Imagine a portable 3D printer you could hold in the palm of your hand. The tiny device could enable a user to rapidly create customized, low-cost objects on the go, like a fastener to repair a wobbly bicycle wheel or a component for a critical medical operation.Researchers from MIT and the University of Texas at Austin took a major step toward making this idea a reality by demonstrating the first chip-based 3D printer. Their proof-of-concept device consists of a single, millimeter-scale photonic chip that emits reconfigurable beams of light into a well of resin that cures into a solid shape when light strikes it.The prototype chip has no moving parts, instead relying on an array of tiny optical antennas to steer a beam of light. The beam projects up into a liquid resin that has been designed to rapidly cure when exposed to the beam’s wavelength of visible light.By combining silicon photonics and photochemistry, the interdisciplinary research team was able to demonstrate a chip that can steer light beams to 3D print arbitrary two-dimensional patterns, including the letters M-I-T. Shapes can be fully formed in a matter of seconds.In the long run, they envision a system where a photonic chip sits at the bottom of a well of resin and emits a 3D hologram of visible light, rapidly curing an entire object in a single step.This type of portable 3D printer could have many applications, such as enabling clinicians to create tailor-made medical device components or allowing engineers to make rapid prototypes at a job site.“This system is completely rethinking what a 3D printer is. It is no longer a big box sitting on a bench in a lab creating objects, but something that is handheld and portable. It is exciting to think about the new applications that could come out of this and how the field of 3D printing could change,” says senior author Jelena Notaros, the Robert J. Shillman Career Development Professor in Electrical Engineering and Computer Science (EECS), and a member of the Research Laboratory of Electronics.Joining Notaros on the paper are Sabrina Corsetti, lead author and EECS graduate student; Milica Notaros PhD ’23; Tal Sneh, an EECS graduate student; Alex Safford, a recent graduate of the University of Texas at Austin; and Zak Page, an assistant professor in the Department of Chemical Engineering at UT Austin. The&nbsp;<a href="https://www.nature.com/articles/s41377-024-01478-2" target="_blank">research appears today</a> in&nbsp;Nature Light Science and Applications.<h2>Printing with a chip</h2>Experts in silicon photonics, the Notaros group previously developed integrated optical-phased-array systems that steer beams of light using a series of microscale antennas fabricated on a chip using semiconductor manufacturing processes. By speeding up or delaying the optical signal on either side of the antenna array, they can move the beam of emitted light in a certain direction.Such systems are key for lidar sensors, which map their surroundings by emitting infrared light beams that bounce off nearby objects. Recently, the group has focused on systems that emit and steer visible light for augmented-reality applications.They wondered if such a device could be used for a chip-based 3D printer.At about the same time they started brainstorming, the Page Group at UT Austin demonstrated specialized resins that can be rapidly cured using wavelengths of visible light for the first time. This was the missing piece that pushed the chip-based 3D printer into reality.“With photocurable resins, it is very hard to get them to cure all the way up at infrared wavelengths, which is where integrated optical-phased-array systems were operating in the past for lidar,” Corsetti says. “Here, we are meeting in the middle between standard photochemistry and silicon photonics by using visible-light-curable resins and visible-light-emitting chips to create this chip-based 3D printer. You have this merging of two technologies into a completely new idea.”Their prototype consists of a single photonic chip containing an array of 160-nanometer-thick optical antennas. (A sheet of paper is about 100,000 nanometers thick.) The entire chip fits onto a U.S. quarter.When powered by an off-chip laser, the antennas emit a steerable beam of visible light into the well of photocurable resin. The chip sits below a clear slide, like those used in microscopes, which contains a shallow indentation that holds the resin. The researchers use electrical signals to nonmechanically steer the light beam, causing the resin to solidify wherever the beam strikes it.<h2>A collaborative approach</h2>But effectively modulating visible-wavelength light, which involves modifying its amplitude and phase, is especially tricky. One common method requires heating the chip, but this is inefficient and takes a large amount of physical space.Instead, the researchers used liquid crystal to fashion compact modulators they integrate onto the chip. The material’s unique optical properties enable the modulators to be extremely efficient and only about 20 microns in length.A single waveguide on the chip holds the light from the off-chip laser. Running along the waveguide are tiny taps which tap off a little bit of light to each of the antennas.The researchers actively tune the modulators using an electric field, which reorients the liquid crystal molecules in a certain direction. In this way, they can precisely control the amplitude and phase of light being routed to the antennas.But forming and steering the beam is only half the battle. Interfacing with a novel photocurable resin was a completely different challenge.The Page Group at UT Austin worked closely with the Notaros Group at MIT, carefully adjusting the chemical combinations and concentrations to zero-in on a formula that provided a long shelf-life and rapid curing.In the end, the group used their prototype to 3D print arbitrary two-dimensional shapes within seconds.Building off this prototype, they want to move toward developing a system like the one they originally conceptualized — a chip that emits a hologram of visible light in a resin well to enable volumetric 3D printing in only one step.“To be able to do that, we need a completely new silicon-photonics chip design. We already laid out a lot of what that final system would look like in this paper. And, now, we are excited to continue working towards this ultimate demonstration,” Jelena Notaros says.

The tiny device could enable a user to rapidly create customized, low-cost objects on the go, like a fastener to repair a wobbly bicycle wheel or a component for a critical medical operation. Credit: Sampson Wilcox, RLE

Smaller than a coin, this optical device could enable rapid prototyping on the go.

