Novel effective spectrum broadening technology pumped by 2 μm picosecond laser for mid-infrared supercontinuum generation

Using thulium-doped fiber laser to pump fluoride fiber is one of the most common methods to generate mid-infrared supercontinuum (SC). But it is difficult to generate SC spectrum with wavelength more than 4 μm by directly pumping short fluoride fiber with 2 μm picosecond (ps) laser. Although some studies with SC exceeding 4 μm have also been reported, the proportion of spectral power in the long-wavelength region is not very high. To address this issue, a novel and simple approach to solve low peak power of 2 μm ps pump sources is introduced by adding a short piece of holmium-doped fiber. This method can make full use of the gain bandwidth of Ho3+ and soliton self-frequency shift effect to enhance soliton energy and promote spectral broadening. The effectiveness of the approach is verified by constructing a theoretical model to solve the generalized nonlinear Schrödinger equation. We demonstrate through simulations that addition of holmium-doped fiber can yield significantly improved output spectral range, power ratio in the long-wavelength region and optical–optical conversion efficiency compared to the previous technical. Especially, the implementation of the new technology can effectively expand the SC long-wavelength edge by ∼470 nm after applying a 3 dB gain, and can easily build a simple, compact and low-cost mid-infrared light source system.