Figure 2: (a) Comparison of coupling efficiency spectra for several different grating periodicities. The coupling efficiency is defined as the fraction of the total incident power that leaves the grating in one direction. Dotted lines indicate second-order peaks. Inset is a plot of the time averaged power flow (magnitude of the Poynting vector) for a grating resonant at 11 μm. The aspect ratio is expanded vertically by 6x for better visibility. (b) Resonant wavelength for several different grating periodicities. Parameters used: μm, nm, nm, nm, .