Bound states in the continuum (BIC) have attracted a great deal of attention in all-dielectric nanophotonics due to their ability to provide spectral features with a very high-quality factor. By definition, BIC cannot be observed in the far field because of the symmetry mismatch with the modes propagating in free space. Despite this, in systems with slightly reduced symmetry, the condition for BIC is lifted, which gives rise to the high-quality resonant features in their optical response. In particular, in photonic crystal slabs, which support the BIC states, the symmetry reduction allows modification of light propagation, reflection, or emission. In this work, using the photonic crystal slabs with embedded Ge nanoislands, we have shown the ability to control their light emission features by symmetry breaking. It was demonstrated that such symmetry breaking due to a change in the basis vectors of the photonic crystal unit cell or a change in the unit cell internal structure could provide independent control knobs to alter the spectral position of photonic crystal modes, their dispersion, and degeneracy. The obtained results reveal additional ways to manage the light emission of active media in photonic crystal slabs.

3D ordered hollow diamond spheres packed into opal structure have been synthesized by chemical vapor deposition using silicon inverse opal template which, in turn, was produced by molding of a bulk silica opal template. These 3D diamond opals demonstrate optical properties of photonic crystal with Bragg reflection peak in the visible range. Numerical modeling of the reflection spectra is performed using a scattering matrix calculation, and agrees well with the measured Bragg peak positions. The porous structure consisting of nanocrystalline diamond shells with thickness of the order of 10 nm composes the light-weight material with density of approximate to 0.50 g/cm3. The diamond opals showed bright photoluminescence at 738 nm wavelength due to siliconvacancy centers formation in course of the growth process. The diamond opals can be a new promising platform for versatile applications, primarily in photonics, due to wide transparency window, high chemical resistance and mechanical strength inherent to diamond.

The features of the bi- and multistability effects in the semiconductor Bragg microcavity with a chiral photonic crystal slab on the upper mirror are investigated theoretically. It is shown that the response of such a chiral structure under a linearly polarized coherent resonant pump demonstrates sharp multistable transitions with abrupt jumps of the exciton intensity and degree of circular polarization. It is shown that the thresholds of bistable transitions in the system with a different sense of circular polarization differ slightly; i.e., in the case of a nonoptimized structure, we can expect to obtain even a larger amplitude of jumps of the degree of circular polarization of the excitonic response due to the multistability than in a specially optimized chiral structure with a high degree of circular polarization at a low pump intensity.

We present the results of theoretical studies of the Purcell effect in infinite photonic crystal slabs without defects or cavities. First, we describe a theoretical model for calculating total and external Purcell factors in two-dimensional photonic crystal slabs in terms of dipole's emissivity to the near field and the far field. Then we apply this theory to silicon photonic crystal slabs with triangular lattice on silica substrate and study how the Purcell factor depends on the wavelength and the dipole's position. We show that by placing the dipoles in the hot spots of modes with the zero group velocity, one can greatly enhance the Purcell factor in comparison to a homogeneous silicon slab. We demonstrate that this effect is associated with Van Hove singularities. We also calculate partial contributions to the total Purcell factor from different energy dissipation channels.

The optical properties of plasmonic metasurfaces are determined not only by the shape and size of the constituting nanostructures, but also by their spatial arrangement. The fast progress in nanofabrication has facilitated the emergence of many advanced metasurface designs that enable controlling the propagation of light on the nanoscale. While simple metasurface designs can be derived from theoretical considerations, it is inevitable to employ computational approaches for complex manipulations of incident light. However, most of the currently available full-wave simulation approaches such as the finite element method (FEM) or finite difference time domain method come with drawbacks that limit the applicability to certain usually simplified or less complex geometries. Within this tutorial, different approaches are outlined for modeling light propagation in complex metasurfaces. We focus on an approach that approximates the nanostructure ensemble as a coupled set of point dipoles and determine their far-field response via the reciprocity theorem. This coupled point dipole approximation (CPDA) model is used to examine randomly distributed, oriented, and scaled nanostructure ensembles. A disorder formalism to introduce the randomness is developed that allows one to progressively perturb periodic arrangements of identical nanostructures and thereby investigate the effects of disorder and correlation. Several disorder metrics are provided that allow one to quantify the disorder, and the relation with the far-field scattering properties is discussed. Spatially and angle resolved hyperspectral datasets are computed for various disordered metasurfaces to assess the capabilities of the CPDA model for different polarization states and incidence angles, among others. The hyperspectral datasets are converted into sRGB color space to deduce the appearances in the image and Fourier planes. Very good agreement of the simulation results with Mie theory, FEM results, and experiments is observed, and possible reasons for the present differences are discussed. The presented CPDA model establishes a highly efficient approach that provides the possibility to rapidly compute the hyperspectral scattering characteristics of metasurfaces with more than 10,000 structures with moderate computational resources, such as state-of-the-art desktop computers with sufficient memory; 16 GB allow for the simulations in this paper, whereas scaling to up to more memory by the factor of N2 allows for the simulation of N times more dipoles. For that reason, the CPDA is a suitable approach for tailoring the bidirectional reflectance distribution function of metasurfaces under consideration of structural perturbations and experimental parameters.