Researchers demonstrate the first chip-based 3D printer

Imaging the hot turbulence of aircraft propulsion systems may now be possible with sturdy sheets of composite materials that twist light beams, according to research led by the University of Michigan and Air Force Research Laboratory.The sheets were produced with a new manufacturing method that opens possibilities beyond aircraft design, as it enables new classes of materials to be used in polarization optics. While the team demonstrated high temperature tolerance, new mechanical, electrical and physical properties are expected to emerge as well—with potential applications in energy, sensors for vehicles and robots, and space exploration.“Combining multiple functionalities into 2D materials opens up a world of possibilities,” said <a href="https://mrs.digitellinc.com/b/sp/dhriti-nepal-34987" target="_blank" rel="noreferrer noopener">Dhriti Nepal</a>, senior research materials engineer at the Air Force Research Laboratory and a co-corresponding author of the study published recently in Nature.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1717115403757-nick-and-jun.jpg" style="width: 100%px;" class="fr-fic fr-dib">Nicholas Kotov, the Irving Langmuir Distinguished University Professor of Chemical Sciences and Engineering, and Jun Lu, an adjunct research investigator, present their light-twisting materials in their chemical engineering laboratory. Photo credit: Brenda Ahearn, Michigan Engineering.“Think of a butterfly’s wings, which allow it to fly, regulate temperature, and reflect light to produce specific colors for attracting mates and avoiding predators. This technique provides new design opportunities for creating multifunctional devices capable of anything one can imagine.”The key is arranging nanomaterials that don’t twist light on their own onto layers that turn light waves into either left- or right-handed spirals, known as circular polarizations. In the aircraft example, turbulence created by the engine spins the light, which is then filtered through the material for imaging. Today, devices like <a href="https://www.hull.ac.uk/work-with-us/more/media-centre/news/2022/the-chemistry-behind-your-lcd-flat-screen-devices-how-a-scientist-changed-the-world" target="_blank" rel="noreferrer noopener">LCD screens</a> and <a href="https://www.qats.com/Products/Instruments/Surface-Thermography/TLC-100" target="_blank" rel="noreferrer noopener">thermochromic paints</a> already control the twist and orientation of light waves using <a href="https://pubs.acs.org/doi/full/10.1021/acsaom.3c00282?casa_token=PCLN4MaiV1UAAAAA%3Aasa8_oPhbylNiDNzYH77VxzwONVZ49_8EuTBj9MZWHJoD8N-Q7GxEwqhEWFR_UdFuonKP_FvpcYviPk" target="_blank" rel="noreferrer noopener">liquid crystals</a>, but they melt not far above ambient temperatures.“There could be situations in which you want to twist light outside the normal operating temperatures of liquid crystals. Now, we can make light-polarizing devices for those kinds of settings,” said <a href="https://che.engin.umich.edu/people/kotov-nicholas/" target="_blank" rel="noreferrer noopener">Nicholas Kotov</a>, the Irving Langmuir Distinguished University Professor of Chemical Sciences and Engineering at U-M and lead author of the study.The new material can twist light at 250 degrees Celsius, and through the imaging of turbulence in aircraft engines and other applications, it could enable aerospace engineers to improve designs for better aircraft flight performance.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1717115422648-composite-sheet-featured-e1717078357451+%281%29.jpg" style="width: 100%px;" class="fr-fic fr-dib">This composite film can twist light into a spiral, thanks to microscopic grooves that cause horizontally and vertically oscillating light waves to pass through the film out of phase. Unlike existing materials that can do this, the film maintains its light-twisting properties when heated up to 250 degrees Celsius. Photo credit: Brenda Ahearn, Michigan Engineering.“Future aerospace systems continue to push the edge of technical feasibility. These low-cost optical materials afford modularity, which is crucial for optimizing solutions for a broad range of future technologies,” said <a href="https://www.af.mil/About-Us/Biographies/Display/Article/1733591/dr-richard-a-vaia/" target="_blank" rel="noreferrer noopener" id="isPasted">Richard Vaia</a>, materials and manufacturing chief scientist at the Air Force Research Laboratory and a corresponding author of the study.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1717115446434-composite-sheet-fire.jpg" style="width: 100%px;" class="fr-fic fr-dib">To measure how well the film twists light at high temperatures, U-M researchers use a small flame as a light and heat source. Photo credit: Brenda Ahearn, Michigan Engineering.To make the materials, the researchers put microscopic grooves into a plastic sheet and covered it with several layers of tiny, flat particles with a diameter 10,000 times smaller than a millimeter. These particles were held in place with alternating layers of a molecular adhesive, and they could be made from any material that can be made into flat nanoparticles. For their heat-tolerant materials, the researchers used ceramic-like materials called MXenes.As light moves through the material, it divides into two beams, one with horizontally oscillating waves and another with vertically oscillating waves. The vertical waves pass through faster than the horizontal waves. As a result, the waves exit out of phase and appear as a spiral of light. The angle of the grooves determines the direction in which the light spirals, and layers of silver nanowires can help ensure the light spirals solely to the left or right.“Our calculations suggest that the optical properties didn’t come from the nanoplates themselves, but from their orientation on the grooves caused by our fabrication process,” said André Farias de Moura, associate professor of chemistry at the Federal University of São Carlos and a co-corresponding author of the study.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1717115465598-Jun-fire.jpg" style="width: 100%px;" class="fr-fic fr-dib">Jun Lu, an adjunct research investigator working in Kotov’s lab and the study’s first author, demonstrates how he uses a fire to test a film’s ability to twist light at high temperatures. Photo credit: Brenda Ahearn, Michigan Engineering.The research was funded by the National Science Foundation Science and Technology&nbsp;<a href="https://compass.engin.umich.edu/" target="_blank" rel="noreferrer noopener">Center for Complex Particle Systems</a>, U.S. Department of Defense, U.S. Office of Naval Research, U.S. Air Force Office of Scientific Research, Brazil’s National Council for Scientific and Technological Development, as well as the São Paulo Research Foundation. The materials were studied at the&nbsp;<a href="https://mc2.engin.umich.edu/" target="_blank" rel="noreferrer noopener">Michigan Center for Materials Characterization</a>.Felippe Colombari from the Brazilian Biorenewables National Laboratory also contributed to the study. Nicholas Kotov is also the Joseph B. and Florence V. Cejka Professor of Engineering and a professor of macromolecular science and engineering.Kotov filed a patent with the help of Innovation Partnerships at U-M, and his company Photon Semantics LLC, a U-M startup, is planning to license the technology. Kotov and the University of Michigan have a financial interest in Photon Semantics LLC.

New manufacturing method builds tougher materials that were previously considered useless for twisting light into more robust optical devices.

Nanoscale engineering brings light-twisting materials to more extreme settings

Quantum computers hold the promise of being able to quickly solve extremely complex problems that might take the world’s most powerful supercomputer decades to crack.But achieving that performance involves building a system with millions of interconnected building blocks called qubits. Making and controlling so many qubits in a hardware architecture is an enormous challenge that scientists around the world are striving to meet.Toward this goal, researchers at MIT and MITRE have demonstrated a scalable, modular hardware platform that integrates thousands of interconnected qubits onto a customized integrated circuit. This “quantum-system-on-chip” (QSoC) architecture enables the researchers to precisely tune and control a dense array of qubits. Multiple chips could be connected using optical networking to create a large-scale quantum communication network.By tuning qubits across 11 frequency channels, this QSoC architecture allows for a new proposed protocol of “entanglement multiplexing” for large-scale quantum computing.The team spent years perfecting an intricate process for manufacturing two-dimensional arrays of atom-sized qubit microchiplets and transferring thousands of them onto a carefully prepared complementary metal-oxide semiconductor (CMOS) chip. This transfer can be performed in a single step.“We will need a large number of qubits, and great control over them, to really leverage the power of a quantum system and make it useful. We are proposing a brand new architecture and a fabrication technology that can support the scalability requirements of a hardware system for a quantum computer,” says Linsen Li, an electrical engineering and computer science (EECS) graduate student and lead author of a paper on this architecture.Li’s co-authors include Ruonan Han, an associate professor in EECS, leader of the Terahertz Integrated Electronics Group, and member of the Research Laboratory of Electronics (RLE); senior author Dirk Englund, professor of EECS, principal investigator of the Quantum Photonics and Artificial Intelligence Group and of RLE; as well as others at MIT, Cornell University, the Delft Institute of Technology, the U.S. Army Research Laboratory, and the MITRE Corporation. The <a href="https://www.nature.com/articles/s41586-024-07371-7" target="_blank">paper appears today</a> in Nature.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1717028405505-MIT-Quantum_Chip-01-press+%281%29.jpg" style="width: 100%px;" class="fr-fic fr-dib">Researchers developed a modular fabrication process to produce a quantum-system-on-chip which integrates an array of artificial atom qubits onto a semiconductor chip. Image: Sampson Wilcox and Linsen Li, RLE<h2>Diamond microchiplets</h2>While there are many types of qubits, the researchers chose to use diamond color centers because of their scalability advantages. They previously used such qubits to <a href="https://news.mit.edu/2020/scaling-quantum-chip-0708" target="_blank">produce integrated quantum chips</a> with photonic circuitry.Qubits made from diamond color centers are “artificial atoms” that carry quantum information. Because diamond color centers are solid-state systems, the qubit manufacturing is compatible with modern semiconductor fabrication processes. They are also compact and have relatively long coherence times, which refers to the amount of time a qubit’s state remains stable, due to the clean environment provided by the diamond material.In addition, diamond color centers have photonic interfaces which allows them to be remotely entangled, or connected, with other qubits that aren’t adjacent to them.“The conventional assumption in the field is that the inhomogeneity of the diamond color center is a drawback compared to identical quantum memory like ions and neutral atoms. However, we turn this challenge into an advantage by embracing the diversity of the artificial atoms: Each atom has its own spectral frequency. This allows us to communicate with individual atoms by voltage tuning them into resonance with a laser, much like tuning the dial on a tiny radio,” says Englund.This is especially difficult because the researchers must achieve this at a large scale to compensate for the qubit inhomogeneity in a large system.To communicate across qubits, they need to have multiple such “quantum radios” dialed into the same channel. Achieving this condition becomes near-certain when scaling to thousands of qubits. To this end, the researchers surmounted that challenge by integrating a large array of diamond color center qubits onto a CMOS chip which provides the control dials. The chip can be incorporated with built-in digital logic that rapidly and automatically reconfigures the voltages, enabling the qubits to reach full connectivity.“This compensates for the in-homogenous nature of the system. With the CMOS platform, we can quickly and dynamically tune all the qubit frequencies,” Li explains.<h2>Lock-and-release fabrication</h2>To build this QSoC, the researchers developed a fabrication process to transfer diamond color center “microchiplets” onto a CMOS backplane at a large scale.They started by fabricating an array of diamond color center microchiplets from a solid block of diamond. They also designed and fabricated nanoscale optical antennas that enable more efficient collection of the photons emitted by these color center qubits in free space.Then, they designed and mapped out the chip from the semiconductor foundry. Working in the MIT.nano cleanroom, they post-processed a CMOS chip to add microscale sockets that match up with the diamond microchiplet array.They built an in-house transfer setup in the lab and applied a lock-and-release process to integrate the two layers by locking the diamond microchiplets into the sockets on the CMOS chip. Since the diamond microchiplets are weakly bonded to the diamond surface, when they release the bulk diamond horizontally, the microchiplets stay in the sockets.“Because we can control the fabrication of both the diamond and the CMOS chip, we can make a complementary pattern. In this way, we can transfer thousands of diamond chiplets into their corresponding sockets all at the same time,” Li says.The researchers demonstrated a 500-micron by 500-micron area transfer for an array with 1,024 diamond nanoantennas, but they could use larger diamond arrays and a larger CMOS chip to further scale up the system. In fact, they found that with more qubits, tuning the frequencies actually requires less voltage for this architecture.“In this case, if you have more qubits, our architecture will work even better,” Li says.The team tested many nanostructures before they determined the ideal microchiplet array for the lock-and-release process. However, making quantum microchiplets is no easy task, and the process took years to perfect.“We have iterated and developed the recipe to fabricate these diamond nanostructures in MIT cleanroom, but it is a very complicated process. It took 19 steps of nanofabrication to get the diamond quantum microchiplets, and the steps were not straightforward,” he adds.Alongside their QSoC, the researchers developed an approach to characterize the system and measure its performance on a large scale. To do this, they built a custom cryo-optical metrology setup.Using this technique, they demonstrated an entire chip with over 4,000 qubits that could be tuned to the same frequency while maintaining their spin and optical properties. They also built a digital twin simulation that connects the experiment with digitized modeling, which helps them understand the root causes of the observed phenomenon and determine how to efficiently implement the architecture.In the future, the researchers could boost the performance of their system by refining the materials they used to make qubits or developing more precise control processes. They could also apply this architecture to other solid-state quantum systems.This work was supported by the MITRE Corporation Quantum Moonshot Program, the U.S. National Science Foundation, the U.S. Army Research Office, the Center for Quantum Networks, and the European Union’s Horizon 2020 Research and Innovation Program.

