Demonstration of broadband inter-modal four-wave mixing in graded-index few-mode fibers

We experimentally demonstrate broadband four-wave mixing (FWM) between two spatial modes of a 5-km-long few-mode fiber. We show that, in contrast to FWM in single-mode fibers, inter-modal FWM (IM-FWM) can be better phase matched for waves well separated in frequency (a few THz) than when they are closely spaced (tens of GHz).