Sech-Shape Time-Stretched Dissipative Solitons in Anomalous Dispersion Cavity Fiber Lasers

New pulse dynamics, which generates time-stretched dissipative soliton, has been analyzed in theory and demonstrated in experiment. With introducing non-equilibrium saturable absorber (SA) into the laser cavity, the time-dependent loss of SA can balance the intracavity dispersion, while gain and nonlinearity assist to stabilize the pulse. The pulse envelop is in exact sech-shape and the duration can be stretched to sub-microsecond by the cavity dispersion. To verify the dynamics, a mode-locked Er-doped fiber laser (EDFL) is fabricated, in which a piece of Tm-doped fiber (TDF) serves as the non-equilibrium SA. The laser delivers stable nanosecond pulse and its temporal intensity is in exact sech ² shape. The pulse duration is invariant with the pump power but determined by the cavity length. As large as 155nJ mode-locked pulse has been generated. Furthermore, such mode-locked pulse can serve as ideal pump source to optical parametric oscillators, and will have wide applications in optical communication, material processing and biomedicine technology.