Asymmetric all-dielectric active metasurface for efficient dual reflection modulation

Abstract

Active metasurface provides an efficient way to achieve optical response in the subwavelength range, dielectric metasurface has attracted much attention due to its low-loss mode and excitable electric/magnetic resonance mode, resulting in a far wider range of applications. However, the resonance spectrum is relatively broad due to the strong radiative loss of the symmetric dielectric metasurface, which limits its application in large modulation extinction ratio. Hence, an active metasurface integrated with the phase change material Ge2Sb2Te5 (GST) is proposed. The active metasurface can support the symmetry-protected quasi bound states in the continuum (QBIC) and excite resonance modes with extremely high quality-factors. As an active medium, the GST layer undergoes a transition from the amorphous state to the crystalline state when the temperature increases, leading to a change in the amplitude/phase of the reflection spectrum. It is demonstrated that dual reflection modulation and the figure-of-merit (FoM) can reach up to 92.0% at the wavelength of 1.45 μm and 92.5% at the wavelength of 1.52 μm as the GST layer is in the middle of nanodisks. An extremely high FoM of 98.5% is also realized when the surface of silicon nanodisks is coated with the GST layer. In addition, the modulation mechanism of the optical response of the active metasurface has been investigated, which is of great significance to the design of the active metasurface. The proposed active all-dielectric asymmetric metasurface has a huge potential in tunable nonlinear optical devices.