Multiple High‐Q Optical Modes in a Polymer‐Lithium Niobate Integrated Metasurface

Abstract With the development of miniaturization and integration, multifunctional optical devices are necessary. However, its practical realization is a critical challenge due to the lack of simple structures with multiple functionalities. Here, a multimode metasurface is proposed by simply placing polymer nanocubes on the lithium niobate (LN) thin film. The intriguing properties of the integrated structure include high‐quality ( Q ) factors and different spectral characteristics, associated with quasi‐guide modes (GM) and Mie modes, respectively. The experiment demonstration reveals that Q factors of four modes are larger than 1000 and a second harmonic generation (SHG) enhancement factor of 25.4 is obtained, featuring strong light‐matter interaction. Importantly, the abundant spectral characteristics greatly boost three degrees of freedom, i.e., polarization, incident angle, and slot, to realize multifunctional designs. The results provide a sophisticated platform for developing high‐performance LN metasurfaces with the advantages of simplified fabrication processes and multifunctionality. The strategy can also be extended to other material systems, enabling the flexibility of metasurface‐inspired subwavelength engineering.