Fig. 1. (a) Experimental setup of the high-peak-power RFL. (b) Simplified operation-principle diagram for generation of the visible-NIR Raman comb. LD, laser diode; FBG, fiber Bragg grating.

Fig. 2. (a) Output characteristics of the RFL as a function of pump power. Inset (from left to right): temporal pulse profiles in the mode-locking, hybrid and random Q-switching states, respectively. Zoomed-in view of the mode-locked pulses (b) and the consumed mode-locked pulses (c) in the hybrid state. (d) Zoomed-in view of the self-Q-switched pulses.

Fig. 3. Temporal characteristics of the RFL in the random Q-switched state. (a), (b) Different transient single-pulse profiles and the 128-times averaged pulse shape under the pump power of 3.35 W, respectively. Inset: zoom-in of the dashed-line denoted part of the pulse. (c) Repetition rate (the error bar shows the standard deviation) and pulse duration versus launched pump power. (d) Pulse energy and peak power versus launched pump power. The inset shows a microscopic image of the gain-fiber damage.

Fig. 4. (a) Visible-NIR Raman comb spectrum in a linear scale under the pump power of 3.35 W. The inset shows the diffracted intensity distribution of visible light. (b) Single-pulse profile of the visible-NIR Raman comb. The inset shows the transverse intensity distribution of the visible beam. (c), (d) Several filtered visible spectral components and the corresponding single-pulse profiles.

Fig. 5. Long-wavelength spectrum of the RFL under the pump power of 3.35 W from (a) the forward direction and (b) the backward direction. (c) Long-wavelength spectral profiles and (d) single pulses of the spectrally filtered-out components (according to different Stokes orders) of the RFL under the pump power of 3.35 W.