“a diamond crystal sensor illuminated from below by a green laser”

Spectral Reconstruction Based on Tunable vdW Junction Spectrometers
by Hoon Hahn Yoon, Weiwei Cai, Fedor Nigmatulin  /  October 6, 2022

“The repository contains a MatLab code that is implemented to reconstruct the unknown spectrum demonstrated in our submitted work “Miniaturized Spectrometers with a Tunable van der Waals Junction“. This code was archived in this link during the submission process and will not be updated here. Further updates on the code can be found at the following link: github.com/fonig/Reconstruction. The learning process allows obtaining a response matrix with elements that are defined by the gate voltage and the wavelength.

The response matrix and input data (photocurrent as a function of the gate voltage) are connected with a matrix equation with a vector of weight coefficients which determine a desired spectral function. For the solution of the matrix equation, one needs to minimize the residual norm (squared error) by solving the non-negative least square problem. For the stabilization of the minimization procedure, Tikhonov regularization is used. A vector of coefficients that provides a global minimum of the modified residual norm allows reconstructing the considered spectrum by substituting it in the initial expansion in basis functions. More details can be found in our manuscript (Miniaturized Spectrometers with a Tunable van der Waals Junction).”

Lab on a chip opens door to widespread use of portable spectrometers
by Steve Lundeberg / October 20, 2022

“Scientists including an Oregon State University materials researcher have developed a better tool to measure light, contributing to a field known as optical spectrometry in a way that could improve everything from smartphone cameras to environmental monitoring. The study, published today in Science, was led by Finland’s Aalto University and resulted in a powerful, ultra-tiny spectrometer that fits on a microchip and is operated using artificial intelligence. The research involved a comparatively new class of super-thin materials known as two-dimensional semiconductors, and the upshot is a proof of concept for a spectrometer that could be readily incorporated into a variety of technologies – including quality inspection platforms, security sensors, biomedical analyzers and space telescopes.

“We’ve demonstrated a way of building spectrometers that are far more miniature than what is typically used today,” said Ethan Minot, a professor of physics in the OSU College of Science. “Spectrometers measure the strength of light at different wavelengths and are super useful in lots of industries and all fields of science for identifying samples and characterizing materials.” Traditional spectrometers require bulky optical and mechanical components, whereas the new device could fit on the end of a human hair, Minot said. The new research suggests those components can be replaced with novel semiconductor materials and AI, allowing spectrometers to be dramatically scaled down in size from the current smallest ones, which are about the size of a grape.

“Our spectrometer does not require assembling separate optical and mechanical components or array designs to disperse and filter light,” said Hoon Hahn Yoon, who led the study with Aalto University colleague Zhipei Sun Yoon. “Moreover, it can achieve a high resolution comparable to benchtop systems but in a much smaller package.” The device is 100% electrically controllable regarding the colors of light it absorbs, which gives it massive potential for scalability and widespread usability, the researchers say. “Integrating it directly into portable devices such as smartphones and drones could advance our daily lives,” Yoon said. “Imagine that the next generation of our smartphone cameras could be hyperspectral cameras.”

Those hyperspectral cameras could capture and analyze information not just from visible wavelengths but also allow for infrared imaging and analysis. “It’s exciting that our spectrometer opens up possibilities for all sorts of new everyday gadgets, and instruments to do new science as well,” Minot said. In medicine, for example, spectrometers are already being tested for their ability to identify subtle changes in human tissue such as the difference between tumors and healthy tissue. For environmental monitoring, Minot added, spectrometers can detect exactly what kind of pollution is in the air, water or ground, and how much of it is there. “It would be nice to have low-cost, portable spectrometers doing this work for us,” he said.

“And in the educational setting, the hands-on teaching of science concepts would be more effective with inexpensive, compact spectrometers.” Applications abound as well for science-oriented hobbyists, Minot said. “If you’re into astronomy, you might be interested in measuring the spectrum of light that you collect with your telescope and having that information identify a star or planet,” he said. “If geology is your hobby, you could identify gemstones by measuring the spectrum of light they absorb.” Minot thinks that as work with two-dimensional semiconductors progresses, “we’ll be rapidly discovering new ways to use their novel optical and electronic properties.” Research into 2D semiconductors has been going on in earnest for only a dozen years, starting with the study of graphene, carbon arranged in a honeycomb lattice with a thickness of one atom. “It’s really exciting,” Minot said. “I believe we’ll continue to have interesting breakthroughs by studying two-dimensional semiconductors.”

