Most of the digital devices we use daily rely on photonics. As artificial intelligence continues to grow, photonics

When evaluating new materials for optoelectronic applications – perhaps promising solar panel materials like halide perovskites or semiconductor compounds for microLED displays – optical characterization is almost always the materials scientists’ first port of call. And up to now steady-state photoluminescence (PL) has been the de facto workhorse for this task.

This non-destructive and highly sensitive technique involves optically exciting a sample and recording the integrated intensity and wavelength of re-emitted photons. Through this, researchers gain a quick understanding into a material’s electronic structure, optical transitions and emission characteristics.

However, these spectra alone can be misleading. Materials with substantially different microscopic properties can generate similar steady-state PL results, masking the fundamental physical dynamics that govern the material’s performance in the real world. To gain deeper understanding of a given material, a more comprehensive and correlated approach is needed.

Blinding average

The core issue lies in the fact that steady-state PL provides a time-integrated view of the emission and depending on the measurement geometry, may also average over spatial variations. Steady-state PL records a static equilibrium in which charge carrier generation balances recombination. This means that, on its own, it does not directly reveal how these excited charge-carriers evolve and ultimately dictate how a device manipulates energy and light.

For example, although two semiconductor thin films may show identical steady-state emission, they can perform very differently in a real device. One film might have long carrier lifetimes consistent with low non-radiative losses – useful in solar cells, for example – while the other could suffer from high defect densities that are masked by strong light absorption or intense excitation light.

Conversely, weak emission does not necessarily mean poor material quality. Again using a layered solar cell as an example, dim luminescence often signals fast, beneficial charge extraction across an interface rather than harmful defect recombination (where structural imperfections convert charge-carrier energy into wasted heat). Because steady-state measurements only show an overall average, they cannot separate these competing mechanisms.

Resolving in time, space and spectrum

Time-resolved PL (TRPL) is a key technique in illuminating these hidden dynamics. Unlike steady-state PL, which continuously bathes a sample with light, TRPL uses a short laser pulse and measures how the photoluminescence intensity evolves afterwards. This can reveal carrier dynamics over timescales ranging from picoseconds to microseconds.

TRPL is particularly important in materials where local variations strongly influence device behaviour. For instance, it can expose the difference between regions that exhibit long-lived emission consistent with efficient radiative recombination, and those that exhibit fast decay caused by, for example, defect recombination.

Of course, steady-state PL averages over time and space, and therefore TRPL only solves part of the problem. Spatially resolved TRPL addresses the missing spatial dimension. Combining a high-precision, motorized XY stage with TRPL’s precise timing, spatially resolved TRPL forms a 2D map that directly correlates localized structural features – such as grain boundaries and defects – with variations in carrier kinetics across the surface.

Complementary to these techniques is time-resolved emission spectroscopy (TRES), which combines spectral selection with time-resolved detection to measure how emission dynamics vary across the spectrum. By recording wavelength-dependent decay behaviour, TRES reveals how different spectral contributions evolve following excitation.

In short, where TRPL reveals kinetics over time and spatially resolved TRPL locates variations in space, TRES adds a spectral dimension, showing how the emission spectrum evolves after excitation. This allows researchers to track changes in the distribution of photon energies over time to understand carrier evolution and gain insight into the mechanisms underlying material behaviour.

A correlative approach

Though powerful in isolation, reconciling insights across these different instruments is slow and prone to errors. There can be microscopic differences between samples or even within positions in a single sample that dramatically alter emission spectra. Moreover, moving a sample between separate instruments is fraught with difficulty, potentially damaging the sample or causing delays that lead to sample degradation.

More comprehensive and reliable physical insight comes when temporal, spatial and spectral factors are recorded correlatively on the exact same sample region. This need for correlation is the motivation behind PicoQuant’s Solira, an integrated workflow platform for steady-state PL, TRPL, spatially resolved TRPL and TRES (the latter when combined with the complementary FlexLambda Kit), as well as additional imaging techniques, such as hyperspectral imaging, required for different scientific questions.

Bringing these techniques together within one configurable microscope system means a materials scientist can gain a more informed interpretation of material behaviour. For instance, they can identify the relevant emission bands at selected points of interest with steady-state PL. They can then wield TRPL to measure the associated decay kinetics, before perhaps applying TRES to resolve how those kinetics vary across the emission spectrum.

