  Single-mode operation is a desirable but elusive property for lasers
operating at high pump powers. Typically, single-mode lasing is attainable
close to threshold, but increasing the pump power gives rise to multiple lasing
peaks due to inter-modal gain competition. We propose a laser with the opposite
behavior: multi-mode lasing occurs at low output powers, but pumping beyond a
certain value produces a single lasing mode, with all other candidate modes
experiencing negative effective gain. This behavior arises in a lattice of
coupled optical resonators with non-fine-tuned asymmetric couplings, and is
caused by an interaction between nonlinear gain saturation and the
non-Hermitian skin effect. The single-mode lasing is observed in both frequency
domain and time domain simulations. It is robust against on-site disorder, and
scales up to large lattice sizes. This finding might be useful for implementing
high-power laser arrays.
