Provided is an optical device. The optical device includes a substrate having a waveguide region and a mounting region, a planar lightwave circuit (PLC) waveguide including a lower-clad layer and an upper-clad layer on the waveguide region of the substrate and a platform core between the lower-clad layer and the upper-clad layer, a terrace defined by etching the lower-clad layer on the mounting region of the substrate, the terrace including an interlocking part, an optical active chip mounted on the mounting region of the substrate, the optical active chip including a chip core therein, and a chip alignment mark disposed on a mounting surface of the optical active chip. The optical active chip is aligned by interlocking between the interlocking part of the terrace and the chip alignment mark of the optical active chip and mounted on the mounting region.