Experimental investigation on mode instability phenomenon of a fiber ring laser

Mode instability phenomenon acts as a common feature in single-frequency fiber ring lasers. Pump power and cavity length are two important control parameters affecting the output SLM stability. In this work, mode instability of an EDFRL has been experimentally investigated by utilizing two effective methods. On the whole, a mode stability map of the EDFRL scaled by pump coefficient is measured and discussed completely through the interferometer scheme, which helps to evaluate the mode stability dependent on pump power in a form of global visualization. Besides, real-time and detailed detection of various mode instability behaviors, including occasional mode hopping, periodic mode hopping and intermittent MLM oscillation, is carried out using the optical heterodyne scheme. The dynamics of mode instability can also be visualized by on-line time-frequency diagrams. This work will contribute to the analysis, understanding and suppression of mode hopping in fiber ring lasers.