Researchers developed a modular fabrication process to produce a quantum-system-on-chip which integrates an array of artificial atom qubits onto a semiconductor chip. Image: Sampson Wilcox and Linsen Li, RLE

A new quantum-system-on-chip enables the efficient control of a large array of qubits, moving toward practical quantum computing.

Modular, scalable hardware architecture for a quantum computer

In this episode, discuss how big of a problem lead contaminated water still is across the world and how a collaboration between MIT & Nanyang University plans to tackle it with a highly accurate and inexpensive water pollution sensor.

Podcast: Is Your Drinking Water Safe? This Sensor Has The Answer

This article was discussed in our <a href="https://www.wevolver.com/profile/the.next.byte" rel="noopener noreferrer" target="_blank">Next Byte podcast</a>.&nbsp;<iframe height="200px" width="100%" frameborder="no" scrolling="no" seamless="" src="https://player.simplecast.com/076af450-88d2-4524-8ec5-df4c5234a282?dark=false" class="fr-draggable" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe> The full article will continue below.<hr>Engineers at MIT, Nanyang Technological University, and several companies have developed a compact and inexpensive technology for detecting and measuring lead concentrations in water, potentially enabling a significant advance in tackling this persistent global health issue.The World Health Organization estimates that 240 million people worldwide are exposed to drinking water that contains unsafe amounts of toxic lead, which can affect brain development in children, cause birth defects, and produce a variety of neurological, cardiac, and other damaging effects. In the United States alone, an estimated 10 million households still get drinking water delivered through lead pipes.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzE1NzM1MzgzNjM4LU1JVC1MZWFkLURldGVjdGlvbi0wMi1wcmVzcy5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 100%px;" class="fr-fic fr-dib">Testing setup of the photonic chip sensor, including microfluidic chamber to transport analyte solutions and optical fibers on the sides to measure the photonic response of the chip. Image: Courtesy of the researchers“It’s an unaddressed public health crisis that leads to over 1 million deaths annually,” says Jia Xu Brian Sia, an MIT postdoc and the senior author of the paper describing the new technology.But testing for lead in water requires expensive, cumbersome equipment and typically requires days to get results. Or, it uses simple test strips that simply reveal a yes-or-no answer about the presence of lead but no information about its concentration. Current EPA regulations require drinking water to contain no more that 15 parts per billion of lead, a concentration so low it is difficult to detect.The new system, which could be ready for commercial deployment within two or three years, could detect lead concentrations as low as 1 part per billion, with high accuracy, using a simple chip-based detector housed in a handheld device. The technology gives nearly instant quantitative measurements and requires just a droplet of water.The findings are described in a <a href="https://www.nature.com/articles/s41467-024-47938-6" target="_blank">paper appearing today</a> in the journal Nature Communications, by Sia, MIT graduate student and lead author Luigi Ranno, Professor Juejun Hu, and 12 others at MIT and other institutions in academia and industry.The team set out to find a simple detection method based on the use of photonic chips, which use light to perform measurements. The challenging part was finding a way to attach to the photonic chip surface certain ring-shaped molecules known as crown ethers, which can capture specific ions such as lead. After years of effort, they were able to achieve that attachment via a chemical process known as Fischer esterification. “That is one of the essential breakthroughs we have made in this technology,” Sia says.In testing the new chip, the researchers showed that it can detect lead in water at concentrations as low as one part per billion. At much higher concentrations, which may be relevant for testing environmental contamination such as mine tailings, the accuracy is within 4 percent.The device works in water with varying levels of acidity, ranging from pH values of 6 to 8, “which covers most environmental samples,” Sia says. They have tested the device with seawater as well as tap water, and verified the accuracy of the measurements.In order to achieve such levels of accuracy, current testing requires a device called an inductive coupled plasma mass spectrometer. “These setups can be big and expensive,” Sia says. The sample processing can take days and requires experienced technical personnel.While the new chip system they developed is “the core part of the innovation,” Ranno says, further work will be needed to develop this into an integrated, handheld device for practical use. “For making an actual product, you would need to package it into a usable form factor,” he explains. This would involve having a small chip-based laser coupled to the photonic chip. “It’s a matter of mechanical design, some optical design, some chemistry, and figuring out the supply chain,” he says. While that takes time, he says, the underlying concepts are straightforward.The system can be adapted to detect other similar contaminants in water, including cadmium, copper, lithium, barium, cesium, and radium, Ranno says. The device could be used with simple cartridges that can be swapped out to detect different elements, each using slightly different crown ethers that can bind to a specific ion.“There’s this problem that people don’t measure their water enough, especially in the developing countries,” Ranno says. “And that’s because they need to collect the water, prepare the sample, and bring it to these huge instruments that are extremely expensive.” Instead, “having this handheld device, something compact that even untrained personnel can just bring to the source for on-site monitoring, at low costs,” could make regular, ongoing widespread testing feasible.Hu, who is the John F. Elliott Professor of Materials Science and Engineering, says, “I’m hoping this will be quickly implemented, so we can benefit human society. This is a good example of a technology coming from a lab innovation where it may actually make a very tangible impact on society, which is of course very fulfilling.”“If this study can be extended to simultaneous detection of multiple metal elements, especially the presently concerning radioactive elements, its potential would be immense,” says Hou Wang, an associate professor of environmental science and engineering at Hunan University in China, who was not associated with this work.Wang adds, “This research has engineered a sensor capable of instantaneously detecting lead concentration in water. This can be utilized in real-time to monitor the lead pollution concentration in wastewater discharged from industries such as battery manufacturing and lead smelting, facilitating the establishment of industrial wastewater monitoring systems. I think the innovative aspects and developmental potential of this research are quite commendable.”Wang Qian, a principal research scientist at the Institute of Materials Research in Singapore, who also was not affiliated with this work, says, “The ability for the pervasive, portable, and quantitative detection of lead has proved to be challenging primarily due to cost concerns. This work demonstrates the potential to do so in a highly integrated form factor and is compatible with large-scale, low-cost manufacturing.”The team included researchers at MIT, at Nanyang Technological University and Temasek Laboratories in Singapore, at the University of Southampton in the U.K., and at companies Fingate Technologies, in Singapore, and Vulcan Photonics, headquartered in Malaysia. The work used facilities at MIT.nano, the Harvard University Center for Nanoscale Systems, NTU’s Center for Micro- and Nano-Electronics, and the Nanyang Nanofabrication Center.

Artist’s impression of the chip surface, showing the on-chip light interferometer used to sense the presence of lead. The lead binding process to the crown ether is shown in the inset. Image: Jia Xu Brian Sia

The chip-scale device could provide sensitive detection of lead levels in drinking water, whose toxicity affects 240 million people worldwide.

