New device could allow for high-speed optical information processing

December 27, 2011

All-silicon passive optical diode (credit: Birck Nanotechnology Center, Purdue University)

Researchers at Purdue University have created a new type of optical device small enough to allow millions of them to fit on a computer chip, leading to faster, more powerful information processing and supercomputers.

The “passive optical diode” is made from two tiny silicon rings, each measuring 10 microns (millionths of a meter) in diameter. Unlike other optical diodes, it does not require external circuitry to transmit signals and can be readily integrated into computer chips.

The diode transmits signals in only one direction, making it capable of information processing, said Minghao Qi, an associate professor of electrical and computer engineering at Purdue University.

“This one-way transmission is the most fundamental part of a logic circuit, so our diodes open the door to optical information processing,” said Qi.

Although fiberoptic cables are instrumental in transmitting large quantities of data across oceans and continents, information processing is slowed and the data are susceptible to cyberattack when optical signals must be converted into electronic signals for use in computers, and vice versa, and expensive equipment is required for the conversion.

The new optical diodes could make for faster and more secure information processing by eliminating the need for this conversion. The devices, which are nearly ready for commercialization, also could lead to faster, more powerful supercomputers by using them to connect numerous processors together.

In operation, infrared light from a laser goes through an optical fiber and is guided by a microstructure called a waveguide. It then passes sequentially through two silicon rings and undergoes “nonlinear interaction” while inside the tiny rings. Depending on which ring the light enters first, it will either pass in the forward direction or be dissipated in the backward direction, making for one-way transmission. The rings can be tuned by heating them using a “microheater,” which changes the wavelengths at which they transmit, making it possible to handle a broad frequency range.

The new optical diodes are compatible with industry manufacturing processes for complementary metal-oxide-semiconductors, or CMOS, used to produce computer chips.

Ref.: Li Fan, et al., An All-Silicon Passive Optical Diode, Science, December 22, 2011; [DOI:10.1126/science.1214383]