The essence of this breakthrough lies in the creation and deployment of what the researchers call a multimode photonic lantern (MM PL), a device meticulously engineered using advanced 3D-printing techniques at the microscale. Photonic lanterns traditionally serve as optical interfaces that merge several single-mode inputs into a multimode waveguide. However, this new “N-MM PL” design uniquely accommodates multiple multimode VCSEL sources simultaneously, fundamentally redefining the operational paradigm for photonic lanterns. Unlike their predecessors, these lanterns effectively multiplex dozens of multimode laser outputs while preserving brightness and ensuring highly efficient coupling to multimode fibers.

In practical terms, the team demonstrated remarkable photonic lantern variants capable of integrating the light from 7, 19, and even 37 distinct VCSEL sources. Each VCSEL exhibits complex spatial mode structures, lasing across six spatial modes, which culminates in effective support for up to 222 spatial modes within a single multimode fiber. This massive-scale multiplexing represents a formidable advancement in optical multiplexing capacity, surpassing conventional methods both in scale and efficiency and enabling far more concentrated laser arrays without the typical penalties of alignment complexity or modal mismatch.

The manufacturing process hinges on precision 3D nanoprinting, allowing the creation of devices less than half a millimeter long—a dramatic size reduction compared to conventional bulky beam combining setups. This compact form factor does not sacrifice performance; on the contrary, it delivers exceptionally low insertion losses, registering as minimal as -0.6 dB for the 19-input lantern and a mere -0.8 dB for the 37-input system. Such low losses are critical in maintaining overall system efficiency and brightness, which directly translates into higher power delivery and improved beam quality in applications spanning industrial laser machining, medical laser systems, and advanced telecommunications.

A critical challenge in previous optical beam combining technologies stemmed from coupling inefficiencies and the inability to handle multimode beams generated by high-power VCSEL arrays. Traditional photonic lanterns were intrinsically single-mode, incompatible with the multimode nature of these VCSEL sources. The research team at Hebrew University ingeniously designed an adiabatic transition within the lantern structure, facilitating a seamless and loss-minimized conversion of multiple few-mode laser outputs into a single multimode fiber. This method preserves the modal richness and brightness of the combined beam, avoiding degradation commonly associated with relay lenses or other beam shaping techniques.

The implications of this research extend deeply into optical communications, where the preservation of modal capacity and brightness is paramount for maximizing data throughput and minimizing transmission losses. Indeed, by harnessing a highly scalable, compact, and efficient photonic lantern, fiber networks could achieve significantly enhanced performance without complex infrastructure overhauls. Moreover, the technology introduces a new dimension to high-power laser systems, where managing heat dissipation and beam quality simultaneously remains a stubborn obstacle. This lantern’s ability to combine many high-power sources without sacrificing optical integrity is poised to unlock fresh industrial and research opportunities.

This advancement is the product of insightful collaboration between the Hebrew University, Civan Lasers, and financial backing from the Israel Innovation Authority. Spearheaded by Ph.D. student Yoav Dana under the mentorship of Professor Dan M. Marom, the team’s work crystallizes years of progress in integrated optics, laser physics, and additive manufacturing. The cross-disciplinary expertise allowed for an inventive fusion of theoretical design and experimental validation, culminating in a demonstrator device whose length measures only 470 micrometers—a scale few optical multiplexers can parallel.

From a technical standpoint, the device’s operation relies on precise modal matching between the multimode inputs and the multimode output fiber. Each VCSEL array emits beams composed of multiple spatial modes, which are notoriously challenging to combine without incurring modal dispersion or brightness loss. The MM photonic lantern accomplishes this by implementing an adiabatic taper geometry that gradually transforms the spatial modes’ distributions, thus preserving the spatial coherence and brightness as these modes are delicately funneled into a fiber that supports all these parallel channel modes simultaneously.

This compact lantern also significantly relaxes the alignment precision typically required for coupling multimode beams into fibers. The intricate 3D-printed waveguide structure internally redistributes the optical paths with nanometer accuracy, easing system integration complexity while enhancing robustness against environmental perturbations—an essential feature for real-world deployment in industrial and communication systems often exposed to mechanical and thermal stresses.

The significance of this achievement is not only in the scale or the compactness but also in its practical applicability. By offering a pathway to spatially multiplexed multimode lasers with minimal insertion loss and preserved brightness, the research opens avenues to scalable, high-brightness laser arrays suitable for next-generation laser manufacturing, aerospace optical systems, and secure high-capacity fiber networks. The lantern’s potential to serve as a universal interface between multimode semiconductor lasers and fibers signals a paradigm shift for photonic system design.

