Fig. 1. (a) Experimental setup. LD pump, laser diode pump; HR FBG, high-reflectivity fiber Bragg grating; YDF, ytterbium-doped fiber; GDF, germanium-doped fiber; CPS, cladding power stripper. (b) Principle of SH gain and feedback. (c) Output SH laser facula after a cladding light stripper attached to the output. (d) GDF glowing visible light while the pump is injected.

Fig. 2. Measured spectra with the FW powers of (a) 0.65 W, (b) 13.6 W and (c) 20.88 W. (d) Comparison of SH band spectra with the FW powers of 13.6 and 20.88 W. (e) The SHG output power with the increase of FW power.

Fig. 3. Measured waveforms of the FW by (a) a Si-based detector and (b) an InGaAs-based detector.

Fig. 4. Temporal characteristics of the SH band with different FW powers. (a) Wide time range waveforms. (b) Histogram of the pulse intensity distribution. (c) Single waveform measurement result.

Fig. 5. Simulated (a) output spectrum and (b) spectral evolution along the passive fiber of the FW.

Fig. 6. Simulated (a) output spectrum and (b) spectral evolution along the passive fiber of the SH. (c) The SH conversion efficiency with different GDF lengths.