An integrated device includes a waveguide, which may be connected to a photonic circuit and an external fiber, and an on-chip device formed on an optical chip by forming a region in which the waveguide terminates. The region is bounded by reflective surfaces. Light coming from the waveguide is essentially trapped inside the region and directed to an on-chip device disposed in the region. An integrated device consists of a low index difference waveguide, an on-chip mode converter, a high index difference waveguide, and an on-chip function formed on a single optical chip so that the high index difference waveguide is close to the substrate surface upon which the mode converter is formed. Substrate surface height differences are provided to define different substrate surface mounting heights for a low index difference waveguide, high index difference waveguide, a mode converter, and an on-chip device. The height differentials provide close proximity of components allowing on-chip devices, such as a Ge detector or electronics, to be integrated on a chip with the high index difference waveguide that is connected to a mode converter.