Scientists develop an affordable sensor for lead contamination

<section id="isPasted">What do volcanic lava, fire smoke, automobile exhaust fumes, and printer toner have in common? They are all sources of ultrafine particles – particles with a diameter below 100 nanometers, which can pose serious health risks if inhaled. Due to their small size, ultrafine nanoparticles are difficult to detect and measure without expensive and sometimes bulky equipment. To overcome these issues, our researchers have designed a new ultra-sensitive fiber-tip sensor that can detect single particles with diameters down to 50 nanometers in size. In the future, the new sensor will be used in studies to control and evaluate indoor air quality at schools.</section><section tabindex="-1">Nanoparticles are very much part of the everyday world that we call home. For example, in medical testing, devices are available to check for nanoparticles like pathogens and biomarkers for diseases such as cancer.And in drug development, a host of nanoparticles are used to make the drug delivery systems of the future.One class of nanoparticle that is garnering plenty of attention due to its connection with the air that we breathe is the ultrafine particle (UFP), a particle with a diameter below 100 nanometers (nm).Exposure to UFPs – which can be found in smoke, exhaust fumes, and even printer toners – can have serious health risks, especially if these particles are directly inhaled.<section tabindex="-1" id="isPasted">“When UFPs lodge in the lungs, it can pose a severe health risk because once in the lungs, they can absorb toxins that we might breathe in from the air around us. As a result, those toxins then stay in the body,” says <a href="https://www.tue.nl/en/research/researchers/arthur-hendriks" target="_blank">Arthur Hendriks</a>, PhD researcher at the Department of Applied Physics and Science Education. “So, to help prevent this, accurate ways of detecting UFPs are needed so as to monitor indoor air quality.”For example, research on indoor air quality is at the forefront of the <a href="https://www.learnproject-heu.eu/" target="_blank" rel="noreferrer">Horizon Europe project LEARN</a>, which is seeking to control and evaluate indoor air quality at schools and to assess the impact of air quality on children’s health, and part of this requires accurate ways to detect UFPs.<h3>The small-big problem</h3>But detecting UFPs is easier said than done though, and ironically, detection of such small particles relies on the use of large and expensive equipment.“Large and expensive isn’t the answer. We need small, compact, accurate, and cheap devices to make it easier to detect UFPs in factories, hospitals, offices, and schools,” notes Hendriks.</section><section tabindex="-1">So, what is the state-of-the-art now then? “There are sensors based on fiber-optic technologies that can measure liquids and gases with good accuracy. But these sensors not suitable for measuring small particles like UFPs and so their application are limited in that sense,” says Hendriks.&nbsp;‘Lab-on-fiber’ technologies have been used to detect biological cells at the micrometer scale (1000 times larger than the nanometer scale). “But this technology cannot detect single nanoparticles similar in size to UFPs,” says Hendriks.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1714987151109-csm_Hendriks+Nanophotonic-fiber-tip-sensor_5fc4f58556.png" style="width: 100%px;" class="fr-fic fr-dib">SEM image of nanophotonic fiber tip sensor. Source: Arthur Hendriks<h3 id="isPasted">A fiber-tip solution</h3>To meet the demand for a new UFP sensing technology, Hendriks and his TU/e collaborators, which includes Andrea Fiore – professor at the Department of Applied Physics and Science Education, developed a nanophotonic fiber-tip sensor that is sensitive to tiny changes in the environment around the sensor, so much so that it can detect a single nanoparticle the same size as UFPs.“Our sensor design is small and compact, and importantly, it clearly indicates when a detection has occurred,” says Hendriks.The researchers’ sensor work is based on a photonic crystal, a periodic or repeating structure that can reflect light in all directions. “A defect, or error, is then added to the crystal, which is known as a photonic crystal cavity, or PhCC for short,” says Hendriks.A PhCC allows light to be trapped in the crystal for an extended period. Hendriks: “In essence, this is something we call the Q-factor, which is a measure of how well light can be trapped in the defect over time. In our case, the light is confined to a tiny volume, which is below 1 µm3. This is known as the mode volume, and to measure tiny nanoparticles, this needs to be very small.”The researchers were able to place the PhCC on the tip of a fiber using a method developed by Andrea Fiore’s group <a href="https://doi.org/10.1063/5.0021701" target="_blank" rel="noreferrer">back in 2020</a>. When a tiny particle comes close to the PhCC in the crystal, it disturbs the cavity by changing its refractive index. “So, the tiny particle changes the wavelength of the trapped light in the cavity, and we measure this change.”<h2 id="isPasted">CHALLENGES</h2><img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1714987186281-csm_Hendriks+Schematic_3e24cc23c3.png" style="width: 100%px;" class="fr-fic fr-dib">The major challenge faced by the researchers was that standard cavities cannot be read out using fibers. A standard cavity on a fiber wouldn’t have worked as light from the fiber will not couple to the cavity.The dream scenario for the researchers was to optimize key factors in the device. First, a high Q-factor was required to allow for more accurate tracking of the wavelength of the cavity. Second, a small mode volume was needed as this allows for the detection of smaller particles. Third, a higher coupling efficiency was a necessity to ensure that light from the fiber can couple to the cavity and back, making it possible to measure the cavity wavelength through the fiber.To solve all these challenges, the researchers used a method developed by researchers at Stanford University to optimize factors such as the Q-factor, mode volume, and coupling efficiency at the same time.<h3 id="isPasted">Unprecedented sensitivity</h3>“Our setup provides unprecedented sensitivity in comparison to previous technologies out there,” points out Hendriks. “Using the sensor, we were able to detect in real-time single UFPs with diameters as low as 50 nanometers. In my opinion, that’s just astounding!”The next step for Hendriks and his colleagues is to suspend the cavities so that the quality factor and the coupling efficiency are even higher, which could result in nanophotonic cavities with best-in-class characteristics, but still readable through the fiber.“Our approach could be used to detect even smaller particles. Or even in other applications like single-photon emitters and nano-optomechanical sensors,” says Hendriks. “And an additional application of the new approach might even be the detection of single biological molecules.”Next up for the UFP sensor will be the European project LEARN, which aims at controlling and evaluating air quality at schools, and it will be done in collaboration with the Microsystems group at TU/e.<hr><h3>Further information</h3>The full paper entitled “Detecting single nanoparticles using fiber-tip nanophotonics” can be read&nbsp;<a href="https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-4-512&id=549037" target="_blank" rel="noreferrer">here</a>.</section></section>

Using an ultrasensitive photonic crystal, TU/e researchers were able to detect single particles down to 50 nanometers in diameter. The new research has just been published in the journal Optica.

A nanophotonic fiber-tip solution to detect the ultrasmall

Quantum simulators (or computers) are a promising means of solving complex computational tasks such as the encryption of data with quantum cryptography. Compared to conventional computers, quantum ones rely not on bits (which can have two states: 1 and 0), but on qubits (which can have many states). It is thanks to this property that quantum computers are expected to be capable of processing all states simultaneously, thus producing solutions faster than regular PCs.One major challenge on the way towards quantum computers is spontaneous emission – the possibility of a qubit being destroyed at any moment by emitting into its environment. This phenomenon shortens the life of quantum states and essentially renders the recording of information impossible in quantum systems. Large atomic structures (containing dozens or hundreds of atoms) are typically used to suppress spontaneous emission. Earlier, scientists from ITMO had <a href="https://www.degruyter.com/document/doi/10.1515/nanoph-2023-0624/html" target="_blank">discovered</a> 2D atomic arrays that can support quantum states of maximal longevity; however, the optimal design of structures with randomly located particles remained unknown.This time, through an optimization of geometry, the physicists were able to acquire structures that can support the quantum states longer by dozens and hundreds of times. For this, they used evolutionary algorithms (AI algorithms that model natural selection processes) to create a program that can predict the appropriate system parameters. Compared to other solutions, in which the atomic structures had predefined geometries, in this one the AI was responsible for identifying the correct atom locations.The suggested solution determines the geometry of molecules made up from ultracold atoms. In a sense, the team has provided a manual for assembling long-lived quantum systems for information recording and storage: the structures predicted by the AI can be used to develop quantum memory algorithms.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1713998613704-1369102.jpg" style="width: 100%px;" class="fr-fic fr-dib">A schematic of the algorithm that determines the optimal design of long-lived quantum structures. Image courtesy of the authorsIn their work, the authors considered two variables: the number of atoms and the minimal space between them. Using the algorithm, they determined the optimal geometry for different interatomic distances: 1D chains and fragments of square and triangle arrays. All of these configurations can support non-radiative – long-lived – quantum states.<blockquote>“There are two paths by which this project may continue. Until now, we have calculated the parameters for single-photon structures; next, we will look for the same things for two-photon tangled states: they can contain twice as much information, as well as be used in quantum communications for information transfer. Moreover, we’d like to improve our algorithm by enabling it to compute systems with a greater number of atoms,” shares&nbsp;Ilya Volkov, one of the paper’s authors and a PhD student at ITMO’s <a href="https://en.itmo.ru/en/faculty/106/fiziko-tehnicheskiy_megafakultet.htm" target="_blank">School of Physics and Engineering</a>.</blockquote>Thanks to this solution, the researchers will be able to extend the recording time of quantum states, thus opening up new possibilities for their application, including the development of quantum computers.<hr><a href="https://pubs.aip.org/aip/apl/article-abstract/124/8/084001/3266785/Non-radiative-configurations-of-a-few-quantum?redirectedFrom=fulltext" target="_blank">Reference</a>: Ilya Volkov, Stanislav Mitsai, Stepan Zhogolev, Danil Kornovan, Alexandra Sheremet, Roman Savelev, Mihail Petrov. Non-radiative configurations of a few quantum emitters ensembles: Evolutionary optimization approach (Applied Physics Letters, 2024)&nbsp;

