Large angle reciprocal electromagnetically induced transparency on fano resonance in metamaterials

The electromagnetically induced transparency (EIT) effect has been widely studied in metamaterials, which has potential applications in optical storage and sensors due to its less stringent implementation conditions. Especially, EIT with reciprocity is flexibility which is not limited by the incident direction of electromagnetic field. In this paper, a reciprocal and large angle electromagnetically induced transparency (EIT) effect in the terahertz range is proposed. The tri-layer metamaterial structure is consisted of one opening ring and four sectors which represented the bright and dark modes, respectively. The physical mechanism of the EIT effect can be attributed to Fano resonance coupling with the bright and dark modes. Influence of structure parameters on the performance of the structure is discussed. The EIT effect is affected by the length of the gaps and environmental refractive index. In addition, changing the incident angle, the EIT effect always exists until the angle of the incidental electromagnetic wave is 60°. The group delay is calculated and shown potential application in slow light effect. These results have many potential applications for slow light devices, terahertz filtering, large-angle switching and sensors.