Twisted chains of resonant particles: optical polarization control, waveguidance, and radiation

Abstract

Linear chains of metallic nanoparticles that are sequentially rotated about the chain axis display interesting polarization-sensitive optical properties. Such twisted chains posses and extend properties of chiral gratings and general periodic gratings. They are characterized by high anisotropy and polarization sensitivity, and have subwavelength transverse dimensions. These structures are shown to support transverse modes with distinct propagation wavenumbers and radiation properties, including slow (bound) and fast (radiative) modes. They also have stop bands of different types, resulting from coupling between distinct transverse modes, as well as coupling with different higher-order diffraction modes.

Magnetized Spiral Chains of Plasmonic Ellipsoids for One-Way Optical Waveguides

“…The propagation in plasmonic particles SDCs subject to a longitudinal magnetic field, is non-reciprocal as it possesses Faraday rotation [8,9]. We suggest an SDC in which the plasmonic particles are prolate ellipsoids arranged in a spiral structure as in [6], but under longitudinal magnetic field. See Fig.…”

“…SDCs are potential candidates for dense integration of optical systems, and were proposed as guiding structures, junctions, and couplers [1]- [5]. Very recently, a spiral SDC was suggested as a chiral waveguide [6].…”

“…A linear array of vertically grown silicon nanopillars was deformed by bending the pillars sideways, with bending angle that gradually increases along the array, thus producing a chain very similar to Fig To study the system, we use the Discrete Dipole Approximation (DDA) and polarizability theory. These are standard tools used in many works on SDCs [3]- [6]. They hold when the particle diameter D is much smaller than the wavelength, and the inter-particle distance d is large compare to D. Studies show excellent agreement with exact solutions even when d = 1.5D [11].…”

Twisted optical metamaterials for planarized ultrathin broadband circular polarizers

“…In this regard, we have extended our analytical model to analyse the eigenmodal properties of this rotated stack for a number of layers N → ∞, considering the generalized Bloch eigenmodes supported in a suitable reference system that rotates with each successive layer, analogous to the approach used to analyse linear arrays of rotated particles 24 . Although the details of this homogenization theory for twisted metamaterials go beyond the focus of the present work, it is relevant to point out that we have verified how one of the two generalized eigenmodes supported by the homogenized twisted metamaterial, based on the parameters of Fig.…”

“…Here we show that broadband circular polarization selectivity may be achieved in twisted arrays of metasurfaces without the need of complicated inclusion shape, with no requirement on the relative alignment, and at optical frequencies. We use a generalized Bloch analysis to model the cascaded structure 24 , in combination with optical transmission-line theory 25 , and show that this concept may relax several constraints in the realization of 3D bianisotropic metamaterials, including inclusion shape requirements and lateral alignment between neighbouring inclusions.…”