The realization of compact on-chip devices with spectroscopic functionality is one central goal in modern photonics. Here, we present a fiber-interfaced on-chip light cage that combines seamless single-mode fiber integration with extended light-gas interaction lengths, enabling precise quantitative gas spectroscopy. By employing two detection schemes, this work establishes the light cage as a platform for laser absorption spectroscopy, realized through 3D nanoprinting of an anti-resonant hollow-core waveguide with side access. Optical characterization and benchmarking confirm reliable gas detection at ppm-level detection sensitivity in a miniaturized format. The platform offers broad potential for applications in environmental monitoring, medical diagnostics, and quantum technologies, and provides a versatile foundation for the development of next-generation hollow-core architectures.

Efficient and selective light coupling into optical fibers is essential for applications ranging from quantum photonics to biomedical imaging, yet conventional methods are constrained by limited efficiency and poor suppression of unwanted diffraction orders. This work introduces a novel metafiber that enables angle-selective coupling into the fundamental mode of single-mode fibers within the telecom spectral range between 1260 and 1650 nm using a compact 3D nanoprinted holographic grating lens integrated directly on the fiber end face. The approach combines a binary phase grating with a tailored kinoform-type focusing profile and decouples the light-collection area from the core size, enabling a significant increase in coupling efficiency and substantial suppression of the zeroth diffraction order. High coupling efficiencies of 10%-20 at large diffraction angles (40-60), along with strong zeroth diffraction order suppression factors up to 20, are demonstrated, exceeding the performance of previously reported concepts related to light coupling at large incidence angles. The findings are supported by analytical modeling, numerical simulations, and automated optical characterization, and open new avenues for reconfigurable fiber-based systems in quantum emitter collection, angular demultiplexing, and lab-on-fiber technologies.

Understanding nanoparticle interactions at the nanoscale is essential for numerous scientific fields and applications, with waveguide-based approaches offering a promising solution. In this work, we present a fiber-integrated platform for nanoparticle tracking analysis based on a fiber-type capillary structure (hereinafter referred to as "capillary") that achieves high performance comparable to more complex microstructured fibers. By combining measurements with optical simulations, we validate light propagation and loss behavior in water-filled capillaries, showing excellent agreement with theoretical predictions. The capillary-based approach provides structural simplicity, robustness, and compatibility with fiber systems, while enabling diffraction-limited imaging and accurate determination of hydrodynamic diameters for mono- and polydisperse nanoparticle ensembles. The demonstrated platform may serve as a future foundation for the characterization of nanoscale species in confined geometries and could be relevant for applications in nanoscience, bioanalytics, and environmental analysis.

Controlling light in photonic waveguides with embedded chirality is essential for advancing emerging technologies in quantum optics, biosensing, and optical communications, yet planar-photonic integration of such chiral structures has long been limited by fabrication and design constraints. In this work, we introduce vertically nanoprinted twisted light cages (tLCs) as a new class, to our knowledge, of chiral hollow-core waveguides that combine record-high geometric twists with strong optical chirality.These waveguides support the robust formation of circularly polarized eigenmodes and exhibit record-high circular birefringence and circular dichroism, even at sub-millimeter lengths. Beyond enabling strong chiral light-matter interaction, tLCs offer a compact and versatile platform for complex light manipulation- alternative to metasurfaces and resonant structures. Their lateral core access and compatibility with planar integration pave the way for advanced polarization control and structured light applications, bridging the gap between chiral photonics and next-generation integrated photonic systems. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Abstract On-chip hollow-core waveguides enable strong light-matter interaction in gases and liquids with high integration density, yet limited side access to the core restricts their use in diffusion-driven processes. We introduce a distinct class of on-chip hollow-core waveguides that confines light in a scaffold membrane geometry composed predominantly of air, reaching cladding-openness fraction up to 80% while maintaining optical losses comparable to fully enclosed waveguides. Light guidance in the photonic scaffold is enabled by the combination of anti-resonant confinement with Bloch-mode formation in a segmented structure. High-precision 3D nanoprinting, extensive optical characterization and a resonator-based theoretical model confirm the guiding principle and loss behavior. We demonstrate application relevance through enhanced molecular diffusion, highly integrated optofluidic spectroscopy, and efficient single-photon transmission enabled by the open scaffold geometry and air-dominant guidance.

