Scattering integral equation formulation for intravascular inclusion biosensing.

A dielectric waveguide, inserted into blood vessels, supports its basic mode that is being scattered by a near-field intravascular inclusion. A rigorous integral equation formulation is performed and the electromagnetic response from that inhomogeneity is semi-analytically evaluated. The detectability of the formation, based on spatial distribution of the recorded signal, is estimated by considering various inclusion sizes, locations and textural contrasts. The proposed technique, with its variants and generalizations, provides a generic versatile toolbox to efficiently model biosensor layouts involved in healthcare monitoring and disease screening.

Giant enhancement of nonreciprocity in gyrotropic heterostructures.

Nonreciprocity is a highly desirable feature in photonic media since it allows for control over the traveling electromagnetic waves, in a way that goes far beyond ordinary filtering. One of the most conventional ways to achieve nonreciprocity is via employing gyrotropic materials; however, their time-reversal-symmetry-breaking effects are very weak and, hence, large, bulky setups combined with very strong magnetic biases are required for technologically useful devices. In this work, artificial heterostructures are introduced to enhance the effective nonreciprocal behavior by reducing the contribution of the diagonal susceptibilities in the collective response; in this way, the off-diagonal ones, that are responsible for nonreciprocity, seem bigger. In particular, alternating gyrotropic and metallic or plasmonic films make an epsilon-near-zero (ENZ) effective-medium by averaging the diagonal permittivities of opposite sign, representing the consecutive layers. The homogenization process leaves unaltered the nonzero off-diagonal permittivities of the original gyrotropic substance, which become dominant and ignite strong nonreciprocal response. Realistic material examples that could be implemented experimentally in the mid-infrared spectrum are provided while the robustness of the enhanced nonreciprocity in the presence of actual media losses is discussed and bandwidth limitations due to the unavoidable frequency dispersion are elaborated. The proposed concept can be extensively utilized in designing optical devices that serve a wide range of applications from signal isolation and wave circulation to unidirectional propagation and asymmetric power amplification.

Electromagnetic fields between moving mirrors: singular waveforms inside Doppler cavities.

Phenomena of wave propagation in dynamically varying structures have reemerged as the temporal variations of the medium's properties can extend the possibilities for electromagnetic wave manipulation. While the dynamical change of the electromagnetic medium's properties is a difficult task, the movement of scatterers is not. In this paper, we analyze the electromagnetic fields trapped inside two smoothly moving mirrors. We employ the method of characteristics and take into account the relativistic phenomena to show that the temporally and spatially local Doppler effects can filter and amplify the electromagnetic signal, tailoring the k - and ω -content of the transients. It is shown using the Doppler factor and the change of the distance between neighbor characteristics that the dynamical movement of the boundaries can lead to condensation or dilution of characteristics resulting in field amplification or attenuation, respectively. In the case of periodically moving mirrors the field distribution is shown that asymptotically leads to exponentially growing delta-like wave packets at discrete points of space with a limiting number of peaks due to the fact that the velocity of the mechanical vibrations cannot exceed that of light. The theoretical analysis is also verified by FDTD simulations and is connected with the theory of mode locking.

Nanotubes as sinks for quantum particles.

Nanotubes with proper thickness, size, and texture make ultra-efficient sinks for quantum particles traveling into specific background media. Several optimal semiconducting cylindrical layers are reported to achieve enhancement in the trapping of matter waves by two to three orders of magnitude. The identified shells can be used as pieces in quantum devices that involve the focusing of incident beams, spanning from charge pumps and superconducting capacitors to radiation pattern controllers and matter-wave lenses.

Uniaxial films of maximally controllable response under visible light.

The controllability of photonic setups is strongly related to how coherently their outputs react to changes in their inputs; such a generic concept is treated in the case of films comprising multilayers of tilted optical axes, under visible light. The optimized designs incorporate ordinary metals or semiconductors while being able to achieve practically all the combinations of reflected, transmitted and absorbed power within the passivity limits. Importantly, most of the proposed structures exhibit substantial robustness to manufacturing defects and are fabricable with various methods. Therefore, they can make indispensable pieces of integrated photonic systems by improving their light-controlling operation for applications ranging from steering and electrodynamic switching to filtering and optical signal processing.

Optimally Sharp Energy Filtering of Quantum Particles via Homogeneous Planar Inclusions.

Some of the most influential players from academia and industry have recently expressed concrete interest for quantum engineering applications, especially for new concepts in controlling and processing the quantum signals traveling into condensed matter. An important operation when manipulating particle beams behaving as matter waves concerns filtering with respect to their own energy; such an objective can be well-served by a single planar inclusion of specific size and texture embedded into suitable background. A large number of inclusion/host combinations from realistic materials are tried and the optimally sharp resonance regimes, which correspond to performance limits for such a simplistic structure, are carefully identified. These results may inspire efforts towards the generalization of the adopted approach and the translation of sophisticated inverse design techniques, already successfully implemented for nanophotonic setups, into quantum arena.

Wide-angle absorption of visible light from simple bilayers.

Color-selective absorption of light is a very significant operation used in numerous applications, from photonic sensing and switching to optical signal modulation and energy harnessing. We demonstrate angle-insensitive and polarization-independent absorption by thin bilayers comprising ordinary bulk media: dielectrics, semiconductors, and metals. Several highly efficient designs for each color of the visible spectrum are reported, and their internal fields' distributions reveal the resonance mechanism of absorption. The proposed bilayer components are realizable, since various physical or chemical deposition methods can be used for their effective fabrication. The absorption process is found to exhibit endurance with respect to the longitudinal dimension of the planar structure, which means that the same designs could be successfully utilized in non-planar configurations composed of arbitrary shapes.

Total absorption in asymmetric hyperbolic media.

Finite-thickness slabs of hyperbolic media with tilted optical axes exhibit asymmetry properties for waves propagating upward and downward with respect to slab interfaces. Under certain conditions, asymmetric hyperbolic media acquire extreme permittivity parameters and the difference between upward and downward propagating waves becomes very large. Furthermore, both waves can be perfectly matched with the free space; such a feature makes possible the development of optically ultra thin perfect absorbers. The proposed approach is unified and allows the use of different -negative materials. Of particular interest is the asymmetric hyperbolic medium, made of silicon nanowires, since it can be directly applicable to solar cell systems.

Convergence analysis and oscillations in the method of fictitious sources applied to dielectric scattering problems.

Several wave scattering phenomena in optics are modeled by the method of fictitious sources (MFS). Despite its interesting features, the effectiveness of the MFS and its applicability are restricted by open issues, including the placement of the fictitious sources (FS) and the fields' convergence. Concerning these issues, we investigate here the MFS convergence and study oscillations in its solutions for a representative scattering problem of a dielectric cylinder illuminated by a current filament. It is shown analytically that, when the FS radii lie in the interior and exterior of two disks with certain critical radii, the MFS currents' series diverge while the respective fields converge, as the FS number N tends to infinity. Asymptotic formulas of the divergent currents are established, exhibiting that they increase exponentially with N and oscillate. Numerical simulations are included, demonstrating that (i) the divergent currents oscillate for sufficiently large N, (ii) the oscillating values are fairly approximated by the derived asymptotic expressions, and (iii) these oscillations are inherent in MFS and are not due to ill-conditioning; hence, they cannot be overcome by improving the hardware or software. The possibility of obtaining convergent and correct fields from divergent intermediary currents may lead to a potential significant advance of the applicability of the MFS.