“A fingertip-sized on-chip spectrometer in the foreground compared to a commercial benchtop-size spectrometer in the background”

An all-in-one detector for thousands of colours / 21.10.2022

“Spectrometers are widely used throughout industry and research to detect and analyse light. Spectrometers measure the spectrum of light – its strength at different wavelengths, like the colours in a rainbow – and are an essential tool for identifying and analysing specimens and materials. Integrated on-chip spectrometers would be of great benefit to a variety of technologies, including quality inspection platforms, security sensors, biomedical analysers, healthcare systems, environmental monitoring tools, and space telescopes. An international research team led by researchers at Aalto University has developed high-sensitivity spectrometers with high wavelength accuracy, high spectral resolution, and broad operation bandwidth, using only a single microchip-sized detector. The research for this new ultra-miniaturised spectrometer was published today in the journal Science.

‘Our single-detector spectrometer is an all-in-one device. We designed this optoelectronic-lab-on-a-chip with artificial intelligence replacing conventional hardware, such as optical and mechanical components. Therefore, our computational spectrometer does not require separate bulky components or array designs to disperse and filter light. It can achieve high-resolution comparable to benchtop systems but in a much smaller package,’ says Postdoctoral Researcher Hoon Hahn Yoon. ‘With our spectrometer, we can measure light intensity at each wavelength beyond the visible spectrum using a device at our fingertips. The device is entirely electrically controllable, so it has enormous potential for scalability and integration. Integrating it directly into portable devices such as smartphones and drones could advance our daily lives. Imagine that the next generation of our smartphone cameras could be fitted with hyperspectral cameras that outperform colour cameras,’ he adds.

Spectral images of the Aalto logo “A!” with the spectrometer. The red uppercase alphabet and the blue exclamation mark are distinguishable from the background. Each image represents a spectral image reconstructed at different wavelengths that cover the visible to the near-infrared range, highlighting the advantages of spectral imaging over conventional RGB colour imaging. Photo: Aalto University
“Spectral images of Aalto logo with spectrometer. The red uppercase alphabet and blue exclamation mark are distinguishable from the background. Each spectral image was reconstructed at different wavelengths that cover the visible to the near-infrared range, highlighting the advantages of spectral imaging over conventional colour imaging.”

Shrinking computational spectrometers is essential for their use in chips and implantable applications. Professor Zhipei Sun, the head of the research team, says, ‘Conventional spectrometers are bulky because they need optical and mechanical components, so their on-chip applications are limited. There is an emerging demand in this field to improve the performance and usability of spectrometers. From this point of view, miniaturised spectrometers are very important for future applications to offer high performance and new functions in all fields of science and industry.’ Professor Pertti Hakonen adds that ‘Finland and Aalto have invested in photonics research in recent years. For example, there has been great support from the Academy of Finland’s Centre of Excellence on quantum technology, Flagship on Photonics Research and Innovation, InstituteQ, and the Otanano Infrastructure. Our new spectrometer is a clear demonstration of the success of these collaborative efforts. I believe that with further improvements in resolution and efficiency, these spectrometers could provide new tools for quantum information processing.’


“Spectroscopic methods exploit the absorption and reflection of light by matter, teasing out spectral patterns to identify the materials present according to their characteristic spectra. The mid-IR range of wavelengths contains the so-called fingerprint region (around 2.5-10 µm) associated with the stretching, vibration and rotation of molecules. The spectral emission pattern, or ‘molecular fingerprint’, is unique to each specific molecule, so mid-IR spectroscopy can very accurately identify molecules in a sample. INsPIRE set out to develop a new germanium-rich silicon integrated photonics platform for the detection of molecular fingerprints. As principal investigator Delphine Marris-Morini explains, “it exploits the advantages of silicon photonics technology, including maturity, large-scale fabrication and strong light confinement. It also takes advantage of the wide transparency window of germanium up to 15 µm. In comparison, silicon oxide is transparent up to 3.8 µm and silicon up to 8 µm.” This wide window of transparency means the optical materials used do not absorb and reflect light in this range so they do not impede its propagation. The monolithic integrated photonics design reduces the space required, resulting in a fingerprinting system-on-chip that fits on your fingertip.

