Input–output characteristics in forward direction (blue curves, see inset) show an up to one order higher output intensity compared to backward direction measurements (orange curves) in some pump power regimes. The curves stem from different spots on a coupled cavity device. All curves are shifted along x- and y-direction to coincide before lasing starts (green cross), see main text for further information. Pump power ranges for every curve from 10⁻¹ μW to 10² μW energy input into the sample.