Reflection-Reduced Two-Layer Grating With Nearly 100% Diffraction Efficiency

A novel reflection-reduced two-layer grating is described with nearly 100% diffraction efficiency. The efficiency of the conventional grating should be improved, or some reported high-efficiency grating can work only for one polarization. The reflection-reduced grating can achieve high efficiency with a covering layer on the surface-relief grating. In addition, the two-layer grating can have wideband property compared with the single-layer grating. The presented novel grating can have merits of high efficiency of reflection-reduced grating and wideband property of two-layer grating. The modal method is applied to analyze the physical mechanism of high efficiency for both TE and TM polarizations. With the optimized grating parameters, efficiencies of 99.69% and 99.64% can be diffracted into the first order for the TE and TM polarizations, respectively. The moderate tolerance should make it possible to be fabricated easily for such a reflection-reduced two-layer grating, which can achieve nearly 100% diffraction efficiency for both the TE and TM polarizations.