Coherent pulse generation based on noise-like-pulse pumped Raman amplification

•Efficient conversion from NLP to coherent pulse via stimulated Raman scattering.•Raman pulse suffers from distortions in shape and phase due to SRS and XPM.•Strong walk-off effect can effectively suppress the deterioration of Raman pulse.•Large normal dispersion is firstly used as the Raman gain medium.•NLP-pumped Raman fiber laser without a SA can generate coherent Stokes pulse. The coherent Raman pulse generation based on the noise-like-pulse (NLP) pumped Raman amplification is numerically investigated in the cases with weak and strong walk-off effects between the pump and Stokes pulses. In the former case, the amplified Stokes pulse suffers from the temporal and spectral distortions because the random time-varying intensity profile of the NLP can be transferred to the Stokes pulse through combined effects of cross-phase modulation (XPM), stimulated Raman scattering (SRS), and spontaneous Raman scattering. In the latter case, the heavily germanium-doped fiber with large normal dispersion is firstly used as the Raman gain medium to improve the walk-off effect and Raman gain. As a result, the Stokes pulse can be amplified undistorted and possess linear frequency chirp and conversion efficiency of up to 82.4 %. Further, it is important to note that the NLP-pumped Raman fiber laser based on the large normal dispersion fiber can generate the Stokes pulse with linear frequency chirp, narrow temporal duration, and dissipative-soliton-like spectrum with steep edges, even though the saturable absorber is not introduced into the Raman fiber cavity.