ABSTRACT
Q-switching and mode-locking are mainly two methods to realize ultrashort pulse laser. Q-switching could generate output pulse with width in the ms and ns, which has the characteristics of high- pulse energy. Many ways are available for integrating a graphene saturable absorber into the laser cavity; the most commonly used is the sandwich structure. Graphene has considerable modulation depth, and the characteristics of working in wideband fully meet the requirements of making Q-switching devices. Being similar to a fiber mode-locked laser, the sandwich structure is the main way to integrate graphene into the Q-switching fiber laser cavity. With the improvement in production process and properties, the indicators of lasers based on graphene also constantly improved, embodied as extended working wavelength, bigger output power, shorter pulse width, and higher repetition rate. The modulation depth can be improved if the number of graphene layers is increased. Unsaturated optical loss is increased with an increase in the number of layers.
