The desire for multi-media content and richly interactive data services is shaping a new era for telecommunications networks. Future networks will need to be capable of offering Triple Play, IPTV, Video-on-Demand, Voice-over-IP and High-Speed Internet Access, combined with guaranteed Quality of Service. These networks will employ optical transport networks with wavelength division multiplexing (WDM) technology, and advanced modulation formats, in order to achieve the high capacities required. In addition, given the bursty nature of this data it is expected that dynamic allocation of the bandwidth will be implemented to efficiently use the available capacity. The key component in these networks will be the tuneable laser transmitters that generate the different wavelength packets. This thesis has explored novel applications and implementations of the sample-grating distributed Bragg reflector (SG-DBR) lasers, in optical WDM networks. Through theory, simulations and experiments, the use of SG-DBR lasers for advanced modulation formats in fast reconfigurable networks has been investigated. Initial work focussed on the detailed characterization of the phase noise properties of the SG-DBR laser and their impact on coherent optical communications. Subsequent work in the thesis proposed techniques to overcome the limitations imposed by employing tuneable lasers with advanced modulation format transmission. Finally, the application of advanced modulation formats in dynamic optical packet switching scenarios employing SG-DBR laser has been evaluated.