Crowbar was a project started at the University of Cincinnati with the goal of expediting smart pixel research (i.e., where optics and digital electronics are integrated into a single chip). The original focus of the project was to combine the reconfigurability of Field Programmable Gate Arrays (FPGAs) with the improved I/O capabilities of integrated optics. In theory, one could then implement any smart pixel based photonic information processing system with a prefabricated chip. Further, the optical devices could be used to rapidly reconfigure the logic by receiving configuration data in a parallel, page-oriented format.
In the Spring of 2000, a proof-of-concept design was created by Jason F. Cantin and Fred R. Beyette in the Photonic Systems Development Laboratory (PSDL). See toplevel image at right. This design consisted of an SRAM-based, sea-of-gates FPGA with 12 blocks, 4 of which had configurable optical detectors based on photodiodes. The design was fabricated on a 2mm "tinychip" via the MOSIS service with 1.5-micron rules in AMI's Mixed Signal Process (2 metal layers, 2 polysilicon). First-silicon was received the following August.
Since the completion of the prototype, the project has grown in both applicability and scope. CAD support will make it possible to specify optoelectronic systems in a high-level language (HLL), and compile the specifications to a given optoelectronic FPGA. Though the prototype contains only binary optical detectors, more advanced receivers and optical emitters are being explored. Detectors and emitters for other types of energy are also under investigation.
In the future, we see chips based on Crowbar's concept being a viable alternative for prototyping optoelectronic systems. In some cases, the reduced turn-around time and cost may make it attractive as a complete solution for multi-technology systems.
