Tag Archives: Semiconductors/Optoelectronics

Topological Photonics: What It Is and Why We Need It

Post Syndicated from Charles Q. Choi original https://spectrum.ieee.org/semiconductors/optoelectronics/topological-photonics-what-it-is-why-we-need-it

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 first topological lasers each required an external laser to excite them to work, limiting practical use. However, scientists in Singapore and England recently developed an electrically driven topological laser.

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 CIRCUITRY Quantum 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.”

Engineers Bang Tiny Laser Drum To Speed Data Transmission

Post Syndicated from Neil Savage original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/acoustic-wave-modulate-quantum-cascade-laser

Societies in Africa, the Amazon basin, and New Guinea used to send messages over long distances by banging on drums. Now a group of scientists in the United Kingdom is adapting that idea, using sound pulses to speed up the transmission of data.

Data centers and satellite relays have vast amounts of information to send from one place to another, so speeding up transmission would help enormously. Quantum cascade lasers (QCLs) can emit light at terahertz frequencies, but data has to be encoded onto the laser beam, and the basic laws of physics place a limit on how fast electronic systems can modulate the beam.

So engineers from the University of Leeds and the University of Nottingham in England decided to skip the electronics and use an acoustic wave to modulate the light instead. They describe their proof-of-concept in a recent paper in Nature Communications.

A QCL consists of a series of quantum wells, small areas that confine electrons at specific energy levels. As an electron drops from one well to the next in a sort of waterfall effect, it emits a photon, so a single electron can produce many photons.

To modulate the emission of those photons, and thus encode data onto the laser beam, the research team attached a thin aluminum film to one contact of the laser. They then hit the film with pulses from a different type of laser. Each brief pulse caused the aluminum skin to produce an acoustic wave that ran through the QCL, slightly deforming the structure.

 “It’s as if the whole system’s being shaken really,” says John Cunningham, a professor of electronic and electrical engineering at Leeds who led the research. “It changes the probability of electron transfer between the quantum wells.”

The team used an off-the-shelf QCL to create its prototype system, and only achieved modulation of about 6 percent. Cunningham says it should be possible to reach 100 percent modulation by redesigning the laser so that the quantum wells are specifically engineered to respond to acoustic waves. He’d also like to incorporate a semiconductor phonon laser—a saser, the sonic equivalent of a laser—invented by Tony Kent, a professor of physics at Nottingham and a co-author of the paper. That would make the system more compact and efficient.

Electronic circuits, limited by inductance, capacitance, and resistance, can modulate a laser at a few tens of gigahertz at most. Cunningham says an acoustic system should increase that to hundreds of gigahertz for a tenfold increase in transmission speed, and might one day get even faster.

Here’s How This Metasurface Lens Could Improve Imaging

Post Syndicated from Neil Savage original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/metasurfaces-metamaterials-image-processing

Processing images to allow self-driving cars to see where they’re going could get easier thanks to a specially sculpted lens that does the work of a computer.

Dutch and American researchers say they can use a metasurface to passively detect the edges of objects in video. Computers can perform such edge detection for autonomous vehicles or virtual reality applications, but that uses power and is not instantaneous. “If you want to do that digitally, it takes time for the computer to compute,” says Albert Polman, who heads the Light Management in New Photovoltaic Materials group at AMOLF, a scientific research institute in Amsterdam, the Netherlands.

In a paper in Nano Letters, Polman and colleagues describe how their material performs the mathematical operations necessary for edge detection. They built a metasurface, which is studded with tiny pillars, smaller than the wavelength of light, which can manipulate light in unusual ways based on their size and arrangement. In this case, they started with a thin sheet of sapphire, less than half a millimeter thick, and added pillars of silicon that were 206 nm thick, 142 nm tall, and spaced 300 nm apart.

When placed on the surface of a standard CCD chip, the metasurface acts like a lens, passing light that strikes it at steep angles but filtering out light hitting it at very slight angles. The features of an image are built from combinations of different light waves, and the waves that get filtered out carry the fine details of the image, leaving only the sharper components, such as the edges of a person’s face compared to the whiteboard behind her.

Depending on the computer and the size of the image, it might take several milliseconds to process this information digitally. With the analog approach, only limiting factor is the thickness of the metasurface. “It’s just the time light takes to travel 150 nm, which is basically nothing,” Polman says.

It’s also a passive technique. “It’s just a piece of glass, so you don’t need to give it power,” he says. Of course, the digital camera and a computer would still have a role, but Polman says this hybrid approach should be more efficient.

