Non-Hermitian Mode Cleaning in Periodically Modulated Multimode Fibers

TL;DR

This paper demonstrates that periodic modulation of multimode fibers can induce unidirectional mode coupling, enabling effective mode cleaning and potentially producing single-mode output through a combination of analytical predictions and numerical simulations.

Contribution

It introduces a novel method of mode cleaning in multimode fibers using non-Hermitian, periodic modulation to control mode excitation.

Findings

Unidirectional mode coupling can be achieved via periodic modulation.

Mode cleaning to single-mode output is theoretically predicted.

Numerical simulations confirm the analytical predictions.

Abstract

We show that the simultaneous modulation of the propagation constant and of the gain/loss coefficient along the multimode fibers results in unidirectional coupling among the modes, which, depending on the modulation parameters, leads to the enhancement or reduction of the excitation of higher order transverse modes. In the latter case, effective mode-cleaning is predicted, in ideal case resulting in single-mode spatially coherent output. The effect is semi-analytically predicted on a simplified Gaussian beam approximation and numerically proven by solving the wave propagation equation introducing the modulated potential.