Numerical study on the optical absorption of one dimension metallic gratings

We investigate the reflected response of one-dimensional metallic grating with rigid coupled-wave analysis. Three types of resonance absorptions, i.e., Rayleigh anomaly, surface plasmon polariton (SPP) standing wave resonance and geometric resonance, are identified in the gray-scale map of the reflectivity as a function of two structural parameters: grating period and groove depth. Furthermore, the interactions among these resonances are discussed. Our calculation reveals that a hybrid mode of SPP standing wave resonance and geometric resonance can be found, while no hybrid mode of Rayleigh anomaly and geometric resonance exists. In the analysis of compound gratings, we find phase resonance. Flow the phase resonance changes the reflection and the absorption of compound metallic gratings is also discussed. When the wavelength of incident light is less than grating period, sharp dip is found in reflectivity as a function of groove depth. In the other case, i.e. Wavelength greater than grating period, phase resonance results in a split of the hybrid absorption branch of SPP standing wave resonance and geometric resonance.