Demonstrator Testbed for Intra-Chip Optical Interconnections: Combining Multi-Channel Free-Space Plastic Micro-Optical Modules and VCSEL Based OE-FPGAs

We fabricated and replicated in semiconductor compatible plastics a multi-channel free-space optical interconnection module designed to establish intra-chip interconnections on an Opto-Electronic Field Programmable Gate Array (OE-FPGA). The micro-optical component is an assembly of a refractive lenslet-array and a high-quality microprism. Both components are prototyped using deep lithography with protons and are monolithically integrated using a vacuum casting replication technique. The resulting 16-channel module shows optical transfer efficiencies of 46% and inter-channel cross talks as low as –22 dB. These characteristics are sufficient to establish multi-channel intra-chip interconnects with OE-FPGA’s. The OE-FPGA we used was designed within a European co-founded MEL-ARI consortium, working towards a manufacturable solution for optical interconnects between CMOS IC’s. The optoelectronic chip combines fully functional FPGA digital logic with the drivers, receivers and flip-chipped optoelectronic components. It features 2 optical inputs and 2 optical outputs per FPGA cell, amounting to 256 photonic I/O links based on multi-mode 980 nm VCSELs and InGaAs detectors. With a careful alignment of the micro-optical free-space module above the OE-VLSI chip, we demonstrated for the first time to our knowledge a multi-channel free-space intrachip optical interconnection. Data-communication was achieved with 4 simultaneous channels working at 10Mb/s. The bit rate was limited by the chiptester. Notwithstanding the use of non-aggressive 0.6 μm CMOS technology the FPGA will provide an 80 Mbit/s information rate per channel using Manchester encoded links. The whole chip therefore has in principle a peak aggregate signalling rate of approximately 20 GBit/s.