Spatial and Spectral Mode-Selection Effects in Topological Lasers with Frequency-Dependent Gain

Topological lasers are a new promising class of devices that exploit the protected edge modes of topological insulators for coherent light emission with unprecedented properties^1,2. A common scheme to select the edge mode is to use a pump spatially localized on the border¹; however, by going beyond the standard theory of broadband gain^3,4 we have recently shown⁵ that a narrowband gain allows to promote lasing of a topologically protected edge mode even with a spatially uniform pumping, provided that the gain is centered in the topological bandgap. In this work we lift these requirements; by building a phase diagram of our topological laser, we show indeed that lasing into a topologically protected edge mode can be promoted even in the case of a spectrally wide gain centered at a bulk band frequency. Our scheme exploits the presence of an active, topologically trivial region surrounding the topologically non-trivial one; such a mechanism may provide an explanation to pioneering experimental observations² that still await theoretical interpretation.


References

1. Bandres et al, Science. 359, eaar4005.
2. Bahari et al, Science. 358, 636.
3. Harari et al, Science. 359, eaar4003.
4. Seclì, Capone, and Carusotto, PRResearch. 1, 033148.
5. Seclì and Carusotto, CLEO/Europe-EQEC 2019.