Unidirectional mode coupling in Non-Hermitian Waveguides

We propose an all optical control of the mode dynamics in GRaded INdex ( multimode waveguides, by a Non Hermitian ( potential (simultaneous modulation of the refractive index and of the gain/loss coefficient) Such potential induces a unidirectional mode coupling Depending on the modulation parameters it yields to the enhancement/ reduction of the excitation of higher order transverse modes 1 2 3 In the latter case, this leads to an all optical mode cleaning. Theproposal is supported by analytical predictions based on a coupled mode theory for 1 D waveguides, which is numerically proven solving the wave propagation equation The proposal is generalized to the more involved case of 2 D waveguides for different geometries controlling the unidirectional mode coupling and final beam shape. 4