Directly modulated lasers provide simple, and cost efficient, optical transmitters for use in optical networks. However, chirp limits the bit rate distance product achievable in such systems, with transmission distances limited to around 10 km when operating at 10 Gbit/s in the 1550 nm window [1, 2], and thereby limiting their suitability as optical transmitters in next generation access networks operating at 10 Gbit/s, where transmission distances of 20 km and beyond will be required. External modulation of lasers is currently the most common method to modulate a light-wave signal in optical communication systems. Although this technique provides high speed and stable data modulation, the large insertion losses and the polarization dependence of the modulator can prove to be cumbersome. The extra optical component also adds to the cost and complexity of the transmitter, rendering this technique unsuitable for cost-sensitive applications. © 2013 IEEE.