We investigate the robustness of bound states in the continuum (BICs) in a bilayer dielectric rod array against geometric and material perturbations. Our analysis focuses on both symmetry-protected and Fabry-P & eacute;rot BICs (FP BICs), examining their transformation into quasi-BICs under three structural modifications: (i) in-plane displacement of one layer, which breaks the C2 symmetry of the system; (ii) introduction of material losses that break time-reversal symmetry; and (iii) variation in the interlayer distance, which preserves structural symmetry. In particular, we demonstrate that material losses inevitably induce radiation in Fabry-P & eacute;rot BICs via second-order perturbation processes, converting them into quasiBICs, while symmetry-protected BICs remain nonradiative. We further show that, despite the inherent instability of BICs under symmetry-breaking effects, their resilience can be significantly enhanced through proper design. Both Fabry-P & eacute;rot and symmetry-protected BICs exhibit exponentially weak sensitivity to C2-breaking perturbations as the interlayer distance increases. Finally, we show that additional FP BICs emerge under oblique incidence, originating from the interference of two high-Q quasi-BICs near the symmetry-protected ones. Our findings pave the way for the development of BIC-based photonic devices with improved robustness against fabrication imperfections, environmental variations, and material losses.

Dielectric metawaveguides that leverage the resonant behavior of individual dielectric scatterers have recently been suggested as a versatile platform for controlling light propagation and tailoring light-matter interactions in integrated optical circuits. Their broad tunability is of particular interest for the realization of various reconfigurable optical elements. Here, we propose an approach for realizing optical isolation based on a metawaveguide composed of silicon nanoparticles exhibiting a predominant in-plane electric dipole response. We show that perturbation of the metawaveguide geometry leads to the formation of modes with a non-zero transverse optical spin through the mode coupling mechanism. Furthermore, by incorporating magnetic material into the waveguide, we demonstrate a compact optical isolator compatible with the silicon-on-insulator platform and provide a general framework for its design. Our results have significant implications for the advancement of high-density photonic circuits and may enable functionalities in directional emission, optical communications, and sensing technologies.

We study the impact of lithography imperfections on quasi-bound states in the continuum (quasi-BICs) supported by a one-dimensional metasurface of Ge_2Sb_2Te_5 (GST) bars with trapezoidal deviations from rectangular cross-sections. Several mechanisms of quality (Q) factor scaling, including the impact of material losses, dispersion, and geometric imperfections are established. We demonstrate that transition to identical isosceles trapezoids, despite preserving the required C_2 symmetry, reduces the Q factor in the amorphous phase due to absorption changes accompanying the resonance shift. Further, the Q factor remains robust for both GST phases under random element-to-element variations of the trapezoid angle, while analytical and numerical estimations in the absence of material losses show inverse-quadratic scaling of the Q factor with the disorder amplitude. We reveal that in the GST-based metasurface, the Q factor is tolerant to geometric imperfections for insignificant dispersion near the BIC wavelength, but changes in case of substantial dispersion. The phase shifting and established robustness of BICs in GST can be useful for applications where stable moderate Q factors are essential.

Gallium Phosphide (GaP) is a premier material for integrated nanophotonics, combining prominent second-order nonlinear properties with near-perfect lattice matching with silicon for CMOS compatibility. However, leveraging these advantages in scalable bottom-up architectures requires understanding optical properties of the geometries defined by the fabrication methods. Here, we reveal the formation of a highly confined electromagnetic "hot spot" at the nanowire-substrate interface in self-assembled GaP nanowires (NW). This robust interfacial field localization is driven by the fundamental TM11 Mie resonance, which is selectively supported by the hexagonal geometry of the epitaxially grown NW. Through full-wave simulations and polarization-resolved dark-field spectroscopy, we find that the hexagonal cross-section also suppresses higher-order modes, yielding a simplified and spectrally clean resonant landscape. Experimental measurements confirm the diameter-dependent tunability of these modes across the visible spectrum. These findings establish a scalable platform for nanoantennas deterministically concentrating light at the substrate interface, ideal for employing the intrinsic nonlinearity of GaP for frequency conversion and enhancing light-matter interactions for quantum emitters and biosensing.

Wavefront manipulation via Huygens metasurfaces is rapidly advancing and holds great potential for a wide range of optical applications. However, in low-cost and low-precision manufacturing scenarios, inevitable positional disorder poses a significant challenge to the realization of conventional Huygens metasurfaces. To address this, we consider a class of Huygens metasurfaces based on congener dipoles that exhibit inherent robustness against positional disorder. In this approach, a Huygens source is engineered by merging two parallel electric dipole modes. We systematically investigate how varying degrees of positional disorder affect the optical performance of metalenses and metadeflectors constructed with these metasurfaces. Simulation results reveal that even with random element displacements of up to 0.5, the congener-based metadevices retain their functional performance, with focusing efficiency decreasing by only 5%. This study demonstrates a robust and flexible design strategy for Huygens metasurfaces, paving the way for disorder-tolerant and cost-effective optical device.