The researchers would like to try other materials, such as titanium oxide or silicon nitride, to see if they can get even better results. And while this metasurface captures edges in one dimension, they’d like to try two-dimensional designs, so they can capture edges at different orientations.

Large-Area MicroLED Display Startup Makes Gallium-Nitride Transistors Too

Post Syndicated from Samuel K. Moore original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/microled-display-startup-makes-galliumnitride-transistors

MicroLEDs appear to be, forgive the pun, the bright future of displays. Made of micrometer-scale gallium-nitride LEDs, the technology offers an unmatchable ratio of brightness to power consumption.

The problem is that the most easily manufacturable ones are so small they’re suitable only for augmented reality and similar applications. Making bigger ones, like for a watch display or a smartphone screen, requires the near-perfect transfer of tens of thousands of individual microLEDs per second onto a prefabricated silicon backplane. It’s a very difficult proposition, but Apple and some startups are trying to tackle it.

If New Mexico-based startup iBeam is correct, even larger microLED displays could be produced quickly and cheaply on flexible substrates. “iBeam is a new paradigm in manufacturing for microLEDs,” says Julian Osinski, the startup’s vice president of product technology. “We have a way of growing microLEDs directly on a roll of metal foil, and that’s something nobody else can do.”

iBeam’s technology is adapted from the superconductor manufacturing industry where something similar has produced product by the kilometer. Founder and CEO Vladimir Matias is a superconductor manufacturing veteran and saw its potential in producing gallium-nitride devices.

LEDs and other gallium-nitride devices are usually grown atop a silicon or sapphire wafer by a process called epitaxy. For that to work, you need a single crystal, preferably with a similar crystal structure, for the gallium nitride to grow on. The iBeam process can produce that crystal-like substrate on an otherwise amorphous or polycrystalline surface such as metal or glass.

When you deposit material on an amorphous substrate you normally get a film of randomly oriented grains of crystal, explains Matias. But briefly blasting that film with ions from just the right angle gets all the grains to line up. iBeam chooses the film’s material so that the aligned grains match well with gallium nitride’s crystal structure. From there, they grow layers of gallium nitride using standard techniques and fashion them into microLEDs. Quantum dots will then be added to convert the color of some of the microLEDs from their natural blue to red and green.

Just as is done with superconductors, the procedure could be rapidly done in a roll-to-roll fashion, Osinski says. Today’s industry processes produce gallium nitride for about US $2 to $3 per square centimeter. “We’d like to take it down to 10 cents [per square centimeter] or less so it becomes competitive with OLEDs,” he says.

The company has used its existing process to produce microLEDs, and last month it announced the production of high-electron mobility transistors (HEMTs), as well. If the HEMTs could be constructed along with the microLEDs, they could form the circuitry that controls the microLED pixels.

(Kei May Lau’s team at Hong Kong University of Science and Technology developed a structure that integrates the HEMT and microLED so tightly that they effectively become one device.)

The startup’s near-term goal is to produce a small prototype display, which Osinki thinks may take until the end of next year. They hope to have large-scale manufacturing nailed down by 2022. That’s later than some microLED firms are planning to commercialize their products, but iBeam is counting on being able to produce much larger displays and at much lower cost. The company plans to sell its manufacturing process and materials to established display makers rather than become a manufacturer itself.

Holding Light (Temporarily) in Place

Post Syndicated from Mark Anderson original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/holding-light-temporarily-in-place

Storing light beams—putting an ensemble of photons, traveling through a specially prepared material, into a virtual standstill—has come a step closer to reality with a new discovery involving microwaves.

The research finds that microwaves traveling through a particular configuration of ceramic aluminum oxide rods can be made to hold in place for several microseconds. If the optical or infrared equivalent of this technology can be fabricated, then Internet and computer communications networks (each carried by optical and infrared laser pulses) might gain a new versatile tool that enables temporary, stationary storage of a packet of photons.

Diode Lasers Jump to the Deep Ultraviolet

Post Syndicated from Jeff Hecht original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/diode-lasers-jump-to-the-deep-ultraviolet

The first electrically powered semiconductor laser emitting in the deep ultraviolet marks a big step into a new field, says Ramón Collazo, a materials science professor at North Carolina State University and a founder of Adroit Materials in Cary, NC.

Researchers had thought “there was a hard wall” blocking diode lasers from emitting ultraviolet light shorter than 315 nm even in laboratory lasers, Collazo says. Now a team including Hiroshi Amano of Nagoya University, who shared the 2014 Nobel Physics Prize for inventing efficient blue light-emitting diodes, has scored another breakthrough by demonstrating a 271.8-nm diode laser, more than 40 nm deeper into the ultraviolet.

