Assisting the mode-locking of a figure-9 fiber laser by thermal nonlinearity of graphene-decorated microfiber.

The self-starting performance of a figure-9 fiber laser is critically dependent on the phase shift difference between the counter-propagating beams. Herein, we propose an effective approach to dynamically control the phase shift difference in a figure-9 fiber laser by utilizing the thermal nonlinearity of graphene-decorated microfiber device. With the adjustment of the control laser power injected into the graphene-decorated microfiber, the self-starting mode-locked threshold of the figure-9 fiber laser can be attained in a flexible pump power range, i.e., from 300 mW to 390 mW. These findings demonstrated that the graphene-decorated microfiber could act as a dynamical control device of phase shift difference for improving the performance of figure-9 fiber lasers, and might also open up new possibilities for applications of microfiber photonic devices in the field of ultrafast optics.