Photonic integrated circuits (PICs) have garnered a lot of interest due to their ability to offer reductions in size, weight and power, improved performance and stability over discrete solutions. The biggest benefits of the implementation of PICs in telecommunication applications are reaped in the cost sensitive short reach networks that include access and datacenter networks. Passive optical networks (PONs) that utilize optical fiber links to provide the end-user connectivity, have become one of the predominant access network options. The PON standards are steadily evolving due to the ever-increasing demand for bandwidth. A relatively recent advance involves the use of wavelength division multiplexing (WDM) together with the more common time division multiplexed (TDM) approach. This format is known as time and wavelength division multiplexing (TWDM) and, while it enables bandwidth growth, it places stringent technical demands on the optical components, increasing the challenge of meeting the cost targets required in high-volume PON applications. To date, externally modulated lasers (EMLs) have typically been required to meet the technical requirements of TWDM networks. However, EMLs are relatively costly when compared with typical PON transmitters. Furthermore, they require more expensive and higher power laser drivers. For these reasons, there is a lot of interest in a directly modulated laser (DML) alternatives to reduce the cost and complexity of TWDM transceivers. A key challenge with direct modulation is the frequency chirp imposed on the modulated signal. It makes the signal more susceptible to fiber dispersion effects, which in turn limits the transmission distance achievable by DML based transmitters. This research thesis investigates the employment of multi-section PICs, designed to enable direct modulation and achieve high bit rate and long-distance transmission. These PICs, intendent of use in next generation optical access networks, are developed using a regrowth-free fabrication technique. In this work, a detailed analysis and characterization of a slot-laser is carried out. Subsequently, a few different PIC architectures are proposed, realized and fully characterized. Finally, the characterized PICs are employed in transmission tests to verify their suitability as PIC based transmitters for next generation optical access networks.