High-gain Far-Detuned Nonlinear Frequency Conversion in a Few-Mode Graded-Index Optical Fiber.

Abstract 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 $$\upmu \hbox {m}$$ μ m , and more specifically achieving gains of hundreds of dB per meter below 0.65 $$\upmu \hbox {m}$$ μ m and beyond 3.5 $$\upmu \hbox {m}$$ μ 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.