Physicists from ITMO University have created an AI-based solution to make quantum states remain stable for longer for the processing, reliable recording, and storage of information. This study, described in a recent article in Applied Physics Letters, may help pave the way to quantum computers.

Longer-Lived Quantum States Suggested at ITMO

Researchers at the Georgia Institute of Technology have developed a light-based means of printing nano-sized metal structures that is significantly faster and cheaper than any technology currently available. It is a scalable solution that could transform a scientific field long reliant on technologies that are prohibitively expensive and slow. The breakthrough has the potential to bring new technologies out of labs and into the world.Technological advances in many fields rely on the ability to print metallic structures that are nano-sized — a scale hundreds of times smaller than the width of a human hair. <a href="https://www.me.gatech.edu/faculty/saha" target="_blank">Sourabh Saha</a>, assistant professor in the <a href="https://www.me.gatech.edu/" target="_blank">George W. Woodruff School of Mechanical Engineering</a>, and Jungho Choi, a Ph.D. student in Saha’s lab, developed a technique for printing metal nanostructures that is 480 times faster and 35 times cheaper than the current conventional method.Their research was <a href="https://onlinelibrary.wiley.com/doi/10.1002/adma.202308112" target="_blank">published</a> in the journal Advanced Materials.Printing metal on the nanoscale — a technique known as nanopatterning — allows for the creation of unique structures with interesting functions. It is crucial for the development of many technologies, including electronic devices, solar energy conversion, sensors, and other systems.It is generally believed that high-intensity light sources are required for nanoscale printing. But this type of tool, known as a femtosecond laser, can cost up to half a million dollars and is too expensive for most research labs and small businesses.“As a scientific community, we don’t have the ability to make enough of these nanomaterials quickly and affordably, and that is why promising technologies often stay limited to the lab and don’t get translated into real-world applications,” Saha said.“The question we wanted to answer is, ‘Do we really need a high-intensity femtosecond laser to print on the nanoscale?’ Our hypothesis was that we don’t need that light source to get the type of printing we want.”They searched for a low-cost, low-intensity light that could be focused in a way similar to femtosecond lasers, and chose superluminescent light emitting diodes (SLEDs) for their commercial availability. SLEDs emit light that is a billion times less intense than that of femtosecond lasers.Saha and Choi set out to create an original projection-style printing technology, designing a system that converts digital images into optical images and displays them on a glass surface. The system operates like digital projectors but produces images that are more sharply focused. They leveraged the unique properties of the superluminescent light to generate sharply focused images with minimal defects.They then developed a clear ink solution made up of metal salt and added other chemicals to make sure the liquid could absorb light. When light from their projection system hit the solution, it caused a chemical reaction that converted the salt solution into metal. The metal nanoparticles stuck to the surface of the glass, and the agglomeration of the metal particles creates the nanostructures. Because it is a projection type of printing, it can print an entire structure in one go, rather than point by point — making it much faster.After testing the technique, they found that projection-style nanoscale printing is possible even with low-intensity light, but only if the images are sharply focused. Saha and Choi believe that researchers can readily replicate their work using commercially available hardware. Unlike a pricey femtosecond laser, the type of SLED that Saha and Choi used in their printer costs about $3,000.“At present, only top universities have access to these expensive technologies, and even then, they are located in shared facilities and are not always available,” Choi said. “We want to democratize the capability of nanoscale 3D printing, and we hope our research opens the door for greater access to this type of process at a low cost.”The researchers say their technique will be particularly useful for people working in the fields of electronics, optics, and plasmonics, which all require a variety of complex metallic nanostructures.“I think the metrics of cost and speed have been greatly undervalued in the scientific community that works on fabrication and manufacturing of tiny structures,” Saha said.“In the real world, these metrics are important when it comes to translating discoveries from the lab to industry. Only when we have manufacturing techniques that take these metrics into account will we be able to fully leverage nanotechnology for societal benefit.”<hr>Citation: J. Choi, S. K. Saha, Scalable Printing of Metal Nanostructures through Superluminescent Light Projection. Adv. Mater. 2024, 36, 2308112.DOI: https://doi.org/10.1002/adma.202308112

The researchers developed a light-based means of printing nano-sized metal structures that is 480 times faster and 35 times cheaper than the current conventional method.

Researchers Create Faster and Cheaper Way to Print Tiny Metal Structures With Light

Lights could soon use the full color suite of perfectly efficient organic light-emitting diodes, or OLEDs, that last tens of thousands of hours, thanks to an innovation from physicists and engineers at the University of Michigan.The U-M team’s new phosphorescent OLEDs, commonly referred to as PHOLEDs, can maintain 90% of the blue light intensity for 10-14 times longer than other designs that emit similar deep blue colors. That kind of lifespan could finally make blue PHOLEDs hardy enough to be commercially viable in lights that meet the Department of Energy’s 50,000-hour lifetime target. Without a stable blue PHOLED, OLED lights need to use less-efficient technology to create white light.The lifetime of the new blue PHOLEDs currently is only long enough to use as lighting, but the same design principle could be combined with other light-emitting materials to create blue PHOLEDs hardy enough for TVs, phone screens and computer monitors. Display screens with blue PHOLEDs could potentially increase a device’s battery life by 30%.“Achieving long-lived blue PHOLEDs has been a focus of the display and lighting industries for over 20 years. It is probably the most important and urgent challenge facing the field of organic electronics,” said <a href="https://eecs.engin.umich.edu/people/forrest-stephen-r/" target="_blank" rel="noreferrer noopener">Stephen Forrest</a>, the Peter A. Franken Distinguished University Professor of Electrical and Computer Engineering at the University of Michigan. He is also the corresponding author of the study published today in Nature.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1703720458568-Haonan-and-Claire-lab-1-1.jpg" style="width: 300px;" class="fr-fic fr-dib">Haonan Zhao and Claire Arneson, two doctoral students in physics and graduate student research assistants in electrical and computer engineering at the University of Michigan, fabricate their blue PHOLED devices in the lab. Their design prevents the excited molecules within the PHOLEDs light-emitting material from colliding, which could break the bonds holding the molecules together. Photo credit: Miranda Felty, University of MichiganPHOLEDs have nearly 100% internal quantum efficiency, meaning all of the electricity entering the device is used to create light. As a result, lights and display screens equipped with PHOLEDs can run brighter colors for longer periods of time with less power and carbon emissions.Before the U-M team’s research, the best blue PHOLEDs weren’t durable enough to be used in either lighting or displays. Only red and green PHOLEDs are stable enough to use in devices today, but blue is needed to complete the trio of colors in OLED “RGB” displays and white OLED lights. Red, green and blue light can be combined at different relative brightness to produce any color desired in display pixels and light panels.So far, the workaround in OLED displays has been to use older, fluorescent OLEDs to produce the blue colors, but the internal quantum efficiency of that technology is much lower. <a href="https://pubs.rsc.org/en/content/articlehtml/2023/tc/d3tc00245d" target="_blank" rel="noreferrer noopener">Only a quarter</a> of the electric current entering the fluorescent blue device produces light.“A lot of the display industry’s solutions are upgrades to fluorescent OLEDs, which is still an alternative solution,” said study first author Haonan Zhao, a doctoral student in physics and electrical and computer engineering. “I think a lot of companies would prefer to use blue PHOLEDs, if they had the choice.”To make blue light, electricity excites heavy metal-containing phosphorescent organic molecules. Sometimes, the excited molecules come into contact before emitting the light, transferring all of the pair’s stored energy into one molecule. Because the energy of blue light is so high, the transferred energy, which is double that of the single excited molecule, can break chemical bonds and degrade the organic material.One way around this problem is to use materials that emit a broader spectrum of colors, which lowers the total amount of energy in the excited states. But such materials appear cyan or even green, rather than a deep blue.The U-M team got around this issue by sandwiching cyan material between two mirrors. By perfectly tuning the space between the mirrors, only the deepest blue light waves can persist and eventually emit from the mirror chamber.Further tuning the optical properties of the organic, light-emitting layer to an adjacent metal electrode introduced a new quantum mechanical state called a plasmon-exciton-polariton, or PEP. This new state allows the organic material to emit light very fast, thus further decreasing the opportunity for excited states to collide and destroy the light-emitting material.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1703720495886-Haonan-and-Claire-lab-2-1.jpg" style="width: 300px;" class="fr-fic fr-dib">The research team constructs their blue PHOLEDs inside a glovebox that keeps the PHOLEDs away from oxygen and water before they are fully encased in nitrogen. It’s a standard procedure that protects the device’s sensitive optics and electronics. Photo credit: Miranda Felty, University of Michigan“In our device, the PEP is introduced because the excited states in the electron transporting material are synchronized with the light waves and the electron vibrations in the metal cathode,” said study co-author Claire Arneson, a doctoral student in physics and electrical and computer engineering.