Bright demonstration

The power of this correlated approach was demonstrated recently by Professor Eva Unger’s group at Helmholtz-Zentrum Berlin, Germany, with measurements carried out by Maxim Simmonds. Investigating perovskite solar mini-modules, the team worked with PicoQuant and used Solira to locate precise laser-patterned lines – microscopic scribes used to interconnect individual cells in a solar module – before verifying emission from the active layer. Localized TRPL measurements then revealed significantly faster decay dynamics next to these laser cuts compared to the pristine bulk material, indicating altered carrier recombination or diffusion near structured features.

However, point measurements alone were not enough to discern whether the laser had fully removed the perovskite or merely modified it. Switching to spatially resolved TRPL imaging on Solira revealed that measurable photoluminescence persisted along the laser-patterned lines. This showed that laser structuring had altered local photophysical properties rather than eliminating the active layer – a conclusion only made possible by consistently mapping charge-carrier dynamics across temporal, spatial and spectral dimensions together on one setup.

As semiconductor materials and optoelectronic devices become more complex, optical characterization tools must keep pace. By unifying these tools within an integrated workflow platform such as Solira, materials scientists now have the means to paint a more complete picture of material characteristics and thereby unlock the next generation of innovative functional materials.

 

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A research team at the Institute of Applied Physics at TU Darmstadt has shown for the first time that atoms that are completely disordered and in constant motion can nevertheless emit jointly directed light preferentially in one direction—even though neither the atoms nor their environment exhibit a direction—and that the strength of this asymmetry can be specifically adjusted. The paper is published in the journal Physical Review Letters.

Within tiny halos of light clinging to a vanishingly thin wisp of optical fiber, scientist Jongmin Lee guides atoms like marbles through a narrow pipe. Rock the fiber and the atoms shift side by side; they just don't fall off. But don't be deceived by the seemingly delicate nature of his experiment. Lee is exploring how to measure motion precisely in rough-and-tumble environments.

Tiny manufacturing imperfections in optical components normally go unnoticed. Yet they can alter light in surprisingly significant ways. An international research team led by TU Darmstadt has shown that such imperfections can affect not only polarization—the direction in which light oscillates—but also the spatial shape of a light beam.

Most people can perceive different colours in the visible range of the electromagnetic spectrum – at wavelengths between about 400 and 700 nm. However, our eyes cannot see infrared radiation, let alone perceive infrared “colours”. But now a team at China’s Beijing Institute of Technology has created colloidal quantum dot-based light upconverters that convert the infrared to the visible while preserving the spectral notion of colour. These nanostructures can be incorporated into wearable eyeglasses and, more ambitiously, could someday be implanted directly into the retina.

Photoreceptors in mammalian eyes contain light-absorbing pigments consisting of opsins and their covalently linked retinals. Infrared light at wavelengths greater than 700 nm cannot be absorbed by these photoreceptors, so when such light reaches the retina no corresponding electric signal is sent to the brain. Seeing infrared radiation could reveal otherwise invisible features and improve night vision, which relies on infrared light.

In recent years, researchers have made great strides in developing materials that capture photons with lower energies (in the infrared, for example) and re-emit them as photons with higher energies (typically visible or ultraviolet light). This process is known as upconversion, and the emitted light is said to be anti-Stokes shifted. This has led to the development of photoreceptor-binding upconversion nanoparticles that convert infrared light into visible emissions. These have been injected into mouse eyes and have been used to create wearable lenses for humans – with nonlinear upconversion projecting infrared-transformed visible light onto the cornea. While effective, these applications are limited to the narrow near-infrared (NIR) spectral range.

Confined electrons

Now, a team led by Ge Mu and Xin Tang studied a structure made up of semiconducting mercury telluride (HgTe) colloidal quantum dots (CQDs) atop an organic light-emitting diode (OLED). The OLED contains two light-emitting layers, one red-light-emitting and one cyan-light-emitting. Because of the small size of the CQDs, the electrons in them are confined in all three directions. This means that the electrons are restricted to discrete and separate atomic-like energy subbands rather than having access to a continuous band of allowed energies as they would in a bulk material.

When the CQDs absorb photons with infrared wavelengths, spanning the NIR to short-wave infrared regions, they produce excited carriers (electrons and holes) that then travel from their different energy levels into the OLED. This is a seamless process because the OLED is designed so that its electronic bands align with the sub-bands of the HgTe. When either the light intensity or the wavelength of the incident infrared light changes, explains Tang, the excited photocarriers are transported and recombined in the different emissive layers of the OLED thanks to the hole-trapping barriers that were engineered in these layers. The result is infrared-to-visible-light (red and cyan) upconversion.

