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

The extraordinary broadband high-reflectivity features of high-contrast gratings are stimulating great interest in many opto-electronic applications. In view of obtaining a simple simulation framework, the analogy of high-contrast grating 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.