Tunable diode lasers with narrow spectral bandwidth are of interest for a large number of applications in, e.g., coherent optical communications, precision metrology, spectroscopy or optical switching. Of particular interest is the investigation of novel types of external cavity lasers based on integrated optics and hybrid integration. In such systems an extensive spectral control can be exerted via low-loss, and high-Q waveguide resonators. This approach can be extended to entire arrays with a large number of lasers. When controlled to form a comb-like spectrum and with appropriate phasing, trains of ultra-short pulses with unprecedentedly high repetition rates in the THz regime can be synthesized. Other modes of operation of such arrays offer solutions for future applications in microwave photonics such as adaptive beam forming networks. In this project we investigate the properties of such light sources.