INsPIRE evaluated the optical properties of the envisioned platform and developed a new set of optical functions. Moving into uncharted territory, Marris-Morini recalls: “We realised the equipment we needed to test our mid-IR devices was much less developed than for near-IR wavelengths, where telecommunications applications have spurred innovation. We had to build our own wideband polarisation rotator and often bought prototypes or devices that were freshly commercialised.” In the end, the team did in fact change the world of mid-IR spectroscopy, an evolution resulting in several world firsts with resonant structures operating in the 8 µm-wavelength range: integrated mid-IR Bragg grating-based Fabry-Perot resonators, broadband integrated racetrack ring resonators, and a high-resolution broadband mid-IR silicon-germanium Fourier-transform spectrometer. Although development of mid-IR optical modulators was not planned at the beginning of the project, the team achieved yet another record, the first optical modulation in a mid-IR photonic circuit operating in the 5.5-11 µm wavelength range. Marris-Morini summarises: “By pushing the frontiers of what was possible, we have built high-resolution on-chip mid-IR spectrometers working in an ultra-wide frequency band (in principle 1.5-15 µm) on a circuit less than 1 square centimetre in surface area.” The technology paves the way to portable and low-cost sensors for applications from real-time environmental monitoring of pollutants to food safety to early medical diagnoses.”


“Scientists from Cambridge University have designed an ultra-miniaturized device – a spectrometer – that could image single cells without the need for a microscope or make chemical fingerprint analysis possible from within a smartphone camera. This ultracompact micro-spectrometer is designed using a single compositionally engineered nanowire. The material composition of this nanowire is varied along its length, enabling it to be responsive to different colours of light across the visible spectrum. Using techniques similar to those used for the manufacture of computer chips, scientists then created a series of light-responsive sections on this nanowire. The spectrometer called a nanowire, is made from a single nanowire 1000 times thinner than a human hair, is the smallest spectrometer ever designed. It could be used in potential applications such as assessing the freshness of foods, the quality of drugs, or even identifying counterfeit objects, all from a smartphone camera.

The first author Zongyin Yang from the Cambridge Graphene Centre said, ‘this nanowire allows us to get rid of the dispersive elements, like a prism, producing a far simpler, ultra-miniaturized system than conventional spectrometers can allow.’ He also added that the individual responses we get from the nanowire sections can then be directly fed into a computer algorithm to reconstruct the incident light spectrum. The co-first author Tom Albrow-Owen said, ‘when you take a photograph, the information stored in pixels is generally limited to just three components – red, green, and blue. With our device, every pixel contains data points from across the visible spectrum, so we can acquire detailed information far beyond the colours which our eyes can perceive. This can tell us, for instance, about chemical processes occurring in the frame of the image.’ Dr. Tawfique Hasan, who led the study said, ‘our approach could allow unprecedented miniaturization of spectroscopic devices, to an extent that could see them incorporated directly into smartphones, bringing powerful analytical technologies from the lab to the palm of our hands.’

In the 17th century, Isaac Newton, through his observations on the splitting of light by a prism, sowed the seeds for a new field of science studying the interactions between light and matter – spectroscopy. Today, optical spectrometers are essential tools in the industry and almost all fields of scientific research. Through analyzing the characteristics of light, spectrometers can tell us about the processes within galactic nebulae, millions of light-years away, down to the characteristics of protein molecules. However, even now, the majority of spectrometers are based around principles similar to what Newton demonstrated with his prism: the spatial separation of light into different spectral components. Such a basis fundamentally limits the size of spectrometers in respect: they are usually bulky and complex and challenging to shrink to sizes much smaller than a coin. Four hundred years after Newton, University of Cambridge researchers have overcome this challenge to produce a system up to a thousand times smaller than those previously reported.

One of the most promising potential uses of the nanowire could be in biology. Since the device is so tiny, it can directly image single cells without the need for a microscope. And unlike other bioimaging techniques, the information obtained by the nanowire spectrometer contains a detailed analysis of the chemical fingerprint of each pixel. The researchers hope that the platform they have created could lead to an entirely new generation of ultra-compact spectrometers working from the ultraviolet to the infrared range. Such technologies could be used for a wide range of consumer, research and industrial applications, including in lab-on-a-chip systems, biological implants, and smart wearable devices. The Cambridge team has filed a patent on the technology and hopes to see real-life applications within the next five years.”