Semi-transparent wearable eyeglasses

As a proof-of-concept, the researchers integrated their upconverter into lightweight, semi-transparent wearable eyeglasses and found that they can project multispectral infrared light onto the retina without affecting normal vision, so allowing the wearer to see infrared light as well as visible light. Indeed, a wearer can detect infrared light at wavelengths greater than 2 μm with a luminance of over 700 cd m⁻².

Looking ahead, Tang says that the upconverter could be bound to light-sensitive proteins in the retina and so serve as an implantable next-generation retinal bionic photoreceptor. This structure would transform infrared light into visible light emissions that stimulate light-sensitive proteins on retinal neurons to bypass damaged photoreceptor cells and potentially restore visual function across both the visible and infrared.

This full colour upconverter has been a long-term project in my group, Tang tells Physics World. “Starting from an efficient single-colour upconverter, we then successfully demonstrated colour-tuneable OLEDs and Si-/Ge-/CMOS-integrated upconverters. And with our recent progress on the understanding of interfacial carrier transport between quantum dots and colour-tuneable OLEDs, we have now demonstrated this new full-colour upconverter.”

The latest work is detailed in Science Advances.

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Over the past two decades, photonic-crystal surface-emitting lasers (PCSELs) have shown promise as a type of advanced semiconductor laser useful in defense- and aerospace-related applications. Typically, these devices are made with photonic crystal patterns that repeat across the area of the device. But new research from the lab of electrical and computer engineering professor Kent Choquette has demonstrated a quasi-periodic photonic-crystal surface-emitting laser (QPCSEL). Fabricated with their buried dielectric platform, the group's device highlights a new avenue for creating tunable, more reliable semiconductor lasers. Their findings appear in Applied Physics Letters.

Researchers at the University of Basel and the Technical University of Munich have developed a new method to reveal the collective motion of electrons in one of the most elusive states of matter: the Wigner crystal. Using light, the physicists were able to uncover previously inaccessible properties of this fragile quantum state.

Researchers at the University of Basel and the Technical University of Munich have developed a new method to reveal the collective motion of electrons in one of the most elusive states of matter: the Wigner crystal. Using light, the physicists were able to uncover previously inaccessible properties of this fragile quantum state.

A radio signal has been amplified by scattering it from a stationary coin-sized electronic circuit that behaves as though it is rotating at an enormous rate. Conceived by a team at the City University of New York, the experiment is said to provide the first observation of rotational super-radiance involving electromagnetic waves. This wave-amplification effect is inspired by rotating black holes and was predicted more than half a century ago. Andrea Alù and colleagues found that only radio waves carrying a particular kind of twist were boosted, by as much as a factor of six in power.

In 1969 Roger Penrose pointed out that a rotating black hole holds a vast reservoir of energy that, in principle, can be tapped. “An object entering the region around the black hole can split into two parts, one falls into the black hole while the other escapes with more energy than the original object had, effectively taking some rotational energy from the black hole,” Alù, explains.

Two years later the Soviet physicist Yakov Zel’dovich realized that the same thing should happen to waves. “If a wave carrying angular momentum reflects from a rapidly rotating absorbing cylinder, the reflected wave could be amplified and come back stronger than it arrived,” says Alù. That amplification is called rotational super-radiance, which Alù describes as, “a process in which a wave becomes stronger by extracting energy from a system that rotates very rapidly”.

The catch has always been the word “rapidly”. For the effect to occur, the rotation must outrun the wave itself, and for light or radio waves that means rotational rates no mechanical object could survive. The effect has been coaxed out of water waves swirling around a vortex and out of sound waves bouncing off a spinning absorber, but electromagnetic waves had been out of reach. “While the idea is fascinating, no experimental demonstration was reported for electromagnetic waves, due to the required very fast speeds,” Alù says.

Clever solution

The CUNY team has found a clever way around the speed restriction. “Instead of physically spinning an object, we created an artificial rotation by periodically changing the properties of a network of resonators in space and time in a way that mimics rotation,” says Alù. The new device is disarmingly simple, comprising three small electrical circuits wired into a loop roughly two centimetres across, each one tuneable like a radio dial. The tuning of all three is wobbled up and down, with each kept slightly out of step with its neighbours, so the pattern sweeps around the loop like a wave passing through a stadium crowd.

