Scientists at the University of Warsaw’s Faculty of Physics, in collaboration with Łódź University of Technology, Warsaw University of Technology, and the Polish Academy of Sciences, have pioneered a remarkable breakthrough in nanophotonics. They have engineered a novel subwavelength grating that traps infrared light within an ultrathin layer just 40 nanometers thick. This groundbreaking structure, fabricated using the layered semiconductor molybdenum diselenide (MoSe₂), demonstrates exceptional ability to confine and manipulate light well below the diffraction limit, a feat that holds immense promise for the future of photonic technologies.
The relentless drive to miniaturize and accelerate information processing systems is pushing electronics to their physical limits. Photonics, leveraging photons instead of electrons for information transmission and processing, promises a faster, more efficient alternative. However, photonics faces a fundamental obstacle: light behaves as a wave with a wavelength ranging from hundreds of nanometers (visible light) to several micrometers (infrared). Conventional photonic devices require components on the order of these wavelengths, limiting how small and dense integrated photonic circuits can become. The crux of advancing photonics thus hinges on manipulating light at scales smaller than its wavelength.
Subwavelength gratings, structures composed of periodic arrays of materials spaced at intervals smaller than the wavelength of the incident light, offer a powerful tool for light manipulation. Acting similarly to prisms, these gratings diffract and control light. When designed with periods shorter than the wavelength, such gratings can function as nearly perfect mirrors while simultaneously confining light within their minuscule volumes. Yet, until now, subwavelength gratings have required thicknesses on the order of hundreds of nanometers to effectively trap light, thus limiting their miniaturization.
The Research Team’s innovation lies in employing molybdenum diselenide (MoSe₂), a layered van der Waals semiconductor with a uniquely high refractive index, to fabricate ultrathin subwavelength gratings capable of confining infrared light in merely a 40-nanometer-thick film. The refractive index of MoSe₂ is approximately 4.5, considerably larger than that of traditional photonic materials like silicon or gallium arsenide, which reduces the effective wavelength of light inside the material. This property facilitates a drastic reduction in grating thickness without impairing light confinement, enabling structures thousands of times thinner than a human hair to manipulate infrared photons with exceptional efficiency.
Beyond its high refractive index, molybdenum diselenide also exhibits intriguing nonlinear optical phenomena. Chief among these is third harmonic generation, a nonlinear process whereby photons interacting within the material combine their energies to produce new photons at triple the original frequency. This means infrared light entering the MoSe₂ grating can emerge transformed into blue light, signifying a frequency tripling effect. Importantly, the intense localization of infrared light within the nanostructured grating enhances this nonlinear response by over 1,500-fold compared to simple layers of MoSe₂ without patterning, showcasing the immense potential for integrated nonlinear photonic applications.
The fabrication method developed by the researchers represents a critical advance that addresses previous challenges in producing high-quality, scalable MoSe₂ films. Traditionally, such layers have been created through mechanical exfoliation — peeling thin sheets from bulk crystals using adhesive tape — a technique well-known from graphene research but limited by randomness, small size, and poor reproducibility. To overcome these problems, the team adopted molecular beam epitaxy (MBE), a sophisticated, controllable thin-film fabrication technique prominently used in semiconductor industry but never before applied to materials like MoSe₂. MBE facilitates the growth of large-area, uniform films with precisely controlled thickness, crucial for industrial-scale photonic device integration.
The subwavelength gratings crafted from these epitaxial MoSe₂ films measure several inches across yet maintain uniform thickness down to 40 nanometers. Such an extraordinary aspect ratio—width and length dimensions millions of times greater than thickness—mimics a factor unattainable in conventional photonic materials and foreshadows a new era of ultrathin, scalable photonic designs. To put it in perspective, the thickness-to-size ratio of these films surpasses that of standard A4 paper by a factor of about 500, underscoring the unprecedented level of thinness combined with structural integrity.
This research heralds a new paradigm in controlling light at the nanoscale. By demonstrating that infrared photons can be confined and nonlinear optical effects amplified within films just a few tens of nanometers thick, the team has overcome a key technological barrier to the miniaturization and performance enhancement of photonic devices. The capacity to fabricate such nanostructured van der Waals materials reliably and at scale elevates their suitability for applications ranging from highly compact optical circuits to advanced sensors, frequency converters, and quantum photonic systems.
The study published in the high-impact journal ACS Nano describes not only the experimental realization of these optical bound states in the continuum — resonant modes trapped within the grating despite continuous radiation bands — but also elucidates their fundamental physical mechanisms through detailed theoretical modeling. The findings pave the way for integrating layered dichalcogenide materials into next-generation photonic platforms, delivering performance and form factors previously constrained by material limitations and fabrication hurdles.
In essence, molybdenum diselenide subwavelength gratings redefine how light can be controlled at scales far below its natural wavelength. These ultrathin nanostructures constitute versatile building blocks for future photonic devices that combine speed, miniaturization, and nonlinear optical functionality. With molecular beam epitaxy facilitating reproducible large-area production, their technological translation from laboratory breakthroughs to real-world applications appears promisingly within reach.
This collaboration between academic and technological institutions in Poland exemplifies the fusion of fundamental physics and applied engineering. It highlights how interdisciplinary approaches and novel material systems can disrupt long-held limitations in optics, photonics, and beyond. As industries increasingly seek to harness photonics for computing, communications, and sensing, such scientific achievements stand to impact the evolving landscape of information technology and optical science globally.
The funding for this cutting-edge research was provided by national and international agencies, including the National Science Centre of Poland, the European Union’s ERC-ADVANCED grant, and the Foundation for Polish Science. The Faculty of Physics at the University of Warsaw, centrally involved in this project, continues to push frontiers in modern physics through collaborative endeavors that merge quantum science, materials engineering, and photonics.
In summary, the advent of ultrathin subwavelength gratings made of epitaxially grown MoSe₂ marks a significant milestone towards the ultimate goal of manipulating light on the nanoscale with unparalleled precision and efficiency. This achievement promises to accelerate the integration of photonics into everyday technology, from ultrafast optical communication devices to compact nonlinear optical converters, heralding a future enriched by light-driven innovation.
Subject of Research: Ultrafast manipulation and confinement of infrared light in ultrathin subwavelength gratings fabricated from epitaxial molybdenum diselenide (MoSe₂).
Article Title: Optical Bound States in the Continuum in Subwavelength Gratings Made of an Epitaxial van der Waals Material
News Publication Date: 26-February-2026
References: Emilia Pruszyńska-Karbownik et al., ACS Nano 2026, 20 (9), 7426-7437. DOI: 10.1021/acsnano.5c12870
Image Credits: E. Pruszyńska-Karbownik, Faculty of Physics, University of Warsaw
Keywords
nanophotonics, molybdenum diselenide, subwavelength grating, infrared light confinement, nonlinear optics, third harmonic generation, molecular beam epitaxy, van der Waals materials, ultrathin semiconductor films, photonic integration, optical bound states, frequency tripling
Tags: advanced photonic engineeringinfrared light confinementinfrared photonic devicesintegrated photonic circuits miniaturizationlayered semiconductor materialslight manipulation below diffraction limitmolybdenum diselenide applicationsnanophotonics researchphotonic information processingsemiconductor nanostructuressubwavelength grating technologyultrathin photonic layers
