Metamaterials and optical filtering functions: a review

After a recall of some basic concepts in close relationship with the definition of the refractive index of a material, we will perform a sweep of the specific properties of some important classes of metamaterials, such as NIM, ENZ or ZIM. These fundamentals will allow us to examine the possible benefits induced by the use of one or more NIM layers into the formula of standard filtering functions, like Bragg quarter-wavelength mirror, Fabry-Perot band-pass filter or antireflective coatings. As a conclusion, we will deal some practical issues showing possible implementation ways for these new and attractive concepts.