Coupling light and acoustic waves via the nonlinear optical effect of stimulated Brillouin-Mandelstam scattering offers exceptional capabilities for photonic signal processing, narrow-linewidth lasers, sensing, and material analysis. A key parameter for high performance in all these applications is the Brillouin gain. However, current platforms have to overcome the challenges of optical losses, limited interaction length, nonlinear effects, and insertion into practical setups. Here, we demonstrate a Brillouin device based on the reversible freezing of a carbon disulfide-filled liquid-core optical fiber. This approach delivers a giant in-fiber Brillouin gain of 434W −1 m −1 . Employing seeded Brillouin spectroscopy, we characterize the spectrum and find a linewidth of 24 MHz while maintaining low propagation losses in a fully spliced architecture and providing the potential for meter-scale interaction lengths. Leveraging this gain, we realize—as an example application—an optoacoustic memory operating at sub-nanojoule pulse energies—more than two orders of magnitude lower than previous implementations. This power reduction is universal for Brillouin-based fiber applications in general and will enable low-power photonic signal processing, efficient microwave photonics, and high spatial resolution sensing, as well as in-fiber quantum optomechanics-based technologies.

Colloidal nanocrystals are unique optical gain materials due to their high intrinsic absorption, excellent quantum yield, and tunable emission. However, integration of colloidal nanocrystal solutions into photonic systems for lasing applications is challenging since high concentration levels are required for optical amplification. Here, we address this challenge by integrating colloidally dispersed core/crown CdSe/CdS 2D nanoplatelets in liquid-core optical fibers as a scalable platform. The platform allowed achievement of sufficient gain for amplified spontaneous emission at a threshold as low as 1.8 kW/cm(2) under quasi-CW pumping, even at a concentration two orders of magnitude lower than the concentration levels considered to be required for gain with conventional colloidal 0D quantum dots. We show that the low-loss optical waveguiding of the fiber is crucial for efficient stimulated emission, rendering liquid-core fibers as a promising and unique platform to realize lasers based on colloidally dispersed nanocrystals.

Quantum memories are essential for photonic quantum technologies, enabling long-distance quantum communication and serving as delay units in quantum computing. Hot atomic vapors using electromagnetically induced transparency provide a simple platform with second-long photon storage capabilities. Light-guiding structures enhance performance, but current hollow-core fiber waveguides face significant limitations in filling time, physical size, fabrication versatility, and large-scale integration potential. In this work, we demonstrate the storage of attenuated coherent light pulses in a cesium (Cs) quantum memory based on a 3D-nanoprinted hollow-core waveguide, known as a light cage (LC), with several hundred nanoseconds of storage times. Leveraging the versatile fabrication process, we successfully integrated multiple LC memories onto a single chip within a Cs vapor cell, achieving consistent performance across all devices. We conducted a detailed investigation into storage efficiency, analyzing memory lifetime and bandwidth. These results represent a significant advancement toward spatially multiplexed quantum memories and have the potential to elevate memory integration to unprecedented levels. We anticipate applications in parallel single-photon synchronization for quantum repeater nodes and photonic quantum computing platforms.

