Efficient one-third harmonic generation in highly Germania-doped fibers enhanced by pump attenuation

We provide a comprehensive study on one-third harmonic generation (OTHG) in highly Germania-doped fiber (HGDF) by analyzing the phase matching conditions for the step index-profile and optimizing the design parameters. For stimulated OTHG in HGDF, the process can be enhanced by fiber attenuation at the pump wavelength which dynamically compensates the accumulated phase-mismatch along the fiber. With 500 W pump and 35 W seed power, simulation results show that a 31% conversion efficiency, which is 4 times higher than the lossless OTHG process, can be achieved in 34 m of HGDF with 90 mol. % GeO2 doping in the core.