Here we present the ability of Nd3+-doped zinc-phosphate glasses to be shaped into rectangular core fibers. At first, the physico-chemical properties of the developed P2O5-based materials are investigated for different concentrations of neodymium oxide and core and cladding glass compositions are selected for further fiber development. A modified stack-anddraw technique is used to produce multimode large rectangular-core optical fibers. Self-guided nonlinear effects acting as spatial beam reshaping processes occurring in these newly-developed photonic structures lead to the generation of spectral broadenings in the visible and near-infrared spectral domains.