Far-detuned frequency conversion beyond 3500 nm in a few-mode graded-index silica fiber

We present both theoretical and experimental evidence of far-detuned nonlinear wavelength conversion towards the mid-infrared, namely beyond 3500 nm, in a few-mode graded-index silica fiber pumped at 1064 nm. Intramodal and intermodal four-wave mixing processes are carefully analyzed by means of the frequency-dependent propagation constants.