Transformation-optical design of adaptive beam bends and beam expanders

TLDR

The devices are discussed within reconfigurable metamaterials, enabling dynamic tuning of bend and split angles. The authors design adaptive beam bends, splitters, and a beam expander/compressor using finite embedded coordinate transformations. They employ finite embedded coordinate transformations and validate the designs with full-wave finite-element simulations. The devices exhibit reflectionless interfaces, achieve realistic permittivity and permeability for both small and large bend radii, yet a pure transformation‑optical expander/compressor cannot be reflectionless.

Abstract

We describe the design of adaptive beam bends and beam splitters with arbitrary bend and split angles by use of finite embedded coordinate transformations. The devices do not exhibit reflection at the entrance or exit surfaces. It is shown that moderate and practically achievable values of the relative permittivity and permeability can be obtained for beam bends and splitters with both small and large bend radius. The devices are also discussed in the context of reconfigurable metamaterials, in which the bend and split angles can be dynamically tuned. The performance of adaptive beam bends and splitters is demonstrated in full wave simulations based on a finite-element method. Furthermore, the design of an adaptively adjustable transformation-optical beam expander/compressor is presented. It is observed that a pure transformation-optical design cannot result in a reflectionless beam expander/compressor.