This thesis describes a theoretical study into the synchronisation of semiconductor lasers subject to unidirectional optical coupling. Numerical modelling of the coupled laser system facilitates a thorough investigation of the known regimes of chaos synchronisation. A detailed examination of the synchronisation quality, and in particular the associated delay time, leads to the discovery of a subtle dependence of the delay time upon operating parameters. This knowledge is then put to use in elucidating the apparent merging of the two known synchronisation regimes. The work then proceeds to study the effects of introducing fibre optic coupling between the two semiconductor lasers. The distortion introduced into the coupling field as a result of this transmission channel is seen for the first time to be recoverable. Here, under certain operating conditions, the driven laser system is observed to compensate for the distortion, leading to the division of the well-known injection-locking regime into two distinct regions: the first at moderate coupling strength where recovery is observed, and a second at strong coupling where optical amplifier-like operation is exhibited. This recovery phenomenon is investigated further through the manipulation of the spectral components of the coupling field via the application of digital filters. Motivated by the need to determine the mechanism behind the observed recovery, attention is turned toward the analysis of the driven laser system, conducted through the application of a large-signal Gaussian white noise stimulus to the optical driving field. The system is then characterised by cross-correlation of the output field with the input stimulus. The obtained system characteristic is utilised in determining the lasers resonant response for varying parameter values. This response is put in the context of synchronisation, before being used to investigate further the synchronisation delay time investigated earlier for a chaotic driving field.