A new model is developed for simulating the injection of short-duration optical pulses into semiconductor lasers. The optical gain of the semiconductor is described by an empirical model which fixes all parameters following a fit to gain curves at two different densities of population inversion. The two-curve fit enforces the correct behaviour with respect to changes in carrier density and is intermediate between a rate equation model and a full microscopic approach. The electromagnetic field is integrated by the finite-difference time-domain method. The model incorporates an accurate complex susceptibility, material and gain dispersion and full phase information, and may be integrated on a desktop computer to simulate time evolution over a period of nanoseconds in a matter of hours. An appropriate choice of the grid resolution may be used to incorporate a realistic frequency dependent refractive index and simultaneously reduce the time for computation. The model is applied to the experimentally observed phenomena of dark pulse formation following injection of optical pulses into semiconductor lasers and furnishes an explanation for their formation, subsequent evolution and stability. The stability of dark pulses is explained as a re-distribution of the steady-state electric field. These investigations led to a hypothesis, and subsequent demonstration by numerical simulation, for generating stable streams of customisable pulse trains by coherent control of the phase of the injected pulse.