Non-Hermitian mode-cleaning and flexible mode management in waveguide amplifiers

We propose a non-Hermitian intrinsic mode management mechanism for nonlinear parabolic waveguide amplifiers, based on an antisymmetric modulation of the refractive index and gain/loss profiles. This configuration induces asymmetric amplification and attenuation of mode amplitudes, enabling flexible and tunable control of the modal distribution. For specific non-Hermitian potentials, we demonstrate a significant increase in brightness by condensing photons into the fundamental Hermite mode, achieving efficient all-optical mode cleaning. The effect is analytically predicted, numerically confirmed, and remains robust against structural imperfections.