Effect of magnetic polaritons on the polarization characteristics of metal–dielectric–metal​ infrared wire-grid polarizers

Abstract

Recently, magnetic polaritons has drawn a lot of attentions on explaining extraordinary optical transmission or absorption in subwavelength periodic structures. In this paper, the role of the magnetic polaritons on the polarization characteristics of metal–dielectric–metal infrared wire-grid polarizers is investigated. The effect of the geometric parameters on the resonance phenomenon is simulated by finite-different time-domain solutions. The results show that the peaks of transverse magnetic transmission, where the magnetic polaritons is excited, shift to longer wavelengths as the thicknesses, refractive indices, periods, and duty cycles of the dielectric gratings increase. The simulation results exhibit similar tendencies with the resulted inference by the equivalent inductor–capacitor circuit model. As seen from the electromagnetic field distribution, the strong magnetic field is highly confined inside the dielectric layer between the upper and lower metal strips where the magnetic polaritons is activated. The transverse electric transmission for the metal–dielectric–metalstructure is two orders of magnitude smaller than that of single metal layer grating. Moreover, the extinction ratio exceeds 42 dB at the wavelength of 4.0μm for the metal–dielectric–metal structure with the optimal values of grating period (500 nm), duty cycle (0.5), and metal layer thickness (h1= h2= h3= 100 nm). The analyzation of magnetic polaritons and the polarization transmission mechanism will be helpful for the design and fabrication of the gratings with good polarization properties.