Rigorous coupled-wave analysis (RCWA) is a very effective tool for studying optical properties of multilayered vertically invariant periodic structures. However, it fails to deal with arrays of small particles because of high gradients in a local field. In this paper, we implement the discrete dipole approximation (DDA) for the construction of scattering matrices of arrays of resonant nanoparticles. This strongly speeds up the calculations and therefore provides an opportunity for thorough consideration of various layered structures with small periodic inclusions in terms of the RCWA. We demonstrate the performance of the proposed method by considering plasmonic lattices embedded in a homogeneous ambience and placed inside and onto an optical waveguide. Both localized surface plasmon resonances (LSPRs) and lattice plasmon resonances (LPRs) are observed as well as their hybridization with photonic guided modes. High accuracy and fast convergence of our approach are shown by comparison with the finite element method (FEM) and RCWA calculations correspondingly.

The transverse magneto-optical Kerr effect (TMOKE) in magnetite-based magnetoplasmonic crystals is studied experimentally and theoretically. We analyze angle-resolved TMOKE spectra from two types of structures where noble metallic stripes are incorporated inside a thin magnetite film or located on top of a homogeneous film. A multiple-wide-band enhancement of the TMOKE signal in transmission is demonstrated. The complex dielectric permittivity and gyration are experimentally determined using the ellipsometry technique as well as Faraday rotation and ellipticity measurements. The obtained parameters are used in rigorous coupled-wave analysis (RCWA) calculations for studying the optical resonances. Our RCWA calculations of transmittance and TMOKE are in good agreement with the experimental data. The role of guiding and plasmonic modes in the TMOKE enhancement is revealed. We demonstrate that the TMOKE provides rich information about the studied optical resonances.

The utilization of periodic structures such as photonic crystals and metasurfaces is common for light manipulation at nanoscales. One of the most widely used computational approaches to consider them and design effective optical devices is the Fourier modal method (FMM) based on Fourier decomposition of electromagnetic fields. Nevertheless, calculating periodic structures with small inclusions is often a difficult task since they induce lots of high-$k_{\parallel }$ harmonics that should be taken into account. In this paper, we consider small-particle lattices with bases (complex unit cells) and construct their scattering matrices via discrete dipole approximation. Afterwards, these matrices are implemented in FMM for consideration of complicated layered structures. We show the performance of the proposed hybrid approach by its application to a lattice, which routes left and right circularly polarized incident light to guided modes propagating in opposite directions. We also demonstrate its precision by spectra comparison with finite-element method calculations. The high speed and precision of this approach enable the calculation of angle-dependent spectra with very high resolution in a reasonable time, which allows resolving narrow lines unobservable by other methods.

In recent years twisted bilayers of two-dimensional (2D) materials have become very popular in the field due to the possibility to totally change their electronic properties by simple rotation. At the same time, in the wide field of photonic crystals, this idea still remains almost untouched, and only some particular problems have been considered. One of the reasons is the computational difficulty of accurate consideration of moiré superlattices that appear due to the superimposition of misaligned lattices. Indeed, the unit cell of the complex lattice is typically much larger than the original crystals and requires many more computational resources for the computations. Here, we propose a moiré-adapted Fourier modal method (MA-FMM) in the form of scattering matrices for the description of twisted one-dimensional (1D) gratings' stacks. We demonstrate that MA-FMM allows us to consider sublattices in close vicinity to each other and account for their interaction via the near field. In the developed numerical scheme, we utilize the fact that each sublattice is only 1D periodic and therefore simpler than the resulting 2D superlattice, as well as the fact that even a small gap between the lattices filters out high Fourier harmonics due to their evanescent origin. Such approach accelerates the computations from 1 up to 3 or more orders of magnitude for typical structures depending on the number of harmonics. In turn, the high computational speed paves the way for rigorous study of almost any photonic crystals of the proposed geometry and demonstration of specific moiré-associated effects.

Multilayer stacks of twisted optical metasurfaces are considered as a prospective platform for chiral nanophotonic devices. Such structures are primarily used for the realization of circularly polarized light sources, artificial optical rotation, and circular dichroism. At the same time, the behavior of their hybrid photonic modes is strongly affected by the moiré pattern of superimposed periodic constituents. In this paper, we show that moiré periodicity in bilayer dielectric photonic crystal slabs (PCSs) leads to a rise of unlimitedly narrow optical resonances, which are very sensitive to the relative twist and gap width between the sublayers. We demonstrate the structure providing twist-tuning of the hybrid mode wavelength in the range of 300–600 nm with the quality factor varying from ${10}^2$ up to ${10}^5$ correspondingly. The obtained results pave the way for the utilization of moiré-assisted effects in multilayer PCSs.

We propose a perfect photonic router based on a specially designed chiral bimetasurface 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 bimetasurface membrane can emit light either upward or downward 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 interchip coupling or as a measurement tool of spin polarization in memory cells.