An omni-directional mid-infrared tunable plasmonic polarization filter.

In this paper, we show that a localized surface plasmon polariton in a plasmonic sandwich structure made of a (metal elliptical disc)/(dielectric spacer)/(metal film) can be used as an efficient angle-independent polarizer in the mid-infrared wavelength regime. The elliptical disc structure is characterized by using a Fourier transform infrared spectrometer and simulated via the rigorous coupled wave analysis (RCWA) method. For the optimum design, we can obtain a degree of polarization of 99% both experimentally and theoretically. A high extinction ratio between 20 and 40 dB can be obtained by changing the axis ratio of the elliptical disc between 0.65 and 0.85. The wavelength of polarized light can be tuned in a wide range by changing the structural parameters. The plasmon-polariton band structures of the elliptical disc structure for both TM and TE polarizations are also studied theoretically via RCWA.