“Although no physical object is rotating, this travelling modulation pattern acts like a rotating system,” Alù explains. And because the apparent speed is set purely by how quickly the electronics are driven, it can be pushed as high as one likes. “In fact, this speed can be faster than the velocity of light without violating any physical law.” Nothing material moves, so nothing outruns light.

The researchers fed a 100 MHz radio signal into the loop. This light was in a specific twisted state (possessing orbital angular momentum). They then swept the rotational rate from 5 MHz up to 195 MHz. Below 100 MHz the reflected light weakened steadily, as expected. Above 100 MHz, however, the synthetic rotation overtook the wave and the behaviour flipped. The reflected signals reappeared at the same frequencies as before — 60, 70 and 80 MHz — but were twisted the opposite way, and were stronger rather than weaker. That reversal, Alù notes, is “a key signature of entering the regime associated with super-radiance”. The gain arises in special windows the team calls angular-momentum bandgaps, which open once the synthetic rotation is fast enough and through which “energy can be transferred from the synthetic rotation to the wave”.

Fussy amplfier

The amplification was fussy about its input. “Our observed amplification was selective to the angular momentum of the input wave, only waves with particular angular-momentum properties experienced gain,” says Alù. Stranger still, the effect feeds on waste. In an ordinary amplifier, energy leaking out of the device is the enemy. Here a leakier circuit gave more gain, exactly as the thermodynamic reasoning behind super-radiance demands.

Alù is careful about what the experiment does and does not deliver. “The experiment does not study actual black holes or quantum gravity. Instead, it creates a laboratory system that reproduces some of the same physical principles involved in rotational energy extraction.” What it offers, he says, is “a controllable analogue platform where researchers can test and explore concepts that are otherwise difficult or impossible to study experimentally in astrophysical black holes”.

Three circuits in the loop allow only three distinct twists, so the immediate goal is bigger loops supporting a wider range. Beyond that lies the jump from radio waves to visible light, and a quantum version in which synthetic rotation might conjure photons out of empty space. Practical spin-offs may arrive sooner. Amplifying only one twist at a time is a natural fit for encoding information, and, Alù suggests, “new forms of lasers, with selective emission of angular momentum, can be envisioned”.

The research is described in Nature.

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In a new Nature Physics study, researchers accelerated electrons to more than twice the energy predicted by the traditional dephasing limit for laser-plasma accelerators operating over the same distance. This was made possible by a specially engineered laser pulse called a flying focus, which counteracts a longstanding limitation known as "dephasing."

In a new Nature Physics study, researchers accelerated electrons to more than twice the energy predicted by the traditional dephasing limit for laser-plasma accelerators operating over the same distance. This was made possible by a specially engineered laser pulse called a flying focus, which counteracts a longstanding limitation known as "dephasing."

Using light to process quantum information is one of the most promising approaches to building future quantum computers. Light particles, known as photons, are excellent carriers of quantum information, but their lack of natural interactions has created a major challenge for researchers seeking to build systems capable of performing a full range of computations.

Using light to process quantum information is one of the most promising approaches to building future quantum computers. Light particles, known as photons, are excellent carriers of quantum information, but their lack of natural interactions has created a major challenge for researchers seeking to build systems capable of performing a full range of computations.

Researchers achieved the first real-world demonstration of quantum entanglement over a busy telecommunications fiber network. A single photon carrying quantum information had to travel more than 24 kilometers through an optical fiber already crowded with powerful internet signals. Despite the noise, it reached downtown Chicago still entangled with its partner at Northwestern University’s Evanston campus. [...]

A few years ago, I was lucky enough to see the Bayeux Tapestry – the famous embroidered cloth depicting the Norman invasion of England in 1066. More than 900 years old, this historic piece of art is only 50 cm wide but more than 68 m long. It’s also extremely fragile, which why I was astonished when I heard that the Bayeux Tapestry was going to leave its home in Normandy and be transported across the English Channel to the UK.

The loan of the artwork, which was agreed between former British prime minister Keir Starmer and French president Emmanuel Macron last year, has now taken place. The tapestry arrived under police escort on 10 July and will be on display at the British Museum in London from September 2026 until July 2027. It is the first time the tapestry has been back in England, the country where this linen cloth was originally made.

