OPTICAL COMMUNICATIONS FOR HIGH-SPEED DIGITAL PROCESSING

THE PROBLEM WHICH WE ADDRESS IN THIS PROPOSAL IS THE UTILIZATION OF III-V SEMICONDUCTOR OPTOELECTRONICS IN MASSIVELY-PARALLEL, GENERAL-PURPOSE PROCESSORS IMPLEMENTED WITH 3-D MULTICHIP MODULE (MCM) TECHNOLOGY. IN PRINCIPLE, SUCH PROCESSORS CAN REPLACE TRADITIONAL SPECIAL-PURPOSE, HARD-WIRED SYSTEMS FOR MANY HIGH-PERFORMANCE SIGNAL PROCESSING APPLICATIONS, PROVIDING FULL PROGRAMMABILITY AS WELL AS IMPORTANT ECONOMIC ADVANTAGES. THE KEY PROBLEM WITH MASSIVELY-PARALLEL ARCHITECTURES, HOWEVER, IS IMPLEMENTATION OF THE REQUIRED INTERPROCESSOR COMMUNICATIONS NETWORK, WHICH GROWS RAPIDLY IN COMPLEXITY AS THE NUMBER OF PROCESSING ELEMENTS INCREASES. IN OUR APPROACH, WE EMPLOY FREE-SPACE OPTICAL INTERCONNECTS WITHIN A STACKED-SUBSTRATE MCM STRUCTURE TO IMPLEMENT A HIGHLY-PARALLEL, EXTREMELY HIGH-BANDWIDTH NETWORK. IN ORDER FOR THE LIGHT TO BE TRANSMITTED THROUGH THE SUBSTRATES, A SUBSTRATE MATERIAL TRANSPARENT TO THE WAVELENGTH EMPLOYED IS USED (OR ALTERNATIVELY, SMALL HOLES ARE FABRICATED IN THINNED PORTIONS OF THE SUBSTRATE). THE SUBSTRATES ARE HELD TOGETHER IN COMPRESSION WITH SPACER ELEMENTS MADE FROM THE SAME MATERIAL AS THE SUBSTRATE, PERMITTING THE FABRICATION OF KEYING STRUCTURES WHICH MAINTAIN PRECISE REGISTRATION (TO WITHIN A FEW MICRONS) AS WELL AS ALLOWING INDIVIDUAL SUBSTRATES TO BE REMOVED FOR REPAIR. THE OPTICAL TRANSMITTERS AND RECEIVERS ARE MOUNTED ON THE SUBSTRATED WITH FLIP-CHIP SOLDER BONDING TECHNIQUES, WHICH PERMIT REGISTRATION OF THESE DEVICES ON THEIR SUBSTRATES TO AN ACCURACY OF ABOUT TWO MICRONS AS WELL AS ANGULAR ALIGNMENT TO WITHIN 0.05 DEGREE. ANTICIPATED BENEFITS: THE PROPOSED PROJECT WILL HAVE POTENTIAL FOR A WIDE RANGE OF BOTH FEDERAL GOVERNMENT AND COMMERCIAL APPLICATIONS, INCLUDING HIGH-SPEED SIGNAL PROCESSORS FOR SYNTHETIC APERTURE RADARS, INFRARED SURVEILLANCE SYSTEMS, ETC., AS WELL AS SUPERCOMPUTERS, ROBOTICS AND PORTABLE INFORMATION-PROCESSING SYSTEMS REQUIRING EXTREMELY HIGH-THROUGHPUT COMPUTATION IN A COMPACT PACKAGE.