We report on light modulation, detection, and emission characteristics of Ge/SiGe multiple quantum well waveguides using the same epitaxial growth and fabrication steps. As an electro-absorption modulator, the device exhibits the capability to achieve high extinction ratio with low swing bias voltages and high modulation bandwidth. As a photodetector, dark currents, optical responsivities, and high speed performance have been studied. High speed light detection up to 10 Gb/s has been obtained simultaneously with good values of optical responsivity. As a light emitting diode, direct gap electroluminescence (EL) from the Ge/SiGe MQW waveguides has been experimentally demonstrated at room temperature within the spectral range of light modulation and detection. (c) 2013 Elsevier Ltd. All rights reserved.