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Plasmon Laser Is Fastest to Switch

Those laying the foundations for future generations of electronics have long had a fondness for photons. But until recently, there was a catch: photons would limit the miniaturization now achieved with silicon chips because they need space—at least half their wavelength—to move around. So structures on photonic chips would have to be at least a few hundred nanometers wide.

But this catch now comes with its own caveat: Researchers expect that dealing with plasmons (electron waves on a metal surface generated by light) instead of photons themselves will allow the creation of photonic chips with structures comparable in size to those on the most advanced silicon chips. Indeed, new plasmonic nanolasers that can focus light in spots much smaller than their wavelength might play a key role in future photonic circuits.

Plasmonic lasers aren’t just important because of their size; they’re also amazingly fast. Their speed was the big news reported by researchers at Imperial College London and the University of Jena in Germany last week in Nature Physics. They’ve created an ultrafast plasmonic semiconductor laser that will ultimately be able to switch its power on and and off a thousand billion times per second. This new terahertz laser is a thousand times as fast as today’s speediest lasers.

 

The laser features zinc oxide semiconductor nanowires as the lasing medium. The nanowires, which are a few hundred nanometers hick and are about 10 micrometers long on average, are deposited on a 10-nm-thick insulating layer that sits atop a silver film.

Like most experimental lasers, this one needed light from another laser to get it going. Pulses from a pump laser hit the nanowire 800,000 times per second, resulting in laser pulses inside the nanowire that lasted 800 femtoseconds.

The light is further amplified by the presence of plasmons in the 10-nm area between the metallic film and the nanowire itself. “The surface plasmons can confine the light much more strongly to the interface between the metal and the dielectric,“ Themis Sidiropoulos, a physicist at Imperial College London who worked on the nanowire laser’s development said in the Nature Physics paper. “And if you place the nanowires on the metal substrate, you get strong confinement of the optical mode, and you also get spontaneous enhanced emission—the Purcell effect.” This spontaneous emission basically makes the nanowire laser faster, says Sidiropoulos.

The fact that the nanowire is optically pumped is still an impediment to it reaching its full potential. Sidiropoulos says that for applications in photonics and communications, optical pumping will have to be replaced by electrical pumping. "This is still very tricky, and there are a lot of people working on it; this is still ongoing work," says Sidiropoulos.

Inventors of Blue LED Win Nobel Prize in Physics

Taking a more practical turn, the Royal Swedish Academy of Sciences has awarded this year’s Nobel Prize in Physics to three inventors of the blue light-emitting diode.

Isamu Akasaki and Hiroshi Amano, who worked together at the University of Nagoya, and Shuji Nakamura, who worked at Nichia Chemicals in Tokushima, developed bright versions of the devices in the late 1980s and early 1990s. 

“Their inventions were revolutionary,” the Nobel Foundation said in a press release. “Incandescent light bulbs lit the 20th century; the 21st century will be lit by LED lamps.”

LEDs can produce as much as 300 lumens per watt of electrical input power, the press release goes on to note, nearly 20 times as much as incandescent bulbs yield and about four times as much as that of fluorescent lamps. The greater efficiency could help conserve resources in a world where about a quarter of the energy produced goes into lighting.

In incandescent bulbs, light is almost an afterthought; the filaments are essentially just big resistors and most of the energy is released in the form of heat. 

LEDs more directly convert electricity into photons. They typically contain two layers of semiconducting materials, one engineered to contain an excess of electrons and the other an excess of holes (absences of electrons that act as positive charges). To make photons, the electrons from one side and holes from the other are drawn together. They meet at a thin, active layer between the two materials, where they join and release energy in the form of photons. 

Nakamura often takes the headlines in discussions of the invention of the blue LED. But, the Nobel Foundation notes, Akasaki and Amano were the first to develop the high-quality gallium nitride used to make the blue diodes, beginning in 1986 (pdf). The three lighting luminaries, all of whom are IEEE members (Akasaki is a Life Fellow), have won multiple IEEE awards including the IEEE Edison Medal and numerous IEEE Photonics Society Awards.  

With the invention of these devices, engineers could now create white light by using blue light to excite a phosphor or by combining red, green, and blue devices. LEDs now light LCD screens, are slowly pushing aside incandescent and fluorescent lighting in homes and offices, and can be used to electronically control color to better mimic the diurnal cycle. The blue LED also formed the basis for a later invention – the blue semiconductor laser.

Development on the blue LED has continued steadily since its invention. One key challenge has been LED droop, a drop in efficiency when currents are raised to produce more light. Last year, a team of researchers claimed they’d found the source of the droop, but others weren't so confident. And engineering a way to circumvent it is another matter.

Photos: Jonathan Nackstrand/AFP/Getty Images

The Internet of Things Gets a New OS

British processor powerhouse ARM Holdings, said last week that it intends to launch a new, low-power operating system that will manage web-connected devices and appliances using chips based on the company’s 32-bit Cortex-M microcontrollers. 

