Atomically thin materials like tungsten disulfide (WS₂) have revolutionized the field of photonics due to their exceptional optical properties, despite being just a single layer of atoms thick. These two-dimensional semiconductors harbor tightly bound excitons—electron-hole pairs—which interact intensely with light and facilitate processes such as second-harmonic generation. This makes monolayer WS₂ an ideal candidate for quantum optics, sensing technologies, and compact, on-chip light sources. Yet, the atomically thin nature imposes a fundamental constraint: the physical thickness provides a minuscule volume for light-matter interaction, limiting emission efficiency and nonlinear optical processes unless the local photonic environment is deftly engineered to amplify these effects.
A groundbreaking study, published in Advanced Photonics, has unveiled a novel hybrid photonic platform that circumvents the limitations of conventional approaches by focusing on restructuring the nanoscale space beneath the 2D semiconductor itself. The research team engineered a heterostructure where a WS₂ monolayer is delicately placed over arrays of Mie void resonators—subwavelength air cavities intricately milled into a bismuth telluride (Bi₂Te₃) substrate, a material known for its high refractive index. This design harnesses a new paradigm of light confinement inside air-filled voids, strongly enhancing emission and nonlinear response from WS₂, while allowing unprecedented visualization of localized optical modes through far-field imaging techniques.
Traditional dielectric nanoresonators typically trap light within solid materials such as silicon, often resulting in the optical fields being concentrated deep inside the resonator’s bulk. This configuration inherently limits interaction with ultrathin materials placed at the surface and suffers performance degradation when the host material exhibits absorption losses, which reduce the quality of resonances and field confinement. In stark contrast, Mie void resonators exploit the high refractive index contrast at the air-dielectric boundary to confine light inside nanoscale air cavities. These subwavelength voids sustain circulating electromagnetic fields that are tightly confined near the surface where the WS₂ monolayer resides, effectively transforming “empty space” into a highly effective resonant cavity for light-matter coupling.
This unique “inverted” resonator geometry confers several vital advantages: the optical field enhancement is naturally accessible to the atomically thin WS₂ layer positioned atop the void; the resonant wavelengths can be finely tuned by modifying cavity dimensions; and the resonators maintain robust performance even though Bi₂Te₃ exhibits significant optical absorption. Notably, materials like Bi₂Te₃, typically unsuitable for conventional photonic resonators due to absorption losses, become ideal substrates in this void-based system, opening pathways to harness a wider class of materials for integrated photonics.
The research team utilized full-wave electromagnetic simulations to meticulously optimize the void resonator geometries. Their goal was to align a dipolar resonance mode with the main photoluminescence signature of WS₂, known as the A-exciton at visible wavelengths. By engineering cavity radius and depth, they tuned both the spectral position and vertical distribution of the resonant optical mode. The cavities were precision-fabricated into mechanically exfoliated Bi₂Te₃ flakes using focused ion beam milling, maintaining enough spatial separation to ensure each void functioned as an individual resonator rather than part of a coupled photonic crystal array. A continuous WS₂ monolayer was then transferred across the patterned surface to cover resonant voids, non-resonant voids, and flat regions of the substrate alike, ensuring direct comparative analysis of emission influenced solely by cavity geometry instead of material inhomogeneity.
Optical characterization through reflectance spectroscopy demonstrated that the resonance wavelengths shifted systematically with changes in cavity size, showing a predictable redshift as void radii increased and spectral shifts as cavity depth varied. The resonances exhibited remarkable tolerance to minor fabrication imperfections, remaining well-defined outside strict optimum geometries, which highlights the platform’s robustness and feasibility for scalable nanophotonic devices. This validates the precision of simulation models used and underscores the practical potential for real-world applications where device fabrication may encounter variability.
Photoluminescence measurements revealed a striking amplification of light emission from WS₂ when the dipolar resonance spectrally overlapped with the monolayer’s intrinsic emission band. Specifically, resonance alignment led to an approximately twenty-fold increase in photoluminescence intensity compared to cavities tuned far off resonance. Intriguingly, the enhancement did not arise from increased absorption of the excitation laser light, as simulations and control measurements with varied pump wavelengths showed negligible field amplification at the excitation frequencies. Instead, emission-side effects predominated: the resonant voids augmented the local density of optical states accessible to excitons and improved photon extraction efficiency, thereby significantly boosting emission yield.