Looking forward, scaling this technology further could facilitate even denser laser arrays, dramatically increasing the combined optical power deliverable through fiber networks. Such scalability ensures this innovation is future-proof, accommodating ongoing trends in miniaturization and integration in photonics. Whether applied to boosting fiber optic communication bandwidth or enhancing laser machining precision, the 3D-printed multimode photonic lantern epitomizes the fusion of cutting-edge fabrication techniques with profound optical design principles.

In summary, the Hebrew University research team has presented a transformative solution to a long-standing photonics challenge: efficiently combining the output of many multimode VCSELs into a single fiber with minimal loss and preserved brightness. The microscale 3D-printed multimode photonic lantern breaks new ground in scalability, efficiency, and compactness, promising broad impacts across scientific and industrial photonics. This work illustrates the power of interdisciplinary collaboration and advanced manufacturing to redefine optical technologies for the next wave of innovation.

Subject of Research: Not applicable

Article Title: Massive-scale spatial multiplexing of multimode VCSELs with a 3D-printed photonic lantern

News Publication Date: 10-Mar-2026

Web References: 10.1038/s41467-026-70458-4

Image Credits: Ksenia Shukhin

Keywords

Photonics, Optical materials, Fiber optics, Laser systems, Physics

Second harmonic generation, a nonlinear optical process that converts photons at a fundamental frequency into photons at twice that frequency, is a cornerstone phenomenon in the realms of frequency doubling, optical sensing, and quantum optics. Traditionally, SHG efficiency has been limited by the intrinsic symmetry properties and bulk responses of materials. However, by exploiting the interfaces in stacked TMD heterostructures, the research team has transcended these limitations, revealing that the interfacial region can serve as a prolific nonlinear source, dramatically enhancing the SHG output far beyond the sum of its parts. This insight taps into the subtle interplay of material symmetry breaking, electronic band structure engineering, and nanophotonic confinement effects.

The study meticulously fabricates hetero-bilayer nanoantennas consisting of bulk WS₂/MoS₂, layered via van der Waals forces. These artificial heterostructures defy conventional bulk material constraints by introducing highly tunable interfacial phenomena not accessible in monolayer or thicker homogeneous crystals. The researchers note that interfaces formed by these TMDs incur substantial lattice mismatch and electronic band offsets, fostering localized states and dipole moments that are instrumental to their enhanced nonlinear response. Careful synchrotron-based characterization and nonlinear optical measurements elucidate the mechanisms by which these interface states dominate the SHG process.

Central to the breakthrough is the exploitation of the so-called “interface second harmonic generation enhancement,” where the spatial confinement of electronic states at the WS₂/MoS₂ boundary breaks inversion symmetry and augments dipolar nonlinear polarization. This contrasts markedly with typical bulk materials, where inversion symmetry largely suppresses bulk SHG contributions. By harnessing the emergent interfacial asymmetry, the team exposes a powerful mechanism to engineer nonlinear optical properties at will, crafting nanoantennas that act as frequency conversion hotspots within optical circuits.

Furthermore, advanced spectroscopy combined with first-principles theoretical models lends credence to the hypothesis that charge transfer and excitonic hybridization at the interface critically facilitate SHG enhancement. The charge redistribution induces localized electric dipoles and modifies selection rules for optical transitions, enabling robust nonlinear coupling. The study highlights how tuning external parameters such as stacking angle and layer thickness alters the strength and directionality of SHG signals, offering a versatile toolkit for custom nonlinear photonic device design.

From a practical perspective, the findings hold transformative potential for integrated photonics, where efficient frequency conversion elements can significantly boost the functionality of on-chip light sources, modulators, and detectors across diverse spectral regimes. These van der Waals nanoantennas show promise in miniaturized optical communication systems, low-threshold quantum emitters, and sensors with enhanced sensitivity enabled by their amplified harmonic generation capabilities. In particular, the ability to integrate layered TMD heterostructures on silicon platforms makes this technology imminently compatible with existing semiconductor fabrication techniques.

Beyond immediate applications, the work poses fundamental questions and opportunities regarding the quantum mechanical origins of nonlinear optics at interfaces. Since excitonic effects dominate TMD optical responses and are highly sensitive to environmental conditions, intricate control over interface chemistry and topology may enable unprecedented control over nonlinear processes. These advances beckon further exploration into stacking sequences, material combinations, and external field manipulations that might unlock even higher order nonlinearities and novel multiphoton interactions.

