Translation of nonlinear phenomena from GRIN fibers to large GRIN waveguides

Determine how nonlinear phenomena observed in graded-index multimode optical fibers—particularly spatial beam self-cleaning—translate to propagation in large graded-index waveguide rods with millimeter-scale cores that support approximately 10^5 transverse modes and exhibit negligible modal dispersion.

Background

The paper contrasts standard GRIN fibers, where modal dispersion and interference shape nonlinear dynamics, with large GRIN rods that have negligible modal dispersion and nearly perfect self-imaging. Prior studies have documented effects such as beam self-cleaning in fibers, but whether and how these effects persist or change in the many-mode, low-dispersion limit of GRIN rods was explicitly highlighted as unknown.

The authors present experiments showing Gaussian-beam stability and off-axis beam cleaning in GRIN rods, offering partial insight. However, the general translation across different nonlinear phenomena and conditions remains a stated open question.