Mutual injection locking of a fibre laser and aDFBsemiconductor laser

Abstract
A fibre laser and a distributed feedback (DFB) laser are coupled through a 50:50 fibre coupler in such a way that the two lasers mutually injection-lock. The DFB laser forces the fibre laser to oscillate in a nearly single longitudinal mode. At the same time, the linewidth of the DFB laser is reduced to below 1.5 MHz because of mutual injection-locking.