Non-uniform modal power distribution caused by disorder in multimode fibers

TL;DR

This work shows that disorder-induced random modal coupling in graded-index multimode fibers drives the system toward steady-state, non-uniform modal power distributions that favor lower-order groups. By combining four approaches—GNLSE-based simulations with disorder, a power-flow model, classical linear-regime experiments, and quantum single-photon experiments—the authors demonstrate that these distributions are robust to MDL and are well described by a weighted Bose–Einstein law, revealing an ergodic-like redistribution of power across modal groups. The findings bridge classical and quantum regimes, highlighting implications for multimode fiber thermodynamics and potential quantum information applications. Collectively, the results establish a universal, disorder-driven mechanism for energy allocation among fiber modes and provide a quantitative framework for predicting modal power distributions in complex MMF systems.

Abstract

The evolution of modal crosstalk in multimode fibers is investigated using four different experimental and numerical approaches. Results converge to demonstrate that the fiber disorder alone is capable of generating steady states characterized by non-uniform modal power distributions, which promote the lower-order modes at the expenses of the higher-order ones and are properly described by a weighted Bose-Einstein law.

Figures (11)

• Figure 1: The experimental setup for the linear regime.
• Figure 2: Experimental output fractional modal power normalized to insertion and modal loss, when individual groups or all input modes are excited.
• Figure 3: Experimental mean modal power fraction of the output groups after uniform excitation of the input modes. A wBE fit is also shown.
• Figure 4: Simulated input and output modal energy distributions when input group $10$ is launched.
• Figure 5: Average modal energy in groups $1$, $5$ and $10$ vs. distance, in the simulation of Fig. \ref{['fig4']}.