Abstract: Described is a new wafer scale optical sub-assembly (OSA) and a method of production of such an OSA. Also described are optical wafers which form the central building block for the OSAs. The optical wafers comprise embedded optical features, which are positioned with reference to a single reference fiducial so as to avoid stacking of alignment errors. The embedded optical features may include refractive and/or waveguide optical channels. Cross-talk reduction features may also be provided between the embedded optical features. Embedding the optical features within the optical wafers protects the optical features from damage or contamination. The design of the optical features allows both transmit and receive functionality and arrays of optical devices to be packaged together.