I am sorry, I thought you are interested in gain flattening filters. For the example shown in the tutorial (RA Optimizing pump power and frequencies – Average model.osd) a Multi-parameter multi-target optimization process (MPO) is used. This is based on nonlinear least-squares implementation. Details on the optimization process is described on page 191 in the User Reference document. You may find this document in the attached documents with OptiSystem software.
regards,
Ahmad