Subwavelength-structured metallic film as polarization-converting element

It is well known that in an anisotropic dielectric material, during propagation a phase shift occurs between the transverse field components. Thus, polarization converters are usually realized by using natural birefringent materials or sub-wavelength-structured elements. Here, we suggest the use of a metallic film with a sub-wavelength structure as polarization shifting component. The idea is based on the physics of a hollow metallic waveguide as known, e.g., from microwave theory. The structure that we consider in particular is an array of rectangular holes with thin metallic sidewalls. The effective indices for the two transverse field components can be tailored independently by a suitable choice of the geometry. Compared to dielectric sub-wavelength gratings, a greater variation of the effective indices (for the same mean value) can be achieved. In this presentation, we discuss the theory of metallic sub-wavelength elements and present numerical and early experimental results.