The frequency response of a resonator is governed by the locations of its quasinormal modes in the complex frequency plane. The real part of the QNM determines the resonance frequency and the imaginary part determines the width of the resonance. For applications such as energy harvesting and sensing, the ability to manipulate the frequency, linewidth and multipolar nature of resonances is key. Here, we present a simple analytical tool to control the location and polarity of radially symmetric resonators.
Metasurfaces that are infiltrated with active materials, such as dyes or up-converting nano-particles, offer many advantages for novel lasing systems, such as high directionality and low lasing threshold. However, such metasurface lasers require the optimisation of two metasurface modes that are resonant at both the absorption and lasing wavelength bands. The absorption band also requires a weak angular dispersion to allow for a large acceptance angle for the absorption. Here we propose and numerically demonstrate a novel technique to quantity and optimise these bands. Our technique is based on symmetry analyses of the eigenmodes of the metasurface and allows us to optimise mode volume into the active media, as well as the directionality of the lasing emission.
We report on our work developing adaptive mesh refinement for nanophotonic simulations in COMSOL. We compare three adaptive mesh refinement strategies and find that a method based on a posteriori error estimation leads to a lower memory footprint and a decrease in wall-clock time for complex three-dimensonal nanophotonic structures.
Hybrid plasmonic-photonic cavities are promising structures for enhancing the emission of quantum emitters by increasing the Purcell factor. In this work, we investigate a novel hybrid structure with a nanoparticle-on-a-mirror configuration coupled to a dielectric photonic crystal. This configuration allows to obtain small mode volumes due to the metallic nanoparticle and large Q-factors due to the photonic crystal. We report Purcell factors larger than $10^{5}$ in the visible spectral region, which are achieved with structures that are experimentally feasible with current technology. We expect that our results may open new avenues for boosting light-matter interactions in nanophotonic systems.
We consider the series-connected Josephson transmission line (JTL), constructed from Josephson junctions, capacitors and resistors. We calculate the velocity of shocks in the discrete lossy JTL. We propose the simple wave approximation, which decouples the continuum JTL equations into two separate equations for the right- and left-going waves. The approximation, in particular, allows to easily consider the formation of shocks.
We present a novel imaging technique that combines quantum ghost and scanning imaging protocol to capture two-dimensional images using only a one-dimensional detector array, enabled by strong spatial correlations and tunable emission angle of entangled photon pairs emitted from an ultrathin nonlinear metasurface.
The development of radar absorbing devices turned at the beginning of the millenium to metasurfaces. Reduced sizes, wide array of possible impedances, easy implementation of electronics are among the main benefits rendering them an adequate solution to the challenges of stealth. However, even these novel systems are intrinsically limited in their bandwidth. Fortunately, the recent interest for time-varying devices highlighted the possibily to overcome such limitations. To serve as a first step towards a functional time-modulated metasurface, this work focuses on the experimental validation of a reconfigurable metasurface absorber. Finite-element simulations and experimental measurements are compared to validate the behavior of the designed metasurface. Despite slight discrepancies, seemingly originating from an inaccurate varactor diode model and unexpected additional resistivity, the experimental results highlight a very good reconfigurability of the metasurface in terms of frequency agility.
Planar arrays of split-ring resonators are known to support the propagation of backward magnetoinductive waves due to the negative coupling coefficient between elements. In this work, it is shown that the dispersion character can be switched to a forward wave if the resonators are touching. In particular, when the shared side is capacitively loaded, the total coupling can be switched from negative to positive values, allowing for forward magnetoinductive waves to propagate on the structure. By varying the value of the capacitor in the shared side of square resonators, the sign and size of the total coupling can be further controlled. This is demonstrated in an 11-element array, where the magnetoinductive wave can switch between forward and backward propagation depending on the capacitance of the shared side. Furthermore, there is a critical value of capacitance where the coupling becomes almost zero, effectively cutting of wave propagation on the structure. Numerical simulations are used to study this behaviour.
We propose a novel design method for monochromatic metalenses. The proposed technique partitions the peripheral region of a metalens into supercells. These supercells are generated by dividing the peripheral region into intervals along the radial direction, where the target phase changes by 2π, and intervals along the circumferential direction with a constant angular periodicity. Therefore, the shape of each supercell can be approximated as rectangular with its size comparable to a wavelength, and its pillar arrangement is determined by metagrating optimization together with the adjoint method that considers interactions among pillars. This makes the design of large-scale wide field-of-view high-efficiency metalenses more tractable than the conventional unit-cell-based method, which is prone to efficiency decrease especially in the peripheral region, and other recently proposed optimization-based methods, which are computationally expensive.
In this work, we present a design-and-manufacture-friendly method for quantization lobes suppression in intelligent reflective surfaces (IRS). Rotation of the 4 identical equally spaced subarrays around their diagonals allows for significant suppression of quantization lobes compared to the panel shift method. Modeling of a 20 × 20 array shows that this method can suppress quantization lobes by more than 10dB with very low losses in the main lobe gain.
