Multichip module with planar-integrated free-space optical vector-matrix-type interconnects.

Even in the semiconductor industry, free-space optical technology is nowadays seen as a prime option for solving the continually aggravating problem with VLSI chips, namely, that the interconnect technology has failed to keep pace with the increase in communication volume. To make free-space optics compatible with established lithography-based design and fabrication techniques the concept of planar integration was proposed approximately a decade ago. Here its evolution into a photonic microsystems engineering concept is described. For demonstration, a multichip module with planar-integrated freespace optical vector-matrix-type interconnects was designed and built. It contains flip-chip-bonded vertical-cavity surface emitting laser arrays and a hybrid chip with an array of multiple-quantum-well p-i-n diodes on top of a standard complementary metal-oxide semiconductor circuit as key optoelectronic hardware components. The optical system is integrated into a handy fused-silica substrate and fabricated with surface-relief diffractive phase elements. It has been optimized for the given geometrical and technological constraints and provides a good interconnection performance, as was verified in computer simulations on the basis of ray tracing and in practical experiments.