PT-symmetry of multimode waveguides: A tool for multichannel communication

The idea of Parity-Time symmetry is to exploit the special eigenvalues of coupled modes experiencing a map of balanced gain and losses. We consider multimode waveguides with transverse PT-symmetry, hence we have N parallel stripe pairs (one gain stripe and one loss stripe) in the waveguide. The evolution of eigenmodes and eigenvalues in clusters of 2N modes that undergo N successive exceptional points is evidenced for realistic and idealised structures. Targeting a regime just above an exceptional point allows a pair of modes to be selected. We show the potential for selecting such modes with a good rejection against other modes, in comparison of non PT-symmetric schemes. This could become a tool for multichannel communication.