  We report on the experimental generation of spatially multiplexed picosecond
40-GHz pulse trains at telecommunication wavelengths by simultaneous
intra-modal multiple four wave mixing and intermodal cross-phase modulation in
km-long bi-modal and 6-LP-mode graded-index few-mode fibers. More precisely, an
initial beat-signal injected into the fundamental mode is first nonlinearly
compressed into well-separated pulses by means of an intra-modal multiple
four-wave mixing process, while several group-velocity matched continuous-wave
probe signals are injected into higher-order modes in such a way to develop
similar pulsed profile thanks to an intermodal cross-phase modulation
interaction. Specifically, by simultaneously exciting three higher-order modes
(LP11, LP02 and LP31) of a 6-LP-mode fiber along group-velocity matched
wavelengths with the fundamental mode, four spatially multiplexed 40-GHz
picosecond pulse-trains are generated at selective wavelengths with negligible
cross-talks between all the modes.
