Buildup of incoherent dissipative solitons in ultrafast fiber lasers

The self-formation of incoherent laser pulses appears paradoxical, involving both a strong instability and a temporal localization process. Incoherent pulse regimes are nevertheless recurrent within ultrafast fiber laser dynamics. In this paper, we bring decisive experimental data, by recording in real time the buildup dynamics of incoherent pulses under different cavity dispersion regimes. Our measurements highlight different dominant mechanisms at play. Whereas soliton pulse shaping contributes to creating a chaotic bunch of pulses in the anomalous dispersion regime, incoherent pulses in the normal dispersion regime follow strongly turbulent dissipative dynamics. Numerical simulations reproduce qualitatively well the final buildup stage of observed dynamics. By displaying common dynamical features as well as disparities, these results support the development of a general concept of incoherent dissipative solitons.

Figure 1

Schematic of the ultrafast fiber laser experiment. EDF: erbium-doped fiber; DCF: dispersion-compensation fiber; ISO: polarization-independent isolator; PC: all-fiber polarization controller; PBS: polarization beam splitter; OC: optical coupler; PD: fast photodiode; OSA: optical spectrum analyzer.

Figure 2

Buildup dynamics of an incoherent short pulse in the normal dispersion cavity regime. Temporal evolution of (a) optical pulse intensity (in color scale); (b) normalized intracavity energy (violet line) and pulse peak intensity (brown line); (c) DFT output (optical intensity, in color scale) zoomed in (e). (d) Evolution of the peak intensity for the dominant pulse (A, amber) and for a competing pulse precursor (B, green). (f) Optical intensity distribution at the first round trip (RT 1); (g) single-shot spectrum at RT 2300 (blue curve), compared with the average of 500 consecutive single-shot spectra (orange) and the OSA-recorded spectrum (red); (h) multishot optical autocorrelation.

Figure 3

Buildup dynamics of an incoherent short pulse in the anomalous dispersion cavity regime. Evolution of (a) pulse intensity; (b) intracavity energy (violet) and pulse peak intensity (brown); (c) DFT output (in color scale). (d) Evolution of the peak intensity, for pulse precursors A and B; (e) magnification of the DFT trace; (f) initial intensity distribution; (g) single-shot spectrum at RT 4000 (blue curve) and the averaging of 500 consecutive spectra (orange) compared with the averaged spectrum recorded by the OSA (red); (h) averaged optical autocorrelation.

Figure 4

Simulation results of incoherent pulse buildup in the normal dispersion cavity regime, with $P_i=45\mathrm{mW}$ and $P_{\mathrm{sat}}=10\mathrm{W}$. (a) Temporal (see also video in Supplemental Material [38]) and (b) spectral evolution from the initial noise that is displayed on the bottom row. Top row: quasistationary chaotic regime. (c) Temporal intensity profile at some characteristic round trip times (RT). (d) Optical spectrum and (e) autocorrelation trace averaged over the 500 last cavity round trips.

Figure 5

Simulation results of incoherent pulse buildup in anomalous dispersion laser cavity at $P_{in}=55\mathrm{mW}$ and $P_{\mathrm{sat}}=10\mathrm{W}$. (a) Temporal (see also video file in Supplemental Material [38]) and (b) spectral evolution from noise displayed in the bottom rows. The top rows display the field characteristics at round trip 1000. (c) Temporal evolution at some characteristic round trip times (RT). (d) Optical spectrum and (e) autocorrelation trace averaged over the 500 last cavity round trips.