High-gain far-detuned nonlinear frequency conversion in a few-mode graded-index optical fiber

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  \(\upmu \hbox {m}\) $\mathrm{\mu }\text{m}$ , and more specifically achieving gains of hundreds of dB per meter below 0.65  \(\upmu \hbox {m}\) $\mathrm{\mu }\text{m}$ and beyond 3.5  \(\upmu \hbox {m}\) $\mathrm{\mu }\text{m}$ . Interestingly, our findings highlight the potential of graded-index fibers for enabling high-gain wavelength conversion into the strong-loss spectral region of silica. Such advancements require an accurate interpretation of intramodal and intermodal four-wave mixing processes.