Coupled-resonator-based metamaterials

In this review, we describe recent developments in functional metamaterials based on coupled resonators. We first consider coupled resonator metamaterials that mimic electromagnetically induced transparency (EIT). We present a circuit model for EIT-like metamaterials and introduce a new coupled resonator in which the coupling is provided by a field gradient so that the group velocity can be varied by varying the incident angle. We then describe the principles for enhancing second harmonic generation (SHG) in nonlinear resonant metamaterials. Optical and microwave experiments of SHG in singly resonant metamaterials are presented. A method for further enhancing SHG using a doubly resonant metamaterial is also described.