Accessing different higher-order modes with nonlinear modal energy transfer under simple, realistic tuning of initial conditions

The initial conditions in multi-mode fibers pumped by ultrashort laser pulses strongly determine the following nonlinear optical interactions. In this work, we firstly compare the detailed spatial mode content of simple initial conditions, transverse offset, and tilt. We then show how those initial conditions can both be used to achieve a nonlinear modal energy transfer into higher-order spatial modes of a model graded-index fiber, with their own slight differences and advantages. Going beyond purely spatial initial conditions, we introduce nonlinear modal energy transfer results using spatial chirp at the input facet, whereby the different temporal envelopes of the spatial modes allow for tuning the nonlinear modal energy transfer process. Our results open up investigations into higher-dimensional tuning of nonlinear processes in multi-mode fibers using initial conditions.