Broadband extraordinary transmission in a single sub-wavelength aperture

Reflectionless compact nonmagnetic optical waveguide coupler design based on transformation optics

The design of an optical waveguide coupler has several challenges, such as reflection losses at the interfaces of the coupler, material complexity for optical applications, and the coupling between arbitrary materials at the input and the output of the coupler. In this paper, for the first time to the best of our knowledge, we propose a solution to overcome the above difficulties. For this purpose, we introduce an auxiliary transformation function and an impedance scaling function. The auxiliary function specifies the matched dielectric materials at the input and output interfaces of the coupler, and the scaling function suppresses the reflections and makes the material nonmagnetic for transverse magnetic (TM) polarization. As a result, an optical waveguide coupler is designed that can ideally couple two waveguides with arbitrary dielectric materials and arbitrary cross sections using a nonmagnetic material. Validation of the design method is done by using COMSOL Multiphysics.

Transformation optics for antennas: why limit the bandwidth with metamaterials?

In the last decade, a technique termed transformation optics has been developed for the design of novel electromagnetic devices. This method defines the exact modification of magnetic and dielectric constants required, so that the electromagnetic behaviour remains invariant after a transformation to a new coordinate system. Despite the apparently infinite possibilities that this mathematical tool introduces, one restriction has repeatedly recurred since its conception: limited frequency bands of operation. Here we circumvent this problem with the proposal of a full dielectric implementation of a transformed planar hyperbolic lens which retains the same focusing properties of an original curved lens. The redesigned lens demonstrates operation with high directivity and low side lobe levels for an ultra-wide band of frequencies, spanning over three octaves. The methodology proposed in this paper can be applied to revolutionise the design of many electromagnetic devices overcoming bandwidth limitations.

Super-thin Mikaelian's lens of small index as a beam compressor with an extremely high compression ratio

Based on a focusing Mikaelian's lens with small refraction index (0<n<<1), an optical device is designed as a super-thin optical beam compressor (e.g., thickness = 3λ0) with an extremely high beam compression ratio (more than 19:1). This device can also be used as a beam collimator or a cylindrical-to-plane wave convertor with a much higher transmissivity than a zero-index metamaterial slab. The output beam shows good directionality in both near field and far field. A metamaterial structure is also designed to realize this device and verify its performance with finite element method (FEM).

Directive radiation from a diffuse Luneburg lens

Transformation electromagnetics has opened possibilities for designing antenna structures. Using an analytical approach, we demonstrate here how directive antenna radiation can be achieved from an omnidirectional source behind a diffuse surface. This diffuse surface has been obtained by an optical transformation of a Luneburg lens. Two different transformation approaches have been proposed (polynomial and sinusoidal), and for both cases, the resulting material properties have been simplified to ease the fabrication by using all-dielectric media. Therefore, the proposed design has no upper boundary to the operational frequency. Directive radiation has been achieved from thin diffuse structures, which demonstrates promising future possibilities for this technique.