High-gain far-detuned nonlinear frequency conversion in optical fibers: intramodal vs. intermodal processes

We present theoretical and experimental evidence of high-gain far-detuned nonlinear frequency conversion, extending towards both the visible and the mid-infrared, in a few-mode graded-index silica fiber pumped at 1.064 μm, and more specifically achieving gains of hundreds of dB per meter below 0.65 μm and beyond 3.5 μm. Our findings highlight the potential of graded-index fibers in terms of strong modal confinement over an ultrabroad spectral range for enabling high-gain wavelength conversion. Such advancements require an accurate interpretation of intramodal and intermodal four-wave mixing processes.