Narrowband filter in a heterostructured multilayer containing ultrathin metallic films

A narrowband reflection and/or transmission filter made of heterostructured multilayer with two different ultrathin metallic films is proposed. The multilayer structure is a cascaded system that is formed by using two narrowband reflection-and-transmission filters. Each individual filter is made of an ultrathin metal film in front of a planar Fabry-Perot resonator. Using the transfer matrix method in a stratified system, the optical filtering properties are theoretically investigated and analyzed. It is found that the reflection peak at the design wavelength in the original individual filter becomes a dip in the heterostructured filter. The role played by the stack number of Bragg reflector in the design of narrowband filter is also clearly elucidated.