arXiv subjects

Markus A. Schmidt

Publications and source records attributed to Markus A. Schmidt.

At least 19 recordsLinked to original sources

arXiv2026

Giant Brillouin gain in frozen CS2 capillaries

Stimulated Brillouin-Mandelstam scattering offers exceptional capabilities for photonic signal processing, but current platforms demand performance trade-offs between long interaction lengths, high gain, low optical losses, and practical implementation. Here, we demonstrate a novel platform based on the reversible freezing of a carbon disulfide filled liquid-core optical fiber. This approach delivers a giant in-fiber Brillouin gain of 434 W-1m-1 with 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, as a proof of principle, we realize an optoacoustic memory operating at sub-nanojoule pulse energies - more than two orders of magnitude lower than state-of-the-art implementations. This power reduction is universal for Brillouin-based fiber applications in general and will enable low-power photonic signal processing and neuromorphic computing, efficient microwave photonics and sensing, as well as in-fiber quantum optomechanics-based technologies.

physics.optics↗

arXiv2025

Stimulated Emission from 2D CdSe/CdS Nanoplatelets Integrated in a Liquid-Core Fiber

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 achieving sufficiently effective gain for amplified spontaneous emission at a threshold as low as 1.8 kW/cm2 under quasi-CW pumping, even at a con-centration two orders of magnitude lower than the minimal concentration considered to be required for gain in conventional colloidal 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.

physics.optics↗

arXiv2025

On-chip twisted hollow-core light cages: enhancing planar photonics with 3D nanoprinting

Twisted optical fibers are a promising platform for manipulating circularly polarized light and orbital angular momentum beams for applications such as nonlinear frequency conversion, optical communication, or chiral sensing. However, integration into chip-scale technology is challenging because twisted fibers are incompatible with planar photonics and the achieved twist rates are limited. Here, we address these challenges by introducing the concept of 3D-nanoprinted on-chip twisted hollow-core light cages. We show theoretically and experimentally that geometrical twisting of light cages forces the fundamental core mode of a given handedness to couple with selected higher-order core modes, resulting in strong circular dichroism (CD). These chiral resonances result from the angular momentum harmonics of the fundamental mode, allowing us to predict their spectral locations and the occurrence of circular birefringence. Twisted light cages enable very high twist rates and CD, exceeding those of twisted hollow-core fibers by more than two orders of magnitude (twist period: 90 $μ$m, CD: 0.8 dB/mm). Moreover, the unique cage design provides lateral access to the central core region, enabling future applications in chiral spectroscopy. Therefore, the presented concept opens a path for translating twisted fiber research to on-chip technology, resulting in a new platform for integrated chiral photonics.

physics.optics↗

arXiv2025

Light Storage in Light Cages: A Scalable Platform for Multiplexed Quantum Memories

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.

quant-ph↗

arXiv2024

Impact of coordinate frames on mode formation in twisted waveguides

Off-axis twisted waveguides possess unique optical properties such as circular and orbital angular momentum (OAM) birefringence, setting them apart from their straight counterparts. Analyzing mode formation in such helical waveguides relies on the use of specific coordinate frames that follow the twist of the structure, making the waveguide invariant along one of the new coordinates. In this study, the differences between modes forming in high-contrast off-axis twisted waveguides defined in the three most important coordinate systems - the Frenet-Serret, the helicoidal, or the Overfelt frame - are investigated through numerical simulations. We explore modal characteristics up to high twist rates (pitch: 50 $μ$m) and clarify a transformation allowing to map the modal fields and the effective index back to the laboratory frame. In case the waveguide is single-mode, the fundamental modes of the three types of waveguides show significant differences in terms of birefringence, propagation loss, and polarization. Conversely, the modal characteristics of the investigated waveguides are comparable in the multimode domain. Furthermore, our study examines the impact of twisting on spatial mode properties with the results suggesting a potential influence of the photonic spin Hall and orbital Hall effects. Additionally, modes of single-mode helical waveguides were found to exhibit superchiral fields on their surfaces. Implementation approaches such as 3D-nanoprinting or fiber-preform twisting open the doors to potential applications of such highly twisted waveguides, including chip-integrated devices for broadband spin- and OAM-preserving optical signal transport, as well as applications in chiral spectroscopy or nonlinear frequency conversion.

