Fano resonance: a route to bound states in the continuum

The physics of bound states in the continuum has enabled a novel approach to achieving high Q-factor resonances, leading to strong field confinements along with enhanced light–matter interactions due to their perfect non-radiative nature. With this background, we have demonstrated the realization of symmetry-protected bound states in the continuum by means of near-field coupled Fano-resonant THz metasurfaces comprising a pair of cut-wires (or dipole resonators). We studied and optimized the metasurfaces through extensive numerical simulations, followed by experimental validations. Our studies demonstrate a Q-factor as high as 124 while operating in a strong near-field coupled regime. Inverse square fitting on experimental results reveals a clear trend toward an infinite Q-factor state for a symmetry-protected situation, indicating the existence of a bound state in the continuum. Hence, this work demonstrates a prominent path through the excitation of Fano resonances to realize BIC. Furthermore, this study has the potential to contribute to THz-based advanced devices requiring high Q-factor resonances.