Like integrated circuit (IC) technology in micro electronics, many applications exploiting photonic technologies can be realized in a compact, power-efficient and cost-effective way by integrating the required functionalities on a single chip (photonic integrated circuit, PIC). This project focuses on realizing an important building block for such photonic integrated circuits, namely an ultra-compact semiconductor optical amplifier based on photonic crystal technology that is feasible for dense integration. The project comprises modelling and design of such devices, emphasizing a good understanding of limitations and trade-offs, and will conclude with the experimental demonstration of devices realizing a size reduction by a factor of 10 or more.