physics.optics↗

arXiv2023

Microfluidic Filling and Spectroscopy of Colloidal CdSe/CdS Nanoplatelets in Liquid Core Fibers

Colloidal 2D semiconductor nanoplatelets are highly efficient light emitters, which exhibit large absorption and emission cross sections, and constitute promising laser gain media. However, if dispersed in solutions, such nanoplatelets lack a suitable optical platform for scalable and application-oriented integration into optical setups such as lasers. Here, we demonstrate the first successful integration of solution-processed 2D CdSe/CdS Core/Crown nanoplatelets in m-scale liquid core optical fibers. We compare the nanoplatelets' spectroscopic properties before and after filling them into the fibers and find that spontaneous emission is shifted and broadened. We even observe a first evidence of stimulated emission at high excitation energies. In conclusion, liquid core fibers constitute a novel and scalable platform for optical integration of nanoplatelets for applications as novel, highly reconfigurable laser gain medium.

physics.optics↗

arXiv2023

Metafiber transforming arbitrarily structured light

Structured light has proven useful for numerous photonic applications. However, the current use of structured light in optical fiber science and technology is severely limited by mode mixing or by the lack of optical elements that can be integrated onto fiber end-faces for complex wavefront control, and hence generation of structured light is still handled outside the fiber via bulky optics in free space. We report a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincaré sphere. Polymeric metasurfaces, with unleashed height degree of freedom and a greatly expanded 3D meta-atom library, were laser nanoprinted and interfaced with polarization-maintaining single-mode fibers. Multiple metasurfaces were interfaced on the fiber end-faces, transforming the fiber output into different structured-light fields, including cylindrical vector beams, circularly polarized vortex beams, and an arbitrary vector field. Our work provides a new paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology.

physics.optics↗

arXiv2022

Exploring extreme thermodynamics in nanoliter volumes through stimulated Brillouin-Mandelstam scattering

Examining the physical properties of materials - particularly of toxic liquids - under a wide range of thermodynamic states is a challenging problem due to the extreme conditions the material has to be exposed to. Such temperature and pressure regimes, which result in a change of refractive index and sound velocity can be accessed by optoacoustic interactions such as Brillouin-Mandelstam scattering. Here we experimentally demonstrate Brillouin-Mandelstam measurements of nanoliter volumes of liquids in extreme thermodynamic regimes. We use a fully-sealed liquid-core optical fiber containing carbon disulfide; within this waveguide, which exhibits tight optoacoustic confinement and a high Brillouin gain of (32.2 $\pm$ 0.8) 1/(Wm), we are able to conduct spatially resolved measurements of the Brillouin frequency shift. Knowledge of the local Brillouin response enables us to control the temperature and pressure independently over a wide range. We observe and measure the material properties of the liquid core at very large positive pressures (above 1000 bar), substantial negative pressures (below -300 bar) and we explore the isobaric and isochoric regimes. The extensive thermodynamic control allows the tunability of the Brillouin frequency shift of more than 40% using only minute volumes of liquid. This work opens the way for future studies of liquids under a variety of conventionally hard-to-reach conditions.

physics.optics↗

arXiv2022

An achromatic metafiber for focusing and imaging across the entire telecommunication range

Dispersion engineering is essential to the performance of most modern optical systems including fiber-optic devices. Even though the chromatic dispersion of a meter-scale single-mode fiber used for endoscopic applications is negligible, optical lenses located on the fiber end face for optical focusing and imaging suffer from strong chromatic aberration. Here we present the design and nanoprinting of a 3D achromatic diffractive metalens on the end face of a single-mode fiber, capable of performing achromatic and polarization-insensitive focusing across the entire near-infrared telecommunication wavelength band ranging from 1.25 to 1.65 um. This represents the whole single-mode domain of commercially used fibers. The unlocked height degree of freedom in a 3D nanopillar meta-atom largely increases the upper bound of the time-bandwidth product of an achromatic metalens up to 21.34, leading to a wide group delay modulation range spanning from -8 to 14 fs. Furthermore, we demonstrate the use of our compact and flexible achromatic metafiber for fiber-optic confocal imaging, capable of creating in-focus sharp images under broadband light illumination. These results may unleash the full potential of fiber meta-optics for widespread applications including hyperspectral endoscopic imaging, femtosecond laser-assisted treatment, deep tissue imaging, wavelength-multiplexing fiber-optic communications, fiber sensing, and fiber lasers.

