Pushing the limits of environmentally stable fibre lasers: 120 fs, 4.2 nJ, all-PM all-fibre

As research and industrial applications of laser systems get more advanced, the pressure to enhance the performance of the front-end oscillators becomes more intense. In the past decade a huge leap in the improvement of the stability and overall environmental robustness has come from fibre-based lasers. Using new designs for the fibre geometry and the laser cavities, this technology is now on par with, or even surpasses in some cases, bulk lasers. However, the majority of the proposed fibre-based oscillators are limited in energy or do not fully profit from the benefits of the waveguide medium such as alignment-free operation and environmental stability since they host free space elements. The laser cavity holding the record for the shortest pulse duration from a fibre-based oscillator is a good illustration of the aforementioned trend [1]. Indeed, these pulses were generated in a dispersion-managed cavity consisting mostly of free-space components and their energy was restricted to 0.7 nJ. The limited scalability of pulse energy in fibre-based lasers has recently been overcome thanks to the use of cavities built exclusively of normal-dispersion elements (ANDi lasers), and several mode-locking techniques have been successfully demonstrated with this design [2-6]. So far, however, each have failed in delivering extremely short pulses with several nJ pulse energy while simultaneously maintaining the environmental robustness innate for all-fiber all-polarization maintaining (PM) cavities.