IBM slows light for chips

IBM has unveiled a device capable of delaying the flow of light on a silicon chip, a requirement for allowing computers to one day use optical communications to achieve better performance.



Using optical instead of electrical signals for transferring data within a computer chip might result in significant performance enhancements since light signals can carry more information faster.



However, buffering, or temporarily holding data on the chip, is critical in controlling the flow of information, so a means for doing so with light signals is necessary. IBM’s new device can buffer optical signals on a chip.



Long delays can be achieved by passing light through optical fibres. However, the current delay line devices for doing so are too large for use on a microchip, where space is precious and expensive. For practical on-chip integration, the area of a delay line should be well below one square millimetre and its construction should be compatible with current chip manufacturing techniques.



IBM scientists were able to meet this size restriction and achieve the necessary level of control of the light signal by passing it through a new form of silicon-based optical delay line built of up to 100 cascaded micro-ring resonators. These were built using current silicon complementary metal-oxide-semiconductor (CMOS) fabrication tools.



When the optical waveguide is curved to form a ring, light is forced to circle multiple times, delaying its travel. The optical buffer device based on this simple concept can briefly store 10 bits of optical information within an area of 0.03 square millimetres. This represents 10 per cent of the storage density of a floppy disk, and a great improvement compared to previous results.



According to IBM, this advancement could potentially lead to integrating hundreds of these devices on one computer chip, an important step towards on-chip optical communications.