As an alternative approach to current electrical interconnection technology, optical interconnections at high speeds offer several potential advantages including small footprint, simple system design (in comparison to transmission lines), and immunity to electromagnetic interference. There are a number of approaches to integrating optical signal paths in electrical interconnection substrates such as backplanes, boards, and modules. One approach utilizes the heterogeneous integration of thin film optoelectronic (OE) devices embedded in waveguides. Optical signals can be coupled in from external fibers or from thin film lasers integrated onto the substrate, propagated, distributed, and processed in a planar waveguide format, and then coupled from the waveguide to an embedded thin film photodetector by evanescent field or direct coupling. This approach achieves alignment through assembly and successive masking layers and thus minimizes alignment issues. In addition, the integrated optical signal distribution system can be integrated onto the electrical interconnection substrate after the substrate has been fabricated using post processing, thus, the board facility is not impacted through the integration of the optical links.
In this paper, a discussion of the fabrication processes as well as coupling efficiency and speed measurement results for thin film InGaAs PDs embedded in polymer waveguides integrated onto Si substrates is included. These results are compared to theoretical estimates of the coupling efficiency, which was estimated using the finite difference beam propagation method.