This chapter describes an alternative, relatively simple, approach to a theoretical analysis of mode‐locking (ML) in semiconductor lasers, without invoking the small gain‐and‐loss approximation. It summarizes some results of numerical and analytical analysis of this delay differential equations (DDE) model. The chapter drives a set of three DDEs for a passively mode‐locked semiconductor laser from the traveling wave equations, which govern spatiotemporal evolution of the electric field amplitude and the carrier densities in the gain and absorber sections. It describes the bifurcations responsible for the appearance and break‐up of ML solution. The chapter outlines the analytical analysis of different ML regimes in the limit when spectral filtering in the cavity is very broad. It discusses the connection between the DDE model and classical approaches developed by New and Haus. The chapter presents analytical stability analysis of the fundamental ML regime with respect to the Q‐switching instability.

laser mode locking; laser stability; Q‐switching; semiconductor lasers