Bidirectional invisibility in Kramers-Kronig optical media

TL;DR

This paper introduces a class of Kramers-Kronig optical media that are fully invisible from both sides, advancing the understanding of bidirectional invisibility and reflection control in complex dielectric structures.

Contribution

It demonstrates the first known class of media exhibiting bidirectional invisibility based on Kramers-Kronig relations, expanding the design principles for invisible optical materials.

Findings

Media are fully invisible from both sides for specific permittivity profiles.

Transition from unidirectional to bidirectional invisibility is characterized.

Sharp reflection can be achieved above a certain incidence angle.

Abstract

A broad class of planar dielectric media with complex permittivity profiles that are fully invisible, for both left and right incidence sides, is introduced. Such optical media are locally isotropic, non-magnetic and belong to the recently discovered class of Kramers-Kronig media [{\it Nature Photon.} 9, 436 (2015)], i.e. the spatial profiles of the real and imaginary parts of the dielectric permittivity are related each other by a Hilbert transform. The transition from unidirectional to bidirectional invisibility, and the possibility to realize sharp reflection above a cut-off incidence angle, are also discussed.