A tiny switch could redirect light between computer chips in mere nanoseconds
Maria Temming | November 14, 2019
[Time 2]
Microscopic switches that route light signals between computer chips like tiny traffic conductors could help make faster, more efficient electronics.
Light waves can carry information more easily than the electric current used in traditional circuitry, because particles of light called photons zip through materials without interacting with their surroundings as much as electrons. But so far, mechanical switches designed to manipulate such data-carrying light waves have run relatively slowly and required impractically high electric voltages to work.
Now, newly designed switches redirect light in less than a millionth of a second using just about one volt of electricity — comparable to the voltages used in ordinary electronics, researchers report in the Nov. 15 Science. Electronics outfitted with the new switch design to process data with light rather than electricity could help self-driving cars scan their surroundings for traffic and pedestrians or read out information from quantum computers.
Each switch comprises an ultrathin gold disk suspended above a silicon plate. Applying a small voltage across the switch forces the gold disk to bend upward like a bowl, or bow downward like an umbrella. The gold disk’s orientation at any given time controls whether light flowing through a nearby wirelike structure called a waveguide continues uninterrupted or gets rerouted.
As light in the waveguide passes by the switch, some light leaks into a racetrack-shaped gap between the gold disk and the silicon plate, whips around the track and recombines with light in the waveguide. If the gold plate is curved upward, the peaks and valleys of light waves that exit the track align with those in the waveguide — reinforcing the light along its original path.
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But if the gold plate is bent down toward the silicon plate, interactions with electrons in the gold delay light as it travels around the racetrack. That causes the valleys of light waves exiting the track to coincide with the peaks of waves flowing through the waveguide, canceling each other out and blocking the flow of light along its original course.
A second waveguide placed on another side of the silicon plate can provide an exit ramp for some light to escape the racetrack and start down a new path. Many interconnected switches choreographing the travel of various light signals between different electronic components could help a computer perform sophisticated operations.
The new switches redirect light waves in tens of nanoseconds, compared with the microseconds-long switching times of similar devices. Such high speeds are possible because the gold plate is more lightweight and easy to manipulate than the bulky components in other switches, says study coauthor Christian Haffner, a nanophotonics researcher at ETH Zurich and the National Institute of Standards and Technology in Gaithersburg, Md. “It’s like [driving] a sports car compared with a truck.”
Leonardo Midolo, a physicist at the University of Copenhagen not involved in the work, is impressed with the new design, which requires only 1.4 volts of electricity to flip a 10-square-micrometer switch. Other designs would require around 10 volts. “It shows the potential for this particular class of devices” to enter real-world use, he says.
But researchers should try to refine the current prototype to better preserve light signals when switching waves to a new waveguide, Midolo says. Currently, a light beam retains only about 60 percent of its original strength when it takes a detour. If each switch washes out almost 40 percent of the original light wave, it only takes a few switches for that information to be almost completely unreadable, he says. “This is definitely something that could be improved.”
[318 words]
Source: Science News
https://www.sciencenews.org/article/tiny-switch-redirects-light-between-computer-chips-nanoseconds
A Dallas museum hosts rare hominid fossils from South Africa
Tara Haelle | November 15, 2019
[Time 4]
For the next few months, visitors to the Perot Museum of Nature and Science in Dallas will have a rare opportunity to see fossils of ancient hominids up close.
A new exhibition, “Origins: Fossils from the Cradle of Humankind,” open through March 22, brings to the museum Australopithecus sediba and Homo naledi. The discoveries of these South African species over the last decade have raised new questions about humans’ family tree.
Almost as amazing as the fossils themselves is the fact that they traveled to the United States. “Origins” marks the first time these fossils have been displayed outside of South Africa, and Dallas is their only scheduled stop.
“There’s something really distinct in our modern world about being able to see something … that’s authentic, that really is 2 million years old or 300,000 years old, and you’re there just inches from it rather than seeing it in virtual reality or on your computer screen,” says Becca Peixotto, director of the museum’s Center for the Exploration of the Human Journey.
