Optical interconnections on silicon herald a future in which photons will replace electrons to shuttle high-speed data streams between multiple microprocessor cores. A key component is an electro-optical modulator that permits one core's electrical output to modulate a silicon laser beam into a coded stream of pulses that can be routed to the input of any other core. IBM's T.J. Watson Research Center (Yorktown, N. Y.) said Thursday (Dec. 6) it has succeeded in shrinking a 10 Gbit/sec Mach-Zehnder electro-optic modulator down to 100 microns, at power levels comparable to today's discrete optical devices.