Tunable narrowband filter driven by quasi-bound states in the continuum using a GST-based metasurface grating

Conventional optical filters exhibit relatively static optical characteristics after manufacture. The integration of phase-change materials (PCMs) into the filter structures offers a route to dynamic tunability. Furthermore, the excitation of quasi-bound states in the continuum (qBICs) provides a mechanism for achieving narrow bandwidth operation in dynamically tunable PCM-based filters. In this work, we present a tunable narrowband optical filter based on Ge 2 Sb 2 Te 5 (GST), employing a metasurface grating composed of double nanorods within a unit cell. The qBIC modes, characterized by the high Q -factor, can be excited by introducing symmetry breaking within the structure. Our analysis indicates that this mode is governed by the hybrid electric quadrupole–magnetic dipole mode, as determined through multipole analysis and field distribution studies. Furthermore, the qBIC modes can also be excited by modulating the permittivity of the GST-based grating. Simulation results demonstrate that the tunable bandwidth of the filter can reach approximately 34 nm through the GST phase transition along with a wavelength tuning capability of 55 nm via variations in the incident angle. This study presents a promising approach for the development of tunable optical devices.