Evidence of dark solitons in all-normal-dispersion-fiber lasers

In a recent paper we reported dark pulse emission of an all-normal-dispersion-fiber laser [Zhang, Tang, Zhao, and Wu, Phys. Rev. A 80, 045803 (2009)]. However, the formation mechanism of the dark pulse in the laser was unclear due to the limited temporal resolution of the measurement system. Using an improved detection system we have further investigated the phenomenon. We not only experimentally, unambiguously confirmed the existence of dark solitons in the fiber laser, but also identified that the dark pulses observed previously were bunches of the dark solitons. Moreover, we show that the dark soliton formation is a generic feature of the all-normal-dispersion-fiber lasers.

Figure 1

A train of the dark pulse emission of the fiber laser. Upper trace: laser emission measured with 33-GHz detection bandwidth; lower trace: laser emisison measured with 1-GHz detection bandwidth.

Figure 2

Oscillscope traces of the laser emission under different pump power. (a) ∼68 mW, (b) ∼100 mW, (c) ∼400 mW, (d) ∼700 mW. Upper trace: laser emission. Lower trace: reference signal showing system noise level.

Figure 3

Optical spectra of the laser under cw and dark pulse emissions.

Figure 4

Zoom-in of the laser emission. (a) Oscilloscope trace measured with 33-GHz bandwidth. (b) Oscilloscope traces measured with 5- and 10-GHz bandwidth. Upper trace: laser emission. Lower trace: reference signal showing system noise level.

Figure 5

A typical state of the dark soliton operation of the fiber laser numerically calculated. (a) The evolution of the dark soliton with the cavity round trips; (b) the soliton pulse profile; (c) the corresponding soliton spectrum.