Bimodal Operation of High-contrast Gratings: The Generalized Fabry-Perot Perspective

Previous works ascribe the broadband high-reflectivity features of high-contrast gratings (HCGs) to dual-mode interference effects occurring in the grating bars, which are a characteristic of their near-wavelength operation regime. Using this fundamental characteristic this work exploits a bimodal Fabry-Perot interferometer approach to better understand the HCG physics. This analytic framework allows to explain the 100% reflectivity peaks at the basis of the broadband operation, predicting their positions by closed-form expressions. A design strategy based on this approach is then presented, including a discussion on the impact of fabrication tolerances on the HCG performance.