Enhanced chiral response from the Fabry–Perot cavity coupled meta-surfaces

The circular dichroism（CD） signal of a two-dimensional（2D） chiral meta-surface is usually weak, where the difference between the transmitted（or reflected） right and left circular polarization is barely small. We present a general method to enhance the reflective CD spectrum, by adding a layer of reflective film behind the meta-surface. The light passes through the chiral meta-surface and propagates towards the reflector, where it is reflected back and further interacts with the chiral meta-surface. The light is reflected back and forth between these two layers, forming a Fabry–Perot type resonance,which interacts with the localized surface plasmonic resonance（LSPR） mode and greatly enhances the CD signal of the light wave leaving the meta-surface. We numerically calculate the CD enhancing effect of an L-shaped chiral meta-surface on a gold film in the visible range. Compared with the single layer meta-surface, the L-shaped chiral meta-surface has a CD maximum that is dramatically increased to 1. The analysis of reflection efficiency reveals that our design can be used to realize a reflective circular polarizer. Corresponding mode analysis shows that the huge CD originates from the hybrid mode comprised of FP mode and LSPR. Our results provide a general approach to enhancing the CD signal of a chiral meta-surface and can be used in areas like biosensing, circular polarizer, integrated photonics, etc.

Highly band-selective meta-surfaces exhibiting perfect near infrared absorption and concurrent visible band sensing:A numerical study

We report a highly band-selective,bifunctional meta-surface that serves as an ultra-wide perfect absorber for near-infrared(NIR)band and a visible-band sensor,based on a rational design strategy involving stacking and/or grating of metals,inorganic insulators,and stimuli-responsive materials.PNIPAAm-based hydrogel was utilized as a layer of stimuli-responsive insulator,which is allowed to reversibly swell and collapse in one dimension in response to stimuli such as ambient temperature and chemical environment to empower the sensing capability in the visible band,with the perfect absorption in NIR region intact.The average absorption reached an impressive 99.4%from 780 to 2500 nm,which is attributed to the synergy of localized surface plasmon(LSP),propagating surface plasmon(PSP),and cavity mode.The reported bi-functional meta-surface is particularly attractive for band-selective solar energy harvesting,naked-eye sensing,and adaptive imaging.

Optimal Design of Wideband Microwave Absorber Consisting of Resistive Meta-Surface Layers

In this paper we propose an optimal design of ultra-wideband (4 ~ 20 GHz) microwave absorbers consisting of two resistive meta-surface layers of different square patch arrays. Gradient Descent and Genetic Algorithm numerical methods are employed to optimize all the parameters through equivalent transmission line circuit model. The circuit parameters are then implemented by a multilayer including two resistive meta-surfaces of square patch structures. Two types of such absorbing structures, with the total thicknesses close to that of the known theoretical limit, are designed and their performance are verified by full wave electromagnetic simulation.

Manipulating electromagnetic waves with metamaterials: Concept and microwave realizations

Our recent efforts in manipulating electromagnetic （EM） waves using metamaterials （MTMs） are reviewed with em- phasis on 1） manipulating wave polarization and transporting properties using homogeneous MTMs, 2） manipulating surface-wave properties using plasmonic MTMs, and 3） bridging propagating and surface waves using inhomogeneous meta-surfaces. For all these topics, we first illustrate the physical concepts and then present several typical practical real- izations and applications in the microwave regime.