Low-threshold topological nanolasers based on the second-order corner state
The applications of topological photonics have been intensively investigated, including one-way waveguide and topological lasers. The topological lasers especially have attracted broad attention in recent years, which have been proposed and demonstrated in various systems, including 1-D edge states in 2-D systems, 0-D boundary states in 1-D lattice, and topological bulk state around band edges. Most of them are at microscale. The topological nanolaser with a small footprint, low threshold and high energy-efficiency has yet to be explored. Recently, a new type of higher-order topological insulators which have lower dimensional boundary states has been proposed and demonstrated in many systems, including 2-D photonic crystal. In the second-order 2-D topological photonic crystal slab, there exist the gapped 1-D edge states and mid-gap 0-D corner state. This localized corner state provides a new platform to realize topological nanolasers.