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Friday 18 September

Optics

All-optical spin-selective control and shaping of frequency conversion pathways

Xiaoxi Xu, Mai Tal, Danielle Ben-Haim et al. (+1 more)

The interplay between optical spin and crystal symmetry provides a powerful mechanism to control light-matter interaction, enabling advances in imaging, holography, sensing, signal processing, and more. Here we reveal that this interplay can also be exploited as a programmable mechanism for selecting and shaping nonlinear frequency-conversion pathways. Using a z-cut lithium niobate thin film, we experimentally demonstrate spin-selective switching between complementary three-wave mixing pathways, where co- and cross-circular-polarization excitations activate sum- and difference-frequency generation, respectively. We further generalize this concept to establish a quantitative spin-to-frequency mapping, that encodes the pump spin composition into the generated frequencies, and enables the reverse retrieval of the pump spin state. Finally, we leverage this concept also to demonstrate mapping of spin patterns to a combination of frequency-dependent real space images, and Fourier-space diffraction patterns. These results pave the way for all-optical programable frequency-conversion and spatiotemporal nonlinear signal manipulation in free-space and integrated photonic systems.
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All authors Xiaoxi Xu, Mai Tal, Danielle Ben-Haim, Tal Ellenbogen

Optics · Cross-listed from quant-ph

Cavity-QED analysis of InAs quantum-dot single photon production

W. W. Chow, S. Peana, D. I. Herman et al. (+6 more)

Cavity quantum electrodynamics is used to study the extent cavity enhancement affects single photon performance of an InAs quantum dot, in terms of emission rate, purity and indistinguishability at different temperatures. Parametric studies show a tradeoff between single photon production rate and purity, as well as between indistinguishability and purity. The results indicate the importance of quantum carrier-photon correlations that yield substantial corrections to mean-field treatments, especially at high light-matter coupling strength, where cavity enhancement is most effective.
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All authors W. W. Chow, S. Peana, D. I. Herman, K. Y. Lee, A. Cejan, C. Shang, G. Moody, J. E. Bowers, F. Jahnke

Optics

Optical Mode Sorting with a Programmable Diffractive Neural Network

Qian Zhang, Shiyue Chen and Juergen W Czarske

Programmable diffractive optical processors are particularly attractive for spatial light manipulation because their optical transformations can be dynamically reconfigured and adapted without modifying the physical hardware. However, their practical performance is often limited by the gap between simulation and experiment caused by optical aberrations, alignment errors, and nonideal phase responses. In this paper, we introduce a hybrid optimization framework that combines high-dimensional numerical design with low-dimensional hardware-in-the-loop calibration, enabling programmable diffractive optical networks to compensate experimentally for mismatch without retraining their underlying optical transformations. We demonstrate a programmable optical diffractive neural network (ODNN) designed by back-propagation to spatially sort six linearly polarized modes supported by a multimode fiber. The experimental distortions are represented using a truncated Zernike basis with only 19 correction coefficients per layer. These coefficients are optimized directly on the physical system using stochastic parallel gradient descent, avoiding re-optimization of the full pixelated phase masks. Experimentally, the proposed calibration yields an SNR improvement of approximately 3.26 dB, and a decrease in amplitude error of 0.04. This separation of high-dimensional optical-function design from low-dimensional physical calibration provides a scalable route towards adaptive and reconfigurable spatial-mode processors for optical router on spatial modes and wavelengths, programmable photonic computer systems and quantum information processing.
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Optics

All-Optical Control over Nonlocality for Ultrafast Image Processing with an Excitonic Metasurface

Bernardo S. Dias, Romain Tirole, Michele Guizzardi et al. (+4 more)

