Research On 2 μm Femtosecond Pulse Fiber Lasers Based On Raman Soliton Self-frequency Shift

Recently, femtosecond pulse fiber lasers around 2 μm become research hotspots because they have various applications in industrial process controlling, atmosphere monitoring, toxic gases detecting, biotherapy, national defense, optical sensing and optical imaging. A few methods have been used to realize femtosecond pulse fiber lasers around 2 μm including mode-locking, optical parametric generation, Raman soliton self-frequency shift, and so on. Compared with others, femtosecond pulse fiber lasers around 2 μm based on Raman soliton self-frequency shift work in a broaden wavelength-tuning range, are easy to implement an all-fiber structure, are low-cost, and they can generate high-power femtosecond pulse without pedestal.It is easy to realize Raman solitons around 2 μm in non-silica fibers. However, the non-silica fiber and silica fiber have different melting temperatures usually, it is difficult to weld them together. So it is difficult to realize all-fiber wavelength-tunable femtosecond pulse fiber lasers around 2 μm. We obtained wavelength-tunable Raman solitons in single-mode step-index silica fibers. And we realized all-fiber wavelengthtunable femtosecond Raman soliton lasers around 2 μm based on soliton self-frequency shift(SSFS), and did the theoretic, simulated, and experimental research on them.Firstly, we introduced the principle of SSFS and the impact factors on SSFS generation such as soliton generation, Stimulated Raman Scattering and high-order soliton splitting. By the processes of deducing and solving Generalized Nonlinear Schr?dinger Equation(GNLSE), we explored how pump parameters and fiber parameters impact SSFS generation in single mode silica fibers. And by using highpower 1.56 μm femtosecond fiber laser from Chirped Pulse Amplication(CPA) system to pump highly nonlinear single step-index silica fibers, and achieved “pure” Raman solitons which tunable wavelength is in range of 1584 nm to 1965 nm. Further, we obtained Raman soliton at 1982 nm by increasing the power of pump laser. After filtering, the Raman soliton was injected the amplifier then the output power of Raman soliton was upto 860 m W, the pulse width was 560 fs correspondingly.