Hollow‐core waveguides are central to advancing low‐loss, high‐speed light transmission, and tailored beam delivery in modern photonics. In this study, we reveal that the fundamental mode of such waveguides shows intrinsic focus‐like light concentration when coupling out to free space, without requiring any external optics, arising solely from the non‐Gaussian nature of leaky modes. Through detailed experiments and simulations, we investigate this phenomenon in both anti‐resonant hollow‐core fibers and air‐silica capillaries, demonstrating that the focus‐like light concentration behavior is a general feature of leaky waveguide systems. We further analyze its impact on inter‐fiber coupling and establish its connection to the underlying mode structure. These insights deepen the understanding of leaky mode physics in complex waveguides and open new opportunities for structured light delivery, compact fiber coupling, and efficient optical interfacing in fiber‐based and integrated photonic platforms.

Antimony trisulfide (Sb_2S_3), as an emerging material for integrated photonic devices, has attracted significant attention due to its high index, low loss, and phase-changing property in the optical regime. However, conventional lithography-based fabrication methods involve complex, time-consuming, multistep processes, rendering the photonic application of Sb_2S_3 challenging. Here, we demonstrate that positive-tone fabrication of Sb_2S_3 nanostructures using wet-etch femtosecond laser processing, a straightforward technique for the engraving of micro- and nanoscale structures, can address major fabrication challenges. The patterning mechanism and factors influencing resolution of Sb_2S_3 thin film structures deposited on quartz (transmissive) and gold (reflective) substrates are experimentally investigated and supported by theoretical modelling. Using this approach, the smallest linewidth fabricated is measured at 178 nm. Consequently, multiple test patterns are demonstrated showing versatile functionalities. Functional Fresnel Zone Plates (FZPs) with varying focal length are fabricated and characterized. This study provides a significantly simplified approach for realizing Sb_2S_3 based integrated photonic devices.

The generation of complex light beams is central to many areas of science and technology. In this work, we introduce a novel metafiber capable of simultaneously generating multiple orbital angular momentum (OAM) beams with tailored topological orders and diffraction angles. Our approach is based on high-quality on-fiber 3D nanoprinted holograms that efficiently produce multiple OAM beams with experimental results in close agreement with theoretical predictions. By integrating an innovative design strategy with advanced on-fiber fabrication and systematic characterization, we demonstrate the robustness and versatility of this metafiber platform for generating beams with helical-phase fronts. This work not only advances the understanding of structured light in fiber-integrated systems but also highlights the potential of metafibers for applications in telecommunications, quantum technologies, optical manipulation, and sensing.

Fabricating high-index materials with designed three-dimensional (3D) micro optical elements is a challenging yet exciting area of research. Here, we develop an approach to 3D print high-index nanostructures of antimony trisulfide (Sb 2 S 3 ) using grayscale electron beam lithography (g-EBL). A key advantage of our approach is its simplicity compared to the conventional complex EBL-based metalens fabrication process. The refractive index of Sb 2 S 3 films is precisely determined using a computational genetic algorithm and the transfer matrix method. The Sb 2 S 3 structures show high fidelity and reproducibility, with the refractive index being tunable through thermal treatment. We demonstrate the fabrication and performance of 3D Fresnel Zone Plates (FZPs) and metalenses with the same design specification. Theoretical and experimental evaluation confirmed the diffraction-limited capability of as-fabricated 3D optical elements and indicates that the focusing efficiency of FZPs is higher compared to metalenses. This work advances the application of Sb 2 S 3 in micro- and nanoscale photonics, highlighting its potential for dynamic optical devices with precise control over output properties.

We present a novel on-chip hollow-core waveguide design featuring a three-channel architecture that operates via the anti-resonant effect. The design incorporates symmetrically arranged thin membranes that create an enhanced reflective environment, achieving superior waveguiding performance over conventional approaches. Through numerical simulations and experimental validation using 3D vertical nanoprinting, we demonstrate low optical losses, smooth spectral transmission, and suppression of structure-induced birefringence while additionally revealing an interchannel coupling mechanism arising from the multi-channel architecture. Our findings establish a promising platform for applications in bioanalytics, quantum technologies, and life sciences while offering new possibilities for exploring complex cladding structures in hollow-core fiber design.