This talk shows how integrating p-type NiO to form NiO/Ga₂O₃ heterojunction rectifiers overcomes that barrier, enabling record-class breakdown and Ampere-class operation. It will cover device structure/process optimization, thermal stability to high temperatures, and radiation response – with direct ties to today’s priorities: EV fast charging, AI data‑center power systems, and aerospace/space‑qualified power electronics.
An interactive Q&A session follows the presentation.
Jian-Sian Li
Jian-Sian Li received the PhD in chemical engineering from the University of Florida in 2024, where his research focused on NiO/β-Ga₂O₃ heterojunction power rectifiers, includes device design, process optimization, fast switching, high-temperature stability, and radiation tolerance (γ, neutron, proton). His work includes extensive electrical characterization and microscopy/TCAD analysis supporting device physics and reliability in harsh environments. Previously, he completed his BS and MS at National Taiwan University (2015, 2018), with research spanning phoretic/electrokinetic colloids, polymers for OFETs/PSCs, and solid-state polymer electrolytes for Li-ion batteries. He has since transitioned to industry at Micron Technology.
A new integrated “snapshot spectroscopy” system developed in China can determine the spectral and spatial composition of light from an object with much better precision than other existing systems. The instrument uses randomly textured lithium niobate and its developers have used it for astronomical imaging and materials analysis – and they say that other applications are possible.
Spectroscopy is crucial to analysis of all kinds of objects in science and engineering, from studying the radiation emitted by stars to identifying potential food contaminants. Conventional spectrometers – such as those used on telescopes – rely on diffractive optics to separate incoming light into its constituent wavelengths. This makes them inherently large, expensive and inefficient at rapid image acquisition as the light from each point source has to be spatially separated to resolve the wavelength components.
In recent years researchers have combined computational methods with advanced optical sensors to create computational spectrometers with the potential to rival conventional instruments. One such approach is hyperspectral snapshot imaging, which captures both spectral and spatial information in the same image. There are currently two main snapshot-imaging techniques available. Narrowband-filtered snapshot spectral imagers comprise a mosaic pattern of narrowband filters and acquire an image by taking repeated snapshots at different wavelengths. However, these trade spectral resolution with spatial resolution, as each extra band requires its own tile within the mosaic. A more complex alternative design – the broadband-modulated snapshot spectral imager – uses a single, broadband detector covered with a spatially varying element such as a metasurface that interacts with the light and imprints spectral encoding information onto each pixel. However, these are complex to manufacture and their spectral resolution is limited to the nanometre scale.
Random thicknesses
In the new work, researchers led by Lu Fang at Tsinghua University in Beijing unveil a spectroscopy technique that utilizes the nonlinear optical properties of lithium niobate to achieve sub-Ångström spectral resolution in a simply fabricated, integrated snapshot detector they call RAFAEL. A lithium niobate layer with random, sub-wavelength thickness variations is surrounded by distributed Bragg reflectors, forming optical cavities. These are integrated into a stack with a set of electrodes. Each cavity corresponds to a single pixel. Incident light enters from one side of a cavity, interacting with the lithium niobate repeatedly before exiting and being detected. Because lithium niobate is nonlinear, its response varies with the wavelength of the light.
The researchers then applied a bias voltage using the electrodes. The nonlinear optical response of lithium niobate means that this bias alters its response to light differently at different wavelengths. Moreover, the random variation of the lithium niobate’s thickness around the surface means that the wavelength variation is spatially specific.
The researchers designed a machine learning algorithm and trained it to use this variation of applied bias voltage with resulting wavelength detected at each point to reconstruct the incident wavelengths on the detector at each point in space.
“The randomness is useful for making the equations independent,” explains Fang; “We want to have uncorrelated equations so we can solve them.”
