Total absorption of light in sub-wavelength metallic waveguides

Resonance cavity modes enhance optical transmission through sub-wavelength metallic apertures but their role in absorption remains unclear. Here, we use full field simulation and a semi-analytical model to report absorption and transmission enhancement in transmission gratings under transverse electric illumination. The fundamental cavity mode of the sub-wavelength grating cavities is the major contributor to absorption. We demonstrate the possibility of tailoring such cavity resonances to induce total absorption in reflection gratings. Our method advances the understanding of transmittance and absorption enhancing mechanisms in metallic nanostructures which constitute fundamental components in energy harvesting, sensing, and spectroscopic applications.