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A computer model is developed to analyze the steady-state and transient responses of circular grating-coupled distributed feedback (CGC DFB) lasers. The model solved the time-dependent coupled-mode equations and carrier rate equation self-consistently by using a modified time-domain finite-difference method. The nonuniform distributions of carrier concentration and refractive index are taken into calculation. Using the model, the temporal and spatial variations of electric field and carrier concentration of the CGC DFB lasers are examined. It is found that the laser performance would be underestimated if the carrier-induced index change is ignored in the calculation. On the other hand, it is noted that the output power and resonant oscillation frequency as well as damping rate of the lasers could be maximized simultaneously by an optimal design for the grating.