  A multi-reflection model of grating diffraction based on the simplified modal
method is proposed. Simulation results for a guided mode resonance Brewster
grating using our method and rigorous coupled wave analysis are presented to
verify our model. The solution of our method is in good agreement with that of
rigorous coupled wave analysis. Benefiting from its clear physical view, this
model helps us to better understand the diffraction process inside
subwavelength gratings. On the basis of the multi-reflection model, we
developed a matrix Fabry-Perot (FP) resonance condition and a single-mode
resonance condition to evaluate the resonance wavelength. These resonance
conditions may be helpful for simplifying design of guided mode resonance (GMR)
gratings.
