Using the same kind of techniques that allow DSL to transmit high-speed Internet over regular phone lines, scientists have transmitted signals at 10 terabits per second or more over short distances, significantly faster than other telecommunications technologies,a new study finds.
Digital subscriber line (DSL) modems delivered the first taste of high-speed Internet access to many users. They make use of the fact that existing regular telephone lines are capable of handling a much greater bandwidth than is needed just for voice. DSL systems leverage that extra bandwidth to send multiple signals in parallel across many frequencies.
Using megahertz frequencies, current DSL technologies can achieve downstream transmission rates of up to 100 megabits per second at a range of 500 meters, and more than 1 gigabit per second at shorter distances. (DSL signal quality often decreases over distance because of the limitations of phone lines; telephone companies can boost voice signals with small amplifiers called loading coils, but these do not work for DSL signals.)
Reprogrammable photonic circuits based on a novel programmable material might speed the rate at which engineers can develop working photonic devices, researchers say.
Electronic integrated circuits (ICs) are nowadays key to many technologies, but their light-based counterparts, photonic integrated circuits (PICs), may offer many advantages, such as lower energy consumption and faster operation. However, current fabrication methods for PICs experience a great deal of variability, such that many of the resulting devices are slightly off base from the desired specifications, resulting in limited yields.
Since topological insulators were first created in 2007, these novel materials, which are insulating on the inside and conductive on the outside, have intrigued researchers for their potential in electronics. However, a related but more obscure class of materials—topological photonics—may reach practical applications first.
Topology is the branch of mathematics that investigates what aspects of shapes withstand deformation. For example, an object shaped like a ring may deform into the shape of a mug, with the ring’s hole forming the hole in the cup’s handle, but cannot deform into a shape without a hole.
Using insights from topology, researchers developed topological insulators. Electrons traveling along the edges or surfaces of these materials strongly resist any disturbances that might hinder their flow, much as the hole in a deforming ring would resist any change.
Recently, scientists have designed photonic topological insulators in which light is similarly “topologically protected.” These materials possess regular variations in their structures that lead specific wavelengths of light to flow along their exterior without scattering or losses, even around corners and imperfections.
Here are three promising potential uses for topological photonics.
TOPOLOGICAL LASERS Among the first practical applications of these novel materials may be lasers that incorporate topological protection. For example, Mercedeh Khajavikhan of the University of Southern California and her colleagues developed topological lasers that were more efficient and proved more robust against defects than conventional devices.
The researchers started with a wafer made of gallium arsenide and aluminum gallium arsenide layers sandwiched together. When electrically charged, the wafer emitted bright light.
The scientists drilled a lattice of holes into the wafer. Each hole resembled an equilateral triangle with its corners snipped off. The lattice was surrounded by holes of the same shape oriented the opposite way.
The topologically protected light from the wafer flowed along the interface between the different sets of holes, and emerged from nearby channels as laser beams. The device proved robust against defects, says electrical and optical engineer Qi Jie Wang at Nanyang Technological University in Singapore.
The laser works in terahertz frequencies, which are useful for imaging and security screening. Khajavikhan and her colleagues are now working to develop ones that work at near-infrared wavelengths, possibly for telecommunications, imaging, and lidar.
PHOTONIC CHIPS By using photons instead of electrons, photonic chips promise to process data more quickly than conventional electronics can, potentially supporting high-capacity data routing for 5G or even 6G networks. Photonic topological insulators could prove especially valuable for photonic chips, guiding light around defects.
However, topological protection works only on the outsides of materials, meaning the interiors of photonic topological insulators are effectively wasted space, greatly limiting how compact such devices can get.
To address this problem, optical engineer Liang Feng at the University of Pennsylvania and his colleagues developed a photonic topological insulator with edges they could reconfigure so the entire device could shuttle data. They built a photonic chip 250 micrometers wide and etched it with oval rings. By pumping the chip with an external laser, they could alter the optical properties of individual rings, such that “we could get the light to go anywhere we wanted in the chip,” Feng says—from any input port to any output port, or even multiple outputs at once.
