Collective photonic response of high refractive index dielectric metasurfaces

Abstract

Sub-wavelength periodic nanostructures give rise to interesting optical phenomena like effective refractive index, perfect absorption, cloaking, etc. However, such structures are usually metallic which results in high dissipative losses and limitations for use; therefore, dielectric nanostructures are increasingly considered as a strong alternative to plasmonic (metallic) materials. In this work, we show light-matter interaction in a high refractive index dielectric metasurface consisting of an array of cubic dielectric nano-structures made of very high refractive index material, Te in air, using computer modelling. We observe a distinct band-like structure in both transmission and reflection spectra resulting from the near-field coupling of the field modes from neighboring dielectric structures followed by a sharp peak in the transmission at higher frequencies. From the spatial distribution of the electric and magnetic fields and a detailed multipole analysis in both spherical harmonics and Cartesian components, the dominant resonant modes are identified to be electric and magnetic dipoles. Specifically at lower frequency (60 THz) a novel anapole-like state characterized by strong-suppression in reflection and absorption is observed, reported very recently as ‘lattice-invisibility’ state. Differently, at higher frequency (62 THz), strong absorption and near-zero far field scattering are observed, which combined with the field profiles and the multipole analysis of the near-fields indicate the excitation of an anapole. Notably the observed novel modes occur in the simple geometry of dielectric cubes and are a result of collective response of the metasurfaces. Periodicity of the cubic metasurface is shown as the significant material tuning parameter, allowing for the near-field and far-field coupling effects of anapole metasurface. More generally, our work is a contribution towards developing far-fetching applications based on metamaterials such as integrated devices and waveguides consisting of non-radiating modes.

Tailoring the resonant modes in liquid crystal based all-dielectric metasurfaces

“…In our earlier work on periodic Te cubic arrays we observed that radiation-less anapole states are exhibited at 62 THz in air medium 50 . In the following sections we discuss in detail the effect of in-plane liquid crystal orientations on the anapole states in nematic medium.…”

“…Figures 1c and 1d as S 12 = Te (ik 0 t) and S 11 = R, where R and T are reflection and transmission coefficients of medium, k 0 is the wave number in free space and t is the thickness of the dielectric layer, respectively. Scattering parameters exhibit a reflection band in the range 40 − 60 THz with two distinct peaks at both the ends in air medium 50 . Presence of nematic medium shifts the reflection band to lower frequencies (42-55 THz) with characteristic peaks varying as a function of LC orientation as shown in figures 1c and 1d.…”

“…Anapoles in the literature are usually observed with specific designs of dielectric metasurfaces such as toroidal meta-atoms, dielectric trimers, hollow disks, etc 10,44,[47][48][49] . In our earlier work, we showed that stable anapoles can also be formed in simple structures such as high refractive index Tellurium cubes 50 . Tailoring the formation of anapoles is highly useful in the areas of communication and stealth technologies and has been achieved till now by tailoring the geometries 51 , periodicity 52 and active materials 53 .…”

Trends in Nanophotonics‐Enabled Optofluidic Biosensors

“…Nanostructured dielectric materials with high refractive index have emerged as a powerful toolkit for controlling light on the nanoscale, [56][57][58][59][60][61] and specifically for biosensing. [62][63][64][65] In contrast to plasmonic systems, where the optical response is dominated by electric multipoles, [22,66] resonances in dielectric particles readily support displacement currents driven by the incident light, allowing for the straightforward excitation of both electric and magnetic multipoles.…”

Enhanced Reflectivity Change and Phase Shift of Polarized Light: Double Parameter Multilayer Sensor

“…[ 19 ] Also, simpler systems were reported, where the point of darkness is achieved by the multistack made of, e.g., Ag (20 nm)/methyl methacrylate MMA (522 nm)/Ge (10 nm) Ag −1 (80 nm). [ 20 ] For our knowledge, there are relatively many publications for multilayer structures with the point of darkness at NIR and IR wavelength range, [ 19–25 ] and just few related to visible spectra range. [ 25,26 ] The reason is that the high efficiency absorption (at specific λ ) is mainly caused by the Fabry–Perot resonance in the non‐absorbing dielectric layer placed in the middle of the stack: that results in trapping of the resonant light in dielectric layer and thus in enhancement of absorption efficiency.…”