The operating system, called mbed OS, is meant to resolve productivity problems that arise from fragmentation—where different devices in the so-called “Internet of things” (IoT) market run on a hodgepodge of different protocols. ARM is looking to consolidate those devices under a single software layer that's simple, secure, and free for all manufacturers to use.

“Instead of having large teams spending years designing a product,” ARM vice president of research and development Kriztian Flautner told the BBC, “we'd like to turn that into months, so that you can take the [hardware] components, assemble the right ones, connect the device and focus on the problem you are solving and not the means to getting there."

In the last few years, ARM has made a push to develop more technologies designed for IoT products. In a Pew survey this past spring, 83 percent of respondents thought the future of IoT would help improve their lives. Gartner, a tech research firm, recently predicted that by 2020 there will be 26 billion Internet-connected devices, an almost 30-fold increase from 2009.

However, this is the first operating system ARM has ever developed.

The mbed OS supports several standards of connectivity, including Wi-Fi, Bluethooth Smart, Thread, and a sub-6-gigahertz version of 6LoWPAN. It also supports many cellular standards, including 3G and LTE. At the same time, ARM is launching mbed server software, which the company says will allow users to gather and analyze data collected from IoT devices.

The OS was designed with power efficiency and battery life in mind. ARM claims it will only take up 256 kilobytes of memory, compared to the several gigabytes worth of storage needed for a smartphone OS. The company hopes developers will use mbed to create devices with battery lives measured in years.

Parts of the OS will be open source, though ARM says it wants to retain control of other parts to ensure mbed remains unfragmented. A recent EETimes study reports that in-house and custom designed systems for IoT devices are on the decline. Open source code already runs in 36 percent of embedded operating systems and is projected to keep rising, with Android and FreeRTOS leading the pack. ARM seems to be trying to balance the advantages of development flexibility with proprietary control, but it remains to be seen how well that plays out.

Chris Rommel from the VDC Research group also told the BBC that while he believed most companies would welcome this news, it was unlikely the mbed OS would find its way into all IoT devices. "There will likely never be any one operating system—or even two or three—that can satisfy the broad ranges of needs of all the various devices that compose the Internet of things. They are just too different."

Already there are some big appliance makers who are sure to resist the mbed OS. GE employs the software Predix in almost all its IoT products, and Samsung is heavily invested into using Tizen for its family of IoT devices. Nest Labs's products run on a proprietary software based on Linux, though that's likely to shift to Android soon due to company's acquisition by Google.

However, that hasn't squelched enthusiasm from other companies yet. ARM will release the OS to hardware manufacturers and other developers before the end of the year, and says 25 companies have already signed up, including Ericsson, Freescale, IBM, NXP, and Zebra. The first devices to use mbed OS are expected to arrive in 2015.

Expedition Brings High Speed Connectivity to the Ocean Floor

Members of the U.S. National Science Foundation's Ocean Observatory Initiative (OOI) are approaching the end of an nearly three month-long cruise during which they installed a fiberoptic cables and power lines that form the backbone of a seafloor observatory in the Pacific Ocean. The observatory will make it possible for oceanographers and other researchers to gather data about the ocean floor in real time from a network of seismometers, cameras, and other sensors hundreds of kilometers off-shore and as deep as 1800 meters beneath the ocean's surface. 

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FAA: Airlines Must Replace Boeing Cockpit Screens to Avoid Wi-Fi Interference

U.S. regulators aren't taking any chances with the discovery that Wi-Fi signals can cause flickering or temporary blank screens in the cockpits of Boeing passenger jets. On Tuesday, the FAA ordered airlines to replace the cockpit displays used by pilots in more than 1,300 Boeing aircraft over the next five years.

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Bright, Bendy Gallium Nitride LEDs

When it comes to light-emitting diodes, both inorganic and organic devices have found their niches. Inorganic LEDs, which beat organic ones hands down in brightness, energy efficiency, and durability, reign in lighting. Organic LEDs, on the other hand, can be tiny and are cheap to manufacture, so they take the prize for large-area, high-resolution and flexible applications such as displays and wearable sensors.

Researchers have now combined the best of inorganic and organic LEDs. They've made bendable inorganic LEDs by growing micrometers-tall gallium nitride rods on graphene. The tiny 50µm x 50µm LEDs glow bright blue and retain their brightness after being bent more than 1000 times. They could lead to inexpensive, high-quality displays and sensors, and could be used in touch panels and smart contact lenses, says Gyu-Chul Yi, a professor of physics at Seoul National University. Yi and his colleagues reported the LEDs in the online journal APL Materials.

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Mantis Shrimp Eyes Inspire Cameras to See Cancer

Millions of years of evolution have given the Mantis shrimp compound eyes to spot delicious meals that it can either spear or club to death in its underwater environment. More recently, the natural design of those eyes has inspired a new camera sensor that could spot cancer cells inside patients' bodies.