Image processing lies at the foundation of many modern technologies, such as augmented reality and autonomous driving, yet conventional digital approaches remain energy-intensive and limited in speed. Nonlocal metasurfaces - 2D structures engineered at the nanoscale to support delocalized, dispersion engineered resonances - provide a fast, energy-efficient and ultrathin platform to perform image processing directly on the light path. Introducing tunability in this platform is an outstanding challenge, and would enable dynamic real-time control over the implemented processing operation, facilitating flexible integration into adaptive and multifunctional photonic architectures. Here, we demonstrate optically tunable edge detection at ultrafast speeds by integrating a dielectric nonlocal metasurface with multilayer WS2, whose strong exciton-driven optical response enables dynamic control of the metasurface nonlocality at sub-ps speeds. Using resonant optical pumping of the A-exciton in WS2, the metasurface transfer function is rapidly switched from edge detection to bright-field imaging by tuning its spatial nonlocality. Operating in the visible spectral range at a wavelength around 700 nm, the device shows ultrafast switching times and reaches an amplitude modulation depth of 11.5 dB for normal incident light. This approach provides a reconfigurable, ultrathin, all-optical platform for adaptive optical computing systems and highlights the potential of the highly nonlinear properties of 2D materials for active metasurfaces at ultrafast speeds.
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All authors Bernardo S. Dias, Romain Tirole, Michele Guizzardi, Andrea Cordaro, Albert Polman, Andrea Alù, Jorik van de Groep

Optics

Momentum microscopy of a holey nanostructure

Kerstin Harland, Julia Altenburg, Xiaofei Wu et al. (+10 more)

Momentum microscopy records the three-dimensional momentum distribution of photoelectrons emitted from a solid sample and, by utilizing sufficiently high photon energies in the ultraviolet spectral range, offers direct access to the electronic band structure of a material. By employing a pump-probe scheme, this method provides a femtosecond view of light-matter interaction and the subsequent relaxation and transport dynamics in a broad range of material systems. However, momentum microscopy has so far been mostly limited to flat and spatially extended surfaces. Photoelectron emission from different three-dimensional facets, in combination with inhomogeneous electric fields around these structures, makes the analysis of the momentum distribution significantly more challenging. Here, we extend the state-of-the-art to a substantially more complex structure and show that a careful analysis of the electron distribution recorded with a momentum microscope provides rich information about both the spatial and momentum distributions on a few-nm and few-mÅ$^{-1}$ scale, respectively. Combined with prior knowledge of the three-dimensional structure, momentum-resolved photoelectrons can be assigned to nano-localized emission spots, permitting a new level of insight into spatio-temporal charge carrier dynamics.
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All authors Kerstin Harland, Julia Altenburg, Xiaofei Wu, Zsuzsanna Pápa, Leon David Schwarz, Lina Hansen, Katrin Meier, Arvid Klösgen, Bert Hecht, Germann Hergert, Péter Dombi, Jer-Shing Huang, Jan Vogelsang

Optics

Quantized Transport of Gap Solitons in the Harper-Hofstadter Model

Oliver Ashfield, Henry Davenport, Tom Sheppard et al. (+6 more)

We investigate the dynamics of gap solitons found in the Harper-Hofstadter model with an additional cubic nonlinearity, such as that describing weakly-interacting cold atoms or a Kerr nonlinearity in an optical platform. We find that certain solitons with frequencies deep in the band gap travel with a robust, quantized velocity perpendicular to the applied force and maintain their spatial profile over long timescales. Crucially, this velocity is linearly proportional to the applied force, allowing for arbitrary steering of the nonlinear wavepacket, without breakdown, using only a tunable external force. This quantized transport persists despite a highly non-uniform occupation of the linear Bloch states, and contrasts with solitons near the band edge, which deform and delocalize under the same force. These results point to a robust and highly controllable mechanism for steering nonlinear solitons in experimentally accessible platforms.
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All authors Oliver Ashfield, Henry Davenport, Tom Sheppard, David G. Reid, Holly A. J. Middleton-Spencer, A. C. Berceanu, Frank Schindler, Iacopo Carusotto, Hannah M. Price

Optics

Performance of Capacitively Loaded RF Electrodes on SiO2/Si Substrates for High-Speed Electro-Optic Modulators

Ayed Sayem, Ting-Chen Hu, Mark Cappuzzo et al. (+3 more)