“Measurement setup with wafer prober, optical fiber probes and wafer”

by Fraunhofer-Gesellschaft  /  July 1, 2021

“Recognizing fake drugs? Testing water samples ourselves? Checking the quality of air? In the future, it could be possible to do all this using a smartphone in a quick, cost-effective and straightforward way. The process is being made possible by a spectrometer, weighing just one gram, from the Fraunhofer Institute for Electronic Nano Systems ENAS. The aim is to mass-produce this component for around a euro using conventional technologies.

Websites sometimes offer drugs at a much lower price than pharmacies. While we can be sure that the medicines we buy from local stores are the quality we expect, online bargains often lead us to question whether we are being palmed off with an ineffective or a differently composed counterfeit. In the future, we will be able to find out quickly and easily: Using a chip spectrometer currently being developed by researchers at Fraunhofer ENAS. “Our infrared spectrometer weighs only about a gram and we plan for it to cost less than a euro to produce,” says Dr. Alexander Weiß, Head of Department Multi Device Integration at Fraunhofer ENAS. “This will allow it to be integrated into smartphones, for instance.” As a comparison: At present, infrared spectrometers weigh several kilograms and cost thousands of euros to produce. Although transportable devices weighing slightly less do exist, they are unsuitable for the mass market—in terms of cost and size and also in terms of operation and analyzing the results. Other requirements crucial to existing on the mass market: The technology must not be overly complex—in other words, it must be easy to operate—and the production method must be suitable for the mass market.

The potential applications are by no means limited to counterfeit drugs. “Our spectrometer lends itself to all kinds of uses—such as assessing the maturity or microbial decomposition of foods for human and animal consumption, measuring the air quality of interiors and vehicles for effective climate control or detecting pollutants in air, water or foodstuffs.” Just like conventional infrared spectrometers, this spectrometer does this by emitting light beams in the infrared range. The light of different wavelengths is then fragmented using a tunable filter and conducted to a detector by means of integrated waveguides. Grating couplers with nanostructures bundle the light reflected by a pill to be tested, for example, into integrated waveguides. If the air quality is to be tested, the light enters a special absorption cell integrated in one plane instead. If we plot how much light reaches the detector at which wavelength, we get a characteristic spectrum that is different for each sample, similar to a fingerprint. A fake pill, with different ingredients, therefore has a different spectrum to that of the original drug.

“The miniaturized mass spectrometer uses microlithography on ceramic and glass plates to miniaturize the ion traps. The space between the plates is less than a millimeter.”

But how did the researcher team manage to reduce the size of the spectrometer so drastically yet still achieve a similar general functionality? “Conventional spectrometers usually consist of discrete more or less well integrated components. We, on the other hand, integrated the beam guidance, the splitting of the individual wavelengths and the detection function in one plane—we are therefore also calling this an inplane spectrometer,” explains Weiß. If the spectrometer is to be capable of being integrated into smartphones, for example, we have to think about more than size. Operation must be easy and intuitive and the system must then provide the user with clear evaluations. The researchers have already developed a concept: Smart learning algorithms. “If many people use the technology, the system will learn quickly,” says Weiß. The user will simply need to pull out their phone, start the spectrometer via a special app and hold it over one of the pills.

They will also see an instruction that guides them through the measurement process. The spectrometer generates the spectrum automatically and the software compares it to reference spectra entered into a database by specialists beforehand. The more people who come to use the system, the greater the possibility for making comparisons. The user sees only the result, “original drug”, for example. Another sticking point is the cost of producing the spectrometer. The researchers had this in mind from the outset too. “We designed the spectrometer in a way that would allow it to be mass-produced inexpensively using conventional microsystems engineering technologies. Manufacturers can use the processes that are standard on the large fabrication lines, fabs for short,” explains Weiß.

The researchers have already produced the first spectrometer chips and provided proof of concept. A number of different characterizations are now on the agenda: Do the individual components move as we want them to? Is the light that is coupled into the waveguide transmitted as it should be? The equipment required for these characterizations has been financed by the Research Fab Microelectronics Germany. If these investigations go as hoped, the spectrometer could be on its way to the mass market in around two years’ time.”



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