A polarization-/angle-insensitive, bandwidth-optimized, metamaterial absorber in the microwave regime

An enhanced metamaterial absorber based on the circumscribed-cross resonator is introduced in this paper. The new structure is polarization-independent, due to the symmetry of its unit cell, and is proven efficient for the attenuation of obliquely incident waves. The absorption mechanism is thoroughly investigated and is found to be mainly related to the losses of the dielectric substrate. Furthermore, by exploiting the scalability property of metamaterials, the operational bandwidth of our design can be drastically improved by placing unit cells with properly scaled resonators adjacent to each other. In this context, various combinations of three, four, and nine unit cells that can increase the full width at half maximum up to as much as 11.18?%, are developed. The overall performance of the proposed configurations is deemed promising for the realization of microwave metamaterial absorbers for several practical applications.     

An FDTD analysis of photonic crystal waveguides comprising third-order nonlinear materials

A finite difference time domain (FDTD) study of two-dimensional photonic crystals containing nonlinear materials is presented in this paper. An appropriate Z-transform oriented formulation of the FDTD method for the simulation of third-order nonlinear Kerr- and Raman-type media is analyzed and applied to model nonlinear photonic crystal waveguide structures. For their reflectionless termination a novel perfectly matched layer (PML) is proposed and evaluated comparatively to other periodic and inhomogeneous absorbers. Furthermore, the absorbing efficiency of the proposed PML is investigated varying its parameters.     

Programmable terahertz metamaterials through V-beam electrothermal devices

We report on the application of various optimization methods as a very promising simulation approach for the design of true integrated optical devices by means of inverse design. We show that these techniques provide a global optimum toward one or various functional objectives at a reasonable computational cost. The results obtained by these methods are far better than intuitive design procedures and clearly outperform trial-and-error based models. We illustrate their performance by using a series of inverse-designed practical photonic devices.     

FDTD analysis of photonic crystal defect layers filled with liquid crystals

Dielectric and metallic photonic crystals comprising nematic liquid crystal materials as defect layers or elements are investigated by the Finite Difference Time Domain (FDTD) method. Appropriate formulations of the FDTD algorithm, for the simulation of anisotropic and dispersive media as well as periodic geometries, are utilised and combined with the proper absorbing and periodic boundary conditions. The spectral properties of the presented structures are tuned by means of applying static electric fields across the defect layers, thus affecting the molecular orientation of the liquid crystal material. Numerical results show that sufficient tuning ranges are achieved, requiring low operating voltages. Moreover, high and sharp resonance peaks are observed.