Polarization-Selective Collimation Effect with a Reflective Plasmonic Cavity

We report that a metal-dielectric-metal cavity with a perforated top metallic film shows a remarkable polarization-selective collimation effect through reflection on the perforated film. According to simulations, such plasmonic cavities can achieve nearly perfect absorption (R < 1.5%) of a transverse magnetic (TM) wave at an optimized incident angle while nearly perfect reflection (R similar to 100%) at normal incidence. A very wide incident angle range (approximately 15 degrees-65 degrees) is found to exhibit a high absorption ratio exceeding over 70%. In contrast, for a transverse electric (TE) wave, the plasmonic cavities remain highly reflective (R similar to 100%) regardless of the incident angles. We elucidate that this polarization-and angle-dependent behavior arises from an even-order (N = 2) horizontal Fabry-Perot (FP) resonant mode inside the plasmonic cavity. This effect may find potential applications for angle filtering of polarized divergent light beams in optics.