Abstract: Based on the ray tracing method and the consideration of the gain distribution with wavelength,the expression of the output spectrum and output power of the fiber grating external cavity semiconductor lasers(FGESL) had been deduced firstly.Combining with carrier rate equation,the fine structure of output spectrum,output power and the P-I characteristics had been digitally simulated. As a result,many peaks existed in the reflective band width of grating and the output spectrum became much firmer with the dec...