Tunable dual quasi-bound states in continuum and electromagnetically induced transparency enabled by the broken material symmetry in all-dielectric compound gratings

Dual quasi-bound states in continuum (quasi-BICs) enabled by the broken geometric symmetry offer an effective way to design high-quality photonic devices, yet challenged by tunable functionalities. Here we employ the material asymmetry originating from the tunable material property of phase-change materials to design quasi-BICs in all-dielectric compound gratings. We find the even and odd quasi-BICs are modulated by the geometric and material asymmetries, respectively, and this effect is ensured by two different types of structural symmetries in the compound structure. Particularly, tunable electromagnetically induced transparency (EIT) can be achieved by modulating the material asymmetry. Furthermore, we systematically design the compound gratings consisting of the phase-change material of Sb2Se3 to demonstrate tunable dual quasi-BICs and EITs. Analytical calculations and numerical simulations are performed to verify these findings. Our work provides a promising way to enhance the flexibility of realizing quasi-BICs, which may boost tunable applications in nanodevices assisted by quasi-BICs.

Automated summary

Dual quasi-bound states in continuum (quasi-BICs) enabled by broken geometric symmetry are designed in all-dielectric compound gratings, using the tunable material property of phase-change materials. The even and odd quasi-BICs are modulated by geometric and material asymmetries, respectively, and this effect is ensured by two different types of structural symmetries in the compound structure. Tunable electromagnetically induced transparency (EIT) can be achieved by modulating the material asymmetry. The compound gratings consisting of Sb2Se3 phase-change material are designed and verified through analytical calculations and numerical simulations.