Subwavelength focusing in the near field in mesoscale air-dielectric structures

Subwavelength focusing in mesoscale structures was measured in the near field. Specifically, we found that plane waves form focused beams in higher topographic regions when they propagate through mesoscale transparent air-dielectric structures. By finite-difference time-domain simulations we verified that light diffracted off topographic edges and its convergence at higher topographic regions are the mechanisms for focus. This subwavelength focusing effect provides a simple way for mass production of mesoscale periodic structures. We made subwavelength gratings and hole arrays to demonstrate their feasibility.