All in all, the chip hosted hundreds of times as many ports as seen in current state-of-the-art photonic routers and switches. Instead of requiring an off-chip laser to reconfigure the chip, the researchers are now developing an integrated way to perform that task.
QUANTUM CIRCUITRYQuantum computers based on qubits are theoretically extraordinarily powerful. But qubits based on superconducting circuits and trapped ions are susceptible to electromagnetic interference, making it difficult to scale up to useful machines. Qubits based on photons could avoid such problems.
Quantum computers work only if their qubits are “entangled,” or linked together to work as one. Entanglement is very fragile—researchers hope topological protection could defend photonic qubits from scattering and other disruptions that can occur when photons run across inevitable fabrication errors.
Photonic scientist Andrea Blanco-Redondo, now head of silicon photonics at Nokia Bell Labs, and her colleagues made lattices of silicon nanowires, each 450 nanometers wide, and lined them up in parallel. Occasionally a nanowire in the lattice was separated from the others by two thick gaps. This generated two different topologies within the lattice and entangled photons traveling down the border between these topologies were topologically protected, even when the researchers added imperfections to the lattices. The hope is that such topological protection could help quantum computers based on light scale up to solve problems far beyond the capabilities of mainstream computers.
This article appears in the April 2020 print issue as “3 Practical Uses for Topological Photonics.”
In novel materials known as photonic topological insulators, wavelengths of light can flow around sharp corners with virtually no losses. Now scientists have witnessed key details of what the light does inside these structures, which could help them to better engineer these materials for real-world applications.
Topology is the branch of mathematics that explores what features of shapes withstand deformation. For instance, an object shaped like a doughnut can get pushed and pulled into the shape of a mug, with the doughnut’s hole forming the hole in the cup’s handle, but it could not get deformed into a shape that lacked a hole.
Using insights from topology, researchers developed the first electronic topological insulators in 2007. Electrons traveling along the edges or surfaces of these materials strongly resist any disturbances that might hinder their flow, much as a doughnut might resist any change that would remove its hole.
A new ultra-fast machine-vision device can process images thousands of times faster than conventional techniques with an image sensor that is also an artificial neural network.
Machine vision technology often uses artificial neural networks to analyze images. In artificial neural networks, components dubbed “neurons” are fed data and cooperate to solve a problem, such as recognizing images. The neural net repeatedly adjusts the strength of the connections or “synapses” between its neurons and sees if the resulting patterns of behavior are better at solving the problem. Over time, the network discovers which patterns are best at computing solutions. It then adopts these as defaults, mimicking the process of learning in the human brain.
Cloud storage services usually charge clients for how much data they wish to store. But charging users only when they actually use that data may be a more cost-effective approach, a new study finds.
Internet-scale web applications—the kind that run on servers across the globe and may handle millions of users—are increasingly relying on services that store data in the cloud. This helps applications deal with huge amounts of data. Facebook, for example, generates 4 petabytes (4 million gigabytes) of data every day.
Graphene can literally be made in a flash by using electricity to zap nearly anything that contains carbon, including discarded food and plastic, a new study finds.
Graphene is made of flexible, transparent sheets each just one carbon atom thick. It’s 200 times stronger than steel, lighter than paper, and more electrically and thermally conductive than copper. Currently the most common way to make graphene in bulk is via exfoliation. It works a bit like how you might exfoliate your skin, and involves sloughing layers of graphene off a block of graphite.
However, chemical exfoliation uses lots of acid and is very expensive, while exfoliation using sound energy or fast-flowing fluid pries off platelets of graphene that are often more than 20 layers thick. Scientists can also produce graphene by depositing it from a vapor onto a surface, but this only makes tiny amounts.
The world’s first programming language based on classical Chinese is only about a month old, and volunteers have already written dozens of programs with it, such as one based on an ancient Chinese fortune-telling algorithm.
After coming up with the idea for the new language, wenyan-lang, roughly a year ago, Huang finished the core of the language during his last month at school. It includes a renderer that can display a program in a manner that resembles pages from ancient Chinese texts.
