FR4 printed circuit board design for Giga-bits embedded optical interconnect applications

As the demand of high data rate increases, electrical interconnects on the board becomes a bottleneck for the overall system performance because of crosstalk, transmission line effects, clock skew, and timing jitter. Thus, considerable effort has been made to investigate alternatives to board-level electrical interconnect, such as optical interconnects. However, current board-level optical interconnects still have limitations such as board fabrication cost, optical loss, and alignment tolerance. In this paper we discuss an optical board-level interconnect that uses optoelectronic devices embedded in an optical waveguide, to provide a solution to for Giga-bit data range interconnect, on FR4 printed circuit board (PCB). FR4 PCB is an attractive candidate because it is low-cost and widely used technology. However, the design of electrical interfaces to the optical interconnect still faces all the challenges of FR4 PCB design. Therefore, careful design of electrical path by EM/Schematic co-simulation is inevitable to use the FR4 PCB for 10 giga-bit per second (Gbps) applications even with optical interconnect. From the results of the measurements and simulations provided in this research, we see that fully embedded optical interconnect is a feasible solution to replace the current board-level electrical interconnect in high speed digital systems, however, the design of the optical electrical interfaces remains a challenging part of the interconnect problem.