  Terahertz waves offer a profound platform for next-generation sensing,
imaging, and information communications. However, all conventional terahertz
components and systems suffer from a bulky design, sensitivity to
imperfections, and transmission losses. Here, we propose and experimentally
demonstrate on-chip integration and miniaturization of topological devices
which may address many existing drawbacks of the terahertz technology. We
design and fabricate topological devices based on valley-Hall photonic
structures that can be employed for various integrated components of on-chip
terahertz systems. More specifically, we demonstrate the valley-locked
asymmetric energy flow and mode conversion with topological straight waveguide,
multi-port couplers, wave division, and whispering gallery mode resonators. Our
devices are based on topological membrane metasurfaces which are of great
importance for developing on-chip photonics and bringing many novel features
into terahertz devices.