We experimentally investigate conventional and capacitively loaded traveling-wave RF electrodes fabricated on thermally grown SiO$_2$ on high-resistivity silicon substrates for high-speed electro-optic modulators. The capacitively loaded electrodes exhibit RF attenuation coefficients as low as approximately $0.23~\mathrm{dB/cm}/\sqrt{\mathrm{GHz}}$, comparable to values reported for electrodes fabricated on insulating quartz substrates, while retaining the silicon handle and avoiding substrate removal or undercut processing. By varying the SiO$_2$ buried-oxide (BOX) thickness and the capacitive-loading geometry, the microwave effective index can be engineered over a broad range while maintaining low RF propagation loss. This enables microwave-optical velocity matching over a wide range of optical wavelengths, from the ultraviolet to the telecom C-band. These results demonstrate that thermally oxidized silicon provides a simple and scalable substrate platform for low-loss traveling-wave electrodes in thin-film lithium niobate and thin-film lithium tantalate electro-optic modulators, as well as for high-speed RF interconnects in integrated transceivers and co-packaged optical systems.
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All authors Ayed Sayem, Ting-Chen Hu, Mark Cappuzzo, Alaric Tate, Rose Kopf, Mark Earnshaw

Optics · Cross-listed from quant-ph

Parameter-Decoupled Quantum Superresolution without Multiparameter Estimation

X.-F. Qian

Quantum superresolution promises to resolve closely spaced sources beyond the diffraction limit, but existing approaches generally rely on idealized source properties or require simultaneous estimation of multiple coupled parameters of realistic sources. Here we introduce a parameter-decoupled measurement that determines the separation of realistic passive sources without estimating their unknown brightness imbalance, mutual coherence, or relative phase. A complete four-parameter quantum Fisher information analysis identifies the separation information that remains accessible in the presence of these nuisance parameters. We then construct a directly measurable log-probability invariant from projection channels whose conditional statistics depend only on the separation. Broad classes of channel pairs satisfy the resulting decoupling condition. For a Gaussian point-spread function, the lowest-order implementation asymptotically attains the four-parameter quantum limit per incident signal in the sub-Rayleigh regime. This approach converts a realistic multiparameter imaging problem into an operationally single-parameter measurement, providing a practical route toward quantum-enhanced resolution of passive spatial, temporal, and spectral signals.
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Optics

When Integrated Photonics Should Be Wavy

Oliver R. Müller, J. J. Erik Maris, Yannik M. Glauser et al. (+2 more)

Increasing demand for high-performance optical devices drives the search for improved fabrication and design paradigms. While photonic circuits have traditionally used structures with two discrete 'binary' height levels, grayscale 'wavy' interfaces, or optical Fourier surfaces, have recently become possible. They provide precise control over the Fourier components that govern the optical response. This capability raises the question: When does a wavy device improve performance and why? Here, we show that wavy integrated processors exhibit superior accuracy and efficiency to binary analogs. Inverse-designed wavy interferometers have the design freedom to minimize outscattering to free space and backreflections. They reach a five-fold lower transmission error than binary counterparts and enable bandwidths up to 300 nm. We formalize these findings for other distinct integrated devices, such as photonic crystals, nanocavities, and beam emitters. A Fourier-optics analysis identifies a trade-off: wavy profiles manipulate light more accurately, whereas binary profiles excel in interaction strength. As such, tailored wavy profiles emit high-quality beams. However, binary profiles remain preferable in photonic crystals and nanocavities, where maximal index contrast is required and binarization-induced higher harmonics are benign. Thus, for quantum information, optical computing, and sensing, optical Fourier surfaces offer a route to miniaturized integrated circuits with improved performance.
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All authors Oliver R. Müller, J. J. Erik Maris, Yannik M. Glauser, Sander J. W. Vonk, David J. Norris

Optics

Symmetry Properties of Bound States in the Continuum in Hexagonal Lattice Photonic Crystal Slabs

