Fundamental wave and second-harmonic focusing based on guided wave-driven phase-change materials metasurfaces

It is an important project to use metasurfaces to extend the manipulation of light field by on-chip photonic integrated circuits to the free-space. In this paper, a waveguide mode-driven embedded metasurface is designed by using the propagation phase method. The phase distribution of the metasurface satisfies the focusing of both the fundamental wave and second harmonic wave. On this basis, a phase-change material is chosen to be embedded in waveguide. Combined with its refractive index difference in different phase states, the fundamental wave and second harmonic wave are focused in two phase states, respectively, through the simulation method. When the fundamental wave (or second harmonic wave) achieves high-quality focusing, the components of the second harmonic wave (or fundamental wave) at the focus are suppressed to a large extent, which is more conducive to the subsequent complete filtering. Furthermore, the efficiency at the fundamental wave and second harmonic wave are increased by 2.2 and 3.7 times by embedding another metasurface at the bottom of the waveguide layer which is exactly the same as that at the top but staggers half a period laterally. This study provides a new alternative approach for the linear and nonlinear multifunctional control of guided wave mode-driven metasurfaces.