Surface plasmon-mediated transmission in double-layer metallic grating polarizers

We study the mechanism of polarization-selective transmission in double-layer gratings. For TM polarized light, the coupling between the surface plasmon waveguide modes of slits in the two metal layers causes most of the energy to pass the gratings. For TE polarized light, there is no surface plasmon coupling effect, and most of the energy in the photoresist waveguide is reflected back because of the cutoff of waveguide modes. In view of the characteristics of surface plasmon waveguide modes, a new polarizer with an undercut profile of the photoresist is proposed to achieve better performance by improving the coupling efficiency. At the pitch of 200nm, the TM transmissions can be over 70% in the visible spectrum and over 80% in the wavelengths from 470nm to 800nm for a bottom width w2<60nm.