All-fiber dissipative soliton resonance mode-locked figure-9 thulium-doped fiber laser

Dissipative soliton resonance (DSR) fiber mode-locked lasers (MLL) are attracting a steadily growing interest over the recent years, due to their ability to generate relatively long (ns-scale), strongly chirped and large energy pulses directly inside a main oscillator. Thulium-doped fiber (TDF) DSR MLLs, optionally enhanced with amplification and compression stages, are in high demand in various application areas in 2-μm spectral region, like surgery, LIDAR and remote sensing, microscopy, etc. Figure-8 (F8) TDF laser, emitting 20 nJ pulses from net-normal-dispersion cavity, was demonstrated [1]. More advanced total-anomalous-dispersion F8 cavity, involving double-clad (DC) TDF and two-stage post-amplification, was used to obtain a pulse energy of 66 μJ [2]. The nonlinear amplifiying loop mirror (NALM) was exploited in both experiments as a mode-locking element. Being mainly fiber-based, above-mentioned configurations include some inherently free-space components, such as isolators, which have lower damage threshold, comparing to all-fiber elements. In this paper, we demonstrate the first truly all-fiber figure-9 (F9) DSR TDF laser that emits nanosecond pulses with energies up to 400 nJ, which is to the best of our knowledge a record value of the energies, extracted directly from the DSR oscillator at 2 μm.