Thousands of stars
The researchers showed that they could achieve 88 Hz snapshot spectroscopy on a grid of 2048×2048 pixels with a spectral resolution of 0.5 Å (0.05 nm) between wavelengths of 400–1000 nm. They demonstrated this by capturing the full atomic absorption spectra of up to 5600 stars in a single snapshot. This is a two to four orders of magnitude improvement in observational efficiency over world-class astronomical spectrometers. They also demonstrated other applications, including a materials analysis challenge involving the distinction of a real leaf from a fake one. The two looked identical at optical wavelengths, but, using its broader range of wavelengths, RAFAEL was able to distinguish between the two.
The researchers are now attempting to improve the device further: “I still think that sub-Ångstrom is not the ending – it’s just the starting point,” says Fu. “We want to push the limit of our resolution to the picometre.” In addition, she says, they are working on further integration of the device – which requires no specialized lithography – for easier use in the field. “We’ve already put this technology on a drone platform,” she reveals. The team is also working with astronomical observatories such as Gran Telescopio Canarias in La Palma, Spain.
Computational imaging expert David Brady of Duke University in North Carolina is impressed by the instrument. “It’s a compact package with extremely high spectral resolution,” he says; “Typically an optical instrument, like a CMOS sensor that’s used here, is going to have between 10,000 and 100,000 photo-electrons per pixel. That’s way too many photons for getting one measurement…I think you’ll see that with spectral imaging as is done here, but also with temporal imaging. People are saying you don’t need to go at 30 frames second, you can go at a million frames per second and push closer to the single photon limit, and then that would require you to do computation to figure out what it all means.”
Future versions of the Laser Interferometer Gravitational Wave Observatory (LIGO) will be able to run at much higher laser powers thanks to a sophisticated new system that compensates for temperature changes in optical components. Known as FROSTI (for FROnt Surface Type Irradiator) and developed by physicists at the University of California Riverside, US, the system will enable next-generation machines to detect gravitational waves emitted when the universe was just 0.1% of its current age, before the first stars had even formed.
Gravitational waves are distortions in spacetime that occur when massive astronomical objects accelerate and collide. When these distortions pass through the four-kilometre-long arms of the two LIGO detectors, they create a tiny difference in the (otherwise identical) distance that light travels between the centre of the observatory and the mirrors located at the end of each arm. The problem is that detecting and studying gravitational waves requires these differences in distance to be measured with an accuracy of 10-19 m, which is 1/10 000th the size of a proton.
Observing waves at lower and higher frequencies in the gravitational wave spectrum remains challenging, however. At lower frequencies (around 10–30 Hz), the problem stems from vibrational noise in the mirrors. Although these mirrors are hefty objects – each one measures 34 cm across, is 20 cm thick and has a mass of around 40 kg – the incredible precision required to detect gravitational waves at these frequencies means that even the minute amount of energy they absorb from the laser beam is enough to knock them out of whack.
At higher frequencies (150 – 2000 Hz), measurements are instead limited by quantum shot noise. This is caused by the random arrival time of photons at LIGO’s output photodetectors and is a fundamental consequence of the fact that the laser field is quantized.
A novel adaptive optics device
Jonathan Richardson, the physicist who led this latest study, explains that FROSTI is designed to reduce quantum shot noise by allowing the mirrors to cope with much higher levels of laser power. At its heart is a novel adaptive optics device that is designed to precisely reshape the surfaces of LIGO’s main mirrors under laser powers exceeding 1 megawatt (MW), which is nearly five times the power used at LIGO today.
Though its name implies cooling, FROSTI actually uses heat to restore the mirror’s surface to its original shape. It does this by projecting infrared radiation onto test masses in the interferometer to create a custom heat pattern that “smooths out” distortions and so allows for fine-tuned, higher-order corrections.
The single most challenging aspect of FROSTI’s design, and one that Richardson says shaped its entire concept, is the requirement that it cannot introduce even more noise into the LIGO interferometer. “To meet this stringent requirement, we had to use the most intensity-stable radiation source available – that is, an internal blackbody emitter with a long thermal time constant,” he tells Physics World. “Our task, from there, was to develop new non-imaging optics capable of reshaping the blackbody thermal radiation into a complex spatial profile, similar to one that could be created with a laser beam.”
