We obtain a hierarchy of nonlinear evolution equations with self-consistent source related to the Wadati-Konno-Ichikawa type spectral problem. The modified NLS equation with a source, which describes the ultrashort light pulse propagation in a nonlinear single-mode optical fiber with resonant impurities, is shown to be a gauge-transformed member of the hierarchy. The soliton solution for this equation is found. © 1995.
Doktorov, E. V., & Shchesnovich, V. S. (1995). Nonlinear evolutions with singular dispersion laws associated with a quadratic bundle. Physics Letters A, 207(3–4), 153–158. https://doi.org/10.1016/0375-9601(95)00678-V