Semiclassical theory of multimode operation of a distributed feedback laser

Nonlinear self-consistency equations, including for the first time the effects of mode competition, are derived for index and gain gratings. Additional terms to those contained in self-consistency equations for lasers with a conventional resonator are found. Approximate analytic solutions for single- and two-mode operation of distributed-feedback (DFB) lasers are obtained with the help of the energy theorem. The analysis includes nonvanishing end reflectors of DFB structure.