I’m fascinated by how non-invasive optical techniques have been crucial in advancing our understanding of the tapestry

So what’s all this got to with physics? Well, I’m fascinated by how physics – and specifically, non-invasive optical techniques – have been crucial in advancing our understanding of the tapestry and its historical significance. Thanks to physics-based equipment developed by hi-tech manufacturers, we’ve learned about how the Bayeux Tapestry was initially made, what damage it subsequently suffered, how it was repaired, and the nature of its current condition.

Such information is vital not only for increasing our historical awareness, but also for current conservators who want to understand the tapestry’s underlying condition and find out how to preserve it for future generations. And before the pedants write in, yes I know that while it’s known as the Bayeux Tapestry, technically it’s an embroidery. That means it was created by stitching woollen threads onto a linen backing, which is helpful to know when reviewing the physics involved.

Optical sleuthing

The beauty of using optical methods to study the Bayeux Tapestry is that they are non-destructive and non-intrusive – and so can typically be applied in situ. In 2017 a three-year project was started, in which conservationists used high-resolution 2D imaging, photogrammetry, multimodal scanning and advanced image reconstruction techniques to determine the tapestry’s condition and conservation needs. The project revealed considerable information about how this artwork was created and modified over time.

Thanks to these high-resolution images, we now have a single digital map of the entire tapestry, making it possible to zoom in and look at individual threads. It’s yielded information such as the width of stitches and the positions where the wool threads cross the original linen background. As a result, historians now believe the tapestry was made by a single group of embroiderers, who – knowing the skills that existed at the time – were probably based in Canterbury, UK.

Techniques such as infrared spectroscopy and fluorescent and reflection ultraviolet imaging have revealed information about what’s underneath the surface of the tapestry

From the size and direction of the stitches, we also think the outlines of the figures were stitched first, with the shapes filled in afterwards using coloured wools in a strict, specific order. Meanwhile, techniques such as infrared spectroscopy and fluorescent and reflection ultraviolet imaging have revealed information about what’s underneath the surface of the tapestry. In particular, they’ve located the presence of stains such as glue, wax (dripped from candles that lit the tapestry) and even oil from the hands of people who touched it.

Infrared light passing through the dark-coloured wools have also revealed original sketch lines that were drawn on the linen base before the wool stitching started. It reveals the original artist’s draft, likely to be someone familiar with manuscript drawing – perhaps an illuminator of religious books.

3D imaging with photogrammetry

Researchers in France, led by Stéphane Le Mouélic from Nantes University, who originally did a PhD in astrophysics, have also used computer software to combine more than 440 overlapping 2D photos taken from multiple angles to create a detailed 3D model of the Bayeux Tapestry (J. Cult. Heritage 71 211).

It digitally “irons out” all the sags and wrinkles in the line fabric, recreating the original, “flat” tapestry and allowing the original physical shape of the artwork to be revealed for the first time. The 3D model can be viewed for free at the Bayeux Museum website, allowing historians, researchers and members of the public to study it without having to handle the delicate material.

Physics-based techniques have also allowed us to deal with the fact that parts of the fabric have been repaired over the last 900 plus years. Some of those repairs used non-authentic dyes and colours, while others covered up the original stitching. But using computer vision and image processing, threads that were added later can be subtracted digitally, providing a clearer, corrected view of what the original tapestry looked like.

Finally, optical tools can help keep the tapestry safe for future generations. Museum curators need to know if the cloth is sagging, tearing, or changing shape over time. Instead of putting heavy tools on the cloth, lasers can scan the cloth to accurately map of the contours of its surface. By repeating this exercise every few years, conservationists can spot if any part of the cloth has stretched or sagged, enabling minor problems to be rectified before they end up causing significant damage.

Without the huge amount of investigative and restorative work carried out, the Bayeux Tapestry would never have been allowed to make the journey to London

In 2025 Le Monde newspaper reported that experts had, over the previous five years, meticulously documented 24,204 stains, 9646 holes and 30 tears in the artwork. Without the huge amount of investigative and restorative work carried out, the Bayeux Tapestry would never have been allowed to make this year’s journey to London. Advanced and detailed optical measurement has “de-risked” the tapestry’s trip.

Tickets to the British Museum exhibition are reportedly being snapped up faster than those for Glastonbury. So if you don’t get to see the tapestry in person, feel free to marvel at this wonderful historical artwork by checking out the interactive online digital copy. It really is physics and history in the making.

The post The Bayeux Tapestry: how optical techniques have let this artwork come home appeared first on Physics World.