Imaging using magnetoinductive (MI) waves has multiple potential applications from structural health monitoring to medical diagnosis. We utilise a 1D magnetoinductive waveguide (MIW) comprising of split ring resonators (SRRs) to successfully determine the proximity and location of a conductive object. By building upon previous work we are able to combine localisation with characterisation and make vital first steps from defect sensing and towards imaging of inhomogeneous conductive media using MI waves.
Magnetic interactions in metamaterial structures have led to a wide variety of applications from wireless power transfer to contactless localisation. Here, we show that in two split ring resonators (SRR), the direction of the induced Lorentz force can be reversed by varying the frequency of the applied AC voltage. An analytical model has been verified by experimental data. These findings have the potential to enable the reconfiguration of programmable structures for new capabilities and functionalities.
In this paper, we explore the conductance properties of a longitudinal slot on a substrate integrated waveguide (SIW) with three different models. These models allow us to evaluate the impact on the slot conductance of covering it with a metasurface to improve the radiation performance. In particular, the influence of the MTS on the coupling between slots will be analyzed. Our results show that the presence of the MTS reduces the slot conductance and slot resonance length, but has limited impact on the coupling.
Plasmonic nanoantennas with constant input impedance within a wide range of mid-infrared frequencies are designed. For antennas working in lower frequencies like radiofrequencies or microwaves, it could be done by using self-complementary geometries if Babinet’s principle is approximately valid. However, the scaling up to the infrared is not trivial since metals are not good conductors in such high frequencies. We have found an alternative way to recover the validity of Babinet’s principle and thus the achievement of constant input impedance.
Self-assembled into superlattice nanocrystals open new opportunities to control unique optical properties. Employing Mie resonances for superlattices contributes to the additional enhancement of emission properties. Here, we theoretically study superlattices from CsPbBr 3 nanocrystals. We show that emission in resonant perovskite superlattices accelerates by 3 times due to Mie resonances. We believe our results are promising for the observation of superfluorescence enhanced by Mie resonances.
Our research explores non-Hermitian elastic lattices with non-local feedback interactions. Proportional feedback in one-dimensional lattices creates complex dispersion relations that exhibit non-reciprocity with gain and loss in opposite directions. This behavior persists across multiple frequency bands. In classical systems, we observed peculiar tunneling phenomena in one-dimensional chains with non-reciprocity. Our findings highlight the fundamental properties of non-Hermitian elastic lattices and suggest opportunities for designing meta materials with unique functionalities such as wave filtering, amplification, and localization.
Perfect plane-wave to surface-wave couplers over non-planar port regions are designed. The conformal couplers transfer all of the available power in the incident beam to the surface wave which delivers it to a spatially dislocated output port. At the output port, the surface wave is leaked as a beam with control over its amplitude and phase. As all of the captured power is leaked into the reradiated beam, the transfer efficiency is near unity. The metasurfaces consist of an arbitrarily shaped impedance sheet supported by a grounded dielectric spacer. The design occurs in three phases, an integral equation modelling/method of moment solution stage often resulting in the need for active and/or lossy unit cells, a subsequent optimization phase to remove the need for loss and/or gain rendering the metasurface passive and lossless, and a final unit cell design stage to translate the purely reactive impedance sheet to printed circuits. The couplers can be useful in new high frequency communications systems to increase fields in shadow zones where diffraction strengths are reduced, or for new conformal cloaks, electromagnetic illusions, and camouflage.
The emergence of photonic time crystals has engendered considerable scientific curiosity, owing to their unique features, including the momentum bandgaps. However, the generation of experimentally detectable momentum bandgaps poses a formidable challenge, particularly at high frequencies, necessitating the use of high-power pumping that may lead to deleterious material overheating. To tackle this problem, we propose two routes toward theoretically unlimited enhancement of the momentum bandgap size.
Implementation of tunable and switchable topological systems is the next step towards realistic applications of topological photonics. Here, we study topological zigzag arrays of dielectric resonators and demonstrate a novel method to control their topological edge states by applying local heating. Numerical and experimental studies confirm that the properties of the topological edge states in such systems can be tuned and controlled by temperature.
The functionality of a fully planar metamaterial-inspired substrate-integrated cavity is thoroughly investigated in the present work. The electromagnetic field confinement of the proposed device is realized with the utilization of broadside-coupled complementary split ring resonators that operate as a virtual electric wall. The numerical results from the eigenvalue analysis verify the presence of the fundamental resonances with a noteworthy quality factor. Subsequently, full-wave simulations are conducted to validate the resonance functionality of the proposed device, with excitation achieved using the metallic core of a coaxial cable. Numerical results highlighted, also, the radiation capabilities exploiting the inherent openings in the device due to the complementary resonators.
