Abstract
We present wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material, thereby eliminating local reflections and phase changes. This critical interface thus possesses zero refractive-index contrast; hence “zero-contrast gratings.” We design reflectors with zero-contrast gratings and high-contrast gratings and compare the results. For simple gratings with two-part periods, we show that zero-contrast grating reflectors outperform comparable high-contrast grating reflectors. An example silicon-on-glass reflector exhibits a 99% reflectance bandwidth of for zero refractive-index contrast , whereas a high-contrast device with yields a bandwidth of . It follows that local Fabry–Perot modes residing in the grating ridges and reflecting off a high-contrast interface are not the root cause of wideband reflection.
© 2014 Optical Society of America
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