Dynamic beam control via Mie-resonance based phase-change metasurface: a theoretical investigation.

Here, a non-volatile optically controllable metasurface is theoretically investigated at the operating wavelength of 1.55 μm by utilizing low loss phase-change Ge2Sb2Se4Te1 (GSST) as the constituent material of high-index resonant element. The GSST nanobar as the proposed building block supports both the magnetic and electric resonances whose strength and spectral positions can be governed by varying the GSST crystallization level. The possibility of operating at off-resonance regime (middle of geometrical resonances) and preventing from the concurrence of high field confinement and large dissipative loss provide the opportunity to obtain high reflection level (varying between 0.6 and 0.8) and wide phase agility (≈270°). The phase distribution at the interface of an array of GSST nanobars can be tailored by selective modification of the crystallization level of nanobars leading to active control over the wave-front of reflected beam with numerically calculated reflection efficiency higher than 45%.