“Bio-sensing and sterilization are expected to be the first key applications” of deep ultraviolet diode lasers, says Ziyi Zhang of the Asahi Kasei Corporate Research Center in Fuji, lead author of a paper coauthored by Amano. Bio-sensors based on diode lasers “could be far smaller, cheaper, and more easily replaceable” than the bulky gas lasers, which are now the only type available at wavelengths shorter than 300 nm, Zhang says.

The U.S. Pentagon had made a significant investment in developing deep-ultraviolet lasers for bio-sensing, says Collazo, but “after three DARPA programs, the Japanese got it,” he said with a chuckle. He says that demonstrating a deep-ultraviolet laser opens the door to making diode lasers across a broad range from 220 to 365 nm.

Commercial LEDs made of the same compound, aluminum-gallium nitride, can emit wavelengths as short as 210 nm. However, their light spreads rapidly, leaving little power after tens of centimeters, which limits their applications. Laser diodes concentrate their beam over a longer distance, delivering higher power to small spots, and their light is concentrated in a band of less than 1 nm, compared to more than 10 nm for LEDs. “These features of laser diodes should enable some medical applications,” says Zhang.

Diode lasers are much harder to make than LEDs because they require passing higher current densities through the layer where current carriers combine to emit light. This is a particular problem for the nitride compounds that emit in the blue, violet and ultraviolet because they are prone to crystalline defects that can cause failures at high current densities. Such material problems had stalled progress in blue LEDs and diode lasers until Amano and Isamu Akasaki at Nagoya University and Shiju Nakamura, then at the Nichia Corporation, developed new ways of processing the mixture of gallium, indium and nitrogen needed for blue emission in the early 1990s. They succeeded first with LEDs and later with diode lasers at the 405-nm wavelength needed to store high-definition digital video on Blu-Ray discs.

Diodes made from gallium, indium and nitrogen emit blue light, with the wavelength decreasing as the indium content decreases, reaching about 370 nm from pure GaN. Aluminum must be added to replace some gallium to reach shorter wavelengths, but adding aluminum also makes the compound more vulnerable to defects. That’s not a severe problem for LEDs, which reached 210 nanometers in the deep ultraviolet in 2006. However, the high current density in diode lasers stalled their development in the ultraviolet. The shortest wavelengths in commercial diodes remain 375 nm, and short-lived laboratory versions remained stalled around 320 nm for years. 

In 2018, a team from North Carolina State and Adroit Materials (Cary, NC) led by Adroit chief operating office Ronny Kirste was able to reduce defect levels in AlGaN containing more aluminum than gallium to produce laser light at 265 nm in the deep ultraviolet.  However, their semiconductor lasers were powered by 193-nm light from a large pulsed gas laser, a technique useful in research, but not practical for applications. The holy grail for practical deep ultraviolet lasers is powering them directly by electrical current passing through the semiconductor.

A team from Asahi Kasei Corporate Research & Development in Fuji, Nagoya, and Crystal IS in Green Island, NY demonstrated the new electrically powered diode laser emitting at 271.8 nm.  The keys to their success, Zhang says, were design of the laser diode structure, their technique for doping the semiconductor, and epitaxial growth on a substrate of single-crystal AlN, which reduced threshold current and operating voltage. Layers in the structure contained up to twice as much aluminum as gallium.

Their laser generated 50-nanosecond pulses at a rate of 2000 Hz, but most applications are expected to require a continuous laser beam. Zhang says that further reductions in threshold current and operating voltage should allow continuous-wave operation. Asahi Kasei plans to continue teaming the Nagoya to improve their understanding of the material system and develop commercial versions.

Adroit Materials had already working on AlGaN, and now is working to duplicate the Asahi Kasei results. “We want to replace those gas lasers” which have long been the only laser sources practical for most short-wavelength ultraviolet applications, says Kirste. “The market is huge for that.”  Much of that market is biological because DNA absorbs strongly at 260 nm. In addition to sensing biological material including potential pathogen, bright deep-ultraviolet sources can break apart DNA, killing pathogens. UV LEDs emitting in that range already can sterilize small volumes of water, such as needed by soldiers in the field where water supplies are suspect. Compact laser sources could sterilize larger volumes quicker.

