In-amplifier soliton self-frequency shift optimization by pre-chirping - experimental demonstration

Soliton self-frequency shift (SSFS) is a fundamental mechanism of optical wavelength conversion and supercontinuum generation. Often, it is desirable to use a nonlinear propagation design that provides a large amount of SSFS, leading to wavelength conversion with a large frequency offset or leading to a broad supercontinuum generation. The most effective approach to enhance SSFS is using an amplifying medium. In this context, it was theoretically predicted that a pre-amplified seed pulse should be chirped to maximize the extent of SSFS. Here, we make the experimental verification of this claim. For this purpose, a chirped seed pulse at a wavelength of 1880 nm is amplified and experiences SSFS in a Tm³⁺-doped fiber amplifier. The resulting soliton reaches a final wavelength that is tuned by adjusting the energy and chirp of the pre-amplified seed pulse. The experiment demonstrates that SSFS and energy conversion efficiency are maximized when the pre-amplified seed pulse is chirped at C₀ ≈ 0.65 g_D, where g_D is the total gain over one dispersion length. This research provides a fundamental conclusion for optimizing SSFS processes using any amplifying medium and finds applications for large offset wavelength conversion and broadband supercontinuum generation.