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Tiny gears on computer chips generate vortex of light that could power optical computing – sciencedaily


For the first time, researchers have used tiny germanium gears to generate a twisted vortex of light that spins around its axis of motion much like a corkscrew. Since germanium is compatible with the silicon used to make computer chips, the new light source could be used to increase the amount of data that can be transmitted with on-chip optical computing and communication.

Researchers at the University of Southampton in the UK and the University of Tokyo, Toyohashi University of Technology and Hitachi Ltd., all in Japan, describe the new electroluminescent devices in The Optical Society (OSA) journal. . Optical Express. With a radius of one micron or less, 250,000 of the gears could be wrapped in a single square millimeter of a computer chip.

The generation of light that is twisted or having orbital angular momentum is of great interest due to its advantages for communications and computing. Today, light is used to convey information by varying the number of photons emitted or by switching between the two polarization states of light. With twisted light, each twist can represent a different value or letter, allowing much more information to be encoded using less light.

“Our new micro gears have the potential for a laser that can be integrated on a silicon substrate – the last component needed to create an integrated optical circuit on a computer,” said the first author of the article, Abdelrahman Al- Attili, of the University of Southampton. . “These tiny optical circuits use twisted light to transmit large amounts of data.”

Use constraint to improve light emission

It was impossible to manufacture a miniaturized light source for use on silicon, the material commonly used to make computer chips and related components, because the properties of the material led to low efficiency of light generation. Although germanium has similar limitations, applying stress by stretching it can improve its light emitting efficiency.

“Previously, the stress that could be applied to germanium was not large enough to efficiently create light without degrading the material,” Al-Attili said. “Our new micro gear design helps overcome this challenge.”

The new design features self-supporting micro gears on the edges so that they can be stretched by an oxide film deposited on the structures. This allows tensile stress to be applied without breaking the crystal structure of germanium. The gears sit on a silicon pedestal that connects it to the top of the silicon substrate and allows heat to dissipate during operation.

To demonstrate their new design, the researchers used electron beam lithography to fabricate the very fine physical features that form the teeth of the gears. They then illuminated the gears with a standard green laser that did not emit crooked light. After the micro gear absorbs the green light, it generates its own photons which circulate around the edges, forming twisted light that is reflected vertically out of the gear by the periodic teeth.

Precision optical simulations

Researchers tested and refined their design using computer simulations that model how light travels through gears over nanoseconds or even shorter periods of time. By comparing the prototype’s light emission with the results of the computer simulation, they were able to confirm that the gears generated twisted light.

“We can precisely design our device to control the number of rotations per propagation wavelength and the wavelength of the light emitted,” Al-Attili said.

Researchers are now working to further improve the efficiency of light emission from germanium micro gears. If successful, this technology would allow thousands of lasers to be integrated on a silicon chip to transmit information.

“The silicon manufacturing technologies that have been developed to make electronic devices can now be applied to make various optical devices,” Al-Attili said. “Our micro gears are just one example of how these capabilities can be used to fabricate devices at the nanoscale and micrometer scale.”

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