Non-Hermitian high-quality-factor topological photonic crystal cavity

Abstract

Non-Hermitian topological photonics possesses abundant and complicated physical effects and phenomena, which have great potential and important applications in integrated photonic devices. However, the light localization properties and approaches for active control of topological states have not been revealed sufficiently so far. Here we prove the phase transition exists in the interface between gain and loss domains of a parity-time symmetric ${C}_{6\mathrm{v}}$ topological photonic crystal from its projected bands. The non-Hermitian topological cavity formed by closed gain-loss boundary has unique resonant responses and better light localization properties compared with the Hermitian counterpart. The cavity modes are composed of edge states and corner states whose eigenfrequencies change with gain-loss quantity in the same way as the projected band. The maximum value of the quality factor of non-Hermitian topological cavity reaches ${10}^{4}$, which is enlarged by one order compared with the Hermitian counterpart. At the same time, the mode volume of non-Hermitian topological cavity is reduced by over tenfold compared with the Hermitian counterpart. The non-Hermitian induced edge states and corner states may open a new route for the design of the topologically protected and reconfigurable localized resonances. This work provides a new degree of freedom to control different topological states and offers a scheme for solving the contradiction between the flexibility of devices and the robustness of topological properties.