Watt-Level Ultrafast Fiber Laser Based on Weak Evanescent Interaction With Reduced Graphene Oxide

We propose a Watt-level, all-fiber, ultrafast Er/Yb-codoped double-clad fiber laser mode-locked by reduced graphene oxide (rGO) interacting with photonic crystal fiber (PCF) ultraweakly. The rGO solution is filled into the cladding holes of PCF, and after evaporation, the rGO flakes, contributing saturable absorption and high nonlinearity, interact with a light intensity of only 1/107 of that in the center of PCF. This ultraweakly interacting structure can enhance the thermal damage threshold and decrease the accumulated nonlinearity, which is proved to be an excellent choice for high-power mode-locked laser. By incorporating the saturable absorber into an Er/Yb-codoped fiber ring cavity, stable soliton laser with femtosecond duration is generated, and harmonic mode-locking is formed when increasing pump strength. The maximum average power of 1.14 W is obtained. To the best of our knowledge, this report is the highest power obtained directly from an all-fiber, graphene-mode-locked laser system operating with fundamental transverse mode. In addition, the experimental results demonstrate that our proposed structure is effective in generating high-power pulses when some other materials are used, including but not limited to graphene oxide, carbon nanotubes, topological insulator, or metal nanoparticles.