A new type of “photonic multi-lane highway” that can carry multiple topologically-protected optical signals at once – without the need for a bulky insulator  – has been demonstrated by researchers in China. The technology, which relies on a new type of material called a photonic valley half-semimetal to achieve topological protection, is currently at the prototype stage. However, the researchers believe that, if fabrication challenges can be addressed, the combination of spatial efficiency and topological robustness could be promising for future photonic technologies.

In the past 20 years, photonic topological insulators have become widespread for connections in devices such as on-chip photonic circuits because their edge modes can only conduct light in one direction and are therefore are inherently immune from scattering off imperfections. However, the protected edge mode of a topological insulator comes at a cost: the bulk must have an optical band gap, which means it must be opaque to the relevant frequency. Meanwhile, the photonic analogue of another concept from electronics has also become popular in optical waveguides. Gapless photonic semimetals – analogous to graphene –  can be placed between topologically distinct optical insulators to broaden the guided modes, but non-guiding insulating claddings are still required.

To address the fundamental trade-off between spatial efficiency and topological protection in conventional topological waveguides, researchers in the group of Che Ting Chan at the Hong Kong University of Science and Technology in China and their collaborators introduced a novel photonic structure called a photonic valley half-semimetal. Here, the valley degree of freedom refers to inequivalent local energy extrema in momentum space, which can be used as independent degrees of freedom for transport. Crucially, a single photonic valley half-semimetal plays a dual role via its two valley channels: one valley acts as a gapless semimetal that enables waveguiding, while the other functions as a topological insulator that provides a topological barrier for the corresponding valley mode in adjacent regions.

Four stacked layers

The researchers designed a waveguide comprising four stacked layers of a honeycomb structure made from interconnected rods of the magnetic material yttrium iron garnet, which interfered with the propagating photons. By altering the diameters of the rods or the magnetic field, the researchers  constructed four inequivalent photonic valley half-semimetal domains and arranged them in a specific periodic sequence. This creates adjacent domains that mutually insulate each other.

Xiaohan Cui is lead author on a paper in Nature that describes the research. She explains that the underlying topological physics is similar to that in a traditional photonic topological insulator.

“The important difference lies in how the mode is spatially implemented,” she says, “In a conventional photonic topological-insulator waveguide, two gapped bulk domains meet at an interface, and the propagating mode is tightly localized to that interface. Most of the surrounding insulating material remains inert, serving only as cladding.”

In the present configuration, however, the researchers were able to use the blocked valley as topological protection for unidirectional propagation in the neighbouring domain, and utilize this to create a four-lane highway, with two lanes in each direction, that could guide signals around sharp bends and through constrictions without backscattering or inter-lane crosstalk:

No wasted space

“The architecture transforms the usual narrow interface state into a set of directly adjacent, large-area waveguiding lanes. Consequently, no region of the device is ‘wasted’ as inert cladding,” explains Cui.

The team’s current device works for microwave radiation but the team says that the design could be adapted and extended to operate at higher frequencies.

“The present experiment is a proof of principle demonstration at microwave frequencies, so one clear next step is to move the concept towards higher-frequency, chip-scale integrated photonics platforms, thereby paving the way toward ultra-compact topological photonic circuitry,” says Cui.

The researchers believe application in the terahertz regime should be possible using magnetized semiconductors such as indium antimonide. However, non-reciprocal applications at higher frequencies could be challenging owing to the weakness of magnetic effects.

“The major experimental challenges will be to realize these higher-frequency designs while managing geometric complexity, fabrication tolerances, and propagation loss, and ensuring efficient coupling with practical sources, detectors and other photonic components,” she explains.

Quantum optician Mahmoud Jalali Mehrabad of Massachusetts Institute of Technology believes the work brings an important issue into focus. “A paper doesn’t always have to have the perfect solution as long as it highlights and really streamlines a key problem…To me this paper does that,” he says. “Spatial efficiency has been a problem in topological physics and the question is why? Is there any other way to destroy this trade-off? It shouldn’t be a side problem in the supplementary material of a paper – this is a big problem.” Whether or not the researchers can make their own solution viable, he says, “time will tell”.

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When Ryan Hamerly was a 15-year-old at Boulder High School in Colorado, he spent his summer building a Tesla coil after seeing a classroom demonstration. “I thought that was really, really cool,” he recalls. “I wanted to make one myself, and as a result I ended up studying the theory of electricity and magnetism over one summer.”

