Fano Resonance in THz Metasurface on Ultrathin Dielectric Substrates

Propagation of tangential electromagnetic modes in an array of split-ring resonators deposited on a thin dielectric plate is analyzed by studying the properties of the Fano resonance. We find a noticeable difference between diffracted modes in freestanding resonators and guided modes in the presence of a dielectric plate. We demonstrate that in the case of a subwavelength dielectric thickness, the tangential modes are guided by both interference and internal reflections of diffracted waves.