Optical interconnection and signal distribution at the backplane, board, and substrate level can be implemented using thin-film active optoelectronic devices embedded in polymer waveguide structures. These active embedded devices eliminate the need for optical beam turning to and from photodetectors and emitters, respectively, for inputs and outputs to the substrate waveguides. In this paper, optical interconnections using fully embedded thin-film metal-semiconductor-metal (MSM) photodetectors in polymer optical waveguides are demonstrated, and the experimental characterization of these thin-film MSMs embedded in polymer waveguides is reported. To illustrate the potential for high-level signal distribution at the backplane, board, and substrate levels, a 1 × 4 balanced multimode interference (MMI) coupler has also been demonstrated in a photoimageable polymer for the first time. Finally, a 1 × 4 thin-film MSM photodetector array has been embedded in the output arms of the a photoimageable polymer MMI for the first time, and the MSM array photocurrent outputs from the 4 arms show that highly balanced optical signal distribution has been achieved. © 2004 IEEE.