An optical mode transformer, a semiconductor optical amplifier (SOA), and a high-bandwidth waveguide-coupled photodiode are monolithically integrated using separately optimized materials based on asymmetric twin-waveguide (ATG) technology. Incident light is collected by a diluted, large fiber guide followed by transfer to an SOA. After amplification, light is coupled into the uppermost In/sub 0.53/Ga/sub 0.47/As light absorption layer by two consecutive taper couplers. The device shows a peak responsivity of 11 A/W (/spl sim/12.5-dB SOA-to-detector gain) and a 3-dB electrical bandwidth of 36 GHz, corresponding to a gain-bandwidth product of 640 GHz. In this SOA/p-i-n chip, separation of optical functions (light guiding, amplification, and detection) into different waveguides allows for optimization of materials for each function without material regrowth. Generalized photonic integrated circuits containing complex combinations of these three optical functions can be realized using the integration scheme demonstrated here.