When it comes to speed, photons leave electrons for dead, which means optical computers will be much faster than their current electron-based cousins. While diodes for use in optical information processing systems already exist, these require external assistance to transmit signals so cannot be readily integrated into computer chips. Now researchers at Purdue University have developed a "passive optical diode" that not only doesn't require any outside help to transmit signals, but is also so small that millions would fit on a computer chip, potentially leading to faster, more powerful information processing and supercomputers.

While massive amounts of data are transmitted around the globe through fiber optic cables, the optical signals must be converted into electronic signals when they arrive at their destination for use in computers - and vice versa. This translation not only requires expensive equipment, but also slows down the speed of information processing and reduces the security of the data. Equipment that allows the transmitted optical information to be processed without translation would overcome these problems.


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Diodes are capable of information processing because they are able to transmit signals - most commonly an electric current - in only one direction, while blocking signals from the opposite direction. This, Purdue professor Andrew Weiner points out, is the most fundamental part of a logic circuit. The passive optical diode developed at Purdue makes this possible with light instead of electrons.

The new diode is made from two silicon rings that measure just 10 microns in diameter, which is about one-tenth the width of a human hair. After being transmitted through an optical fiber, infrared light from a laser at telecommunications wavelength 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.

Being composed of silicon, Purdue graduate student Jian Wang says the optical diodes are compatible with current industry manufacturing processes for complementary metal-oxide-semiconductors (CMOS) used to produce computer chips.

"These diodes are very compact, and they have other attributes that make them attractive as a potential component for future photonic information processing chips," she said.

By eliminating the need for translation from electronic to optical signals, the new optical diodes could make for faster and more secure information processing and, by using them to connect numerous processors together, could also lead to faster, more powerful supercomputers.

The Purdue team's optical diodes, which are nearly ready for commercialization, are described in a paper published online in the journal Science.