A photonic device can include an optical detector (e.g., a photodetector) coupled to silicon waveguides. Unlike silicon, germanium is an efficient detector at the wavelength of optical signals typically used for data communication. Instead of directly coupling the waveguide to the germanium, in one embodiment, the waveguide extends below the germanium but is spaced sufficiently away from the germanium so that the optical signal is not transferred. Instead, an optical transfer structure (e.g., a tapered waveguide or an optical grating) is disposed between the germanium and the waveguide. The waveguide first transfers the optical signal into the optical transfer structure which then transfers the optical signal into the germanium.