Bend-resolved modal basis extraction in multimode fibers

We present a model-free framework for extracting a~deformation-resolved modal basis in bent multimode fibers using a two-stage singular value decomposition of speckle field correlation matrices. The resulting data-driven basis captures dominant optical field variations across controlled mechanical deformations and enables robust tracking of modal transformations without requiring prior knowledge of the fiber’s structural or modal properties. Its robustness is experimentally verified using spatially localized diffraction-limited excitations, including orbital angular momentum carrying beams, demonstrating resilience to coupling-condition variations, with residual differences confined to basis-vector permutations arising from near-degenerate singular values. The framework supports distributed sensing, network resilience, and predictive fault diagnostics, with potential integration into mode-division multiplexing systems. Its statistical structure suggests extensibility to other complex scattering environments, including atmospheric turbulence in free-space optical systems.