Polarization Selective Modulation of the Supercavity Resonance from Friedrich-Wintgen Bound States in the Continuum

Abstract: Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Recent experiments have demonstrated the existence of exotic modes which occur in off-$\Gamma$\ points not accessible by symmetry-protected BICs, Freidrich-Wintgen (FW) BICs. In previous works, FW BICs were formed by either varying the incident angle or through geometric manipulation. On the contrary, in this work we demonstrate the formation of FW BICs induced by different linear polarization states of incident terahertz waves. Furthermore, as predicted by theory, the position of the FW BIC region is verified to change as a function of asymmetry. This allows for a unique parameter, incident polarization, to induce the FW BIC and modulate the supercavity resonance with the degree of asymmetry. The polarization-selective quasi-BICs observed near the FW BIC have potential applications in lasing, spectral filtering and high-performance sensing devices.