Experimental demonstration of merging quasi-BICs in photonic crystal slabs

Merging bound states in the continuum (BICs) and avoided crossing of resonances (ACR) are promising theoretical approaches to greatly enhance the quality (Q) factors of quasi-BICs in reciprocal space. We observe the phenomena of merging BICs and ACR in millimeter-sized C4v symmetry photonic crystal structures. The ACR at Γ point is obtained in the variation of the structural parameter. In off-Γ region, the merging BICs at arbitrary locations are observed in the experimental measurements. The findings offer a pathway to high-performance photonic devices with potential applications in optoelectronics and microwave experimentation.