Manipulating optical reflections using engineered nanoscale metasurfaces

We propose a comprehensive scheme for the efficient design of graded optical metasurfaces capable of rerouting the impinging energy at will in a flexible way. We show that carefully designed conjoined optical nanoelements may be used as basic building blocks to arbitrarily shape the reflected phase front, while providing large controllability and low loss over deeply subwavelength thicknesses. The metasurface elements are designed using transmission line concepts combined with nanocircuit theory, and they can be realized with conventional lithographic techniques. Based on these concepts, we put forward a fast and accurate analytical model to design the optical analog of reflectarrays for light bending, steering, and focusing. The proposed designs show large efficiency over a broad angular spectrum, accompanied by broad bandwidths of operation. Our technique may lead to significant advances in the field of planarized nanophotonics and light manipulation over a surface, with potential applications in light trapping and efficient photonic couplers.