We propose a rigorous algorithm for checking and replacing meta-atoms in the arbitrary metasurface layout, based on any preconditioned element library. To showcase the algorithm performance, we design the small metalens based on arbitrarily shaped nanoparticles with four-fold symmetry. We note that layout and lookup tables can depend on any desired optical parameters provided by the atom, and for each point, the best compatible element will be chosen. This algorithm can help the photonics community to fully exploit the design degree of freedom associated with the generation of arbitrary meta-atom shapes, and to access the new properties of metadevices.
We reveal the peculiarities of the trapped mode manifestation in metasurfaces composed of an array of MoS2 disk-shaped resonators. The corresponding resonance arises as a result of the excitation of the electric octupole moment existing in each meta-atom of the metasurface and multipole coupling effects in the array. In particular, we show that the effect appears due to a lattice-induced coupling between the electric octupole and electric dipole moments in the metasurface. The coupling effect between the resonant quasi-trapped octupole mode and the suppressed electric dipole results in the appearance of the narrow-band transparency conditions in the metasurface spectra with a simultaneous storing of electromagnetic energy inside the resonators. The discussed approach is quite general and can be implemented in metasurfaces supporting Mie-type modes in meta-atoms made of different materials.
Transverse spin angular momentum (t-SAM) is a spin with a vector perpendicular to the light propagation direction, naturally appearing in tightly confined electromagnetic waves. For the first time, we successfully generated t-SAM in a spatial point of maximum intensity of focused light using an asymmetric metasurface. The designed metasurface provides complete phase and polarization control and allows for the manipulation of both electric and magnetic transverse spin distribution. The results were obtained through both theoretical and experimental methods, demonstrating the metasurface's ability to generate a strong transverse spin in a focal point ensuring non-zero net spin in the focal plane. This discovery has potential applications in optomechanics, quantum optics, nanometrology, and directional scattering.
In contrast to the conventional Gaussian beams or plane waves, the interaction of structured lights with matter and meta-matter can pave the way toward novel optical effects such as exciting higher order multipolar moments or enabling nonradiating anapole states. In this work, Laguerre-Gaussian (LG) beams with various orbital angular momentum are used to excite and control the spectral location of the magnetic quadrupole modes within the all-dielectric meta-atoms. To experimentally validate this phenomenon, silicon-based meta-atoms are fabricated and illuminated by various LG beams. The experimental results are in good agreement with the theoretical predictions.
Structured light carrying spin and orbital angular momentum brings about new light-matter interactions in optical nanostructures. We demonstrate the possibility of using structured light beams carrying orbital angular momentum (OAM) to access resonant modes of all-dielectric meta-atoms that cannot be excited by the conventional Gaussian beam or by a plane wave. We use multipole decomposition approach to match extinction resonances with high-order multipole excitation. These results can find applications in sensing, spectroscopy, and enable new regimes of nonlinear optical interactions.
Dielectric nanophotonics became a hot topic during the last decade. Particularly, a lot of relevant studies were devoted to metasurfaces and their optical properties. Here we propose and numerically study the quadrumerbased silicon metasurface supporting magnetic octupole response. Specific meta-atoms allow to excite magnetic octupole moment in optical range without going beyond the diffraction limit. Comparing to a metasurface based on solid blocks of similar size, the quadrumer-based metasurface feature significant absorption enchantment and strong change of a reflection spectrum. Obtained results can be exploited in development of novel sensors, optical elements and energy harvesting devices.
Bound states in the continuum (BIC) attracted great attention in the photonics community. The existence of such states has led to numerous applications, including optical sensors and filters. Here we report on the approach to externally tune a magnitude and spectral position of high-Q resonances, associated with not symmetry-protected BIC state in silicon nitride (Si3N4) photonic crystals. We show that BIC properties can be controlled by the external thermal impact. These results can be used to construct compact and thermally stable optical sensors immune to harsh environmental conditions.
Light scattering by all-dielectric nanoparticles attract significant attention of photonics community. Single nanoparticles can be used both as nanoantennas and as building blocks to construct 2D and 3D meta-structures. In this work we study scattering effect when silicon nanoparticles are embedded in different media. To analyze the evolution of multipole moments and their contributions to the scattering cross-sections of the nanoparticles in media, we use semi-analytical multipole decomposition approach. Explicitly, we investigate the behavior of electric and magnetic multipoles, up to third order, while dielectric nanoparticle made of silicon is embedded in a media. We found that electric and magnetic multipoles experience different red shift as refractive index increases. Due to this behavior separated high-order multipole resonances overlap with each other; thereby, scattering cross section peaks, which could be observed when a particles are in air, merge to the joint scattering cross section peaks. Such resonances overlap also affect both far-field radiation diagrams and field distribution inside the nanoparticle. Importantly, we noticed that when index of a surrounding media increases, the cubical nanoparticles provide spectral broadening of forward scattering effect.
Our results provide fundamental information for understanding the scattering effect in all-dielectric nanoantennas or metasurfaces embedded in different dielectric media and operating in wide spectral range. For practical utilization, explored here dielectric nanoparticles could be used in broad range of applications such as in-vitro and in-vivo biomedical devices for sensing and drug delivering, sub-wavelength nano-amplifiers, and many other emerging applications.
The effective multipole decomposition approach is applied to study the optical features of the silicon metasurface in the near-infrared. The spectral regions of perfect transmission and reflection have been analyzed using the Cartesian multipole decomposition. It is shown that transmission peaks appear due to the mutual interaction of multipole moments up to the third order, while reflection peaks are due to the dominant contribution of one of the multipole moments. The results of this work can be broadly applied to design novel metasurfaces, sensors, and optical filters.
In this work we theoretically study spectral multipole resonances of parallelepiped- and pyramid- silicon nanoparticles excited by linearly polarized light waves. We apply the numerical finite element method to calculate the scattering cross-sections as a function of the nanoparticles geometrical parameters. We use the multipole decom- position approach to explore optical resonances in silicon nanoparticles and the influence of second and third order multipoles to scattering diagrams. In contradistinction to our previous investigations, now we explore effects in near-IR spectral range. Apart from basic study we also obtained non-symmetrical combination of multipole contributions due to illumination from top and bottom sides of pyramids. Our work provides important information about the role of high-order multipoles in the light scattering by non-spherical and non-symmetrical nanoparticles. Our results can be applied, for example, for development of metasurfaces and metamaterials in near-IR spectral range.
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