Fig. 1. (a) Typical Raman gain spectrum of phosphosilicate fiber [27]. (b) The Raman output spectra of the phosphosilicate fiber we used under different pump powers.

Fig. 2. Experimental setup of our low-quantum-defect Raman fiber laser. ASE, amplified spontaneous emission; HR, highly reflective; FBG, fiber Bragg grating; LR, low reflective.

Fig. 3. (a) Spectral evolution of the oscillator-pumped Raman fiber laser. (b) Spectral evolution of the ASE-source-pumped Raman fiber laser. (c) Temporal behaviors of the oscillator and ASE source under the same power level.

Fig. 4. (a) Total output, Raman output, and residual pump power of the ASE-source-pumped Raman fiber laser as a function of pump power. (b) Output spectrum of the ASE-pumped Raman fiber laser with a spectral purity of 96.03% (inset: the corresponding output spectrum in linear scale).

Fig. 5. (a) Threshold power, maximum Raman output power, and (b) corresponding output spectra at the same pump level of the ASE-source-pumped Raman fiber laser under different pump wavelengths.