Multilayer Optical Interconnections Integrated on a Printed Circuit Board

摘要

The integration of optical interconnects on PCB- and backplane-level requires compatibility with the established manufacturing and assembly processes of the conventional electrical board technology. In spite of repeated predictions that the optical interconnect is soon going to replace the electrical interconnect on board-level, this turned out not to be the case yet. Fiber-based interconnections are already available, but the fiber-inboard approach cannot lead to a practical solution as it results in expendable assembly processes being unsuitable for high volume production at reasonable costs. A better solution is the realization of optical layers that contain optical waveguides as well as passive optical structures. By stacking different waveguide layers the two-dimensional character of VCSELs and photodetectors can be fully used, allowing very high integration densities. For the realization of the optical layers, we have chosen to use Truemode backplane™ polymer. The material is chosen in view of its compatibility with standard FR4-based electrical board manufacturing, temperature stability, manufacturability, excellent optical and planarization properties. Arrays of 50 x 50 μm~2 multimode waveguides have been fabricated in a two layer structure using photolithography. Laser ablated micromirrors are used to provide surface-normal light coupling, and coupling between waveguides in different layers. This opens the way towards an embedded three-dimensional optoelectronic interconnection.