Synchronous multi-wavelength mode decomposition in few-mode fiber using multi-modal ptychography

Space-division and wavelength-division multiplexing require synchronous multiwavelength modal characterization in few-mode fibers, but single-wavelength methods are limited by spectral mixing, increased modal density, and wavelength-dependent distortions. We experimentally demonstrate synchronous multiwavelength mode decomposition in a few-mode fiber using a multimodal ptychographic iterative engine (SMW-MM-PIE). Using a static imaging system, the method reconstructs complex fields at four wavelengths from a single acquisition without mechanical realignment. Based on an established incoherent intensity-sum constraint, the framework integrates spectral decoupling, digital refocusing, scale compensation, and phase-guided cross-correlation registration for wavelength-resolved modal projection. The reconstructed fields show intensity correlation coefficients above 0.97 with their LP-basis projections at all wavelengths, including 21-mode cases, and agree with single-wavelength results under identical excitation conditions.