Coupled-mode theory for resonant gratings with a varying period

We propose a coupled-mode theory for resonant diffraction gratings with varying period. consider diffractive structures, in which the reciprocal lattice vector, quantity inversely proportional to period, varies linearly direction of periodicity. It is shown that optical properties such structure essentially depend on period change rate. On basis comparison results rigorous numerical simulations using coupled-wave analysis, high accuracy proposed theoretical model demonstrated. In particular, developed describes broadening peak and appearance secondary maxima caused by non-zero The obtained can be used development linear variable filters based parameters.