The production of a narrow-band microwave modulated light beam by active mode-locking of a monolithic semiconductor laser diode is modelled. A self-consistent calculation of the light field, following a sinusoidal current injection into a restricted section of the component, allows evaluation of the microwave amplitude and phase response of the light emission as well as determining the stability of the solutions. We show that the propagation parameters inside the laser diode, such as the gain bandwidth and group velocity dispersion can be optimised to improve this response. The use of multisection laser diodes, similar to the devices presently developed to obtain cw tunable laser diodes, is proposed to engineer those propagation parameters.