When the going gets tough, future soft robots may break into a sweat to keep from overheating, much like marathon runners or ancient hunters chasing prey in the savannah, a new study finds.
Whereas conventional robots are made of rigid parts vulnerable to bumps, scrapes, twists, and falls, soft robots inspired by starfish, worms, and octopuses can resist many such kinds of damage and squirm past obstacles. Soft robots are also often cheaper and simpler to make, comparatively lightweight, and safer for people to be around.
However, the rubbery materials that make up soft robots often trap heat, exacerbating problems caused by overheating. Moreover, conventional devices used to control heat such as radiators and fans are typically made of rigid materials that are incompatible with soft robotics, says T.J. Wallin, a co-author and research scientist at Facebook Reality Labs.
Practically any kind of crap can boost graphene’s properties as a catalyst—even chicken droppings, say the authors of a new tongue-in-cheek study.
Graphene is often hailed as a wonder material—flexible, transparent, light, strong, and electrically and thermally conductive. Such qualities have led researchers worldwide to consider weaving these one-atom-thick sheets of carbon into advanced devices. Scientists have also explored graphene’s properties as a catalyst for the kinds of oxygen reduction reactions often used in fuel cells and the hydrogen evolution reactions used to split apart water molecules to generate hydrogen fuel.
To further enhance graphene’s catalytic properties, researchers have tried doping it with a variety of elements. Seemingly all such studies have claimed graphene’s catalytic abilities improved, regardless of whether the doping materials had contrasting properties with each other. This is “contrary to what any material scientist might expect,” says Martin Pumera, a materials scientist at the University of Chemistry and Technology in Prague.
A nearly zero-energy alternative to Bitcoin and other blockchain-based cryptocurrencies that promises as much security but far greater speeds is now under development in Europe, a new study finds.
Cryptocurrencies such as Bitcoin are digital currencies that use cryptography to protect and enable financial transactions between individuals, rendering third-party middlemen such as banks or credit card companies unnecessary. The explosion of interest in Bitcoin made it the world’s fastest-growing currency for years.
Which algorithms are best at integrating solar arrays with electrical grid storage?
By analyzing the kinds of algorithms that control the flow of electricity between solar cells and lithium-ion batteries, scientists have identified the best types of algorithms to govern electrical grid storage of solar power.
A dizzying number of algorithms exist to help manage the flow of electricity between photovoltaic cells and lithium-ion batteries in the most profitable manner. These come in a variety of complexities and have diverse computational power requirements.
“Lithium-ion batteries are expensive components, and photovoltaic plant owners have to pay large amounts of money in order to install lithium-ion batteries on plant,” says study lead author Alberto Berrueta, an engineering researcher at the Public University of Navarre’s Institute of Smart Cities in Pamplona, Spain. “Management algorithms are of capital importance in order to preserve a long lifetime for the batteries to make the most out of the batteries.”
To see which types of these algorithms work best at getting the most out of lithium-ion batteries, researchers developed models based off the amount of power generated over the course of a year from a medium-sized roughly 100-kilowatt solar cell array located in Navarre. They focused on concerns such as the computational requirements needed, the price of electricity, battery life, battery costs, and battery charging and discharging rates.
The researchers looked at three families of algorithms currently used in managing electricity from commercial solar cell arrays: dynamic, quadratic and linear. Dynamic algorithms tackle complex, sequential optimization problems by breaking them down into several simpler sub-problems. Quadratic algorithms each involve at least one squared variable and often find use in calculating areas, computing the profit of a product, and pinpointing the speed and position of an object. Linear algorithms each involve variables that are not squared and have the simplest computational requirements.
The scientists found the dynamic algorithms required far more computational power than the other two families of algorithms; as the number of variables grew, they experienced an exponential increase in problem complexity. A commercial PC that would take about 10 seconds to compute the energy flow between the solar cells and lithium-ion batteries using the linear and quadratic algorithms would take 42 minutes with the dynamic algorithms.