In metaphotonics single nanoparticles considered as a resonators supporting optical modes. When several nanoparticles are located nearby each other the coupling through the free space takes place. Here we review recent reports describing different coupling regimes, such as strong and weak coupling and regimes of parity-time symmetry and exception points in clusters of nanoparticles. The nature of the by free-space coupling is in essential retardation effects, which modifies the mathematics and observable behavior of such systems.

Most of the proposed all-dielectric metasurfaces operate with a specific polarization that limits the performance of its applications. Here we propose a concept which is allows to support polarization independent qBIC resonances. Our approach is based on an all-dielectric metasurface consisting of a periodic array of cut silicon disks on the $\text{SiO}_{2}$ substrate and supports symmetryprotected quasi-bound states in the continuum (quasi-BIC) in the near-infrared range. We achieve polarization independence of the metasurface by combining two independent qBICs for two orthogonal polarizations. By tuning the geometric parameters, we develop a metasurface with the desired properties and achieve stability in the quality factor.

Engineering nanoscale light matter interaction in mixed dimensional semiconductor heterostructures offers a pathway to mitigate the intrinsic gain bandwidth trade off in photodetectors. Here, we report a broadband, high responsivity 2D and 1D photodetector formed by integrating monolayer p type WSe2 with electrospun p type NiO nanowires. The device photoresponse spans 350 to 780 nm and is governed by a nanophotonic field confinement mechanism rather than bulk optical absorption. The high index NiO nanowire acts as a dielectric Mie type nanoresonator that supports geometry defined optical modes and produces antenna like near field concentration at the nanoscale WSe2 and NiO junction. This localized optical mode increases the local absorption cross section and enhances the photocarrier generation rate within the junction region, identified as the dominant active volume for photocurrent. A coupled optoelectronic model linking full wave electromagnetic simulations to carrier generation, recombination, and extraction accurately captures the measured responsivity spectrum and its power dependence using only two electronic fitting parameters. The device achieves responsivities of 627 A/W in the visible region, 227 A/W in the UV, and 167 A/W in the NIR, demonstrating broadband operation with ultrahigh gain. These results show that geometric resonance in mixed dimensional junctions is a powerful design principle for next generation high gain optoelectronic detectors.

Over the past decade, phase-change materials (PCMs) have found widespread use across photonics, optoelectronics, and electronics. Their ability to reversibly tune optical and electronic properties through phase switching is increasingly being leveraged to enhance device functionality. Here, we develop a new optoelectronic device that integrates a perovskite emitter with a phase-change material. We demonstrate reversible "on/off" control of electroluminescence emission through PCM phase switching as well as the ability to write distinct emission patterns by locally modifying the PCM phase without lithography. These results highlight a pathway toward new classes of fast-response LEDs with reconfigurable and repeatedly rewritable emission patterns.

Huygens metasurfaces have emerged as a powerful platform for wavefront manipulation with broad potential across a range of photonic applications. However, their performance is often sensitive to positional disorder, which is unavoidable in large-scale, low-cost, or low-precision fabrication scenarios. In this work, we consider a metasurface design based on congener dipole elements: two parallel electric dipole modes that together form a Huygens source with inherent resilience to spatial perturbations. We demonstrate, through comprehensive simulations, that metalenses and metadeflectors constructed from such metasurfaces maintain their intended functionality under significant disorder. This approach offers a robust and versatile route toward disorder-tolerant optical metasystems, opening pathways for scalable and reliable integration in real-world photonic devices.

At the end of the last century, Allen et al. showed that light has angular orbital momentum in addition to spin. This discovery contributed to the active development of free-space optical communication. In the modern world, free-space optical communication is the main competitor to fiber optical communication lines. However, they are still inferior in throughput to fiber systems. In this work, we experimentally demonstrate the implementation of a free-space orbital angular momentum comb, as an analogue of a frequency comb for free-space optical communication. We present a simple approach to the generation of the orbital angular momentum comb, based on the generation of the second harmonic of the Hermite-Gauss mode with its subsequent conversion into the orbital comb of the Laguerre-Gauss mode. Our results are supported by analytical theory simulations and experimental evidence.