We develop the resonant mode coupling approximation to calculate the optical spectra of a stack of two photonic crystal slabs in terms of the scattering matrix. The method is based on the derivation of input and output resonant vectors in each slab in terms of the Fourier modal method in the scattering matrix form. We show that using the resonant mode coupling approximation of the scattering matrices of the upper and lower slabs, one can construct the total scattering matrix of the stack. The formation of the resonant output and input vectors of the stacked system is rigorously derived by means of an effective Hamiltonian. We demonstrate that the proposed procedure dramatically decreases the computation time without sufficient loss of accuracy. We believe that the proposed technique can be a powerful tool for fast-solving inverse scattering problems using stochastic optimization methods such as genetic algorithms or machine learning.

The resonant mode approximation of the scattering matrix is considered for calculating the optical properties of multilayered periodic structures within the formalism of the Fourier-modal method for two diffraction thresholds in close proximity of the spectral-angular range of interest. The developed approximation opens up possibilities for the fast calculation of the scattering matrix of these structures when describing the integral characteristics of spectra and dispersion curves containing high-Q resonances, such as bound states in the continuum.

Engineering the chirality of optical microcavities is a central concept of modern photonics to gain full control the polarization of the confined electromagnetic mode. Here, we demonstrate a compact source of coherent radiation based on an electrically driven, chiral semiconductor microcavity. The device is composed of an AlAs/(Al, Ga)As microcavity containing multiple GaAs quantum wells in the active region and a chiral photonic crystal slab etched in the upper distributed Bragg reflector. The structure promotes laser oscillation under electrical current injection in the near-infrared spectral range (h omega similar or equal to 1.565 eV) and degrees of circular polarization exceeding 90%. The sense of circular polarization is controlled by the handedness of the chiral photonic crystal slab and changes to the opposite one in a mirror-symmetrical structure. Our results represent an important step towards the practical implementation of compact sources of circularly polarized light.

Resonant structure consisting of waveguide layer with metallic strips array is a promising design for various optical effects control and enhancement at the nanoscale due to its strong resonant properties and light localization phenomena. However, different applications require understanding the nature of eigenmodes of the structure, that possess peculiar properties. In this research, the optical properties of the planar waveguide with one-dimensional periodic gold grating on it was examined. Emitting layer of a-Si1-xCx:H was deposited by plasma chemical vapour deposition technique and the gold array was created by the e-beam lithography. Angle-resolved reflection and photoluminescence spectra in s- and p-polarizations were measured by the Fourier-imaging spectroscopy method. The theoretical analysis was performed to reveal the physical nature of the observed spectral features and their effect on the waveguide layer emitting properties was studied.

The height dependence of Raman light scattering on organic molecules deposited onto thick one-dimensional metal-dielectric gratings is investigated theoretically and experimentally. We observe oscillations of the intensity of Raman light scattering as a function of the height of the metastructure's strips and demonstrate that these oscillations are explicitly associated with a type of Fabry-Perot effect. We show that the intensity of surface-enhanced Raman scattering can be additionally increased by local field enhancement (by an order of magnitude) at resonances of both pump and Stokes as well as anti-Stokes frequency, due to coupling of the surface plasmon polaritons on the top and bottom metal parts of the gratings via the vertical Fabry-Perot resonances over their middle dielectric part. A semianalytical one-mode model to describe the effect qualitatively is proposed. A significant deviation of the dispersion of Fabry-Perot-coupled plasmon polaritons from the surface-plasmon-polariton dispersion just folded into the first Brillouin zone is demonstrated.

The method of spectral Fourier microscopy was used to study the reflection spectra with an angular resolution of submicron periodic gratings based on amorphous and crystalline Ge 2 Sb 2 Te 5 . The form of the dispersion curves of quasi-waveguide modes in the structures under study was established. The experimental data were compared with the calculations of dispersion curves in synthesized diffraction gratings. Reasonable agreement between theoretical and experimental data was obtained.