Lights could soon use the full color suite of perfectly efficient organic light-emitting diodes, or OLEDs, that last tens of thousands of hours, thanks to an innovation from physicists and engineers at the University of Michigan.

Blue PHOLEDs: Final color of efficient OLEDs finally viable in lighting

The team at EPFL’s <a href="https://phosl.epfl.ch/" target="_blank">Photonic Systems Laboratory</a> (PHOSL) has developed a chip-scale laser source that enhances the performance of semiconductor lasers while enabling the generation of shorter wavelengths. This pioneering work, led by Professor Camille Brès and postdoctoral researcher Marco Clementi from EPFL’s School of Engineering represents a significant advance in the field of photonics, with implications for telecommunications, metrology, and other high-precision applications.The study, published in the journal Light: Science &amp; Applications, reveals how the PHOSL researchers, in collaboration with the <a href="https://www.epfl.ch/labs/k-lab/" target="_blank">Laboratory of Photonics and Quantum Measurements</a>, have successfully integrated semiconductor lasers with silicon nitride photonic circuits containing microresonators. This integration results in a hybrid device capable of emitting highly uniform and precise light in both near-infrared and visible ranges, filling a technological gap that has long challenged the industry."Semiconductor lasers are ubiquitous in modern technology, found in everything from smartphones to fiber optic communications. However, their potential has been limited by a lack of coherence and the inability to generate visible light efficiently," explains Professor Brès . "Our work not only improves the coherence of these lasers but also shifts their output towards the visible spectrum, opening up new avenues for their use."Coherence, in this context, refers to the uniformity of the phases of the light waves emitted by the laser. High coherence means the light waves are synchronized, leading to a beam with a very precise color or frequency. This property is crucial for applications where precision and stability of the laser beam are paramount, such as time keeping and precision sensing.Increased accuracy and improved functionality The team's approach involves coupling commercially available semiconductor lasers with a silicon nitride chip. This tiny chip is created with industry-standard, cost-efficient CMOS technology. Thanks to the material’s exceptional low-loss properties, there is little to no light that is absorbed or escapes. The light from the semiconductor laser flows through microscopic waveguides into extremely small cavities, where the beam is trapped. These cavities, called micro-ring resonators, are intricately designed to resonate at specific frequencies, selectively amplifying the desired wavelengths while attenuating others, thereby achieving enhanced coherence in the emitted light.The other significant achievement is the hybrid system’s ability to double the frequency of the light coming from the commercial semiconductor laser— enabling a shift from the near-infrared spectrum to the visible light spectrum. The relationship between frequency and wavelength is inversely proportional, meaning that if the frequency is doubled, the wavelength is reduced by half. While the near infrared spectrum is exploited for telecommunications, higher frequencies are essential for building smaller, more efficient devices where shorter wavelengths are needed, such as in atomic clocks and medical devices.These shorter wavelengths are achieved when the trapped light in the cavity undergoes a process called all-optical poling, which induces what is known as second-order nonlinearity in the silicon nitride. Nonlinearity in this context means that there is a significant shift, a jump in magnitude, in the light's behavior that is not directly proportional to its frequency, arising from its interaction with the material. Silicon nitride does not normally incur this specific second order nonlinear effect, and the team performed an elegant engineering feat to induce it: The system takes advantage of the light’s capacity, when resonating within the cavity, to produce an electromagnetic wave that provokes the nonlinear properties in the material.<h2>An enabling technology for future applications</h2>"We are not just improving existing technology but also pushing the boundaries of what's possible with semiconductor lasers," says Marco Clementi, who played a key role in the project. "By bridging the gap between telecom and visible wavelengths, we're opening the door to new applications in fields like biomedical imaging and precision timekeeping."<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1703080828384-ezgif-2-416faa76dd.jpg" style="width: 300px;" class="fr-fic fr-dib">Professor Camille Brès and Marco Clementi in the lab. - 2023 EPFL/Alain Herzog - CC-BY-SA 4.0One of the most promising applications of this technology is in metrology, particularly in the development of compact atomic clocks. The history of navigational advancements hinges on the portability of accurate timepieces—from determining longitude at sea in the 16th Century to ensuring the accurate navigation of space missions and achieving better geo-localization today. "This significant advancement lays the groundwork for future technologies, some of which are yet to be conceived," notes Clementi.The team’s deep understanding of photonics and material science will potentially lead to smaller and lighter devices and lower the energy consumption and production costs of lasers. Their ability to take a fundamental scientific concept and translate it into a practical application using industry standard fabrication underscores the potential of solving complex technological challenges that can lead to unforeseen advances.<hr>ReferencesClementi, M., Nitiss, E., Durán-Valdeiglesias, E., Belahsene, S., Liu, J., Kippenberg, T. J., Debrégeas, H., &amp; Brès, C.-S. (2023). A chip-scale second-harmonic source via injection-locked all-optical poling. Light: Science &amp; Applications.&nbsp;<a href="https://doi.org/10.1038/s41377-023-01329-6" title="https://doi.org/10.1038/s41377-023-01329-6" target="_blank" rel="noopener">https://doi.org/10.1038/s41377-023-01329-6</a>

The micro-resonator being activated by a semi-conductor laser. - 2023 EPFL/Alain Herzog - CC-BY-SA 4.0

EPFL researchers have developed a hybrid device that significantly improves existing, ubiquitous laser technology.

