An invisibility cloak should completely hide an object from an observer, ideally across the visible spectrum and for all angles of incidence and polarizations of light, in three dimensions. However, until now, all such devices have been limited to either small bandwidths or have disregarded the phase of the impinging wave, or worked only along specific directions.
In our recent work1, we have shown that these seemingly fundamental restrictions can be lifted by using cloaks made of fast-light media, termed tachyonic cloaks, where the wave group velocity is larger than the speed of light in vacuum. On the basis of exact analytic calculations and full-wave causal simulations, we demonstrated three-dimensional cloaking of electrically-small objects that cannot be detected even interferometrically across the entire visible regime.
Our ongoing research is directed towards achieving broadband invisibility of electrically-large objects, with direct implications for stealth and information technology2, non-disturbing sensors, near-field scanning optical microscopy imaging, and superluminal propagation1.