physics.optics↗

arXiv2021

Influence of non-Hermitian mode topology on refractive index sensing with plasmonic waveguides

We evaluate the sensing properties of plasmonic waveguide sensors by calculating their resonant transmission spectra in different regions of the non-Hermitian eigenmode space. We elucidate the pitfalls of using modal dispersion calculations in isolation to predict plasmonic sensor performance, which we address by using a simple model accounting for eigenmode excitation and propagation. Our transmission calculations show that resonant wavelength and spectral width crucially depend on the length of the sensing region, so that no single criterion obtained from modal dispersion calculations alone can be used as a proxy for sensitivity. Furthermore, we find that the optimal detection limits occur where directional coupling is supported, where the narrowest spectra occur. Such narrow spectral features can only be measured by filtering out all higher-order modes at the output, e.g., via a single-mode waveguide. Our calculations also confirm a characteristic square root dependence of the eigenmode splitting with respect to the permittivity perturbation at the exceptional point, which we show can be identified through the sensor beat length at resonance. This work provides a convenient framework for designing and characterizing plasmonic waveguide sensors when comparing with experimental measurements.

physics.optics↗

arXiv2021

In-fiber second-harmonic generation with embedded two-dimensional materials

Silica-based optical fibers are a workhorse of nonlinear optics. They have been used to demonstrate nonlinear phenomena such as solitons and self-phase modulation. Since the introduction of the photonic crystal fiber, they have found many exciting applications, such as supercontinuum white light sources and third-harmonic generation, among others. They stand out by their low loss, large interaction length, and the ability to engineer its dispersive properties, which compensate for the small chi(3) nonlinear coefficient. However, they have one fundamental limitation: due to the amorphous nature of silica, they do not exhibit second-order nonlinearity, except for minor contributions from surfaces. Here, we demonstrate significant second-harmonic generation in functionalized optical fibers with a monolayer of highly nonlinear MoS2 deposited on the fiber guiding core. The demonstration is carried out in a 3.5 mm short piece of exposed core fiber, which was functionalized in a scalable process CVD-based process, without a manual transfer step. This approach is scalable and can be generalized to other transition metal dichalcogenides and other waveguide systems. We achieve an enhancement of more than 1000x over a reference sample of equal length. Our simple proof-of-principle demonstration does not rely on either phase matching to fundamental modes, or ordered growth of monolayer crystals, suggesting that pathways for further improvement are within reach. Our results do not just demonstrate a new path towards efficient in-fiber SHG-sources, instead, they establish a platform with a new route to chi(2)-based nonlinear fiber optics, optoelectronics, and photonics platforms, integrated optical architectures, and active fiber networks.

physics.optics↗

arXiv2020

Scalable functionalization of optical fibers using atomically thin semiconductors

Atomically thin transition metal dichalcogenides are highly promising for integrated optoelectronic and photonic systems due to their exciton-driven linear and nonlinear interaction with light. Integrating them into optical fibers yields novel opportunities in optical communication, remote sensing, and all-fiber optoelectronics. However, scalable and reproducible deposition of high quality monolayers on optical fibers is a challenge. Here, we report the chemical vapor deposition of monolayer MoS2 and WS2 crystals on the core of microstructured exposed core optical fibers and their interaction with the fibers' guided modes. We demonstrate two distinct application possibilities of 2D-functionalized waveguides to exemplify their potential. First, we simultaneously excite and collect excitonic 2D material photoluminescence with the fiber modes, opening a novel route to remote sensing. Then we show that third harmonic generation is modified by the highly localized nonlinear polarization of the monolayers, yielding a new avenue to tailor nonlinear optical processes in fibers. We anticipate that our results may lead to significant advances in optical fiber based technologies.

physics.app-ph↗

arXiv2020

An improved spectrophotometry tests the Einstein-Smoluchowski equation: a revisit and update