Recently, electromagnetically induced transparency (EIT) has emerged in nanophotonics for filtering, thermal camouflaging, sensing, and others. However, most of the proposed concepts operate for a specific polarization of excitation, which limits their performance in applications. Here we propose a design providing a polarization-independent EIT resonance. Our approach is based on a silicon metasurface supporting symmetry-protected quasi-bound states in the continuum (quasi-BICs) in the near-infrared range. The metasurface consists of a periodic array of cut silicon disks on a SiO2 substrate. We achieve polarization independence by combining two different quasi-BIC EIT modes for two orthogonal polarizations of exciting light. By tuning the interference of broad and narrow Mie-resonant multipoles, we have developed a metasurface with the desired properties. The effect is robust for various geometrical parameters. Furthermore, we have fabricated the optimized structure and experimentally confirmed our approach.

The transport properties of electromagnetic waves change at the transition of high-index dielectric photonic structures to the metamaterial regime. Here, we demonstrate the changes in the properties of the waves traveling through photonic quasicrystalline structures made of dielectric rods arranged in the nodes on a Penrose tiling lattice with C5 rotation symmetry. We cannot use Bloch theorem in the study of aperiodic structures, so we consider full-scale structures to reveal Bragg- and Mie-type band gaps. A real-space metric allows us to define the period of the effective crystallographic planes in the quasicrystal and to relate the Bragg band gap to the lattice nodes in reciprocal space. We compared the quasicrystal structure with photonic crystals and found that transmission spectra in the band gap have similar profiles for both types of structures. The analysis of the magnetic field distribution in quasicrystal structures with high dielectric permittivity allowed us to recognize mu near-zero modes, which indicates that the structure acquires the metamaterial regime. The constructed phase diagram specified the metamaterial regime for the structure. Our results reveal the transport properties of photonic quasicrystalline systems in the metamaterial regime.

Quasicrystal-based photonic structures are rigorously ordered but aperiodic systems and the theoretical description of their properties is relatively poor developed yet. The lack of translation symmetry enables many wave phenomena that are prohibited in periodic systems. Quasicrystal-based structures give more degrees of freedom for designing photonic systems that demonstrate novel effects. On the other hand, their rigorous order still limits the degree of freedom to a reasonable value. The aim of this article is to review some recent wave effects observed in quasicrystal-based structures including the intrinsic light localization, complete photonic bandgap formation in low-refractive index systems and frequency-angular selective absorption of electromagnetic radiation.

Eigenmodes in equilateral and isosceles triangular trimers of infinite cylinders have been studied using the theory of multiwave scattering. Equations have been derived for the eigenfrequencies of the exceptional points where eigenfrequencies and eigenvectors are degenerate. The symmetry of the isosceles triangular trimer determines the separation of modes antisymmetric in the base direction. In the case of the equilateral triangular trimer, modes are separated into symmetric and double degenerate rotational modes. It has been found that damping symmetric modes in the trimer have a higher Q-factor compared to a dimer, which is of significant importance for applications of effects based on exceptional points. The behavior of complex eigenfrequencies in the isosceles triangular trimer has also been studied depending on the ratio of the lengths of its base and leg. At the point corresponding to the equilateral triangular trimer, the Q-factors of symmetric and antisymmetric modes have the local maximum and minimum, respectively.

A bandgap in the continuum spectrum of photons in addition to its basic physical significance has strong potential for applications. Analogous to semiconductor crystals for electrons, periodic dielectric structures named photonic crystals were proposed to control photon flux propagation. In our search for low refractive index (RI) structures with a photonic bandgap, initial research efforts were focused on photonic crystal design, while aperiodic structures allow lower values of refractive index contrast to sustain a photonic bandgap. Here, we report on a two-dimensional quasicrystalline structure designed as a set of one-dimensional lattices merged into a single binary structure made of two materials with refractive index contrast 2| n 1 − n 2 |/( n 1 + n 2 ) = 0.16 and even less in theory. We confirmed the theoretical prediction of bandgap exciting by measuring the radiation suppression of a dipole source placed in the center of the quasicrystalline structure. The full-wave numerical simulations and the experimental study appear to be in good agreement with the theoretical model.

Optical vortex beams have found wide applications in telecommunications, biophotonics, medicine and other fields due to their unique properties. Here, we propose a method to generate a vortex beam with post fabrication variable topological charge using inherently two-dimensional structures based on phase change materials. We fabricate Ge-Sb-Te thin films with a spatial pattern of amorphous and crystalline states written by using the direct laser writing technique. In our report the rewritable pattern represents a pitch-fork grating. We verify that the mechanical rotation of the films leads to a change in the topological charge of the output beam. We demonstrate an erase-and-rewrite modification of the pattern, that results in the change of the topological charge of the generated beam, when all optical elements are fixed, i.e. no mechanical displacement takes place.

We introduce a refractive index sensor based on metasurface supported bound states in the continuum. Two low-frequency symmetry-protected supercavity modes are examined. The sensor achieves improved sensitivity which is provided by quality factor law Q ~ α −x , where the value of x is less than 2, that will give us the opportunity to control the quality factor of the proposed sensor device.