Meta-Waveguides for Scalable and Robust Optical Mode Manipulation on Etchless Thin Film Lithium Niobate

Meta-waveguides are a novel type of integrated optical waveguide structure that can enable refractive index manipulation by engineering photonic structures at subwavelength scales. Such meta-waveguides offer the advantage of providing flexible and highly customizable manipulation over multidimensional optical fields. Meta-waveguide-based optical mode manipulation technologies can control the spatial dimensions in optical waveguides. In contrast to traditional design strategies that are specific to certain mode orders, meta-waveguide-based technologies overcome the inherent limitations of mode order, offering more flexible scalability and robustness. Recently, a thin-film lithium niobate (TFLN) platform with its unique electro-optic properties and low material loss becomes an ideal choice for constructing integrated optoelectronic chips. By leveraging the lithium niobate's etchless approach, meta-waveguides based on the TFLN platform enable innovative optical mode processing paradigms, significantly enhancing the transmission capabilities of optical communication systems. Here, we report a scalable on-chip optical mode manipulation system that utilizes the flexible refractive index distribution of meta-waveguides to excite arbitrary high-order optical modes. As a proof of concept, a 6-channel optical mode multiplexer is designed and experimentally demonstrated, which achieves low insertion loss (<1.9 dB) and crosstalk (<−19 dB) at 1550 nm, while exhibiting enhanced fabrication tolerance. This demonstration alleviates the scalability limitations in mode scalability for TFLN photonic devices, addressing the capacity bottleneck issues in optical signal processing, optical interconnects, and brain-inspired photonic computing.