Parity-time symmetry mode of coupled subwavelength silicon rectangular gratings

The paper investigates the resonances of reflection (transmission) of a structure consisting of two optically coupled subwavelength silicon rectangular diffraction gratings, separated by a layer of optically transparent dielectric. The considered structure combines gain, loss and optical coupling coefficient of the periodic structure to effectively operate in parity-time symmetry mode. The spectral characteristics of the resonant reflection (transmission) of the metastructure are analyzed both in PT-symmetry mode and when switching the system to broken PT-symmetry mode. The advantages and disadvantages of using optical parity-time symmetry to control resonant reflection (transmission) for TM- and TEpolarized light incidence are demonstrated. It is shown that changing the relative arrangement of the gain and loss gratings with respect to the incident signal field significantly affects the ratio of transmission and reflection coefficients. All results are obtained considering the dispersion of the materials used.