Silicon nanostructure cloak operating at optical frequencies

The ability to render objects invisible using a cloak (such that they are not detectable by an external observer) has long been a tantalizing goal(1-6). Here, we demonstrate a cloak operating in the near infrared at a wavelength of 1,550 nm. The cloak conceals a deformation on a flat reflecting surface, under which an object can be hidden. The device has an area of 225 mu m(2) and hides a region of 1.6 mu m(2). It is composed of nanometre-size silicon structures with spatially varying densities across the cloak. The density variation is defined using transformation optics to define the effective index distribution of the cloak.