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We revisit the design of cloaks, without resorting to any geometric transform. Cancellation techniques and anomalous resonances have been applied for this purpose. Instead of a deductive reasoning, we propose a novel mono-objective optimization algorithm, namely a ternary grey wolf algorithm, and we adapt a bi-objective optimization algorithm. Firstly, the proposed chaotic ternary grey wolf algorithm searches three-valued spaces for all permittivity values in the cloak while minimizing the summation of a protection criterion and an invisibility criterion. Secondly, a bi-objective genetic algorithm is adapted to find pairs of optimal values of invisibility and protection.

A fully integrated waveguide-based, efficient surface plasmon coupler composed of a realistic nontapered dielectric waveguide with graphene patches and sheet is designed and optimized for the infrared. The coupling efficiency can reach nearly 80% for an optimized coupler as short as 700 nm for an operating wavelength of 12µm. This work is carried out using rigorous numerical models based on the finite element method taking into account 2D materials as surface conductivities and the finite number of graphene patches contrarily to the usual methods based on grating analysis. The key numerical results are supported by physical arguments based on a modal approach or resonance conditions. These arguments can help to design other similar couplers or tofind the optimized parameters at other wavelengths.

Circular dichroism spectroscopy is a sensitive and widely applied technique to detect chiral molecules. Recent studies have shown high prospects for plasmonic metasurfaces of pseudo-chiral nano-resonators in enhancing chiral sensitivity. Here we study the far-field circular dichroism for gold U-shaped metasurfaces by calculating Mueller matrix elements with the Finite element method and investigate its response in light of the near field electric energy and optical chiral density.