The present invention provides an optical device integrating an active device with a passive device without any butt joint structure between two devices. The optical integrated device of the invention includes a GaAs substrate, first and second cladding layers, and an active layer sandwiched by the first and second cladding layers. These layers are disposed on the GaAs substrate. The GaAs substrate provides a first region and a second region. The active layer comprises of the first active layer disposed on the first region and the second active layer disposed on the second region of the GaAs substrate. The first active layer has a quantum well structure whose band-gap energy smaller than 1.3 eV, while the second active layer has a quantum well structure whose band-gap energy is greater than that of the first active layer.