Scientific communities investigating valleytronics and spintronics will also find relevance in these discoveries. The enhanced interface SHG is intimately connected to valley-contrasting physics inherent in WS₂ and MoS₂ monolayers, where spin-valley locking mechanisms might be exploited to induce polarization-dependent nonlinear optical effects. Such phenomena could seed novel quantum information platforms harnessing valley degree of freedom for coherent photonic control at the nanoscale.

Moreover, the research underscores the versatility of van der Waals heterostructures as a platform that transcends classical semiconductor architectures. By layering atomically thin materials with distinct lattice constants, band alignments, and symmetry properties, the emergent phenomena such as interface-enhanced SHG exemplify how heterogeneity at the atomic scale can be a resource rather than limitation. This represents a conceptual leap towards designing bespoke photonic materials from the bottom up, leveraging quantum materials science to tailor light-matter interactions with exquisite precision.

The experimental techniques leverage state-of-the-art nonlinear optical microscopy, ultrafast pump-probe measurements, and electron microscopy to confirm structural integrity and quantify nonlinear coefficients. These rigorous evaluations are complemented by density functional theory calculations and many-body perturbation frameworks to map the energy landscape and transition dipole moments across the interface. The synergy between theory and experiment provides a comprehensive understanding that paves the way for rational device engineering.

Importantly, this study also opens avenues toward exploring other transition metal dichalcogenide combinations and complex stacking orders, potentially revealing a vast parameter space of interfacial nonlinear optical responses. The modularity and scalability of van der Waals assembly suggest possibilities for creating multi-layered multifunctional nanoantennas capable of complex nonlinear operations, surpassing traditional nonlinear crystals in flexibility and functionality.

Environmental considerations such as thermal stability, defect tolerance, and operational bandwidth are also addressed, underscoring the robustness of these nanoantennas under realistic device conditions. Initial findings indicate that these heterostructures maintain enhanced SHG efficiency across relevant temperature ranges and remain stable under continuous optical excitation, signifying their readiness for integration into photonic circuits and harsh operating environments.

In summary, the team’s work symbolizes a landmark achievement in nonlinear nanophotonics, demonstrating that interface engineering within bulk WS₂/MoS₂ hetero-bilayers can fundamentally augment second harmonic generation efficiencies. These findings chart an exhilarating course towards next-generation photonic devices rooted in quantum 2D materials, where interface phenomena serve as tunable handles for designing ultra-efficient nonlinear optical nanoantennas. The implications ripple through fundamental science and looming technological revolutions alike, heralding a new era where atomic scale engineering sculpts the future of light control.

Subject of Research: The enhancement of second harmonic generation (SHG) at the interfaces of bulk WS₂/MoS₂ hetero-bilayer van der Waals nanoantennas.

Article Title: Interface second harmonic generation enhancement in bulk WS₂/MoS₂ hetero-bilayer van der Waals nanoantennas

Article References:
Tognazzi, A., Franceschini, P., Biechteler, J. et al. Interface second harmonic generation enhancement in bulk WS₂/MoS₂ hetero-bilayer van der Waals nanoantennas. Light Sci Appl 14, 346 (2025). https://doi.org/10.1038/s41377-025-01983-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41377-025-01983-y

At its core, this discovery builds upon years of research into metasurfaces, which emerged as a pivotal solution to the limitations imposed by traditional optical systems that rely on bulky lenses. These lightweight devices, characterized by their nanoscale structures, have proven invaluable in a plethora of applications, allowing for precise control over light behavior at wavelengths previously deemed unattainable. The transition from conventional optics to metasurfaces marks a significant turning point in optical engineering and design, offering potential solutions for advancements in communications and imaging technologies.

The recent innovation—the bilayer metasurface—is notable for featuring two distinct layers of titanium dioxide nanostructures, effectively doubling the design’s capabilities. Under microscopic examination, the new structure resembles a cityscape of miniature skyscrapers, reflecting the intricate engineering that underpins its functionality. More than just an aesthetic improvement, this layering enables enhanced control over light’s properties such as wavelength, phase, and polarization, pushing the boundaries of what is possible with light manipulation.

