Metallic optical filters with low sheet resistance

A photonic band gap structure is periodic lattice of high and low refractive index materials that form pass bands and stop bands (band gaps) in analogy with electronic band gaps. Since metals are highly reflective, it was thought that a photonic band gap crystal containing alternating layers of metal and dielectric would not exhibit a photonic band structure. It was expected that all electromagnetic radiation would be reflected or absorbed and none would be transmitted. However, resonant tunneling through multiple metal films can enhance the transmission by several orders of magnitude. The periodic nature of the metal/dielectric lattice causes the light to propagate through the metal layers with extremely low loss. Perhaps the most unique feature of the metallic optical filter is the ability to have a single pass band and block all other radiation from static fields to soft X-rays. This remarkable property is a result of the highly dispersive nature of metals.