“Origins” focuses primarily on two specimens. First there’s Karabo, the male A. sediba skeleton that paleoanthropologist Lee Berger’s 9-year-old son Matthew discovered at a site called Malapa in 2008. Karabo, at the time of his death, about 1.97 million years ago, was close to Matthew’s age. Then there’s Neo, one of over a dozen H. naledi individuals found deep in the Rising Star cave system near Johannesburg in 2013. Neo, an adult male, lived about 300,000 years ago, about the time H. sapiens emerged.
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The exhibition encourages visitors to compare the mix of physical traits that these hominids had, in the same way scientists might as they piece together where species fit in humans’ evolutionary story. A panel points out how A. sediba had hands, feet, teeth and hips similar to modern people’s, yet also had small brains and long, apelike arms. In analyzing A. sediba’s features, Berger, of the University of the Witwatersrand in Johannesburg, has argued that A. sediba is a contender for a direct ancestor of the genus Homo.
As scientists have discovered more and more fossils, it has become clear that the traditional view of human evolution as a “march of progress,” with a straight line of species leading to H. sapiens, is too simplistic, says Berger, who oversaw the discoveries of A. sediba and H. naledi. “What we’re seeing, as we get a clearer picture, is that we grossly underestimated the complexity of hominids in the past.”
What “Origins” does best is showcase the process of science — to the point of putting actual working scientists on display. Researchers can apply to study the fossils during the exhibition’s run — “as long as they do it in front of the public,” says Linda Silver, the museum’s chief executive officer. About halfway through the exhibition is a glass-enclosed lab where researchers can work while visitors watch.
One way of getting people to trust science, Berger says, is to understand its process — and to see the real deal.
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For visitors, coming face-to-face with the real deal begins with Karabo, whose skeleton is roughly 30 percent complete, according to Berger. A nearby case displays a rocky sphere that probably contains the rest of Karabo’s bones, allowing visitors to see how the fossils are typically found.
Visitors have several opportunities to learn about the process of science. In one section, a “video tree” describes H. naledi’s discoveryand shows scientists from different specialties talking about their work on the species. A map and 3-D model of the Rising Star cave system are also on display. Visitors can attempt to squeeze through the tiny opening — 18 centimeters wide — of a life-size model of the entrance to the chamber where Peixotto and five other scientists dropped 12 meters down to excavate H. naledi fossils.
After visitors see Neo’s skeleton, the exhibition concludes with a re-created dig site, where visitors become paleoanthropologists and search through a large box of sand containing 15 fossil models. After photographing their finds with iPads, visitors can go to a science tent for a guided analysis of the images. “It’s kind of realistic because one of the things we’re starting to do is leave more [fossils] in place” in the field, Peixotto says. But Neo’s and Karabo’s excavated bones are meant to inspire visitors. “Just being able to see those real things,” Peixotto says, “there’s a sense of awe and an emotional connection that’s really important for us in understanding that these are our common roots as a species.”
[250 words]
Source: Science News
https://www.sciencenews.org/article/dallas-museum-hosts-rare-hominid-fossils-south-africa
Tiny low-energy device to rapidly reroute light in computer chips
National Institute of Standards and Technology (NIST) | November 14, 2019
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Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have developed an optical switch that routes light from one computer chip to another in just 20 billionths of a second -- faster than any other similar device. The compact switch is the first to operate at voltages low enough to be integrated onto low-cost silicon chips and redirects light with very low signal loss.
The switch's record-breaking performance is a major new step toward building a computer that uses light instead of electricity to process information. Relying on particles of light -- photons -- to transport data within a computer offers several advantages over electronic communications. Photons travel faster than electrons and don't waste energy by heating up the computer components. Managing that waste heat is a major barrier to improving computer performance. Light signals have been used for decades to transmit information over great distances using optical fibers, but the fibers take up too much room to be used to carry data across a computer chip.
The new switch combines nanometer-scale gold and silicon optical, electrical and mechanical components, all densely packed, to channel light into and out of a miniature racetrack, alter its speed, and change its direction of travel. (One nanometer is a billionth of a meter, or about one-hundred-thousandth the width of a human hair.) The NIST-led international team describes the device online today in Science.
