This paper shows that accurately optimised asymmetric three phase-shift (3PS)-distributed feedback (DFB) laser structures can strongly improve the stability of the single-longitudinal mode (SLM) operation, described by the mode selectivity and the flatness of the photon density profile, through an extended range of current injection, when compared to optimised symmetric 3PS-DFB structures reported elsewhere.This study reveals its importance in modern high bit-rate optical communication systems, by enhancing the possibility of attaining high performance DFB lasers, in easily fabricated structures.The procedure, based on matrix techniques, aims at the description of the optimal design of the laser structure and it is described step-by-step.Above-threshold calculations have been accomplished to evaluate the performance of the optimised asymmetric 3PS-DFB structure, namely: the mode selectivity ( $G$ ), the flatness, the lasing wavelength, the optical power, and the side-mode suppression ratio (SMSR) evolutions with the current injection. For a current injection five times bigger than the threshold current, substantially improvements in $G$ (five times bigger) and in the SMSR (about 9 dB higher) are achieved when compared to similar, but symmetric, DFB structures.

Earlier we reported that the pits generated in CR-39 detectors during Pd/D co-deposition experiments are consistent with those observed for pits that are of a nuclear origin. Spacer experiments and track modeling have been done to characterize the properties of the particles that generated the tracks in the CR-39 detectors. The effect of water on the energetics of the particles and their resultant tracks is discussed.

Saccharomyces Cerevisiae (S. Cerevisiae) and Mrakia Frigida (M. Frigida) were deactivated using alternative current dielectric barrier discharge (DBD). The deactivation was done in argon and oxygen plasma under different discharge currents. It has been found that ozone and atomic oxygen play a significant role in the deactivation of S. Cerevisiae and M. Frigida when using DBD discharge, while argon ions are less important in the deactivation of the same microorganisms in argon DBD.

This paper discusses homogenization formulas and mixing rules that connect effective dielectric properties of mixtures with their microstucture. The special point of view in this paper is that all parameters appearing in mixing formulas are treated with equal status. The parameters that can be varied are the permittivities (which are allowed to be negative as well as positive) of the inclusion, environment, and composite, the volume fraction, spatial dimension, and an abstract parameter which chooses the given mixing formula type. The analysis helps in the interpretation of predictions from classical mixing rules when they are extended into the domain of negative-permittivity metamaterials.

We propose a theoretical study of optimization of metal-dielectric multilayer in order to approach -1 effective refractive index for transverse magnetic waves and a wavelength in the visible. The absorption losses of metal appear to be a crucial factor that affects the effective properties of the multilayer. Taking advantage of the dispersion relation of Bloch modes, we show that the losses not only decrease the transmission of the stack, but also change the negatively refracted angle. Then, we propose that using a gain-providing semiconductor (GaN) may allow compensating for the losses in metal layers. In theory, the performances of the structure can be improved greatly when gain is involved. When considering finite thickness structures, and with appropriate thickness for the terminating layers, it is possible to obtain a high transmission of the structure. A near -1 effective index metal-dielectric stack with high transmission may pave the way to the realization of negative quasi-isotropic refraction in the visible or ultraviolet wavelength range.

It is shown that the space fluctuations of concentration of conducting inclusions might be responsible for the well-known disagreement between theory and experiment at determining microwave losses in metal-dielectric mixture: the theories (percolation theory, effective medium theory, etc.) predict much lower losses than those measured in experiment. It is demonstrated that if the effective skin depth in the regions occupied by the fluctuation is comparable to the mean diameter of these regions we can expect additional losses.

The complete spectrum of eigenwaves including surface plasmon polaritons (SPP), dynamic (bulk) and complex waves in the layered structures containing semiconductor and metallic films has been explored. The effects of loss, geometry and the parameters of dielectric layers on the eigenmode spectrum and, particularly, on the SPP modes have been analysed using both the asymptotic and rigorous numerical solutions of the full-wave dispersion equation. The field and Poynting vector distributions have been examined to identify the modes and elucidate their properties. It has been shown that losses and dispersion of permittivity qualitatively alter the spectral content and the eigenwave properties. The SPP counter-directional power fluxes in the film and surrounding dielectrics have been attributed to vortices of power flow, which are responsible for the distinctive features of SPP modes. It has been demonstrated for the first time that the maximal attainable slow-wave factor of the SPP modes guided by thin Au films at optical frequencies is capped not by losses but the frequency dispersion of the actual Au permittivity.

Novel metamaterial, based on wire medium embedded into magnetizedferrite, is studied. Waves in unbounded ferrites filled with wire media, surface wave at the interface of this metamaterial and the air as well as waves in a ferrite slab adjacent to a wire medium are considered. Different geometries of wires arrangement and different magnetization directions are discussed. Effective permeability was introduced for the case where both plasma and magnetic properties take place.Dispersiondiagrams and applicability of the Drude model for the description of the wiremedium in a host matrix, possessing high permittivity andpermeability, are discussed.

In this article we study helical inclusions of a certain shape(called the “optimal shape”), such that the electric, magnetic, andmagneto-electric polarizabilities are equal, and discuss unusualrefractive and absorptive properties of artificial chiral materialsbased on such inclusions. We propose a new method of analyticalcalculation of resonant susceptibility of non-canonical, but true three-dimensionalspirals. This method takes into account spiral trajectories andeffective concentration of conduction electrons.

A technique incorporating the reflection matrix ofa semi-infinite discrete layered periodic structure is employed to analyze theelectromagnetic properties of a half-space filled with a layered metamaterial.

A new class of negative refractive index (NRI) transmission line is proposed. Differential operational amplifiers are used to form the required lumped elements, i.e., negative-impedance-converted (NIC) inductors and capacitors. When the gain of the differential operational amplifiers in the NIC circuits is very large over the entire frequency band, the equivalent material parameters are non-dispersive, and the phase response of the new NRI transmission line can be complimentary to that of a conventional transmission line over the entire frequency band. As an application example, a broadband 1:4 power divider based on the proposed NRI transmission line is studied.

The general approach to a design of miniature microwave devices based on a combination of transmission line sections with positive and negative dispersion is considered. Such lines, which are also known as right- and left-handed transmission lines, exhibit different dispersion characteristics. Using combination of these lines gives additional degrees of freedom for improvement of microwave device performance. At the same time, there is a possibility to decrease dimensions of the devices drastically. The following passive devices are under consideration: broadband digital phase shifters, directional couplers, dual-band resonators and filters exhibiting no spurious response. The potential benefit of this approach to the design of microwave devices is discussed.


This paper presents the principle of two types of conformable and controllable spherical radome based on Electromagnetic Band Gap (EBG) materials operating at around 10 GHz. The EBG structure is composed of a grid of metallic wires conformed on a hollow spherical object. Two switching control configurations are considered: (1) between an EBG structure made of electrically continuous wires and another one made of discontinuous wires, and (2) between two EBG structures made of discontinuous wires where each has a different period of discontinuities. Both switching configurations are simulated and experimentally characterized on passive prototypes. An excellent agreement is observed between simulations and measurements. The radiation patterns of two types of antennas, a horn antenna and a meteorological antenna, are also measured in the presence of the radome.