Coherent beam combining (CBC) of fiber lasers and amplifiers has attracted increasing attentions due to its capability to scale fiber lasers to high power levels and overcome the limits set by the nonlinear optical process of single fibers. Recently, the theory and application of laser injection locking have been emphasized. Thanks to its power ratio tunable feature, the injection locked fiber laser can be used in a passive CBC system to solve this problem.

Researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM/China) have proposed and demonstrated passive CBC of four YDF amplifier chains with an injection-locked seed laser. They achieved the phase locking of four laser beams. [Optics Letters, Vol. 38, Issue 6, pp. 854-856 (2013)]. The 1063.9 nm output laser of the injection-locked fiber laser is extinguished automatically as the feedback injection power is high enough, and the injection-locked fiber laser acts as an amplifier for the feedback laser with 7.4 dB gains. We find that the phase-locked far-field interference pattern of our system with seed laser extinguished is stable, and the visibility is up to 91.5%, which is slightly higher than the prevalent method with auxiliary seed laser (88.2%).