In this paper

1.5μm GRINROD external-cavity semiconductor lasers and the beat experiments are reported. A stable intermediate frequency with 6MHz linewidth is obtained by the beating of the two identical external-cavity semiconductor lasers. The drifting of the intermediate frequency is less than 100MHz in 2 hours continuous observation without any external active frequency stabilization. The results show that this kind of external cavity semiconductor laser is practical in FSK coherent optical communication systems. The linewidth-power characteristics and the frequency modulation responsibilities are also studied in this paper using the beating method. The experimental results are in agreement with the previously published theories.