Optical devices and methods for constructing the same are disclosed. An example optical device includes an optical transmitter, a photodetector and a waveguide optically coupling the optical transmitter and the photodetector. It also includes a substrate having a first cavity to receive the optical transmitter and a second cavity to receive the second transmitter. The first and second cavities are located and dimensioned to passively align the optical transmitter, the waveguide and the photodetector when the transmitter is inserted into the first cavity and the photodetector is inserted into the second cavity.