Low-threshold topological nanolasers based on the second-order corner state

Nanophotonics: Creating better performing topological lasers A high-performance topological laser could pave the way for its use in a wide range of nanophotonic applications. Semiconductor lasers are the most common type of laser, but their performance deteriorates if there are any structural defects in the lasing material. Topological lasers allow light to travel around a cavity of any shape without scattering, promising better performing lasers. However, creating a topological laser with a low threshold for lasing and high efficiency has proved challenging. A team of Chinese researchers led by Xiulai Xu from the Chinese Academy of Sciences have now developed a topological laser made from a two-dimensional photonic crystal nanocavity slab with a lasing threshold of about one micro-watt and high spontaneous emission coupling factor of 0.25 and is comparable to the performance of conventional semiconductor lasers. Topological lasers are immune to imperfections and disorder. They have been recently demonstrated based on many kinds of robust edge states, which are mostly at the microscale. The realization of 2D on-chip topological nanolasers with a small footprint, a low threshold and high energy efficiency has yet to be explored. Here, we report the first experimental demonstration of a topological nanolaser with high performance in a 2D photonic crystal slab. A topological nanocavity is formed utilizing the Wannier-type 0D corner state. Lasing behaviour with a low threshold of approximately 1 mu W and a high spontaneous emission coupling factor of 0.25 is observed with quantum dots as the active material. Such performance is much better than that of topological edge lasers and comparable to that of conventional photonic crystal nanolasers. Our experimental demonstration of a low-threshold topological nanolaser will be of great significance to the development of topological nanophotonic circuitry for the manipulation of photons in classical and quantum regimes.