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Browser Beware: Wi-Fi Users Sign Over First-Born Children

The results of a social experiment in London suggest that on-the-go Internet users are not being as careful as they should be when connecting to unfamiliar networks. In order to connect to a rigged Wi-Fi network set up by mobile security firm F-Secure, six users agreed to sign over their first born children to the company.

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New Neurological Map Could Be Key To Psychiatric Brain Stimulation Treatments

Treating mental illness doesn't always refer to talk and prescriptions. Psychiatrists nowadays are increasingly embracing innovative technologies that alter neural circuits electrically instead of chemically. Still, the growing field of "brain stimulation" treatment has been consistently stunted by one big uncertain question: what regions of the brain should you target to best help the patient?

New research from Beth Israel Deaconess Medical Center (BIDMC) in Boston could finally provide some clarity. The findings, reported in the Proceedings of the National Academy of Sciences (PNAS) paint a map of “functionally-connected” sites in the brain that better illustrate which brain networks are affected by different diseases—and how psychiatrists can best go about treating them through brain stimulation. They may one day reveal sites in the brain where noninvasive forms of stimulation—like transcranial magnetic stimulation—could be administered in lieu of invasive ones—like deep brain stimulation implants—and still be just as effective.

“Although different types of brain stimulation are currently applied in different locations, we found that the targets used to treat the same disease are nodes in the same connected brain network,” says BIDMC's Michael Fox, one of the study’s researchers. He hopes the results will help psychiatrists make more informed decisions when evaluating treatment options.

The most widely used brain stimulation—deep brain stimulation (DBS)—requires an electrode to be implanted deep within the brain. Neurons in the area are stimulated at at least 100 Hz. In the last decade, DBS has been a successful treatment option for patients with Parkinson’s, dystonia, and essential tremor.

Repetitive transcranial magnetic stimulation (rTMS) on the other hand, is a noninvasive approach that uses a powerful electromagnet placed on the scalp to stimulate brain cells up to several centimeters below the surface. It provides less frequent and less powerful stimulation, and does not carry the same risks that invasive surgery does. However, the FDA currently approves rTMS for the treatment of depression only.

With some exceptions (such as treating Parkinson's with DBS), there is a lack of information about which specific brain regions should be targeted when treating diseases with brain stimulation; this is especially true for noninvasive interventions like rTMS. When using rTMS to treat depression, there is little agreement on which regions to stimulate to alleviate symptoms. “We don’t know exactly where to go,” says Fox. “This might help to verify where best to stimulate for patients.”

For the study, Fox and his research team looked at brain stimulation treatment data for 14 conditions, including addiction, Alzheimer’s, depression, dystonia, epilepsy, essential tremor, Huntington’s, and Parkinson’s. They listed the stimulation sites, deep in the brain and near the surface, thought to be effective for the treatment of each disease. Fox and his team wanted to determine if some of these sites were actually connected to one-another as part of the same brain networks—and if so, where they were located.

Through a data set of functional MRI images of people’s brains at rest, the research team found fluctuations in spontaneous brain activity that correlated with one-another, illustrating which sites were functionally connected. The researchers drew a map of connections from deep brain stimulation sites to the surface of the brain. When they compared this map to sites on the brain surface that work for noninvasive brain stimulation, the two matched up.

“It’s a beautifully synthetic study,” says George Mark, a pioneer of the use of rTMS in psychiatry at the Medical University of South Carolina who was not involved with the study. “We’ve always wondered how much we really know about any of these brain stimulation treatments. The study looks at invasive and noninvasive techniques like a jigsaw puzzle, and finds out where they match up.”

Sarah Lisanby, chair of psychiatry at Duke University Medical School and a brain stimulation researcher, called the approach “significant”, but expressed concerns about the level of efficacy the evidence pointed to. Besides fMRI, she thinks other measurements of neurological fluctuations may be important to take a look at.

Fox acknowledged the findings do not actually verify the map of connections they’ve drawn up: “It’s a retrospective review of the data we have thus far.” But he’s eager to follow up on this study soon with real data. “We actually want to test it and see if we’re right!”

Fox and others are hopeful the findings can be used to help psychiatrists determine when invasive or noninvasive techniques are more appropriate, and how they can be administered most effectively. Mark believes the study—and the marriage of technology and neuroscience in general—is “part of a larger goal to be able to permanently modify brain circuits” in a way that will completely cure many psychiatric diseases. “Until we figure out how to permanently affect brain, it’s unlikely either of these techniques will replace one-another."

Printed, Flexible, and Organic Wearable Sensors Worth $244 Million in 10 Years

Wearable sensors capable of checking someone's heart rate or breathing may not rely on traditional microchip technology in the near future. Instead, the next generation of printed, flexible, and organic electronic sensors could enable new medical and athletic wearable devices in a market worth an estimated $244 million within a decade, according to market analysis firm Lux Research.

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