The device has myriad applications, notes study co-author Christian Haffner of NIST, ETH Zurich and the University of Maryland. In driverless cars, the switch could rapidly redirect a single light beam that must continually scan all parts of the roadway to measure the distance to other automobiles and pedestrians. The device could also make it easier to use more powerful light-based circuits instead of electricity-based ones in neural networks. These are artificial intelligence systems that simulate how neurons in the human brain make decisions about such complex tasks as pattern recognition and risk management.
The new technology also uses very little energy to redirect light signals. This feature may help realize the dream of quantum computing. A quantum computer processes data stored in the subtle interrelations between specially prepared pairs of subatomic particles. However, these relationships are extremely fragile, requiring that a computer operate at ultralow temperatures and low power so that the particle pairs are disturbed as little as possible. Because the new optical switch requires little energy -- unlike previous optical switches -- it could become an integral part of a quantum computer.
Haffner and his colleagues, who include Vladimir Aksyuk and Henri Lezec of NIST, say their findings may come as a surprise to many in the scientific community because the results contradict long-held beliefs. Some researchers have thought that opto-electro-mechanical switches would not be practical because they would be bulky, operate too slowly and require voltages too high for the components of a computer chip to tolerate.
The switch exploits the wave nature of light. When two identical light waves meet, they can superpose such that the crest of one wave aligns or reinforces the crest of the other, creating a bright pattern known as constructive interference. The two waves may also be exactly out of step, so that the valley of one wave cancels the crest of the other, resulting in a dark pattern -- destructive interference.
In the team's setup, a light beam is confined to travel inside a miniature highway -- a tube-shaped channel known as a waveguide. This linear highway is designed so that it has an off-ramp -- some of the light can exit into a racetrack-shaped cavity, just a few nanometers away, etched into a silicon disk. If the light has just the right wavelength, it can whip around the racetrack many times before leaving the silicon cavity.
The switch has one other crucial component: a thin gold membrane suspended just a few tens of nanometers above the silicon disk. Some of the light traveling in the silicon racetrack leaks out and strikes the membrane, inducing groups of electrons on the membrane's surface to oscillate. These oscillations, known as plasmons, are a kind of hybrid between a light wave and an electron wave: The oscillating electrons resemble the incoming light wave in that they vibrate at the same frequency, but they have a much shorter wavelength. The shorter wavelength lets researchers manipulate the plasmons over nanoscale distances, much shorter than the length of the original light wave, before converting the oscillations back into light. This, in turn, allows the optical switch to remain extremely compact.
By changing the width of the gap between the silicon disk and the gold membrane by only a few nanometers, the researchers could delay or advance the phase of the hybrid light wave -- the point in time when the wave reaches a crest or valley. Even minuscule variations in the width of the gap, which the team accomplished by electrostatically bending the gold membrane, dramatically altered the phase.
Depending on how much the team had advanced or delayed the phase of the wave, when it recombined with light still traveling in the tube-shaped highway, the two beams interfered either constructively or destructively (see animation). If the light beams match up to interfere constructively, the light will continue in its original direction, traveling down the tube. But if the light beams interfere destructively, canceling each other out, that pathway is blocked. Instead, the light must move in another direction, determined by the orientation of other waveguides, or routes, placed close to the blocked pathway. In this way, the light can be switched at will to any of hundreds of other computer chips.
Scientists had once thought that a plasmonic system would greatly attenuate light signals because photons would penetrate the interior of the gold membrane, where electrons would absorb much of the light energy.
But the researchers have now proved that assumption wrong. The compactness of the device and a design that ensured that few photons would penetrate the membrane resulted in a loss of just 2.5% of the light signal, compared with 60% with previous switches. That puts the switch, although still a prototype, within reach of commercial applications.
The team is now working to make the device even smaller by shortening the distance between the silicon disk and the gold membrane. This would further reduce signal loss, making the technology even more appealing to industry.
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Source: Science Daily
https://www.sciencedaily.com/releases/2019/11/191114140820.htm
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发表于 2019-11-19 09:01:11
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