Ming Lun Tseng

We report a robust meta-optical platform based on low-aspect-ratio GaP Huygens Integrated Resonant Units (HIRUs) for underwater applications. By engineering diverse geometries—including disks, squares, and cross-disk structures—we achieve full 2π phase control with significantly reduced sensitivity to fabrication errors compared to conventional designs. These meta-atoms are designed to satisfy the Generalized Kerker Condition (GKC), utilizing multipolar interference to maximize forward scattering and transmittance in water. To ensure long-term reliability, the metasurfaces are encapsulated in a 300-nm SiO ₂ protective layer, maintaining structural integrity under ultrasonic stress that typically destroys high-aspect-ratio TiO ₂ structures. We demonstrate the generation of diverse structured light, including Bessel and Abrupt Autofocusing (AAF) beams, and verify their unique self-healing and obstacle-bypassing properties in aqueous environments. This work provides a versatile, mechanically resilient solution for underwater imaging, trapping, and sensing.

Underwater photonics is essential for imaging and analysis in biomedical technologies, as well as for communication and autonomous vehicle networks in the Internet of Underwater Things (IoUT). Structured light enables spatial control of beams, offering new opportunities for underwater sensing, imaging, and signal transmission. However, compact and robust water‐immersed photonic devices remain challenging to realize. Among various approaches, dielectric metasurfaces are particularly promising for underwater optics due to their flat form factor and subwavelength phase control. Nevertheless, current platforms suffer from instability in liquids, incomplete phase modulation, or strong sensitivity to fabrication imperfections. Here, ultrathin water‐immersed metasurfaces composed of gallium phosphide (GaP) Huygens’ integrated resonance units (HIRUs) operating in the visible regime are demonstrated. By leveraging the high refractive index and low optical loss of GaP, and integrating both forward and inverse design strategies, metasurfaces with planar geometry (≈1/5 of the operating wavelength), enhanced fabrication tolerance, and stable in‐liquid operation are realized. These metasurfaces generate various structured light beams in water, including abruptly autofocusing (AAF) beams, Bessel beams, optical vortices, and Gaussian focusing beams. This work establishes a scalable and reliable platform for underwater nanophotonics and emerging IoUT‐related applications.

Metasurfaces provide an ideal platform for optical sensing because they produce strong light-field confinement and enhancement over extended regions that allow us to identify deep-subwavelength layers of organic and inorganic molecules. However, the requirement of using external light sources involves bulky equipment that hinders point-of-care applications. Here we introduce a plasmonic sensor with an embedded source of light provided by quantum tunnel junctions. An optically resonant, doubly periodic nanowire metasurface serves as a top contact for the junction and provides extremely uniform emission over large areas, amplified by plasmonic nanoantenna modes that simultaneously enhance the spectral and refractive index sensitivity. As a proof of concept, we demonstrate spatially resolved refractometric sensing of nanometre-thick polymer and biomolecule coatings. Our results open exciting prospects based on a disruptive platform for integrated electro-optical biosensors.

Deep-ultraviolet (DUV) light is essential for applications including fabrication, molecular research, and biomedical imaging. Compact metalenses have the potential to drive further innovation in these fields, provided they utilize a material platform that is cost-effective, durable, and scalable. In this work, we present aluminum nitride (AlN) metalenses as an efficient solution for DUV applications. These metalenses, with a thickness of only 380 nm, deliver DUV focusing and imaging capabilities close to the theoretical diffraction limit. Leveraging their robustness to intense ultrafast laser irradiation, we demonstrate successful DUV ultrafast laser direct writing of microstructures on a polymer film and silicon substrate. These results underscore the significant promise of advancing photonic technologies in this critical wavelength regime.

High‐performance deep ultraviolet (DUV) spectroscopy is crucial in driving innovations for biomedical research, clinical diagnosis, and material science. DUV resonant nanostructures have shown capabilities for significantly improving spectroscopy sensitivity. However, they encounter significant challenges in practical applications, including instability due to oxidation and light‐induced damage, and the strong photoluminescent noise background from their constituent materials. An efficient and robust DUV spectroscopy platform based on the polaritonic properties in all‐dielectric silicon (Si) metasurfaces is proposed. Unlike conventional dielectric metasurfaces that rely on Mie‐type modes, this approach leverages the polaritonic resonances in Si nanostructures—a striking yet underexplored property driven by interband transitions in the DUV regime—for nanophotonic sensing. A polaritonic Kerker‐type void metasurface providing strong near‐field enhancement localized on the surface is designed and fabricated. The metasurface facilitates double‐resonance Raman scattering, a process that reveals key information about lattice dynamics and electronic structures, for analyzing 2D semiconductor monolayers. It also demonstrates superior stability in solvents and enhances biomolecule autofluorescence. These capabilities demonstrate the versatile potential of Si metasurfaces as a scalable, robust platform for interdisciplinary DUV spectroscopy applications, including advanced biomedical research and the investigation of emerging nanomaterials.

High-performance DUV spectroscopy drives advancements in biomedical research, clinical diagnosis, and material science. Existing DUV resonant nanostructures face instability and photoluminescent noise challenges. We propose robust Si metasurfaces leveraging polaritonic resonances, a unique property driven by interband transitions, for enhanced nanophotonic sensing. Our polaritonic Kerker-type void metasurface enables double-resonance Raman scattering to analyze 2D semiconductors, improves biomolecule autofluorescence, and offers superior stability. This scalable platform unlocks versatile applications in interdisciplinary DUV spectroscopy and emerging nanomaterials research.

Chirality (C) is a fundamental property of objects, in terms of symmetry. It is extremely important to sense and distinguish chiral molecules in the fields of biochemistry, science, and medicine. Vibrational circular dichroism (VCD) spectroscopy, obtained from the differential absorption of left- and right- circularly polarized light (CPL) in the infrared range, is a promising technique for enantiomeric detection and separation. However, VCD signals are typically very weak for most small molecules. Dielectric metasurfaces are an emerging platform to enhance the sensitivity of VCD spectroscopy of chiral molecules via superchiral field manipulation. Here, we demonstrate a dielectric metasurface consisting of achiral germanium (Ge) tetramer nanoresonators that provide a proper and accessible high C enhancement (C_E). We realize a maximum C enhancement (C_{E_max}) with respect to the incident CPL (C_{E_max} = C_max/C_RCP) of more than 750. The volume-averaged C enhancement (C_{E_ave} = C_ave/C_RCP) is 148 in the 50 nm thick region above the sample surface and 215 in the central region of the structure. Especially, the corresponding C_{E_ave} values are more than 89 and 183 even when a 50 nm thick chiral lossy molecular layer is coated on the metasurface. The metasurface benefits from geometrically achiral nanostructure design to eliminate intrinsic background chiral-optical signal from the substrate, which is useful in chiral sensing, enantioselectivity, and VCD spectroscopy applications in the mid-infrared range.