A buried heterojunction laser optically coupled with a buried waveguide electro-absorption (EA) optical modulator via an active layer is fabricated on a substrate carrying a number of deposited semiconductor layers. The laser component includes a laser current conduction region and an adjacent laser current confinement region. The waveguide component includes a waveguide current confinement region comprising first and second current blocking structures formed from different grown semiconductor layers. An extension of the first current blocking structure is interposed between the second current blocking structure and the waveguide current conduction region. Because each of the components is flanked by current confinement regions of differing structures, the resistive and capacitative properties of the current confinement regions can be selected to optimise the performance of that component for a particular use.