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

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.