It sounds like you’re looking for help with the from Govind Agrawal’s Nonlinear Fiber Optics (likely the 5th or 6th edition). This book is the standard graduate text, and its problems are notoriously math-heavy (involving coupled GNLSE, split-step Fourier, perturbation theory, etc.).
Derive the dispersion length (L_D = T_0^2/|\beta_2|) and nonlinear length (L_NL = 1/(\gamma P_0)). Problems Nonlinear Fiber Optics Agrawal Solutions
# Nonlinear step (half) A *= exp(1j * gamma * dz/2 * abs(A)**2) It sounds like you’re looking for help with