Design of compact surface-emitting nanolasers based on topological guided-mode resonance

We numerically design a compact nanolaser based on a topological guided-mode resonance (GMR) structure. It consists of a topological junction formed by two GMR gratings, which induces a leaky Jackiw-Rebbi (JR) edge state that confines in-plane light within a small mode volume. Using the finite-difference time-domain (FDTD) method to simulate active optical responses, we show that surface-emitting lasing is achieved with a threshold of 4.5 µJ/cm² within a cavity length of approximately 2.0 µm. In addition, by replacing the junction with an array of equally spaced ridges in a critical phase, the edge mode transitions into a bulk mode. This modification allows for controllable cavity sizes of 4.9, 7.8, and 10.7 µm, with corresponding thresholds of 6.0, 8.4, and 9.0 µJ/cm², achieved by using 5, 10, and 15 cycles of critical state grating. The topological GMR holds promise for compact coherent sources.