Tunable supercontinuum in multimode fiber via bending-induced dispersion modification

Nonlinear pulse propagation in multimode fibers (MMFs) offers a compact, low-cost route to broadband, tunable femtosecond light. Most control schemes act by changing the spatial mode composition, typically resulting in irregular or speckled beams in exchange for spectral tunability. Here, we introduce a complementary mechanism: bending-induced local dispersion modification of a high-order mode (HOM) to steer the spectrum while keeping the spatial mode fixed. We launch an LP 0,7 mode into a step-index MMF and apply programmable macrobends near the input. With a standard Yb pump at 1,030 nm, this yields spatially clean, continuous spectral tuning across 700–1,350 nm, while the output profile remains Bessel-like and robust to controlled bend reconfiguration. A perturbative model explains the observed spatial-spectral decorrelation, showing that moderate curvature produces first- and second-order shifts in group delay and group-velocity dispersion of the HOM with minimal change in modal composition; these dispersion shifts control soliton fission, dispersive-wave emission, and the soliton self-frequency shift. We further validate application utility by driving multicolor, extended-depth-of-focus multiphoton microscopy directly from this all-fiber source. Overall, we demonstrate bending-induced dispersion modification to tune the MMF supercontinuum spectra without sacrificing beam quality, providing an alternative pathway to tunable femtosecond illumination for imaging and spectroscopy.