Federico Capasso, the senior author of the study, articulates the importance of this development, stating that it represents a pinnacle achievement in nanotechnology. The bilayer design signifies a shift towards more sophisticated optical solutions, allowing researchers to explore dual functionalities within a single device. For example, these meta-optical systems could theoretically project one vivid image from one side and entirely different information from the opposite, showcasing a transformative approach to how visual data is conveyed through optical means.

The evolution from single-layer to bilayer metasurfaces addresses inherent constraints found in earlier models, particularly in how they handle light polarization. Historically, single-layer metasurfaces necessitated specific conditions to manipulate light’s polarization effectively. The flexibility introduced by the bilayer design paves the way for more complex optical devices without the need for intricate setups, making them vastly more practical for a range of applications.

Creating the bilayer metasurface demanded an unprecedented level of precision and innovation in fabrication techniques. Researchers utilized the facilities at Harvard’s Center for Nanoscale Systems to pioneer a fabrication process for robust, freestanding structures that maintain chemical independence between the two layers. This multi-level fabrication approach is a significant technical achievement, bridging the gap between advanced nanostructures and their practical optical applications.

The significance of this advancement is further underscored by its potential applications. With their newfound capabilities, these bilayer metasurfaces may facilitate the development of devices that integrate various functionalities into one compact unit, thus streamlining several aspects of optical engineering. The potential to create multifunctional optical devices signifies a monumental step towards sophisticated design in the field of optics, promoting innovation in commercial applications such as smartphone cameras, virtual reality headsets, and more.

Capasso and his team validated their groundbreaking design by demonstrating its functionality in a controlled experiment that manipulated polarized light. This proof-of-concept not only showcases the efficacy of their bilayer system but also hints at a future where additional layers may further enhance control over light. The prospects of incorporating more layers into metasurface designs open the door to extreme broadband operations with both high efficiency and precision, enhancing the potential for even more intricate optical functionalities.

The research team employed various federal funding sources to support this ambitious endeavor, with backing from the Office of Naval Research and the Air Force Office of Scientific Research, among others. This collaborative support highlights the broader implications of their work, emphasizing its significance in both academic and applied contexts. Moreover, the deployment of their technology through partnerships, such as with Harvard’s Office of Technology Development and the establishment of Metalenz, signifies a trajectory aimed at expert spin-off ventures that aspire to commercialize breakthrough optical technologies.

In addition to the compelling scientific advancements, this work exemplifies how interdisciplinary collaboration drives progress in complex fields like nanotechnology. In their pursuit of innovation, the team relied on contributions from various experts to refine their fabrication methods, reiterating the importance of collaboration in today’s research landscape. Such teamwork fosters growth, ensuring that cutting-edge technologies can transition swiftly from research labs to real-world applications.

In conclusion, the introduction of the bilayer metasurface represents a pivotal moment in optical science, and it may herald a new era of technology that enhances our capability to understand and utilize light. From augmented reality to advanced imaging systems, the implications of this research are vast and varied. As further studies unfold and newer applications are envisioned, the ability to manipulate light at unprecedented levels promises to facilitate changes across myriad scientific fields. The advancements driven by this technology will surely stimulate curiosity and further investigation into the exciting world of optical engineering.

Subject of Research:
Article Title: Free-standing bilayer metasurfaces in the visible
News Publication Date: 1-Apr-2025
Web References: https://www.nature.com/articles/s41467-025-58205-7
References: https://seas.harvard.edu/news/2016/06/metalens-works-visible-spectrum-sees-smaller-wavelength-light
Image Credits: Credit: Capasso group / Harvard SEAS

Keywords

Metasurfaces, visible light, light sources, nanostructures, light polarization, fabrication, applied physics, engineering, materials engineering, materials processing, microstructures, optics, nonlinear optics, optical properties, quantum optics.

Flat optics, characterized by ultra-thin and lightweight surfaces, represents the next frontier in optical engineering, allowing for the creation of compact devices that outperform traditional bulky optical systems. The advantages of this technology are profound, particularly in the miniaturization of devices such as smartphone cameras and the enhancement of augmented and virtual reality technologies. In essence, flat optics holds the potential to redefine how we interact with light and the components we use to harness it.

Metasurfaces are an exciting application of flat optics, composed of countless nanostructures that enable precise manipulation of light at an unprecedented level. The challenge, however, lies in the process of sampling; this refers to the conversion of continuous optical signals into discrete data points, akin to how our brains interpret visual stimuli. Traditional sampling techniques are fraught with difficulties. If the sampling rate is insufficient, it leads to aliasing artifacts, which can create distorted images and reduce the efficiency of optical systems.

