  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.
