Loss Compensation Symmetry for TE Modes of Asymmetrical Optical Coupler with Gain and Loss

By exploiting recent advances in optical couplers, we introduce the concept of a quasi-PT-symmetric lasing system with balanced gain and loss. Loss compensation (LC) symmetry is investigated for an asymmetric waveguide coupler composed of two unequally sized cylinders with gain and loss. It is shown that the LC-symmetric threshold (exceptional point) exists for the TE operating modes of the coupler provided that the constitutive parameters and dimensions of the coupler are properly selected.