A classic example of aliasing is the wagon-wheel effect, a phenomenon observed in videos where a rotating wheel appears to spin backward. This distortion arises due to an inadequate frame rate when capturing motion. Similarly, in the context of metasurface technology, insufficient sampling can severely compromise the optical performance, necessitating a more robust approach to sampling methodologies.

Historically, researchers have leaned heavily on the Nyquist sampling theorem to guide their efforts in mitigating aliasing effects. While this theorem proves valuable in the domain of digital signal processing, the POSTECH research team uncovered critical limitations when applying it to the complexities inherent in optical metasurfaces. The Nyquist theorem defines frequency thresholds for digital systems; however, it fails to accurately account for the unique attributes of metasurfaces and the wave characteristics of light, resulting in optical distortions that diminish image quality and efficiency.

To rectify these limitations, the POSTECH team formulated a groundbreaking multidimensional sampling theory that embraces the intricate interplay between the two-dimensional lattice arrangement of metasurfaces and the wave properties of light. This innovative approach marks the first time that the geometric relationship between a metasurface’s nanostructured structure and its spectral response has been explicitly linked to enhancing optical performance.

By introducing an anti-aliasing strategy that marries lattice rotation with elemental diffraction, the researchers significantly minimized optical noise. This enhanced light control was demonstrated across various spectrum regions, from visible light to ultraviolet wavelengths. The team showcased the functionality of high-numerical-aperture metasurfaces and wide-angle meta-holograms operating specifically in the ultraviolet spectrum.

The implications of this research are not just theoretical; they open new avenues for the development of advanced optical devices. The ability to address and mitigate aliasing effects means that high-NA metalenses and wide-angle meta-holograms can be realized more effectively, pushing the boundaries of optical engineering. Professor Rho emphasizes that this new sampling theory is versatile enough to span the entire electromagnetic spectrum, including microwaves and extreme ultraviolet light, significantly lowering the fabrication hurdles typically encountered with short-wavelength ultraviolet optics.

As technology progresses, the need for precise optical components will only grow. Devices operating in the ultraviolet spectrum, for instance, require meticulous fabrication processes due to their sensitivity to manufacturing defects. By easing the underlying fabrication challenges, the research by Professor Rho and his team not only paves the way for practical applications but also encourages further exploration into the potential of ultraviolet metasurfaces, which has remained largely untapped.

Support from prominent entities such as POSCO, Samsung Electronics, the Ministry of Science and ICT, and the National Research Foundation of Korea underscores the importance of this research. Their backing highlights the vital role of collaboration between academic institutions and industry in driving innovative research to fruition.

The upcoming publication of these findings in Nature Communications serves as a testament to the rigorous validation process underlying this groundbreaking work. It sets the stage for discussions within the scientific community and encourages ongoing investigations into the nuances of optical metasurfaces and the fundamental principles governing light manipulation.

In a world increasingly dependent on technology, the potential for next-generation flat optical devices to transform industries—from consumer electronics to scientific research—is profound. As researchers tirelessly work on refining metasurface technologies, it is evident that the future of optics is not merely about enhancing existing functionalities but also about rewriting the fundamental rules of light manipulation.

The development of multidimensional sampling theory signifies a leap forward, providing a robust framework for designing advanced optical systems that ensure high efficiency and precision. As we continue to unravel the complexities associated with waves and light, the applications of this research promise to enhance the capabilities of various technologies critical to communication, imaging, and beyond.

In conclusion, the collaborative effort between researchers and institutions has shed light on the significant challenges within optics while also illuminating potential pathways for innovation. The future of flat optics, particularly through the lens of improved metasurface design, is an exciting domain ripe for exploration, promising advancements that could revolutionize our interaction with light in the years to come.

Subject of Research: Advanced Metasurface Design through Multidimensional Sampling Theory
Article Title: Anti-aliased metasurfaces beyond the Nyquist limit
News Publication Date: 6-Jan-2025
Web References: http://dx.doi.org/10.1038/s41467-024-55095-z
References: Nature Communications
Image Credits: Credit: POSTECH

Keywords

Flat optics, Metasurfaces, Sampling theory, Optical technology, Ultraviolet optics, Antialiasing strategy, Image distortion, Optical efficiency, Light manipulation, Nanostructures, High-numerical-aperture metalenses, Optical performance.