Fig. 1: Quasi PT-symmetric laser.
From: Single-mode quasi PT-symmetric laser with high power emission
The concept of quasi PT-symmetric edge emitting laser is implemented by detuned coupled waveguide cavities. The mode propagation constant, β, decreases with the mode number, while mode coupling is denoted by κ. Isospectral engineering via a careful choice of the cavity dimensions can enforce a resonant interaction between the second-order mode of the main potential and the fundamental mode of its lossy partner, thus establishing quasi or modal PT-symmetry. Electrical pumping of the main potential (waveguide) in this design can act as a modal filter allowing for single-mode lasing
