A new type of optical device that is small enough to fit millions on a computer chip could lead to faster, more powerful information processing and supercomputers. The “passive optical diode” developed by scientists in the Birck Nanotechnology Center at Purdue University is made from two tiny silicon rings measuring 10 µm in diameter. Unlike other optical diodes, it does not require external assistance to transmit signals and can be readily integrated into computer chips. The diode is capable of “nonreciprocal transmission,” meaning it 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. Although fiber optic 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 translated into electronic signals for use in computers, and vice versa. Purdue University researchers have developed the new “all-silicon passive optical diode,” a device small enough to fit millions on a computer chip. It could lead to faster, more powerful information processing and supercomputers. (Image: Birck Nanotechnology Center, Purdue University) Electronic diodes are critical junctions in transistors and help facilitate integrated circuits to switch on and off and to process information. The new optical diodes are compatible with industry manufacturing processes for complementary metal oxide semiconductors, or CMOS, used to produce computer chips, the scientists explained. The new diodes, which are nearly ready for commercialization, could make for faster and more secure information processing by eliminating the need for this translation. They could also lead to faster, more powerful supercomputers by using them to connect numerous processors together. The current factor that limits supercomputers is the speed and bandwidth of communication between individual superchips within the system, explained Leo Varghese, a graduate student. “Our optical diode may be a component in optical interconnect systems that could eliminate such a bottleneck,” Varghese said. Infrared light from a laser at telecommunication wavelength goes through an optical fiber and is guided by a waveguide. It then passes sequentially through two silicon rings and undergoes a 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 optical diodes are described online Dec. 22 in the journal Science. For more information, visit: www.purdue.edu