Photonics Meets Plasmonics in New Switch that Could Steer Lidar Laser Beams

Post Syndicated from Jeff Hecht original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/new-electro-mechanical-switch-integrated-photonics

The synergy of electronic processing and optical communications has powered the decades-long boom in information technology. But the need to convert signals back and forth between electrical and optical forms is becoming a bottleneck for the emerging field of integrated photonics.

A new type of switch that combines electrical and mechanical effects to redirect light could open the door to large-scale reconfigurable photonic networks for several applications including beam steering for lidars and optical neural networks for computing. 

Currently, integrated photonics are used in high-performance fiber-optic systems , and a joint government-industry program called AIM Photonics is pushing their manufacture. However, current optical switches are too big and require too much power to blend well into integrated photonics. The new hybrid nano-opto-electro-mechanical switch has a footprint of 10 square micrometers and runs on only one volt—making it compatible with the CMOS (complementary metal-oxide-semiconductor) silicon electronics used in integrated photonics, says Christian Haffner from the Swiss Federal Institute of Technology in Zurich now working at the National Institute for Standards and Technology (NIST) in Gaithersburg, Maryland and the researcher who led the team that developed it.

The root of the problem Haffner set out to solve is that photons and electrons behave very differently.

Photons are great for communications because they travel at the speed of light and interact weakly with each other and matter, but they are much larger than chip features and require high voltages to redirect them because of their weak interactions.

Electrons are much smaller and interact much more strongly than photons, making them better for switching and for processing signals. However, electrons move slower than light, and more energy is needed to move them.

Long-distance communication systems process signals electronically and convert the signal into light for transmission, but converting between signal formats is cumbersome for local transmission. The new switch makes it possible to redirect optical signals on the integrated photonic circuit without having to convert them to electrical format and then back to optical format for further transmission. 

In Science, Haffner and colleagues describe a hybrid nano-opto-electro-mechanical switch that would occupy only about 10 square micrometers on an integrated photonic circuit. Their switch is a small multilayered disk sitting at a T-junction between two optical waveguides—stripes of transparent silica that guide light—that meet at a right angle. The top layer of the disk is a four-micrometer circle of 40-nanometer gold membrane resting on a small piece of alumina on layer of silicon deposited on silica. That structure acts as a curved waveguide resonant with both the input and output waveguides, so it can transfer resonant light between the two. 

Light within the silica waveguides remains as photons, but within the switch the light excites oscillations of surface electrons in the gold, producing plasmons that vibrate at the frequency of the light wave but over a light much smaller than the optical wavelength. That tight confinement of the plasmonic part of the energy in the air gap between the gold and silicon creates a strong opto-electro-mechanical effect concentrated in the small volume of the switch. 

With no voltage applied to the switch, the plasmonic waveguide remains resonant with the silica waveguides, so it couples light from the input waveguide to the output waveguide with minimal loss, as shown in the animation.

Applying one volt to the switch produces a static charge that pulls the gold membrane toward the silicon layer, changing the shape of the waveguide in the switch so it shifts the phase of the light by 180 degrees. This causes destructive interference in the switch, breaking the resonance and the coupling of light into the side waveguide, so the light instead continues through the input waveguide to another switch.

“What we have in the end,” says Haffner, “is a hybrid [switch], partly photonic and partly plasmonic, that manipulates light very efficiently.” The plasmonic part concentrates the switching in a small area; the photonic part experiences low loss. Applying a one-volt bias compatible with CMOS electronics across such a short distance can produce a very strong force. That gives the switch a small footprint, low loss, and lower power consumption, which conventional electro-optic switches cannot achieve simultaneously.

Mass of the gold film is so low that the switch can operate millions of times a second. That’s adequate for most switching, says Haffner, but it does have limits. The mechanical part of the switch cannot reach the picosecond speeds needed to modulate light in an optical transmitter. 

The first applications are likely to be in laser beam steering for lidar, particularly for autonomous vehicles where continual information on the local environment is vital for safety. Another potential application is optical routing of signals on integrated photonic chips to create optical neural networks for deep-learning applications. The switch can redirect signals millions of times a second, a time scale needed by such applications.

“I don’t see any issues in fabricating [the switches] with high yield,” says Haffner. 

A Simple Filter Turns Blue OLED Light Into White

Post Syndicated from XiaoZhi Lim original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/a-simple-filter-makes-blueemitting-oleds-give-off-white-light

Organic light-emitting diodes (OLEDs) have come a long way since the first working device was reported three decades ago. Prized for their dark blacks, crisp image reproduction, and power efficiency, today’s OLEDs dominate the screens of Android phones and LG televisions. They may take over iPhones as early as next year.