Richardson anticipates that FROSTI will be a critical component for future LIGO upgrades – upgrades that will themselves serve as blueprints for even more sensitive next-generation observatories like the proposed Cosmic Explorer in the US and the Einstein Telescope in Europe. “The current prototype has been tested on a 40-kg LIGO mirror, but the technology is scalable and will eventually be adapted to the 440-kg mirrors envisioned for Cosmic Explorer,” he says.
Jan Harms, a physicist at Italy’s Gran Sasso Science Institute who was not involved in this work, describes FROSTI as “an ingenious concept to apply higher-order corrections to the mirror profile.” Though it still needs to pass the final test of being integrated into the actual LIGO detectors, Harms notes that “the results from the prototype are very promising”.
Richardson and colleagues are continuing to develop extensions to their technology, building on the successful demonstration of their first prototype. “In the future, beyond the next upgrade of LIGO (A+), the FROSTI radiation will need to be shaped into an even more complex spatial profile to enable the highest levels of laser power (1.5 MW) ultimately targeted,” explains Richardson. “We believe this can be achieved by nesting two or more FROSTI actuators together in a single composite, with each targeting a different radial zone of the test mass surfaces. This will allow us to generate extremely finely-matched optical wavefront corrections.”
A new high-speed multifocus microscope could facilitate discoveries in developmental biology and neuroscience thanks to its ability to image rapid biological processes over the entire volume of tiny living organisms in real time.
The pictures from many 3D microscopes are obtained sequentially by scanning through different depths, making them too slow for accurate live imaging of fast-moving natural functions in individual cells and microscopic animals. Even current multifocus microscopes that capture 3D images simultaneously have either relatively poor image resolution or can only image to shallow depths.
“Because the M25 microscope is geared towards advancing biomedical imaging we wanted to push the boundaries for speed, high resolution and looking at large volumes with a high signal-to-noise ratio,” says Hirata-Miyasaki, who is now based in the Chan Zuckerberg Biohub in San Francisco.
The M25, detailed in Optica, builds on previous diffractive-based multifocus microscopy work by Abrahamsson, explains Hirata-Miyasaki. In order to capture multiple focal planes simultaneously, the researchers devised a multifocus grating (MFG) for the M25. This diffraction grating splits the image beam coming from the microscope into a 5 × 5 grid of evenly illuminated 2D focal planes, each of which is recorded on one of the 25 synchronized machine vision cameras, such that every camera in the array captures a 3D volume focused on a different depth. To avoid blurred images, a custom-designed blazed grating in front of each camera lens corrects for the chromatic dispersion (which spreads out light of different wavelengths) introduced by the MFG.
The team used computer simulations to reveal the optimal designs for the diffractive optics, before creating them at the University of California Santa Barbara nanofabrication facility by etching nanometre-scale patterns into glass. To encourage widespread use of the M25, the researchers have published the fabrication recipes for their diffraction gratings and made the bespoke software for acquiring the microscope images open source. In addition, the M25 mounts to the side port of a standard microscope, and uses off-the-shelf cameras and camera lenses.
The M25 can image a range of biological systems, since it can be used for fluorescence microscopy – in which fluorescent dyes or proteins are used to tag structures or processes within cells – and can also work in transmission mode, in which light is shone through transparent samples. The latter allows small organisms like C.elegans larvae, which are commonly used for biological research, to be studied without disrupting them.
The researchers performed various imaging tests using the prototype M25, including observations of the natural swimming motion of entire C.elegans larvae. This ability to study cellular-level behaviour in microscopic organisms over their whole volume may pave the way for more detailed investigations into how the nervous system of C. elegans controls its movement, and how genetic mutations, diseases or medicinal drugs affect that behaviour, Hirata-Miyasaki tells Physics World. He adds that such studies could further our understanding of human neurodegenerative and neuromuscular diseases.
