Buffers in computer chips temporarily store data as needed to smooth information flow. Future optical-based circuits also will need buffers, though "storing" light is a bit trickier. Long transmission delays are possible by passing light through optical fibers, though current "delay line" devices are too big to put on a microchip. Now, IBM scientists may have gotten around the problem.

Their device passes light signals through an optical delay line consisting of 100 cascaded "micro-ring resonators" built using standard CMOS methods. Forming the optical waveguide into a ring forces light to circle multiple times, delaying its travel.

Such an optical buffer can briefly store 10 bits of optical information within an area of 0.03 mm2. That's just 10% the storage density of a floppy disk, but a big improvement over previous results. The advancement may lead to integrating hundreds of these devices on a single chip, an important step towards on-chip optical communications.

Support for the work comes from Darpa through the Defense Sciences Office program Slowing, Storing and Processing Light.