Designing Spatial Kramers–Kronig Media Using Transformation Optics.

Spatial Kramers–Kronig (KK) relations have been recently proposed to achieve perfect absorption without using any gain elements or highly anisotropic materials. However, such perfect absorption is limited to the surface of an infinitely long planar slab in the Cartesian coordinate, and the cases of surfaces with bends or sharp corners are still challenging. In this article, we apply conformal transformation optics methods to design spatial KK media, which can achieve smooth perfect absorption both in cylindrical spaces and in polygonal spaces with sharp corners. Moreover, it is demonstrated that we can also control the scattering direction of the designed polygonal spatial KK media to realize invisibility. Our work opens new avenues for perfect absorption devices based on transformation optics and spatial KK relations. [ABSTRACT FROM AUTHOR]