And because OLEDs are cheap and easy to make, we ought to also use them to make white light for general illumination, says Konstantinos Daskalakis, a post-doctoral researcher at Aalto University in Finland.

Except white is an OLED’s Achilles’ heel. Typically, to get white light, individual red, green, and blue emitters shine at the same time. This makes white the most power-hungry color, reportedly requiring six times as much power as it takes to produce the color black on a Google Pixel. Other strategies to generate white light include carefully doping emitting layers with chemicals, but this approach makes it harder to fabricate devices.

In a proof-of-concept experiment, Daskalakis and his supervisor Paivi Torma converted conventional blue-emitting OLEDs to white-emitting ones simply by depositing a distributed Bragg reflector (DBR)—a stack of two alternating materials with high and low refractive indexes—on top of the OLEDs.

Microsize Lens Pushes Photonics Closer to an On-Chip Future

Post Syndicated from Mark Anderson original https://spectrum.ieee.org/nanoclast/semiconductors/optoelectronics/microsize-lens-pushes-photonics-closer-to-an-onchip-future

Optical microcomputing, next-generation compact LiDAR units, and on-chip spectrometers all took a step closer to reality with the recent announcement of a new kind of optical lens.

The lens is not made of glass or plastic, however. Rather, this low-loss, on-chip lens is made from thin layers of specialized materials on top of a silicon wafer. These “metasurfaces” have shown much promise in recent years as a kind of new, microscale medium for containing, transmitting, and manipulating light.

Photonics at the macro-scale is more than 50 years old and has applications today in fields including telecommunications, medicine, aviation, and agriculture. However, shrinking all the elements of traditional photonics down to microscale—to match the density of signals and processing operations inside a traditional microchip—requires entirely new optical methods and materials.

A team of researchers at the University of Delaware, including Tingyi Gu, an assistant professor of electrical and computer engineering, recently published a paper in the journal Nature Communications that describes their effort to build a lens from a thin metasurface material on top of a silicon wafer.

Gu says that metasurfaces have typically been made from thin metal films with nanosized structures in it. These “plasmonic” metasurfaces offered the promise of, as a Nature Photonics paper from 2017 put it, “Ultrathin, versatile, integrated optical devices and high-speed optical information processing.”

The problem, Gu says, is that these “plasmonic” materials are not exactly transparent like windowpanes. Traveling just fractions of a micrometer can introduce signal loss of a few decibels to tens of dB.

“This makes it less practical for optical communications and signal processing,” she says.

Her group uses an alternate kind of metasurface made from etched dielectric materials atop silicon wafers. Making optical components out of dielectric metasurfaces, she says, could sidestep the signal loss problem. Her group’s paper notes that their lens introduces a signal loss of less than one dB.

Even a small improvement (and going from handfuls of dB down to fractions of a dB is more than small) would make a big difference, because a real-world photonics chip might one day have many such components in it. And the more lossy the photonics chip, the greater the amount of laser power needed to be pumped through the chip. More power means more heat and noise, which might ultimately limit the extent to which the chip could be miniaturized. But with her team’s dielectric metasurface lens, “We can make a device much smaller and more compact,” she says.

Her group’s lens is made from a configuration of gratings etched in the metasurface — following a wavy pattern of vertical lines that looks a bit like the Cisco company logo. Gu’s group was able to achieve some of the familiar properties of lenses, including converging beams with a measurable focal length (8 micrometers) and object and image distance (44 and 10.1 µm).

The group further used the device’s lensing properties to achieve a kind of optical signal Fourier Transform—which is also a property of classical, macroscopic lenses.

Gu says that next steps for their device include exploring new materials and to work toward a platform for on-chip signal processing.

“We’re trying to see if we can come up with good designs to do tasks as complicated as what traditional electronic circuits can do,” she says. “These devices have the advantage that they can process signals at the speed of light. It doesn’t need logic signals going back and forth between transistors. … It’s going to be fast.”

This MicroLED Display Is Smaller Than a Bug

Post Syndicated from Samuel K. Moore original https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/this-microled-display-is-smaller-than-a-bug

Mojo Vision’s microLED display has record-breaking pixel density and a somewhat mysterious purpose

A Silicon Valley-based startup has recently emerged from stealth mode to reveal what it claims is the smallest, most pixel-dense dynamic display ever built. Mojo Vision’s display is just 0.48 millimeters across, but it has about 300 times as many pixels per square inch as a typical smartphone display.