A micro-ring resonator with big potential

Exploring Silicon Photonics: Shaping the Future of Optical Communication

Silicon Photonics: A Comprehensive Guide to the Future of Optical Communications

New research from the lab of Caltech's&nbsp;<a href="https://www.eas.caltech.edu/people/lvw" target="_blank">Lihong Wang</a>, the Bren Professor of Medical Engineering and Electrical Engineering, is the latter. In a paper published in the journal&nbsp;Nature Biomedical Engineering, Wang and postdoctoral scholar Yide Zhang show how they have simplified and improved&nbsp;<a href="https://www.caltech.edu/about/news/advancement-simplifies-laser-based-medical-imaging" target="_blank">an imaging technique</a> they first announced in 2020.That technique, a form of photoacoustic imaging technology called PATER (Photoacoustic Topography Through an Ergodic Relay), is a specialty of Wang's group.In photoacoustic imaging, laser light is pulsed into tissue where it is absorbed by the tissue's molecules, causing them to vibrate. Each vibrating molecule serves as a source of ultrasonic waves that can be used to image the internal structures in a fashion similar to how ultrasound imaging is performed.However, photoacoustic imaging is technologically challenging because it produces all its imaging information in one short burst. To capture that information, early versions of Wang's photoacoustic imaging technology required arrays of hundreds of sensors (transducers) to be pressed against the surface of the tissue being imaged, which made the technology complicated and expensive.Wang and Zhang reduced the number of required transducers by using a device called an ergodic relay, which slows down the rate at which information (in the form of vibrations) flows into a transducer. As explained in a&nbsp;<a href="https://www.caltech.edu/about/news/advancement-simplifies-laser-based-medical-imaging" target="_blank">previous story</a> about PATER:In computing, there are two main ways to transmit data: serial and parallel. In serial transmission, the data are sent in a single stream through one communication channel. In parallel transmission, several pieces of data are sent at the same time using multiple communication channels.The two types of communication are roughly analogous to the way cash registers might be used in a store. Serial communication would be like having one cash register. Everyone gets in the same line and sees the same cashier. Parallel communication would be like having several registers and a line for each.The system Wang designed with 512 sensors is similar to the store with many cash registers. All of the sensors are working at the same time, with each taking in part of the data about the ultrasonic vibrations generated by the laser pulse.Since the ultrasonic vibrations from the system come in one short burst, a single sensor would be overwhelmed if it were used to try and collect all the data in that short amount of time. That's where the ergodic relay comes in.As Wang describes it, an ergodic relay is a sort of chamber around which sound can echo. When the ultrasonic vibrations pass through the ergodic relay, they are stretched out in time. To return to the cash-register metaphor, it would be like having another employee assisting the single cashier by telling the customers to walk a few laps around the store until the cashier is ready to see them, so the cashier does not become overwhelmed.The latest version of this technology, called PACTER (Photoacoustic Computed Tomography Through an Ergodic Relay) goes even further, allowing the system to operate using a single transducer that, through the use of software, can collect as much data as 6,400 transducers.<iframe width="640" height="360" src="https://www.youtube.com/embed/L7r5eNtaLq4?&amp;wmode=opaque&amp;rel=0&amp;enablejsapi=1&amp;origin=https://www.wevolver.com" frameborder="0" allowfullscreen="" class="fr-draggable" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true"></iframe>PACTER improves on PATER in two other ways, says Wang, who is also the Andrew and Peggy Cherng Medical Engineering Leadership Chair and executive officer for medical engineering.One improvement is that PACTER can create three-dimensional images, whereas PATER can only generate 2D images. This was enabled by the development of improved software."Transitioning to 3D imaging significantly escalates the data requirement. The challenge was funneling the immensely increased data through a single transducer," Zhang says. "Our solution emerged by altering our approach. Rather than a direct and computationally intensive method of reconstructing 3-D images from the single-transducer data, we first expanded one transducer into thousands of virtual ones. This idea simplified the process of 3D image reconstruction, aligning it more closely with the traditional methods in our photoacoustic imaging."Secondly, unlike PATER, PACTER does not need to be calibrated each time it is used."With PATER, we had to calibrate it each time to use it and that's just not practical. We got rid of this per-use single-time calibration," Wang says.Calibration was needed because when the system fires a pulse of laser light into tissue, an "echo" of that pulse would bounce back into the transducer, preventing it from sensing direct ultrasound information.Wang says PACTER gets around that issue by adding something called a delay line to the system. The delay line forces the echo to take a longer physical path on its way back to the transducer so that it arrives after the direct ultrasound information has been received."Even though I always said this was possible, I knew it would be challenging," Wang says.The paper describing the work, "Ultrafast longitudinal imaging of haemodynamics via single-shot volumetric photoacoustic tomography with a single-element detector," appears in the November 30 issue of&nbsp;Nature Biomedical Engineering. Co-authors are Peng Hu (PhD '23), former graduate student in medical engineering; Lei Li (PhD '19), former postdoc in medical engineering; Rui Cao, postdoc in medical engineering; Anjul Khadria, former postdoc in medical engineering; Konstantin Maslov, former staff scientist at Caltech; Xin Tong, graduate student in medical engineering; and Yushun Zeng, Laiming Jiang, and Qifa Zhou of USC.

There are times when scientific progress comes in the form of discovering something completely new. Other times, progress boils down to doing something better, faster, or more easily.

Advancements Make Laser-Based Imaging Simpler and Three-Dimensional

The practice of keeping time hinges on stable oscillations. In a grandfather clock, the length of a second is marked by a single swing of the pendulum. In a digital watch, the vibrations of a quartz crystal mark much smaller fractions of time. And in atomic clocks, the world’s state-of-the-art timekeepers, the oscillations of a laser beam stimulate atoms to vibrate at 9.2 billion times per second. These smallest, most stable divisions of time set the timing for today’s satellite communications, GPS systems, and financial markets.A clock’s stability depends on the noise in its environment. A slight wind can throw a pendulum’s swing out of sync. And heat can disrupt the oscillations of atoms in an atomic clock. Eliminating such environmental effects can improve a clock’s precision. But only by so much.A new MIT study finds that even if all noise from the outside world is eliminated, the stability of clocks, laser beams, and other oscillators would still be vulnerable to quantum mechanical effects. The precision of oscillators would ultimately be limited by quantum noise.But in theory, there’s a way to push past this quantum limit. In their study, the researchers also show that by manipulating, or “squeezing,” the states that contribute to quantum noise, the stability of an oscillator could be improved, even past its quantum limit.“What we’ve shown is, there’s actually a limit to how stable oscillators like lasers and clocks can be, that’s set not just by their environment, but by the fact that quantum mechanics forces them to shake around a little bit,” says Vivishek Sudhir, assistant professor of mechanical engineering at MIT. “Then, we’ve shown that there are ways you can even get around this quantum mechanical shaking. But you have to be more clever than just isolating the thing from its environment. You have to play with the quantum states themselves.”The team is working on an experimental test of their theory. If they can demonstrate that they can manipulate the quantum states in an oscillating system, the researchers envision that clocks, lasers, and other oscillators could be tuned to super-quantum precision. These systems could then be used to track infinitesimally small differences in time, such as the fluctuations of a single qubit in a quantum computer or the presence of a dark matter particle flitting between detectors.“We plan to demonstrate several instances of lasers with quantum-enhanced timekeeping ability over the next several years,” says Hudson Loughlin, a graduate student in MIT’s Department of Physics. “We hope that our recent theoretical developments and upcoming experiments will advance our fundamental ability to keep time accurately, and enable new revolutionary technologies.”Loughlin and Sudhir detail their work in an open-access&nbsp;<a href="https://www.nature.com/articles/s41467-023-42739-9" target="_blank">paper published in the journal&nbsp;Nature Communications</a>.<h2>Laser precision</h2>In studying the stability of oscillators, the researchers looked first to the laser — an optical oscillator that produces a wave-like beam of highly synchronized photons. The invention of the laser is largely credited to physicists Arthur Schawlow and Charles Townes, who coined the name from its descriptive acronym: light amplification by stimulated emission of radiation.A laser’s design centers on a “lasing medium” — a collection of atoms, usually embedded in glass or crystals. In the earliest lasers, a flash tube surrounding the lasing medium would stimulate electrons in the atoms to jump up in energy. When the electrons relax back to lower energy, they give off some radiation in the form of a photon. Two mirrors, on either end of the lasing medium, reflect the emitted photon back into the atoms to stimulate more electrons, and produce more photons. One mirror, together with the lasing medium, acts as an “amplifier” to boost the production of photons, while the second mirror is partially transmissive and acts as a “coupler” to extract some photons out as a concentrated beam of laser light.Since the invention of the laser, Schawlow and Townes put forth a hypothesis that a laser’s stability should be limited by quantum noise. Others have since tested their hypothesis by modeling the microscopic features of a laser. Through very specific calculations, they showed that indeed, imperceptible, quantum interactions among the laser’s photons and atoms could limit the stability of their oscillations.“But this work had to do with extremely detailed, delicate calculations, such that the limit was understood, but only for a specific kind of laser,” Sudhir notes. “We wanted to enormously simplify this, to understand lasers and a wide range of oscillators."<h2>Putting the “squeeze” on</h2>Rather than focus on a laser’s physical intricacies, the team looked to simplify the problem.“When an electrical engineer thinks of making an oscillator, they take an amplifier, and they feed the output of the amplifier into its own input,” Sudhir explains. “It’s like a snake eating its own tail. It’s an extremely liberating way of thinking. You don’t need to know the nitty gritty of a laser. Instead, you have an abstract picture, not just of a laser, but of all oscillators.”In their study, the team drew up a simplified representation of a laser-like oscillator. Their model consists of an amplifier (such as a laser’s atoms), a delay line (for instance, the time it takes light to travel between a laser’s mirrors), and a coupler (such as a partially reflective mirror).The team then wrote down the equations of physics that describe the system’s behavior, and carried out calculations to see where in the system quantum noise would arise.“By abstracting this problem to a simple oscillator, we can pinpoint where quantum fluctuations come into the system, and they come in in two places: the amplifier and the coupler that allows us to get a signal out of the oscillator,” Loughlin says. “If we know those two things, we know what the quantum limit on that oscillator’s stability is.”Sudhir says scientists can use the equations they lay out in their study to calculate the quantum limit in their own oscillators.What’s more, the team showed that this quantum limit might be overcome, if quantum noise in one of the two sources could be “squeezed.” Quantum squeezing is the idea of minimizing quantum fluctuations in one aspect of a system at the expense of proportionally increasing fluctuations in another aspect. The effect is similar to squeezing air from one part of a balloon into another.In the case of a laser, the team found that if quantum fluctuations in the coupler were squeezed, it could improve the precision, or the timing of oscillations, in the outgoing laser beam, even as noise in the laser’s power would increase as a result.“When you find some quantum mechanical limit, there’s always some question of how malleable is that limit?” Sudhir says. “Is it really a hard stop, or is there still some juice you can extract by manipulating some quantum mechanics? In this case, we find that there is, which is a result that is applicable to a huge class of oscillators.”

