New Method For Trapping Light May Improve Communications Technologies

The discovery could be used to develop newstructures that would work in the same fashion as an elbow joint inplumbing by enabling light to make sharp turns as it travels throughphotonic circuits. Fiber-optic cables currently used in computers,televisions and other devices can transport light rapidly andefficiently, but cannot bend at sharp angles. Information in the lightpulses has to be converted back into cumbersome electrical signalsbefore they can be sorted and redirected to their proper destinations.

Inan experiment detailed in the Aug. 18 issue of Nature, the researchersconstructed a three-dimensional model of a quasicrystal made frompolymer rods to test whether such structures are useful for controllingthe path of light. A quasicrystal is an unusual form of solid composedof two building blocks, or groups of atoms, that repeat regularlythroughout the structure with two different spacings. Ordinary crystalsare made from a single building block that repeats with all equalspacings. The difference enables quasicrystals to have more sphericalsymmetries that are impossible for crystals.

Ordinary crystalshad been considered the best structure for making junctions in photoniccircuits. But the researchers proved for the first time thatquasicrystal structures are better for trapping and redirecting lightbecause their structure is more nearly spherical. Their model, whichhad the same symmetry as a soccer ball, showed that the quasicrystaldesign could block light from escaping no matter which direction ittraveled.

The finding represents an advance for the burgeoningfield of photonics -- in which light replaces electricity as a meansfor transmitting and processing information -- and could lead to thedevelopment of faster telecommunications and computing devices.

"Thesearch for a structure that blocks the passage of light in alldirections has fascinated physicists and engineers for the past twodecades," said Princeton physicist Paul Steinhardt, a co-author of theNature paper, who invented the concept of quasicrystals with hisstudent Dov Levine at the University of Pennsylvania in 1984.

"Controlledlight can be directed, switched and processed like electrons in anelectronic circuit, and such photonic devices have many applications inresearch and in communications," Steinhardt noted.

Co-author PaulChaikin, a former Princeton professor now at the Center for Soft MatterResearch at New York University, said, "Ultimately, photonics is abetter method for channeling information than electronics -- itconsumes less energy and it's faster."

The paper's otherco-authors are Weining Man, who worked on the project as part of herdoctoral thesis in Princeton's physics department, and Mischa Megens, aresearcher at Philips Research Laboratories in the Netherlands.

Toconduct their experiment, the researchers constructed the world's firstmodel of a three-dimensional photonic quasicrystal, which was a littlelarger than a softball and made from 4,000 centimeter-long polymerrods. They observed how microwaves were blocked at certain angles inorder to gauge how well the structure would control light passingthrough it.

Building the physical model was a breakthrough thatproved more valuable than using complex mathematical calculations,which had been a hurdle in previous efforts to evaluate theeffectiveness of photonic quasicrystals in blocking light.

"Thepattern in which photons are blocked or not blocked had never reallybeen computed," Steinhardt said. "In the laboratory, we were able toconstruct a device that was effectively like doing a computersimulation to see the patterns of transmission."

Chaikin added,"We showed that it has practical applications, and we also found outsome properties of quasicrystals that we didn't know before."

Theresearchers are now exploring ways of miniaturizing the structure inorder to utilize the device with visible light instead of microwaves.They also are examining whether the quasicrystal designs may be usefulin electronic and acoustic applications.

Further details and images related to the study are available at: http://www.physics.princeton.edu/~steinh/quasiphoton