SMT-compatible large-tolerance "OptoBump" interface for interchip optical interconnections

A new optical interface called OptoBump has been developed to couple optoelectronic packages to an optoelectronic printed circuit board, thus enabling economical chip-to-chip optical interconnections. The optoelectronic packages have vertical-cavity surface-emitting laser (VCSEL) and PD-array chips in their cavity and an large scale integrated (LSI) mounted on top. A package converts high-speed electrical signals from the LSI into an array of optical signals, which are emitted from the bottom. The PCB contains integrated polymer optical waveguides to optically connect packages, and the use of surface-mount technology (SMT) to mount packages on the printed circuit board (PCB) keeps assembly costs low. The key to making the OptoBump interface fully compatible with SMT is the integration of microlens arrays directly into both packages and the PCB. A wide, collimated optical beam couples a package to the board across a narrow air gap and provides a large tolerance to misalignment during the SMT process. This paper explains the concept of the OptoBump interface, the optical coupling design by ray-trace simulation, and the fabrication of polymer microlenses and polymer waveguides. Experimental results revealed that the OptoBump interface provides a large tolerance of ±50 μm, which is large enough for use with SMT. The OptoBump interface can replace high-speed electrical wiring at the chip level and also offers the benefit of not having any optical fibers or connectors on the board. Thus, it has the potential to bring about a revolutionary change in optoelectronic packaging.