Clocks, lasers, and other oscillators could be tuned to super-quantum precision, allowing researchers to track infinitesimally small differences in time, according to a new MIT study. Image: MIT News; iStock

More stable clocks could measure quantum phenomena, including the presence of dark matter.

With a quantum "squeeze," clocks could keep even more precise time, MIT researchers propose

Integrated photonics, also known as planar lightwave circuits or integrated optical circuits, revolutionizes optical communication by leveraging the properties of light to process and transmit information. This cutting-edge technology offers superior efficiency and compactness compared to traditional electronic components, paving the way for faster and more energy-efficient communication systems. With its interdisciplinary nature encompassing materials science, quantum physics, and electrical engineering, integrated photonics presents an exciting and promising field of study and research in today's digital era.


Integrated Photonics: Comprehensive Guide to Optical Communication

This article was first published on&nbsp;<a href="https://news.mit.edu/2023/study-reveals-new-ways-exotic-quasiparticles-relax-0512" id="isPasted" rel="noopener noreferrer" target="_blank">MIT News</a>. &nbsp;<hr>New findings from a team of researchers at MIT and elsewhere could help pave the way for new kinds of devices that efficiently bridge the gap between matter and light. These might include computer chips that eliminate inefficiencies inherent in today&rsquo;s versions, and qubits, the basic building blocks for quantum computers, that could operate at room temperature instead of the ultracold conditions needed by most such devices.The new work, based on sandwiching tiny flakes of a material called perovskite in between two precisely spaced reflective surfaces, is detailed in the journal&nbsp;Nature Communications, in a&nbsp;<a href="https://www.nature.com/articles/s41467-023-37772-7" target="_blank">paper</a> by MIT recent graduate Madeleine Laitz PhD &rsquo;22, postdoc Dane deQuilettes, MIT professors Vladimir Bulovic, Moungi Bawendi and Keith Nelson, and seven others.By creating these perovskite sandwiches and stimulating them with laser beams, the researchers were able to directly control the momentum of certain &ldquo;quasiparticles&rdquo; within the system. Known as exciton-polariton pairs, these quasiparticles are hybrids of light and matter. Being able to control this property could ultimately make it possible to read and write data to devices based on this phenomenon.&ldquo;What&rsquo;s particularly fascinating about exciton-polaritons,&rdquo; Laitz says, is that they lie &ldquo;on a spectrum between purely electronic and photonic systems.&rdquo; These quasiparticles &ldquo;have the characteristics of both, and thus you can leverage exciton-polaritons to utilize the best properties of each.&rdquo;For example, purely electronic transistors, she explains, have inherent losses to capacitance effects at each interface between devices, whereas &ldquo;purely photonic systems have challenges in engineering, in that it&rsquo;s very hard to get photons to interact, and you have to rely on complex interferometric schemes.&rdquo; By contrast, the quasiparticles used by this team can be easily controlled through multiple variables.The quasiparticle is &ldquo;a combined state of light and neutral charge,&rdquo; Bulovic says. &ldquo;As a result, you can perturb that combined state either with light or charge, and hence, if you need to modulate that state, you have extra levers you can utilize. These extra levers can now allow one to manipulate this combined state of matter in a more energy-efficient manner.&rdquo;What&rsquo;s more, the materials involved are easily manufactured using room-temperature, solution-based processing methods, and thus could be relatively easy to produce at scale once practical systems are designed. So far, the work is at a very early stage, as researchers are still studying newly discovered effects; practical applications could be five to 10 years away, Laitz says.Perovskites have attracted much attention in recent years as materials for new lightweight, flexible solar photovoltaic panels, so there has been a great deal of research on their properties and fabrication methods. The team settled on a particular version of perovskite called phenethylammonium lead iodide.&ldquo;Halide perovskites harvest light really well, and turn photons into electrons or excitons, depending on the dimensionality and material properties of the perovskite,&rdquo; she says, which is why the researchers chose this particular version of this large class of materials for their research.Then, to create what is known as an optical cavity that can trap photons of light, the researchers placed tiny flakes of the material between mirrored surfaces. Two of these ultrathin layers, just tens of nanometers thick, were spaced a precise distance apart using spacer layers, so that the mirrors were separated by half the wavelength of light that this perovskite material both absorbs and emits.Using perovskite tuned to a wavelength of green light, the emitted green light then bounces back and forth between the mirrors. &ldquo;It&rsquo;s reabsorbed by the material, re-emitted, reabsorbed, re-emitted, reabsorbed over and over again so quickly that you&rsquo;re interconverting between the photon and the exciton, such that you generate a superposition of both,&rdquo; Laitz says.This can lead to the state of matter known as a Bose-Einstein Condensate, in which all the particles have identical energy states and behave much like one large particle. Laitz says that such condensates carry a property known as spin, and this can be modified by light or electrical stimulation; the resulting changes can be measured by observing photoluminescence from the material using a spectroscopic imaging system. And unlike purely photonic systems, where there is little interaction between photons, these materials have strong interactions with both light and electrons.Arrays of such condensates have been produced, but typically only at ultralow, cryogenic temperatures so far. &ldquo;Perovskites offer the opportunity for realizing this phenomenon at elevated temperatures,&rdquo; but it&rsquo;s hard to form the condensates in perovskites. This new research shows fundamental characteristics of the process that leads to condensation, Laitz says. In their paper, &ldquo;we propose several strategies from a material perspective and a device architecture perspective to enable this.&rdquo; And that could be a key step toward eventual room-temperature qubits, she says.While such devices may take several years to develop, a more near-term application of the new findings could be in producing new kinds of light-emitting devices, deQuilettes says, including ones that could provide a steerable light source with directional output that can be controlled electronically.&ldquo;There has been quite a bit of interest in using exciton-polaritons as the basis for low-power coherent light sources, similar to lasers,&rdquo; says St&eacute;phane K&eacute;na-Cohen an associate professor of engineering physics at the Montreal Polytechnic, who was not associated with this work.&nbsp;&ldquo;In that area, the challenge is to get polaritons to relax efficiently to their lowest energy state. This paper helps us understand the details of how this happens in perovskite microcavities, and how to better design cavities to make this happen at very low power.&rdquo;The research team also included Alexander Kaplan, Jude Deschamps, Ulugbek Barotov, Andrew Proppe, and Anna Asherov at MIT, Ines Garcia-Benito at Complutense University of Madrid, and Giulia Grancini at the University of Pavia. The work was supported by the Tata-MIT GridEdge Solar Research Program, the National Science Foundation, and the European Research Council.<hr>&quot;Reprinted with permission of&nbsp;<a href="https://news.mit.edu/2023/study-reveals-new-ways-exotic-quasiparticles-relax-0512" id="isPasted" rel="noopener noreferrer" target="_blank">MIT News</a>&quot; &nbsp;

By sandwiching bits of perovskite between two mirrors and stimulating them with laser beams, researchers were able to directly control the spin state of quasiparticles known as exciton-polariton pairs, which are hybrids of light and matter. Image: Courtesy of the researchers

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