Phase locking technique of fiber lasers by using a common ring cavity and its characteristics investigation

Passive phase locking of multiple fiber lasers by using a common all-fiber ring cavity is proposed and demonstrated. The cavity is chiefly composed of multiple 2x2 fiber couplers, which are insets of component fiber lasers of an array. The common ring cavity not only acts as a ring filter for mode selection and stabilization of component fiber lasers, but also provides a common channel for mutual injection coupling among them. We have demonstrated efficient phase locking of multiple Erbium-doped fiber lasers with linear and ring resonators based on the common ring cavity configuration, and obvious interference patterns and stable coherent output have been observed in experiment. The power transmission and resonance properties of the ring cavity are investigated theoretically by the intensity and amplitude addition methods. The research results indicate that increasing the coupling ratio of fiber couplers can increase the coupling strength, and decreasing the loss of the common ring cavity can increase both the coupling strength and combining efficiency. Finally, the phase locking mechanism of the presented scheme is discussed, and we believe that the phase locking array forms a composite resonator on account of the common ring cavity, and the array achieves phase locking states through mutual injection coupling among component lasers.