An asymmetric twin waveguide (ATG) structure with an integrated amplifier and detector fabricated in a single active waveguide layer is disclosed. The structure comprises an active waveguide layer formed on a passive waveguide layer. The active and passive waveguides have different effective indices of refraction such that a first mode of light is confined primarily to the active waveguide and a second mode of light is confined primarily to the passive waveguide in the area where the waveguides overlap.