The objective of the study is to optimize the optical fiber structure for mode-division multiplexing systems using nanostructurization. The nanostructuring technique allows to fabricate fibers with arbitrarily designed (free-form) refractive index distribution based on two glasses. Three optimization schemes have been proposed. The nanostructuring method allows for designing fibers with optical properties similar and even better parameters impossible to produce by other methods. In this proposal, we examined four linearly polarized (LP) few-mode fibers. We report a high effective refractive index difference between modes while maintaining other important parameters for the weakly coupled approach.