Low-loss directional cloaks without superluminal velocity or magnetic response

TL;DR

This paper proposes a new approximation method for optical cloaking that achieves limited invisibility without requiring superluminal phase velocities or magnetic responses, avoiding losses associated with traditional metamaterials.

Contribution

It introduces a piecewise-uniform refractive index scaling technique that preserves ray paths and enables directional, wavelength-dependent invisibility without superluminal or magnetic materials.

Findings

Achieves directional invisibility with phase delay manipulation.

Avoids superluminal phase velocities and magnetic responses.

Provides a practical approach to optical cloaking without losses.

Abstract

The possibility of making an optically large (many wavelengths in diameter) object appear invisible has been a subject of many recent studies. Exact invisibility scenarios for large (relative to the wavelength) objects involve (meta)materials with superluminal phase velocity (refractive index less than unity) and/or magnetic response. We introduce a new approximation applicable to certain device geometries in the eikonal limit: piecewise-uniform scaling of the refractive index. This transformation preserves the ray trajectories, but leads to a uniform phase delay. We show how to take advantage of phase delays to achieve a limited (directional and wavelength-dependent) form of invisibility that does not require loss-ridden (meta)materials with superluminal phase velocities.