Principal modes in multimode fibers: exploring the crossover from weak to strong mode coupling

TL;DR

This paper investigates how principal modes in multimode fibers transition from weak to strong mode coupling through experiments and simulations, revealing their spectral characteristics and potential for advanced optical applications.

Contribution

It introduces a comprehensive study of principal modes under varying mode coupling regimes, highlighting the transition mechanisms and effects of mode-dependent loss.

Findings

Principal modes exhibit distinct spatial and spectral features in different coupling regimes.

Bandwidth of principal modes depends on delay time and mode-dependent loss.

Two mechanisms govern principal mode bandwidths in weak and strong coupling regimes.

Abstract

We present experimental and numerical studies on principal modes in a multimode fiber with mode coupling. By applying external stress to the fiber and gradually adjusting the stress, we have realized a transition from weak to strong mode coupling, which corresponds to the transition from single scattering to multiple scattering in mode space. Our experiments show that principal modes have distinct spatial and spectral characteristic in the weak and strong mode coupling regimes. We also investigate the bandwidth of the principal modes, in particular, the dependence of the bandwidth on the delay time, and the effects of the mode-dependent loss. By analyzing the path-length distributions, we discover two distinct mechanisms that are responsible for the bandwidth of principal modes in weak and strong mode coupling regimes. Taking into account the mode-dependent loss in the fiber, our numerical results are in good agreement with our experimental observations. Our study paves the way for exploring potential applications of principal modes in communication, imaging and spectroscopy.