Fig. 1. Operating principle and output characteristics of the incoherently pumped random fiber laser (not to scale).

Fig. 2. Output characteristics of the incoherently pumped random fiber laser. (a) Output powers of first-order Stokes light and residual pump light as functions of pump power. (b) Typical spectra of the backward first-order Stokes light at different pump levels. The spectra are recorded with a resolution of 0.02 nm. (c) FWHM linewidth of backward spectral envelope as a function of injected pump power. The circles indicate the average FWHM linewidth of 20 measurements. The corresponding error bars mark the variation range of FWHM linewidth at fixed pump level.

Fig. 3. Temporal characteristics and statistical features of output random laser. (a) and (b) Typical temporal trace of the output random laser around threshold. (c) Histograms (log scale) showing the distribution of optical intensity maxima for 105 trace events. The peak intensities are normalized by the corresponding SWH values. The vertical dashed lines indicate 2 × SWH and thus mark the limit for a pulse to be considered as an optical RW. (d) Evolution of consecutive traces around optical RW events at threshold. (e) Pulse shapes of typical normal and optical RW events.

Fig. 4. Long-term average power stabilities of output lasers and injected pump. The average powers are measured by power meters with 1 s/point resolution and half-hour recorded length.

Fig. 5. RF spectra of output random laser. (a) Long-span RF spectra (measured with a resolution of 1 kHz). (b) RF spectral envelopes corresponding to SBS effect (recorded with a resolution of 10 Hz). (c) Evolution of spectra from mass independent peaks to quasi-cw envelopes (measured with a resolution of 1 Hz). (d) Enlarged view of selected RF peaks around the lasing threshold.