Strong resonant mode coupling of Fabry–Perot and grating resonances in stacked two-layer systems

In stacked grating systems, it is possible to observe not only coupling between the resonances of each subgrating, but for larger inter-grating distances also the occurrence of Fabry–Perot modes. When such a Fabry–Perot resonance approaches an individual grating resonance in linewidth and resonance energy, strong coupling and anticrossing may take place. For an appropriate description of this phenomenon, we present an extension of the resonant mode coupling method that allows us to describe the combined resonances of two grating layers even in the strong coupling regime.

► Description of combined modes in stacked gratings from the resonances of the individual gratings. ► The method can be applied easily for varying inter-grating distances and is valid from the near- to the far-field. ► Extension of the resonant mode coupling to the regime of strong coupling with Fabry-Perot modes. ► Resulting equations provide additional insight in the coupling mechanisms. ► The method exhibits a good agreement with exact result.