Researchers at the University of California, Berkeley, have found a new way to harness the properties of light waves that can dramatically increase the amount of data they carry. They demonstrated the emission of discrete torsion lasers from antennas made up of concentric rings roughly equal to the diameter of a human hair, small enough to be placed on computer chips.
The new work, reported in an article published on Thursday, February 25 in the magazine Physics of nature, opens wide the amount of information that can be multiplexed, or transmitted simultaneously, by a coherent light source. A common example of multiplexing is the transmission of multiple phone calls over a single cable, but there were fundamental limits to the number of coherent twisted light waves that could be directly multiplexed.
“This is the first time that lasers that produce bent light have been directly multiplexed,” said the study’s principal investigator, Boubacar Kanté, an associate professor of Chenming Hu in the Department of Electrical Engineering and Computer Science at UC Berkeley. “We have been experiencing an explosion of data in our world, and the communication channels we have now will soon be insufficient for what we need. The technology we are reporting exceeds current limits of data capacity through a feature of light called Orbital angular momentum … It’s a game changer with applications in biological imaging, quantum cryptography, communications and high-capacity sensors. “
Kanté, who is also a faculty scientist in the Lawrence Berkeley National Laboratory’s Division of Materials Sciences (Berkeley Lab), has continued this work at UC Berkeley after beginning research at UC San Diego. The first author of the study is Babak Bahari, a former Ph.D. student in Kanté’s laboratory.
Kanté said that current methods of transmitting signals through electromagnetic waves are reaching their limits. The frequency, for example, has been saturated, so there are only a limited number of stations that can be tuned into the radio. Polarization, where the light waves are separated into two values, horizontal or vertical, can double the amount of information transmitted. Filmmakers take advantage of this when creating 3D movies, allowing viewers with specialized glasses to receive two sets of signals, one for each eye, to create a stereoscopic effect and the illusion of depth.
Unleashing the potential in a vortex
But beyond frequency and polarization is the orbital angular momentum, or OAM, a property of light that has attracted the attention of scientists because it offers an exponentially greater capacity for data transmission. One way to think of OAM is to compare it to the vortex of a tornado.
“The vortex in light, with its infinite degrees of freedom, can, in principle, support an unlimited amount of data,” said Kanté. “The challenge has been to find a way to reliably produce the infinite number of OAM beams. No one has ever produced such high load OAM beams in such a compact device.”
The researchers started with an antenna, one of the most important components of electromagnetism and, they noted, critical to ongoing 5G and upcoming 6G technologies. The antennas in this study are topological, which means that their essential properties are preserved even when the device is twisted or bent.
Creating rings of light
To make the topological antenna, the researchers used electron beam lithography to etch a grid pattern in indium gallium arsenide phosphide, a semiconductor material, and then attached the structure to a surface made of iron ytrium garnet. The researchers designed the grid to form quantum wells in a pattern of three concentric circles, the largest about 50 microns in diameter, to trap photons. The design created the conditions to support a phenomenon known as the photonic quantum Hall effect, which describes the motion of photons when a magnetic field is applied, forcing light to travel in only one direction in the rings.
“People thought that the quantum Hall effect with a magnetic field could be used in electronics but not optics because of the weak magnetism of existing materials at optical frequencies,” Kanté said. “We are the first to show that the quantum Hall effect works with light.”
By applying a magnetic field perpendicular to its two-dimensional microstructure, the researchers successfully generated three OAM lasers that traveled in circular orbits over the surface. The study further showed that the lasers had quantum numbers as large as 276, referring to the number of times light rotates around its axis in one wavelength.
“Having a larger quantum number is like having more letters to use in the alphabet,” Kanté said. “We are allowing light to expand its vocabulary. In our study, we demonstrated this ability at telecommunication wavelengths, but in principle, it can be adapted to other frequency bands. Although we created three lasers, multiplying the data rate by three, there is no limit to the possible number of beams and the data capacity. “
Kanté said the next step in his lab is to make quantum Hall rings that use electricity as a power source.
Laser cavities take on new shapes and functionality
Bahari, B., Hsu, L., Pan, SH et al. Photonic quantum Hall effect and multiplexed light sources of large orbital angular moments. Physics of nature (2021). DOI: 10.1038 / s41567-021-01165-8
Provided by the University of California – Berkeley
Citation: Unconsolidated Light: Data Limits Could Disappear With New Optical Antennas (2021, Feb 25) Retrieved Feb 25, 2021 from https://phys.org/news/2021-02-unbound-limits-optical -antennas.html
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