Polarization-Independent High Q-Factor Resonance Achieved by Efficiently Selecting and Perturbing the Unit Cell of Nanostructure

Bound states in the continuum (BIC) is an important platform to achieve high quality (Q) factor resonance modes, and their excitation usually requires changing the size of the structure to introduce the symmetry-breaking of the structure, so these high-Q modes are commonly polarization-dependent, and they need to be excited at a specific polarized light. If a resonant response is obtained under arbitrarily polarized light, a polarization-independent mode needs to be designed. In this work, we effectively perturb the same mode by selecting multiple unit cells while maintaining $\mathrm{C_{4v}}$ symmetry, and these excited modes are polarization-independent. Firstly, we design a degenerate eigenmode supported by a square nanohole photonic crystal slab, and then select four kinds of unit cells respectively, and excite the mode by changing the size of the nanohole, moving the relative position of the nanohole, and changing the lattice constant. These resonance modes are confirmed to be polarization-independent by calculating the eigenfrequency, transmission spectra, and multipole scattering responses. In addition, we also fabricate sample and test resonance spectra under different polarization angles to fully confirm these polarization independent strategies. Our work provides guidance for polarization-independent resonant photonic devices.