“We live in a 3D world that is also very dynamic. So with this microscope I really hope that we can keep pushing the boundaries of acquiring live volumetric information from small biological organisms, so that we can capture interactions between them and also [see] what is happening inside cells to help us understand the biology,” he continues.
As part of his work at the Chan Zuckerberg Biohub, Hirata-Miyasaki is now developing deep-learning models for analysing dynamic cell and organism multichannel dynamic live datasets, like those acquired by the M25, “so that we can extract as much information as possible and learn from their dynamics”.
Meanwhile Abrahamsson, who is currently working in industry, hopes that other microscopy development labs will make their own M25 systems. She is also considering commercializing the instrument to help ensure its widespread use.
Optical fibres form the backbone of the Internet, carrying light signals across the globe. But some light is always lost as it travels, becoming attenuated by about 0.14 decibels per kilometre even in the best fibres. That means signals must be amplified every few dozen kilometres – a performance that hasn’t improved in nearly four decades.
Physicists at the University of Southampton, UK have now developed an alternative that could call time on that decades-long lull. Writing in Nature Photonics, they report hollow-core fibres that exhibit 35% less attenuation while transmitting signals 45% faster than standard glass fibres.
“A bit like a soap bubble”
The core of conventional fibres is made of pure glass and is surrounded by a cladding of slightly different glass. Because the core has a higher refractive index than the cladding, light entering the fibre reflects internally, bouncing back and forth in a process known as total internal reflection. This effect traps the light and guides it along the fibre’s length.
The Southampton team led by Francesco Poletti swapped the standard glass core for air. Because air is more transparent than glass, channelling light through it cuts down on scattering and speeds up signals. The problem is that air’s refractive index is lower, so the new fibre can’t use total internal reflection. Instead, Poletti and colleagues guided the light using a mechanism called anti-resonance, which requires the walls of the hollow core to be made from ultra-thin glass membranes.
“It’s a bit like a soap bubble,” Poletti says, explaining that such bubbles appear iridescent because their thin films reflect some wavelengths and lets others through. “We designed our fibre the same way, with glass membranes that reflect light at certain frequencies back into the core.” That anti-resonant reflection, he adds, keeps the light trapped and moving through the fibre’s hollow centre.
Greener telecommunications
To make the new air-core fibre, the researchers stacked thin glass capillaries in a precise pattern, forming a hollow channel in the middle. Heating and drawing the stack into a hair-thin filament preserved this pattern on a microscopic scale. The finished fibre has a nested design: an air core surrounded by ultra-thin layers that provide anti-resonant guidance and cut down on leakage.
To test their design, the team measured transmission through a full spool of fibre, then cut the fibre shorter and compared the results. They also fired in light pulses and tracked the echoes. Their results show that the hollow fibres reduce attenuation to just 0.091 decibels per kilometre. This lower loss implies that fewer amplifiers would be needed in long cables, lowering costs and energy use. “There’s big potential for greener telecommunications when using our fibres,” says Poletti.
Poletti adds that reduced attenuation (and thus lower energy use) is only one of the new fibre’s advantages. At the 0.14 dB/km attenuation benchmark, the new hollow fibre supports a bandwidth of 54 THz compared to 10 THz for a normal fibre. At the reduced 0.1 dB/km attenuation, the bandwidth is still 18 THz, which is close to twice that of a normal cable. This means that a single strand can carry far more channels at once.
Perhaps the most impressive advantage is that because the speed of light is faster in air than in glass, data could travel the same distance up to 45% faster. “It’s almost the same speed light takes when we look at a distant star,” Poletti says. The resulting drop in latency, he adds, could be crucial for real-time services like online gaming or remote surgery, and could also speed up computing tasks such as training large language models.
Field testing
As well as the team’s laboratory tests, Microsoft has begun testing the fibres in real systems, installing segments in its network and sending live traffic through them. These trials prove the hollow-core design works with existing telecom equipment, opening the door to gradual rollout. In the longer run, adapting amplifiers and other gear that are currently tuned for solid glass fibres could unlock even better performance.
