Topological Edge Mode Tapering

Mode tapering, or the gradual manipulation of the size of some mode, is a requirement for any system that aims to efficiently interface two or more subsystems of different mode sizes. While high-efficiency tapers have been demonstrated, they often come at the cost of a large device footprint or challenging fabrication due to backscattering or excitation of higher-order modes. Topological photonics, offering robustness to certain types of disorder as well as chirality, has proved to be a well-suited design principle for numerous applications in recent years. Here we present a new kind of mode taper realized through topological band gap engineering. We numerically demonstrate a 6-fold change in mode width over an extremely compact 8 μm distance with near unity efficiency in the optical domain. With suppressed backscattering and no excitation of higher-order modes, such a taper could enable new progress in the development of scalable, multicomponent systems in classical and quantum optics.