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. Here, we show 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 demonstrate three-dimensional cloaking that cannot be detected even interferometrically across the entire visible regime. Our results open the road for ultrabroadband invisibility of large objects, with direct implications for stealth and information technology, non-disturbing sensors, near-field scanning optical microscopy imaging, and superluminal propagation.

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We report a thorough theoretical study of the optical response of two-and three-dimensional periodic assemblies of metallic nanorods by means of full-electrodynamic calculations using the extended layermultiple-scattering method. We show that these systems support various types of resonant-and boundcollective plasmon modes, which are tunable over a broad spectral range, and provide a consistent interpretation of the underlying physics. In particular, we reveal the existence of slab plasmon modes with zero group velocity, which can cause evanescent-wave enhancement and enable subwavelength imaging. We discuss extinction spectra of single-layer and multilayer slabs of nanorods in conjunction with relevant complex band-structure diagrams and present a rigorous analysis of the results using group theory. Moreover, we explain some peculiar spectral features which are due to the existence of surface resonances. These can modify the optical response of the system in a controllable manner by using a supporting substrate.

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