Fig. 1. Model of mutual injection locking

Fig. 2. Schematic of iteration relationship

Fig. 3. Simplified model of mutual injection locking

Fig. 4. One periodic unit of refractive index coupled DFB lasers

Fig. 5. Threshold gain distribution of mutual injection locking with different fiber lengths (or coupling delays)

Fig. 6. Threshold gain distribution of mutual injection locking with different coupling strengths

Fig. 7. Frequency noise of mutual injection locking with different coupling delays

Fig. 8. Influence of detuning and coupling strength on the linewidth

Fig. 9. Experiment setup of mutual injection locking

Fig. 10. Simulated frequency noise of point F