Ultra-High Q-Factors Dynamical Modulation in a Si-GSST Metasurface Induced by Quasi-BICs

High quality (
${Q}$
)-factor dynamical modulation has attracted increasing interests in tunable opto-electronic devices. Phase change material Ge2 Sb 2 Se4 Te (GSST) with tunable loss paves an excellent platform for dynamical modulators. In this work, we build a dynamically optical modulator with ultra-high
${Q}$
-factors based on the metasurface consisting of a double-layer array of GSST-silicon (Si) square nanocubes etched with two elliptical air columns. Two prominent quasi-bound states in continuum (BICs) with
${Q}$
-factors upto
$\sim 10 ^{5}$
are obtained by breaking the structural symmetry. Moreover, these two quasi-BICs both display great dependence on the crystallization ratio
${m}$
of GSST and the polarization state of incident light. The transmission light can be actively regulated from ~0% to more than 80% by employing the polarizer or GSST material. These demonstrate our proposed metasurface with excellent quasi-BICs modulation capability, which provide a new pathway for ultra-high
${Q}$
-factor dynamically tunable optical devices.