Polarization-selective modulation of supercavity resonances originating from bound states in the continuum

Bound states in the continuum (BICs) are widely studied due to their applications in light confinement, sensors, and lasing action with topological characteristics. The formation of BICs in periodic photonic band gap structures are primarily driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two methods to drive the formation of BICs in terahertz metasurfaces. First, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light at normal incidence. Recent experiments have demonstrated the existence of exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs called Freidrich-Wintgen (FW) BICs. Here, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs. The capacitance-mediated strong coupling at 0° polarization is shown to have a normalized coupling strength ratio of 4.17% calculated by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ φ <90°), the Freidrich-Wintgen BIC can be modulated until it is completely switched off at 90°.