Transition from a color filter to a polarizer of a metallic nano-slit array

Wire grid polarizer is a well-known optical element with many important applications. We observed a transition from a polarizer (broadband transmission) to a color filter (resonant transmission) of a metallic nano-slit array as the period of the array is increased. The effect is explained in terms of the mode mismatch between the slit waveguide mode and the incident plane wave, which causes light confinement inside the slit and thus a resonance. By putting the slits near to each other, the mode mismatch is weakened so that a broadband of light can penetrate through.