Three variants of binary blazed gratings with subwavelength features are considered, which have high first-order efficiencies in the non-paraxial domain for arbitrarily polarized light. A combination of effective medium theory and further parametric optimization with the Fourier modal method are used in design. Experimental demonstration is provided by electron beam lithography on a structure etched in a Si3N4 layer on top of a SiO2 substrate, with period ~ 3.5λ at λ = 633 nm. The measured efficiency (81% for TE and 85% for TM polarization) agrees well with the calculated value, 84%.
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