Light-matter interaction in solvents has attracted continuous attention for theoretical prediction and experimental measure, due in part to the simple curiosity to nature, and in part to increasing calls from solvent-involved applications. Yet hitherto, a majority of reliable spectrophotometric measurements on transparent solvents upon visible light end up using long-path-length cells, usually over dozens of cm, rendering the measures costly and complex; meanwhile, the guidance for choosing the best formula to describe solvent scattering has remained unsettled. Here we theoretically and experimentally demonstrate a simple, low-cost, and versatile spectrophotometric method, recording sensitivity 10-4 dB/cm over 0.5 cm differential path length based on using a standard double-beam spectrophotometer. We attest the method reduces the path length by a factor of 100 while still making its closest approach to the record-low measurements. Revisiting the present equations of solvent scattering, we unfold that they all give similar-predictive-values, revealing the criterion of choice merely on the formula's simple practicality. Following the clarification of wavelengths over which light scattering dictates the solvent's extinction, we identify that the discrepancies persist between the calculated scattering coefficients and those measured results, suggesting the need for improving solvent scattering theory to comprehend the phenomenon in greater depth.

physics.chem-ph↗

arXiv2019

Tuning the Effective PT-Phase of Plasmonic Eigenmodes

We experimentally observe an effective PT-phase transition through the exceptional point in a hybrid plasmonic-dielectric waveguide system. Transmission experiments reveal fundamental changes in the underlying Eigenmode interactions as the environmental refractive index is tuned, which can be unambiguously attributed to a crossing through the plasmonic exceptional point. These results extend the design opportunities for tuneable non-Hermitian physics to plasmonic systems.

physics.optics↗

arXiv2017

Soliton explosion driven multi-octave supercontinuum generation by geometry-enforced dispersion design in antiresonant hollow-core fibers

Ultrafast supercontinuum generation in gas-filled waveguides is one enabling technology for many intriguing application ranging from attosecond metrology towards biophotonics, with the amount of spectral broadening crucially depending on the pulse dispersion of the propagating mode. Here we show that the structural resonances in gas-filled anti-resonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, allowing for the generation of more than three octaves of broadband light ranging deep UV wavelength towards the near infrared.Our observation relies on the introduction of a geometric-induced resonance in the spectral vicinity of the pump laser outperforming the gas dispersion, thus yielding a dispersion being independent of core size, which is highly relevant for scaling input powers.Using a Krypton filled fiber we observe spectral broadening from 200 nm towards 1.7 μm at an output energy of about 23 μJ within a single mode across the entire spectral bandwidth. Simulations show that the efficient frequency generation results from a new physical effect the soliton explosion originating from the strongly non-adiabatic mode dispersion profile.This effect alongside with the dispersion tuning capability of the fiber will enable compact ultrabroadband high energy sources spanning from the UV to the mid-infrared spectral range.

physics.optics↗

arXiv2015

Fast, label-free tracking of single viruses and weakly scattering nanoparticles in a nano-fluidic optical fiber

High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber containing a sub-wavelength, nano-fluidic channel and illuminate them using the fiber's strongly confined optical mode. The diffusing particles in this cylinderical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions - 4.6 megadaltons in size - at rates of over 2 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems.

physics.optics↗

arXiv2012

Thermo-modulational interband susceptibility and ultrafast temporal dynamics in nonlinear gold-based plasmonic devices

Starting from first principles, we theoretically model the nonlinear temporal dynamics of gold-based plasmonic devices resulting from the heating of their metallic components. At optical frequencies, the gold susceptibility is determined by the interband transitions around the X,L points in the first Brillouin zone and thermo-modulational effects ensue from Fermi smearing of the electronic energy distribution in the conduction band. As a consequence of light-induced heating of the conduction electrons, the optical susceptibility becomes nonlinear. In this paper we describe, for the first time to our knowledge, the effects of the thermo-modulational nonlinearity of gold on the propagation of surface plasmon polaritons guided on gold nanowires. We introduce a novel nonlinear Schroedinger-like equation to describe pulse propagation in such nanowires, and we predict the appearance an intense spectral red-shift caused by the delayed thermal response.

physics.optics↗

arXiv2010

Emergence of geometrical optical nonlinearities in photonic crystal fiber nanowires

We demonstrate analytically and numerically that a subwavelength-core dielectric photonic nanowire embedded in a properly designed photonic crystal fiber cladding shows evidence of a previously unknown kind of nonlinearity (the magnitude of which is strongly dependent on the waveguide parameters) which acts on solitons so as to considerably reduce their Raman self-frequency shift. An explanation of the phenomenon in terms of indirect pulse negative chirping and broadening is given by using the moment method. Our conclusions are supported by detailed numerical simulations.

physics.optics↗