Ultrafast Fiber Laser Emitting at 2.8 µm Based on a SESAM and a Broadband FBG

Ultrafast mid-infrared fiber lasers have been intensely studied in the last decade for the generation of high harmonics, molecular spectroscopy, material processing and remote sensing. Different designs have been investigated but most of them lacked the ease of use and reliability needed for their democratization. In this paper, we demonstrate a self-starting mode-locked mid-IR erbium-doped fiber laser based on a SESAM and a broadband uniform FBG that produces pulses as short as 15 ps. Different laser cavities were tested with varying FBG peak reflectance, spectral bandwidth and active fiber length. In addition, one cavity uses a pump combiner instead of injecting free-space the pump power through the fiber tip. The results of this study confirm that the FBG spectral bandwidth can efficiently control the duration of the almost Fourier-transform-limited pulses up to a limit seemingly dictated by the presence of water vapor in the laser cavity acting as narrow spectral filters. To a lower effect, the active fiber length influences the pulse duration. Finally, the use of an all-fiber pump combiner allows for a more compact and rugged design without altering the laser performances. This study represents a step towards the development of robust mid-infrared ultrafast all-fiber lasers.