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.