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 , 2 , 3 , 4 , 5 , 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 µm 2 and hides a region of 1.6 µm 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. A triangular array of silicon nanostructures is experimentally demonstrated to function as an optical cloaking device, operating in the near-infrared at a wavelength of 1550 nm. This approach could, in principle, be extended to larger areas using fabrication techniques such as nanoimprinting.