Transmittable Nonreciprocal Cloaking

Cloaking is typically reciprocal. We introduce here the concept of \emph{transmittable nonreciprocal cloaking} whereby the cloaking system operates as a standard omnidirectional cloak for external illumination, but can transmit light from its center outwards at will. We demonstrate a specific implementation of such cloaking that consists in a set of concentric bianisotropic metasurfaces whose innermost element is nonreciprocal and designed to simultaneously block inward waves and pass -- either omnidirectionaly or directionally -- outward waves. Such cloaking represents a fundamental diversification of conventional cloaking and may find applications in areas such as stealth, blockage avoidance, illusion and cooling.