High speed optical interconnections offer an attractive alternative to electrical interconnections, particularly when they can be integrated into electrical systems. In particular, waveguide signal distribution and optical to electrical (O/E) conversion are critical to the integration of optical signals into electrical systems. The integration and interfaces between waveguides and O/E devices is a topic under intensive study. One approach to the integration of optical interconnections into electrical systems is to use fully embedded thin film optoelectronic (OE) devices in planar lightwave components on electrical interconnection substrates. In this approach, the propagating optical signal from the optical waveguide can be evanescently or directly coupled into the embedded thin film OE devices based on the embedded structure. Efficient and high speed optical signal distribution and O/E conversion, such as those using planar channel polymer waveguides with embedded thin film photodetectors, are examples of optical interconnection critical functions that are optimally implemented in electrical systems. In this paper, a 1 by 4 thin film metal semiconductor metal (MSM) photodetector (PD) array is embedded in a 1 by 4 photoimageable polymer multimode interference (MMI) coupler. This optical distribution and E/O system was fabricated and experimentally characterized at a wavelength of 1.3 μm. The measured overall loss, including the propagation loss and splitting loss of the MMI coupler was -0.18 dB at λ = 1.3 μm.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.