Researchers from MIT, the University of California at Berkeley, and the University of Colorado have developed a working prototype optoelectronic microprocessor that computes electronically but uses light to move information. The microprocessor was built without altering existing semiconductor manufacturing processes. The chip has 850 optical components and 70 million transistors, which is less than a typical microprocessor, but is enough to demonstrate all the functionality that a commercial optical chip would require. In testing, the researchers found that the performance of their transistors was virtually indistinguishable from that of all-electronic computing devices built in the same facility. Optical data connections should be more energy efficient, and the power requirements don’t increase with distance. The chip was manufactured using a silicon-on-insulator process, while the waveguides is atop a thin layer of glass on a silicon wafer that is etched away. In an optoelectronic chip, light signals have to be converted to electricity, but contact with metal also interferes with optical data transmission. The researchers found a way to pattern metal onto the inner ring of a ring resonator. The metal doesn’t interact with light traveling around the resonator’s outer ring, but when a voltage is applied to it, it can translate back and forth between optical and electrical signals.