Parallel processing demonstrator with plug-on-top free-space interconnect optics

We demonstrate a setup with 10 optically interconnected chips, which can perform a distributed radix-2-butterfly calculation for fast Fourier transformation (FFT). The setup consists of a motherboard, five multi-chip-modules (MCMs, with processor/transceiver chips and laser/detector chips), four plug-on-top optics modules that provide the bi-directional optical links between the MCMs, and external control electronics. The design of the optics and optomechanics satisfies numerous real-world constraints, such as compact size (< 1 inch thick), suitability for mass-production, suitability for large arrays (up to 10³ parallel channels), compatibility with standard electronics fabrication and packaging technology, and potential for active misalignment compensation by integrating MEMS technology. We successfully demonstrated all the steps that are necessary to run the algorithm, such as bi-directional optical MCM-to-MCM communication, data movement within the system and basic arithmetic operations. We also made a number of experiments that showed the robustness of our plug-on-top approach. We demonstrate for example how we can unplug and re-insert the optics module during operation without need for realignment, even after rotating the symmetric module by 180 degrees. We will report on the numerous aspects of this work, and on our conclusions for the practical implementation of free-space optoelectronic systems.