The continuous nature of the WS₂ sheet over the substrate was pivotal, enabling a direct head-to-head comparison of photoluminescence from resonant Mie voids, non-resonant voids, and flat Bi₂Te₃ areas under identical experimental conditions. This setup eliminated variability caused by differing material quality or laser excitation conditions, conclusively attributing the enhanced photoluminescence to resonant photonic mode engineering. This demonstration of controlled enhancement marks a critical step toward practical photonic devices where modulation of optical response relies on structural design rather than material alteration.
Extending their approach to the nonlinear optical regime, the researchers adjusted the cavity geometry to bring the dipolar resonance into the near-infrared wavelength range, resonant with the fundamental excitation in second-harmonic generation experiments. Here too, the hybrid platform excelled, with second-harmonic signals from WS₂ increasing by approximately twenty-five times compared to off-resonant cavities. The nonlinear emission intensity exhibited a sharp spectral peak when the pump laser was tuned through the resonant frequency, underscoring the precision and efficacy of the Mie void resonators in enhancing nonlinear photonic processes with atomically thin materials.
Beyond quantifying intensity enhancements, the system’s design revealed a striking capability: near real-time, far-field visualization of localized optical modes within individual Mie void resonators. Using the spatially resolved second-harmonic emission, the researchers observed bright, well-defined photoluminescence “hotspots” precisely matching the void positions. Remarkably, by varying pump wavelength or cavity depth, these hotspots migrated predictably across the array, offering a direct, intuitive window into the spatial dynamics and dispersion of localized electromagnetic modes. This ability to map optical fields in real space without invasive near-field scanning techniques provides a powerful diagnostic tool for nanophotonics.
With its unique combination of resonant mode tunability, robust field enhancement, and direct spatial control, the Mie-void heterostructure platform stands poised to advance studies in nonlinear light generation, enhanced optical sensing, and spatially programmable photonic devices leveraging van der Waals atomic layers. Crucially, the approach circumvents reliance on large-scale metasurfaces with periodic patterns, offering a nanoscale engineering route that remains effective even with strongly absorbing substrates. This opens vast opportunities to integrate emerging 2D materials into complex photonic architectures previously limited by material constraints and coupling inefficiencies.
More broadly, this work redefines the conventional paradigm of photonic device design by focusing on engineering the “empty” spaces beneath atomically thin layers rather than modifying the 2D materials themselves. By sculpting nanoscale voids that support deeply subwavelength resonant modes in air, researchers can dramatically amplify light-matter interactions and introduce spatial programmability directly into heterostructure platforms. This insight could accelerate the development of next-generation photonic technologies that are both highly efficient and versatile, spanning applications from quantum information processing to ultrafast programmable optical networks.
As the photonics community pursues ever-thinner, more compact, and more efficient light sources and sensors, innovations like Mie void resonators represent powerful new tools. This research bridges theoretical modeling, precision nanofabrication, and sophisticated optical characterization to transform fundamental understanding into practical device concepts. Future work will undoubtedly explore integrating other transition metal dichalcogenides and layered materials with tailored void geometries, expanding functionality to cover broader spectral ranges and complex optical phenomena, heralding a new era in two-dimensional material photonics.
Subject of Research: Not applicable
Article Title: Light–matter interaction in van der Waals heterostructures with Mie voids
News Publication Date: 14-Feb-2026
References:
Z. Lu et al., “Light–matter interaction in van der Waals heterostructures with Mie voids,” Adv. Photon., 8(2), 026002 (2026). DOI: 10.1117/1.AP.8.2.026002
Image Credits: Zhuoyuan Lu (Australian National University)
Keywords
Semiconductors, Applied optics, Photonic nanostructures, Two-dimensional materials, Tungsten disulfide, Mie void resonators, Van der Waals heterostructures, Nonlinear optics, Light emission enhancement, Nanoscale photonics, Bismuth telluride, Second-harmonic generation
