Bimodal Resonance Phenomena—Part III: High-Contrast Grating Reflectors

The extraordinary broadband high-reflectivity features of high-contrast gratings (HCGs) are stimulating great interest in many optoelectronic applications. In view of obtaining a simple simulation framework, the analogy of HCG reflectors with bimodal Fabry–Pérot interferometers is proposed. The closed-form expressions of the interferometer reflectivity, obtained starting from a novel parametrization of the scattering matrices characterizing the bar–air interface, allow a complete exploration of the device parameter space, explaining and predicting the phenomenon of ultra-broadband quasi-100% reflectivity. In this paper, an optimized and numerically efficient design procedure is described and compared with the standard rigorous coupled wave analysis, both for the classical bar-in-air configuration and for a more robust and practical one, with bars lying on a dielectric support. It is shown that the model can be applied also in the more realistic case of lossy gratings.