Fig. 2.

Topological laser action. a Lasing spectrum of the structure of the topological hybrid silicon microlaser as a function of the pumping power much below the threshold (top panel), approaching the threshold (middle panel) and well above the threshold (bottom panel). As expected, as the pump power is increased, the output emission experiences a transition from broadband photoluminescence to a single narrow band lasing with an increased extinction ratio. b Pump dependence of the laser emission intensity, demonstrating the fingerprint of single-mode lasing: only one threshold with no other kinks in the light–light curve. Blue dots are experimental data and the red lines are linear fits with least squares of the data before and after the lasing threshold, respectively