Phase-Change Metasurface by U-Shaped Atoms for Photonic Switch with High Contrast Ratio

Currently, diverse metasurfaces act as exotic platforms enabling versatile wave regulations in deep-subwavelength level for ultracompact integration. To address the existing issues of passive nature and low-efficiency in wave controls, one type of metasurface for active phase tuning is proposed in this paper by integrating the phase-change dielectric of Ge2Sb2Te5 into the of U-shaped meta-atoms. Specifically, the phase-change-based hybrid design of Ge2Sb2Te5-integrated metalens switch is demonstrated and numerically confirmed with switchable focusing. The well-defined metal-insulator-metal (MIM) setup is used to enable high-efficiency reflective wavefront tunig and practical Ge2Sb2Te5 phase transition. Upon the phase transition between the amorphous and crystalline states of Ge2Sb2Te5, the cross-polarized component of reflected waves in the given wavelength range is switched “on” (maximized) for as-designed geometric phase plus meta-lensing or “off” (minimized) for no lensing with ultra-high contrast ratio of ~36:1. As a result, such hybrid design of phase-change metasurface may provide a promising route for active photonic device with compact integration.