As integrated circuit linewidths are reduced, single-chip system functionality and speed increase. Conventional electronic chip input/output does not follow this trend: bonding pad sizes and off chip capacitive loads remain essentially constant. Shortage of chip interconnect capability has become critical. Integrated free-space optical interconnect has the potential to overcome this problem by providing a large number of high-speed connections between chips. A description is given of the application of free-space optics, quantum-well modulators, and CMOS photodetectors to this task.>

The authors discuss digital optics, a technology for processing, transport, and storage of optical digital information. Digital optics offers both the high temporal bandwidth of fiber communications and the high connectivity and information density of optical imaging. The energy dissipation per bit of communicated information, as well as the chip area dedicated to interconnections, can be significantly lower in optics than in high-speed electronics. This motivates the introduction of parallel optical interconnections through free space in communication-intensive areas of digital information processing such as switching in telecommunications and within multiprocessors. Digital optical circuits can be constructed by cascading two-dimensional planar arrays of optical logic gates interconnected in free space. The state of the art and the trends in digital optical information processing systems for optical logic, optoelectronic interfaces, and optical free-space interconnection systems are reviewed.>