission can reach 20–40% at low temperatures. The effect in reflection amounts to 1–2% for a 300-nm-thick film and can be substantially amplified through multibeam interference in the symmetric and antisymmetric structures of magnetophotonic crystals with a built-in defect.     

Effect of the imperfect flat Earth on the vertically polarizedradiation of a cylindrical reflector antenna

The radiation of a circular cylindrical reflector antenna in the presence of imperfect flat Earth is treated in an accurate manner. The boundary value problem is formulated in terms of a full-wave integral equation converted to the dual-series equations and then regularized by using analytical inversion of the static part. The resulting Fredholm second-kind matrix equation is solved numerically with guaranteed accuracy. The feed directivity is included in the analysis by using the complex source-point method. Various antenna features, which include the overall directivity, efficiency, gain, and radiated and absorbed power fractions have been calculated and compared with the free-space antenna characteristics. They show some phenomena not predicted by approximate techniques     

Optimizing Gold Nanoparticle Cluster Configurations (n ≤ 7) for Array Applications

Nanoparticle cluster arrays (NCAs) are novel electromagnetic materials whose properties depend on the size and shape of the constituent nanoparticle clusters. A rational design of NCAs with defined optical properties requires a thorough understanding of the geometry dependent optical response of the building blocks. Herein, we systematically investigate the near- and far-field responses of clusters of closely packed 60 nm gold nanoparticles (n ≤ 7) as a function of size and cluster geometry through a combination of experimental spectroscopy and generalized Mie Theory calculations. From all of the investigated cluster configurations, nanoparticle trimers with D(3h) geometry and heptamers in D(6h) geometry stand out due to their polarization insensitive responses and high electric (E-) field intensity enhancement, making them building blocks of choice in this size range. The near-field intensity maximum of the D(6h) heptamer is red-shifted with regard to the D(3h) trimer by 125 nm, which confirms the possibility of a rational tuning of the near-field response in NCAs through the choice of the constituent nanoparticle clusters. For the nanoparticle trimer we investigate the influence of the cluster geometry on the optical response in detail and map near- and far-field spectra associated with the transition of the cluster configuration from D(3h) into D(∞h).     

Radiation and absorption losses of the whispering-gallery-modedielectric resonators excited by a dielectric waveguide

The scattering of a surface wave of a dielectric layer backed by a ground plane from the whispering-gallery-mode dielectric resonators is considered by use of the surface potential approach and analytical regularization. Efficient numerical algorithms have been developed with applications to the bandstop filter design. Transmitted and reflected power fractions and radiation and absorption losses are calculated and compared for two alternative field polarizations. The effect of excitation of the higher order modes of the waveguide is also studied     

Synthesis of pyrroloquinolines

The ethyl ester of -(2,3-dimethylindolyl-5)aminocrotonic acid under Vilsmeier reaction conditions is converted into isomeric linear and bent pyrroloquinolines with predominant formation of the latter. The enaminoketone which is obtained from the same aminoindole and dibenzoylmethane under the same conditions underoges the usual Comb cyclization with a change in the ratio for the yield of isomeric pyrroloquinolines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 228–230, February, 1989.