A multimode time domain model is used to study the large signal dynamics of complex distributed feedback lasers with nonuniform grating pitch and coupling coefficient. Lasers with longitudinal variation of their grating pitch &Lgr; (corrugation-pitch-modulated lasers) can exhibit poor steady-state side mode suppression ratios. Numerical simulations show that an adequate profile of the coupling coefficient &kgr; (stronger coupling at the center of the cavity) can help to achieve improved steady-state single mode operation with respect to conventional Bragg-detuned cavities (uniform coupling coefficient). However, it is found that in such lasers(z-dependent &kgr;), side modes are liable to be excited during the turn-on transient interval. A careful study of the turn-on transient is needed to determine the maximum (keeping dynamic single mode regime) bias current. ©1997 American Institute of Physics.