Researchers at Washington University in St. Louis have built what could become a critical component for microprocessor circuits that crunch data using light rather than electricity. The group developed a system of optical resonators that intensifies light traveling in one direction and weakens it to virtually nothing in the other -- and shrank the whole thing down so it's small enough to fit on a silicon chip.
The component does the same job that a simple diode would in an electrical system. It does so using a twisting concept of quantum mechanics that not only keeps light flowing in one direction and not the other, but appears to let more energy out of the device than went in. Inside a doughnut-shaped component, two microresonators reflect light back and forth. One tends to lose energy, while the other increases it. When the loss equals the gain at a specific wavelength, the system goes through a phase change in which the roles of the resonators are reversed, “their temporal relationships reverse, loss becomes gain and gain becomes loss," according to a paper describing the technique that was published in the April 6 issue of Nature Physics.
In an optical diode, the light input in one direction is transmitted, while the light input in the opposite direction is blocked. The new optical diode, designed by the university researchers, is made from parity time symmetric microresonators in which the loss of one of the resonators is balanced by the gains in the other.
(Source: Washington University)
The result could make it practical to build integrated computing circuits that use beams of light that travel along channels far narrower than would ever be possible using wire and electricity, and at far lower energy levels. The process could still support standard semiconductor circuitry designs.
"We believe that our discovery will benefit many other fields involving electronics, acoustics, plasmonics and meta-materials," according to lab director Lan Yang, who oversaw the study, wrote in a statement from Washington University.
"Coupling of so-called loss and gain devices using PT (parity-time)-symmetry could enable such advances as cloaking devices, stronger lasers that need less input power, and perhaps detectors that could ‘see’ a single atom."
"At present, we built our optical diodes from silica, which has very little material loss at the telecommunication wavelength. The concept can be extended to resonators made from other materials to enable easy CMOS compatibility," according to Bo Peng, a graduate student in Yang’s group and lead author of the paper.
Metaphorically, the device works in a way similar to the Whispering Gallery in St. Paul's Cathedral, in which oddities of acoustics make quiet noises audible at one end of the side of the gallery when they are nearly inaudible to those standing nearby.
In theory, the device is more problematic. It takes advantage of the concept of parity-time (PT) symmetry in quantum physics, which describes ways in which the energy coming out of a closed space may not equal the real and potential energy of the particles inside. (There is a more detailed explanation at the end of the story.)