Mode-cleaning in Non-Hermitian Fibers and Waveguides

We propose an all-optical control of the mode dynamics in multimode waveguides, by simultaneous modulation of the refractive index and of the gain/loss coefficient. The induced unidirectional mode-coupling, yields to the enhancement or reduction of the excitation of higher order transverse modes, depending on the modulation parameters [1, 2]. In the latter case, the all-optical mode-cleaning is observed. We analytically predict the effect on a coupled mode theory for 1D waveguides, which is numerically proven solving the wave propagation equation. The proposal is generalized to the more involved case of 2D waveguides for different geometrics.