A bi-directional optical device includes: a TO cap; a TO header defining a receiving space together with the TO cap; a laser chip provided on the TO header and in the receiving space; and a light-receiving chip provided on the TO header and in the receiving space. The TO cap has a cap body and a lens embeddedly mounted on the cap body. The laser chip emits a first laser beam toward the lens. The light-receiving chip faces the lens and receives a second laser beam transmitted through the lens. The laser chip and the light-receiving chip are packaged together within the receiving space defined by the TO cap and the TO header, so as to effectuate a bi-directional optical device for emitting and receiving light of different wavelengths.