Germanium quantum dots are promising but their photoluminescence intensity is still insufficient for practical applications. It is demonstrated that their PL in silicon photonic crystal slab can be dramatically enhanced due to the involvement of the bounds states in the continuum into the emission process.

Germanium self-assembled nanoislands and quantum dots are very prospective for CMOS-compatible optoelectronic integrated circuits but their luminescence intensity is still insufficient for many practical applications. Here, we demonstrate experimentally that photoluminescence of Ge nanoislands in silicon photonic crystal slab with hexagonal lattice can be dramatically enhanced due to the involvement in the emission process of the bounds states in the continuum. We experimentally demonstrate more than two orders of magnitude peak photoluminescence enhancement and more than one order of magnitude integrated PL enhancement in a photonic crystal slab compared with the non-structured sample area. We theoretically study this effect by the Fourier modal method in the scattering matrix form and demonstrate the appearance of quasi-normal guided modes in our photonic crystal slab. We also describe their symmetry in terms of group theory. Our work paves the way towards a new class of optoelectronic components compatible with silicon technology.

The cover image illustrates the photonic crystal slab's eigenmode as demonstrated in article number 2000242 by Sergey Dyakov and co-workers. The cones represent the rotation of the electric vector during one period of electromagnetic oscillations. From this figure, one can determine the symmetry type of this mode and predict the features of the far-field emissivity of quantum emitters at the corresponding frequency.

Using the resonant-state expansion for leaky optical modes of a planar Bragg microcavity, we investigate the influence of disorder on its fundamental cavity mode. We model the disorder by randomly varying the thickness of the Bragg-pair slabs (composing the mirrors) and the cavity and calculate the resonant energy and linewidth of each disordered microcavity exactly, comparing the results with the resonant-state expansion for a large basis set and within its first and second orders of perturbation theory. We show that random shifts of interfaces cause a growth of the inhomogeneous broadening of the fundamental mode that is proportional to the magnitude of disorder. Simultaneously, the quality factor of the microcavity decreases inversely proportional to the square of the magnitude of disorder. We also find that first-order perturbation theory works very accurately up to a reasonably large disorder magnitude, especially for calculating the resonance energy, which allows us to derive qualitatively the scaling of the microcavity properties with disorder strength.

We propose a perfect photonic router based on a specially designed chiral bi-metasurface membrane for spin-polarized point light sources. Due to the mirror symmetry breaking in the chiral metamembrane, the radiation power flux of the clockwise and counterclockwise spinning dipoles to the opposite sides of the slab becomes different. We show that spinning dipoles in the specially designed chiral D$_4$-symmetrical bi-metasurface membrane can emit light either upwards or downwards depending on their rotation direction. We attribute this phenomenon to the Fano-resonance effect which is a result of the guided modes coupling with the far field. We show the advantage of D$_4$-symmetrical structures for the achievement of 100\% routing efficiency. This phenomenon can find applications in spintronics for spin-selective inter-chip coupling or as a measurement tool of spin polarization in memory cells.

In this work, we study theoretically and experimentally the reflection and photoluminescence spectra of SiC slab waveguide with a two-dimensional plasmonic lattice of gold nanodisks. We demonstrate the appearance of the plasmonic modes in the lattice and their interaction with guided modes in SiC slab. Experimental reflection and photoluminescence spectra are in agreement with theoretical predictions.

In this study reflection and photoluminescence spectra of a-Si: C:H thin film with gold grating on it was examined theoretically and experimentally. The hydrogenated amorphous amorphous silicon-carbon alloy films were fabricated by the PECVD technique. Arrays of gold stripes with different gold width were created by lift-off e-beam lithography. Reflection, and PL spectra has been measured by a Fourier imaging spectroscopy. The theoretical calculations are in a good agreement with experimental results. From the PL spectra it follows, that the TE polarization gives sharper and more efficient PL signal than the TM polarization, and PL efficiency almost does not depend on gold stripes widths. It was shown that only in TE modes the PL outcouples from the gratings owing to the fact that there is no plasmon's affect in this polarization.

Transverse magneto-optical Kerr effect (TMOKE) is known to be an effective tool for external magnetic field control of optical properties of magnetoplasmonic crystals. In some applications there is a demand for the pronounced TMOKE in the wide wavelength range. In this work we experimentally and theoretically demonstrate that a magnetite based magnetoplasmnic crystal exhibit a multiple wide band enhancement of TMOKE response in transmission compared to a plain magnetite film without metal. Our RCWA calculations are in good agreement with experimental results.