In hindsight, Hamerly realizes he didn’t use much theory to construct the coil, which became part of a school physics project. “Most of the design was based on things I had read on the Internet,” he explains, “but I did try to teach myself electricity and magnetism – and it did work in the end.”

In 2006 Hamerly’s interest in physics took him to the California Institute of Technology (Caltech) for his undergraduate studies. Keen to do graduate research, Hamerly was most fascinated by fundamental theoretical problems in quantum field theory, such as dark matter and quantum gravity. But as he started toying between different options, he had a chance encounter with Hideo Mabuchi, an applied physicist at Stanford University.

“One thing that Hideo told me that I thought was particularly fascinating,” says Hamerly, “is that quantum field theory is just a generic tool that applies in many other fields.” He therefore ended up doing a PhD in optical and quantum computing under Mabuchi’s supervision, which he completed in 2016.

Hamerly then moved to Japan, where he studied at the National Institute of Informatics in Tokyo – a time he characterizes as “sort of a postdoc, but more an excuse to travel for a year”. He did, though, get a paper out of it “so it wasn’t wasted”. In Tokyo, Hamerly worked with Mabuchi’s longtime friend Yoshihisa Yamamoto – a quantum optics researcher who had previously led a group at Japanese telecoms giant NTT for over two decades.

Step into industry

When Hamerly returned to the US in 2017, he did a formal postdoc under quantum photonics engineer Dirk Englund at the Massachusetts Institute of Technology (MIT). And in a fortuitous turn of events, Yamamoto also came to the US to establish the Silicon Valley start-up NTT Research, with the intention of forming collaborations with US universities.

“[Yamamoto] just called me up and said they had a position at NTT to work in optical computing,” he says. “At the time it made most sense to stay at MIT working as a collaborator [rather than relocate to the NTT campus] because that was where a lot of our experiments were being done.”

Today, Hamerly is a senior research scientist at NTT Research’s Physics and Informatics (PHI) Lab in Sunnyvale, California. He divides his time between MIT – where his collaboration with Englund continues – and the PHI laboratory, about 15 km from Stanford. He works at the intersection of optics, deep learning and quantum computation. For example, one of Hamerly’s projects looks into ways to reduce the energy consumption of AI data centres using optical interconnects in place of electronic ones.

Researchers hope it might one day be possible to design processors that perform calculations using optical logic that are either impossible, or at least energetically unfeasible, using electronic logic. To this end, in January 2026 Hamerly co-founded Opticore – a company producing photonic integrated circuits for energy-efficient, high-speed AI – with UC Berkeley professors Mengjie Yu and Zaijun Chen, who was previously a postdoc in Englund’s MIT group.

Different setting, same science

Hamerly does not view his place at NTT Research as purely an industry position. “The mission at NTT Research is about generating ideas that will ultimately have some use in industry,” he explains, “but the fundamental focus is on those ideas and on the research.”

The mission at NTT Research is about generating ideas that will ultimately have some use in industry

His experience at NTT Research has shown him that an industrial lab can be smaller and more focused than one at a university – but that can be a double-edged sword. “[At a university] it’s nice to be able to go into seminar rooms and see a talk from a travelling world expert in a different field,” he says, “but on the other hand, the average person [at NTT] tends to be a lot more experienced and productive than say a graduate student in academia who is still learning.”

However, the chance to meet and interact with scientists from different areas is still the same. “Science is science, regardless of what institution you’re affiliated with,” he says. “We’re still doing the same things: we do research in a lab, we write up the results, submit them and publish them in journals, and we go to conferences and present our work.”

Hamerly still sees himself as principally a theorist. He spends much of his time writing computer code – occasionally for models that run on a supercomputer but usually for models that can run on his laptop. The rest of his time is focused on writing papers, travelling to present work, responding to reviews or in meetings.

Looking to the future, Hamerly believes that technology will impact research, but that the core elements of a researcher’s role are likely to remain similar for the foreseeable future. “The job of a researcher before the Internet, for example, is not too different from a post-Internet researcher,” he says, pointing to how you still have to communicate research via papers and conferences, and understand the field by reading others’ publications.

“There will definitely be changes in the way you do every one of these things in the next 10 years, especially with AI, but I don’t see any of them becoming optional.”