Poletti believes the team’s new fibres could one day replace existing undersea cables. “I’ve been working on this technology for more than 20 years,” he says, adding that over that time, scepticism has given way to momentum, especially now with Microsoft as an industry partner. But scaling up remains a real hurdle. Making short, flawless samples is one thing; mass-producing thousands of kilometres at low cost is another. The Southampton team is now refining the design and pushing toward large-scale manufacturing. They’re hopeful that improvements could slash losses by another order of magnitude and that the anti-resonant design can be tuned to different frequency bands, including those suited to new, more efficient amplifiers.
Other experts agree the advance marks a turning point. “The work builds on decades of effort to understand and perfect hollow-core fibres,” says John Ballato, whose group at Clemson University in the US develops fibres with specialty cores for high-energy laser and biomedical applications. While Ballato notes that such fibres have been used commercially in shorter-distance communications “for some years now”, he believes this work will open them up to long-haul networks.
Traumatic brain injury (TBI), caused by a sudden impact to the head, is a leading cause of death and disability. After such an injury, the most important indicator of how severe the injury is intracranial pressure – the pressure inside the skull. But currently, the only way to assess this is by inserting a pressure sensor into the patient’s brain. UK-based startup Crainio aims to change this by developing a non-invasive method to measure intracranial pressure using a simple optical probe attached to the patient’s forehead.
Can you explain why diagnosing TBI is such an important clinical challenge?
Every three minutes in the UK, someone is admitted to hospital with a head injury, it’s a very common problem. But when someone has a blow to the head, nobody knows how bad it is until they actually reach the hospital. TBI is something that, at the moment, cannot be assessed at the point of injury.
From the time of impact to the time that the patient receives an assessment by a neurosurgical expert is known as the golden hour. And nobody knows what’s happening to the brain during this time – you don’t know how best to manage the patient, whether they have a severe TBI with intracranial pressure rising in the head, or just a concussion or a medium TBI.
Once at the hospital, the neurosurgeons have to assess the patient’s intracranial pressure, to determine whether it is above the threshold that classifies the injury as severe. And to do that, they have to drill a hole in the head – literally – and place an electrical probe into the brain. This really is one of the most invasive non-therapeutic procedures, and you obviously can’t do this to every patient that comes with a blow in the head. It has its risks, there is a risk of haemorrhage or of infection.
Therefore, there’s a need to develop technologies that can measure intracranial pressure more effectively, earlier and in a non-invasive manner. For many years, this was almost like a dream: “How can you access the brain and see if the pressure is rising in the brain, just by placing an optical sensor on the forehead?”
Crainio has now created such a non-invasive sensor; what led to this breakthrough?
The research goes back to 2016, at the Research Centre for Biomedical Engineering at City, University of London (now City St George’s, University of London), when the National Institute for Health Research (NIHR) gave us our first grant to investigate the feasibility of a non-invasive intracranial sensor based on light technologies. We developed a prototype, secured the intellectual property and conducted a feasibility study on TBI patients at the Royal London Hospital, the biggest trauma hospital in the UK.
It was back in 2021, before Crainio was established, that we first discovered that after we shone certain frequencies of light, like near-infrared, into the brain through the forehead, the optical signals coming back – known as the photoplethysmogram, or PPG – contained information about the physiology or the haemodynamics of the brain.
When the pressure in the brain rises, the brain swells up, but it cannot go anywhere because the skull is like concrete. Therefore, the arteries and vessels in the brain are compressed by that pressure. PPG measures changes in blood volume as it pulses through the arteries during the cardiac cycle. If you have a viscoelastic artery that is opening and closing, the volume of blood changes and this is captured by the PPG. Now, if you have an artery that is compromised, pushed down because of pressure in the brain, that viscoelastic property is impacted and that will impact the PPG.
Changes in the PPG signal due to changes arising from compression of the vessels in the brain, can give us information about the intracranial pressure. And we developed algorithms to interrogate this optical signal and machine learning models to estimate intracranial pressure.
