Optical Properties of Resonant Diffraction Gratings with a Slowly Varying Period

We consider a guided-mode resonant grating, the period of which slowly varies in the direction of the periodicity. Optical properties of this structure are investigated rigorously using the Fourier modal method and the scattering matrix formalism. By simulating the diffraction of a plane wave on the considered structure, we demonstrate that it can be used as a linear variable filter (LVF). We also investigate how the line shape of the resonances depends on the rate of the variation of the period. The considered structure can find application in novel multi- and hyperspectral optical systems.