Evanescent-Field-Guiding 2D Ultrathin Waveguides for Seamlessly Integrated Devices

Seamless integration of active devices into photonic integrated circuits remains a challenge due to the limited accessibility of the optical field in conventional waveguides, which tightly confine light within their cores. In this study, we propose a two-dimensional (2D) ultrathin waveguide as a photonic platform that enables efficient interaction between guided light and surface-mounted devices by supporting optical modes dominated by evanescent fields. We show that the guided light in a monolayer MoS₂ film propagates over millimeter-scale distances with more than 99.9% of its energy residing in the evanescent field. As a representative active device, we develop a WSe₂ photodetector and directly integrate it onto the MoS₂ waveguide. The integrated photodetector demonstrates nanowatt-level sensitivity, microsecond-scale response times, and a polarization selectivity of 0.94. These results establish 2D ultrathin waveguides as a compact, robust, and versatile photonic platform that leverages evanescent-field guiding for the seamless integration of passive and active photonic components.