A key component for high-speed communication systems is the electro-absorption modulator (EAM). An EAM integrated with a passive waveguide section or a DFB laser has been explored to reduce cost and simplify packaging. Several approaches have been developed to accomplish monolithic integration. These technologies include butt-joint coupling (in which the laser and EAM are grown separately) and selective-area growth. Butt-joint (BJ) coupling is attractive because it allows independent optimization of the laser and EAM. However, it requires multiple growths. In contrast, selective-area growth (SAG) is an elegant solution because both the active regions of the laser and modulator can be grown in a single epitaxial growth whilst allowing a shift of similar to100nm to be obtained in the characteristic wavelength of the two device regions. Also the vertical alignment between them is ensured. In this paper, we will compare the performance of both SAG and BJ integration processes. The interfaces between laser and waveguide sections grown with SAG and BJ were characterized via optical low-coherence reflectometry (OLCR). Fifty-micrometer long EAMs integrated with a 250 mum long passive waveguide region using both SAG and BJ structures exhibited total capacitance values lower than 70fF with 3dB bandwidths over 28GHz. Open eye diagrams were obtained for both integrated and stand alone EAMs at a peak-to-peak driving voltage of 2.9V under 40Gbit/s modulation. (C) 2004 Elsevier B.V. All rights reserved.