Linear algorithms had the lowest computational requirements but suffered in terms of accuracy. For instance, their simplified models did not account for how electrical current can reduce battery lifetime. All in all, the linear algorithms provided an average of 20 percent lower profits than the maximum achievable.
The researchers concluded that quadratic algorithms provided the best trade-off between accuracy and computational simplicity for solar power applications. Quadratic algorithms had about the same low computational requirements as linear algorithms while achieving revenues similar to dynamic algorithms for all battery sizes.
In the future, scientists can investigate which management algorithms might work best with hybrid energy storage systems, Berrueta says. Future research can also investigate which computer models work best at calculating all the factors affecting the lifetime of lithium-ion batteries, including batteries discarded from electric vehicles that might find a second life working in renewable energy plants, he adds.
Electrolyte additives can boost lithium-ion battery temperature range
New additives can help lithium-ion batteries perform over a wider range of temperatures, a potential boon for electric cars, a new study finds.
Electric cars struggle with extreme temperatures, which can degrade the electrolyte solutions that conduct ions between the negative electrodes, or anodes, and positive electrodes, or cathodes, within lithium-ion batteries.
A key additive to most of these electrolyte solutions is ethylene carbonate, which helps produce a protective layer that prevents further decomposition of electrolyte components when they interact with the anode. However, ethylene carbonate has a high melting point, which limits its performance at low temperatures.
Materials scientist Wu Xu at Pacific Northwest National Laboratory in Richland, Washington, and his colleagues previously showed they could extend the temperature range of lithium-ion batteries by partially replacing ethylene carbonate with propylene carbonate and adding cesium hexafluorophosphate. However, they wanted to improve the temperature range of lithium-ion batteries even further, so they could perform well from -40 to 60 degrees C.
In the new study, Xu and his colleagues tested the effects of five electrolyte additives on the performance of lithium-ion batteries within this temperature range. Through a combination of computational modeling, decades of experience with the chemical and electrochemical properties of liquid electrolytes and additives, and trial and error, they identified an optimized combination of three compounds that they added to their previous electrolyte solution.
This new mixture caused the formation of highly conductive, uniform and robust protective layers on both the anode and the cathode. At -40 degrees C, batteries containing this blend achieved 67 percent of the discharging performance they saw at room temperature. In comparison, regular lithium-ion batteries only experience about 20 percent discharge capacity, Xu says.
Normally, including a variety of additives within electrolytes results in thick layers on both positive and negative electrodes at low temperatures that are fairly resistant to ion transport, “leading to very poor low-temperature discharge performance,” Xu says. “Our additive mixture still results in very thin surface layers on both electrodes, and their resistance is low, and does not change much with cycling. This is achieved by the synergistic effects of these additives.”
The new batteries also displayed long-term cycling stability at 25 degrees C, retaining more than 85 percent of their original capacity after 1,000 cycles. In addition, at 60 degrees C, the new batteries maintained more than 60 percent of their original capacity after 300 cycles, whereas conventional lithium-ion batteries only kept about 10 percent of their original capacity, Xu says.
The scientists aim to validate these results in “commercial lithium ion batteries under practical testing conditions, and then hope that battery companies will use the electrolytes in their battery systems for electric vehicles,” Xu says. They also hope to experiment with electrolyte additives to improve other aspects of battery performance, such as boosting their charging speed and reducing their flammability, Xu adds.
The scientists detailed their findings June 19 in the journal ACS Applied Materials & Interfaces.
Chinese researchers are developing an airborne quantum communications network with drones as nodes
Quantum drones under development in China could lead to nigh unhackable airborne quantum communication networks, a new study finds.
Quantum mechanics makes possible a strange phenomenon known as entanglement. Essentially, two or more particles such as photons that get linked or “entangled” can, in theory, influence each other no matter the distance between them. Entanglement is essential to the workings of quantum computers, the networks that would connect them, and the most sophisticated kinds of quantum cryptography—a means of information exchange that is impervious to hacking.
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