For young researchers entering the field, Hamerly advises keeping your options open. He did not envisage himself leaving full-time academia and work in an industrial lab, but switched because it offered a better opportunity to pursue the research he wanted to do. “They are both good routes to do research,” he concludes, “but you might find – based on which offers you get – that one is better than another.”

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Photonic glasses containing gold-cored, silica-shelled nanoparticles can produce high-purity colours across the visible spectrum. Crucially, the colours are independent of viewing angle. Developed by researchers in Korea, their design avoids the short-wavelength scattering that has prevented the attainment of a true red – and blurred other colours – in previous photonic glasses.

Synthetic materials are usually coloured using pigments, such as those found in dyes or paints. A pigment has a chemical composition that causes it to reflect light at certain wavelengths and absorb light at other wavelengths. Nature, however, makes widespread use of structural colour, whereby the physical structure of a material dictates which wavelengths are reflected and which are absorbed. A familiar example is iridescence, which is responsible for rainbow-like colours on some plants and animals.

Creating colour using structure rather than chemistry has several advantages. One is that there are no chemical chromophores to be bleached by sunlight, so the colour tends to be more durable. Another benefit is that there is no dye to leach if the material comes into contact with water or another solvent.

While structural colour can be created using traditional photonic crystals, these can be tricky to produce controllably. Moreover, a surface that relies on interference effects is inevitably iridescent – which means that its colour changes with the viewing angle.

Short-range order

One solution is colloidal photonic glasses, which are not physically textured but have particles such as silica or polymers dispersed throughout them with short-range order. These can be produced simply by solution processing, and their colour does not vary with viewing angle. The principal problem with these glasses is the attainment of colour purity – especially in the red. The challenge is that the glasses scatter light more effectively at shorter (bluer) wavelengths owing to Rayleigh scattering. This effect makes the sky appear blue and adds unwanted blue light to structural colour.

In the new work, nanophotonics expert Seungwoo Lee of Korea University in Seoul and colleagues synthesized 230 nm core–shell nanoparticles in which silica surrounds a 20 nm gold cluster. This has a plasmonic resonance that absorbs shorter wavelengths. The researchers then dispersed the nanoparticles in ethoxylated trimethylolpropane triacrylate. This is a photocurable resin that has a very similar refractive index as the nanoparticles. The resin was applied to surfaces by painting or solution deposition and then cured under ultraviolet light.

The resulting photonic glass scatters red light randomly, while absorbing shorter wavelengths. Lee stresses that this is different from a traditional paint. “The reflected colour is determined by particle size, spacing, refractive-index contrast, and the degree of structural order, rather than by a molecular chromophore alone,” he says. When the researchers reduced the size of the nanoparticle shells, first to 180 nm and then to 160 nm, they found that they packed more closely together, producing first green and then deep blue colours.

The explanation for the blue scattering is more subtle than for the red: “The gold core is not needed to ‘make’ blue in the same way that a blue dye would,” explains Lee. “However, the gold core can still improve perceived colour purity by reducing broadband diffuse scattering and nonresonant background light.” explains Lee “Without this suppression, silica-only photonic glasses tend to look milky or whitish because many wavelengths are scattered together.”

Durable coatings

The researchers are now exploring several possible extensions of their research. They believe that the work could provide easily applied coatings that are durable as the light scattering comes from within the material structure rather from than a surface pigment.

They also believe it could have anti-counterfeiting properties: “In a normal ink or paint, its colour mainly originates from chemical pigments or dyes,” says Lee; “Our material produces a nanoscale structural signature: a specific reflectance spectrum, bandwidth, angular response, and microstructural arrangement determined by the particle diameter, core–shell geometry, refractive-index matching, volume fraction, and assembly pathway. This gives several possible authentication handles.”

Lee believes that it should be possible to reduce the cost of the material using a metal that is cheaper than gold. However, the precious metal is only 0.022% of the film by weight, so the technology may already be economically viable.

The film is described in Proceedings of the National Academy of Sciences.

“I think it’s really neat,” says materials scientist Aaswath Raman of the University of California, Los Angeles. “The concept of structural colour has been around for a really long time but to me it’s, like, the last steps before we see it out it the real world.”

He says the largest problems he foresees are the simple economics of competing with industrially-optimized paint industry – even if the technology is, in principle, superior. Nevertheless, he says, “of the technologies we see in research this is likely quite a good candidate for commercialization”. The next step, he says, is to actually find a “first use” application – he suspects the aerospace industry, which values ultralight, durable coatings, could be a candidate.

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