  We report on polarization combining 2D grating couplers (2D GCs) on amorphous
Si:H, fabricated in the backend of line of a photonic BiCMOS platform. The 2D
GCs can be used as an interface of a hybrid silicon photonic coherent
transmitter, which can be implemented on bulk Si wafers. The fabricated 2D GCs
operate in the telecom C-band and show an experimental coupling efficiency of
-5 dB with a wafer variation of +/-1.2 dB. Possibilities for efficiency
enhancement and improved performance stability in future design generations are
outlined and extension towards O-band devices is investigated as well.
