The impact of contact and contactless interactions between the meta-atoms on terahertz bound states in the continuum

Abstract

The excitation and manipulation of symmetry protected bound state in the continuum (SP-BIC) is significantly valuable for metasurface-based biosensors. The interaction between adjacent meta-atoms determines the basic properties of SP-BIC, however, this topic has not been profoundly explored. In this work, we experimentally and numerically investigate the impact of contactless and contact interaction between adjacent dual-gap split-ring resonators (DSRR) on the SP-BIC. We show that there is only one SP-BIC at 0.9 THz when the incident radiation polarization is parallel to the gap in both contactless and contact coupling condition. When the polarization is vertical to the gap, the individual SP-BIC shift the frequency to 0.8 THz under contactless coupling. Under contact coupling, the SP-BIC degrade to be an electromagnetically-induced transparency (EIT) windows at 0.8 THz. We calculated a 3.6 ps group delay slow light for EIT. Numerical simulations indicate that the combination of one magnetic dipole on inner-arm and another electric dipole on outer-arm of DSRR results to quasi-BIC at 0.9 THz and 0.8 THz under contactless coupling. Under contact coupling condition, the formation of quasi-BIC at 0.9 THz is similar to contactless coupling. However, two magnetic dipoles of opposite polarity results in the EIT windows at 0.8 THz. Our results reveal excitation and manipulation of terahertz SP-BIC via contactless and contact coupling which is significant for the innovation of terahertz biosensors.