How did the establishment of Crainio help to progress the sensor technology?
Following our research within the university, Crainio was set up in 2022. It brought together a team of experts in medical devices and optical sensors to lead the further development and commercialization of this device. And this small team worked tirelessly over the last few years to generate funding to progress the development of the optical sensor technology and bring it to a level that is ready for further clinical trials.
Panicos Kyriacou “At Crainio we want to create a technology that could be used widely, because there is a massive need, but also because it’s affordable.” (Courtesy: Crainio)
In 2023, Crainio was successful with an Innovate UK biomedical catalyst grant, which will enable the company to engage in a clinical feasibility study, optimize the probe technology and further develop the algorithms. The company was later awarded another NIHR grant to move into a validation study.
The interest in this project has been overwhelming. We’ve had a very positive feedback from the neurocritical care community. But we also see a lot of interest from communities where injury to the brain is significant, such as rugby associations, for example.
Could the device be used in the field, at the site of an accident?
While Crainio’s primary focus is to deliver a technology for use in critical care, the system could also be used in ambulances, in helicopters, in transfer patients and beyond. The device is non-invasive, the sensor is just like a sticking plaster on the forehead and the backend is a small box containing all the electronics. In the past few years, working in a research environment, the technology was connected into a laptop computer. But we are now transferring everything into a graphical interface, with a monitor to be able to see the signals and the intracranial pressure values in a portable device.
Following preliminary tests on patients, Crainio is now starting a new clinical trial. What do you hope to achieve with the next measurements?
The first study, a feasibility study on the sensor technology, was done during the time when the project was within the university. The second round is led by Crainio using a more optimized probe. Learning from the technical challenges we had in the first study, we tried to mitigate them with a new probe design. We’ve also learned more about the challenges associated with the acquisition of signals, the type of patients, how long we should monitor.
We are now at the stage where Crainio has redeveloped the sensor and it looks amazing. The technology has received approval by MHRA, the UK regulator, for clinical studies and ethical approvals have been secured. This will be an opportunity to work with the new probe, which has more advanced electronics that enable more detailed acquisition of signals from TBI patients.
We are again partnering with the Royal London Hospital, as well as collaborators from the traumatic brain injury team at Cambridge and we’re expecting to enter clinical trials soon. These are patients admitted into neurocritical trauma units and they all have an invasive intracranial pressure bolt. This will allow us to compare the physiological signal coming from our intracranial pressure sensor with the gold standard.
The signals will be analysed by Crainio’s data science team, with machine learning algorithms used to look at changes in the PPG signal, extract morphological features and build models to develop the technology further. So we’re enriching the study with a more advanced technology, and this should lead to more accurate machine learning models for correctly capturing dynamic changes in intracranial pressure.
The primary motivation of Crainio is to create solutions for healthcare, developing a technology that can help clinicians to diagnose traumatic brain injury effectively, faster, accurately and earlier
This time around, we will also record more information from the patients. We will look at CT scans to see whether scalp density and thickness have an impact. We will also collect data from commercial medical monitors within neurocritical care to see the relation between intracranial pressure and other physiological data acquired in the patients. We aim to expand our knowledge of what happens when a patient’s intracranial pressure rises – what happens to their blood pressures? What happens to other physiological measurements?
How far away is the system from being used as a standard clinical tool?
Crainio is very ambitious. We’re hoping that within the next couple of years we will progress adequately in order to achieve CE marking and all meet the standards that are necessary to launch a medical device.
The primary motivation of Crainio is to create solutions for healthcare, developing a technology that can help clinicians to diagnose TBI effectively, faster, accurately and earlier. This can only yield better outcomes and improve patients’ quality-of-life.
Of course, as a company we’re interested in being successful commercially. But the ambition here is, first of all, to keep the cost affordable. We live in a world where medical technologies need to be affordable, not only for Western nations, but for nations that cannot afford state-of-the-art technologies. So this is another of Crainio’s primary aims, to create a technology that could be used widely, because there is a massive need, but also because it’s affordable.
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