An optical device may include an optical coupling structure to couple a silicon-germanium photodetector to an integrated optics circuit. The optical coupling structure may comprise a silicon waveguide. The silicon waveguide may be tapered such that a thickness of the silicon waveguide at a first end of the optical coupling structure is smaller than a thickness of the silicon waveguide at a second end of the optical coupling structure, and may be tapered such that a width of the silicon waveguide at the first end is smaller than a width of the silicon waveguide at the second end. The optical coupling structure may include a silicon-nitride waveguide that covers the silicon waveguide, and is tapered such that a width of the silicon-nitride waveguide at the first end is smaller than a width of the silicon-nitride waveguide at the second end. The optical coupling structure may include a silica waveguide.