Fig. 3.

Intrinsic single-supermode topological laser action. a Multimode lasing from an identically sized microlaser array as the topological microlaser, but without on-top Cr deposition on every second ring to introduce the distributed gain/loss profile. b Measured lasing mode profile of the topological microlaser without on-top Cr deposition. c Single-supermode lasing from the topological microlaser under the same pumping condition. d Measured lasing mode profile of the topological microlaser with the distributed gain/loss profile. The broad spectrum in a is due to mode competition between the transverse and longitudinal modes of the single-ring resonators, each of which forms its own collective state. In c, the distributed gain and loss judiciously spoils the quality factors of the strongly hybridised modes, topologically favoring only the zero mode centred around λ = 1523 nm