Rhys Jones and Sang Soon Oh

Bound states in the continuum (BICs) within photonic crystal (PhC) cavities realise the full confinement of light despite lying within the continuum of radiation modes. While their diverse practical applications has attracted considerable research interest, developing the fundamental understanding of BICs is important for the design of future devices. This paper uses a group theoretical approach to determine the basis functions of the irreducible representations (irreps) of a PhC with the symmetry of the $C_{6v}$ space group, from which the spatial distribution of the electromagnetic fields within the cavity can be determined. Furthermore, the reflection parity of the electric field and a $k \cdot p$ perturbation theory approach are used to determine the far-field polarisation of each irrep. The $k \cdot p$ perturbation explains why the $E_2$ irrep has a topological charge of $-2$, as well as showing that a topological charge does not necessarily indicate the presence of a BIC. Additionally, it is found that the quality factor of the modes do not necessarily scale as $Q \propto 1/|k|^{2|q|}$, but are instead dependent on the coupling to the radiative mode in the $k \cdot p$ perturbation, which is determined from the symmetry of each irrep.
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Optics

Programmable Intrinsic Circularly Polarized Emission

Yujie Jiao, Zhenqin Li, Yide Chang et al. (+11 more)

Circularly polarized luminescence (CPL) is central to chiral photonics, yet programming circularly polarized emission at the nanoscale remains challenging. Here, we program intrinsic CPL at its microscopic origin in laser-written all-inorganic perovskite nanocrystals embedded in glass. High-resolution transmission electron microscopy reveals a core-shell-like variation in interplanar spacing associated with intrinsic CPL, consistent with torsional lattice distortion. The torsional lattice distortion breaks inversion symmetry, while density functional theory calculations show that it lifts the spin degeneracy of the band-edge electronic states. Power-dependent measurements further reveal a transition from birefringence-mediated circular polarization to intrinsic CPL, accompanied by the emergence of a distinct core-shell-like lattice distortion in the nanocrystals. By tuning the incident linear polarization angle and focal depth, we deterministically control both the handedness and magnitude of the intrinsic CPL, with |glum| of approximately 4 ^ 10^-3. These results show that programmable intrinsic CPL originates from the structural and electronic properties of the emitting nanocrystals, enabling circularly polarized emission to be controlled at its microscopic origin and spatially encoded within a monolithic material.
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All authors Yujie Jiao, Zhenqin Li, Yide Chang, Yongsen He, Xiaoyu Sun, Wei Lyu, Jiayu Ding, Zhaolin Zhong, Puxin Yang, Chi Chen, Bangjie Song, Min Qiu, Yanming Wang, Siying Peng

Optics

Frequency-swept Brillouin spectroscopy

Lin Kang, Shahrin Jahan Jaima and Jitao Zhang

Spontaneous Brillouin microscopy provides non-contact access to the viscoelastic properties of materials. Standard measurements typically utilize a single-wavelength continuous-wave laser to illuminate a specimen and excites a spontaneous Brillouin scattering signal, which is then recorded by a spectrometer. Existing Brillouin spectrometers are mostly built around either a scanning Fabry-Pérot etalon or a virtually imaged phased array (VIPA) etalon. While performing well, these setups are bulky and demand significant optical expertise to construct and maintain. Here, we propose a new approach to conducting Brillouin spectroscopy. In this approach, a frequency-swept laser excites a series of Brillouin spectra with incrementally shifted central frequencies, while a frequency picker, consisting of a narrow bandpass filter and a highly sensitive single-photon detector, sequentially records each spectral component to reconstruct the full spectrum. We demonstrate that the frequency-swept Brillouin spectroscopy can run under shot-noise limited condition using standard samples. Compared with conventional spectrometers, our system features a much more compact design for portable applications and holds potential for rapid mechanical imaging through multiplexing.
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Optics

Mechanical Activation of Terahertz Tunneling in Metallic Nanogaps

Dasom Kim, Dukhyung Lee, Young-Mi Bahk et al. (+1 more)

Metallic nanogaps concentrate terahertz (THz) fields into deep subwavelength volumes and support field-driven electron tunneling when the insulating barrier becomes sufficiently narrow. Here, we demonstrate mechanical control of tunneling-mediated nonlinear THz transmission in a flexible nanogap metasurface. The metasurface consists of Au/PMMA/Au nanogaps fabricated on a polyethylene terephthalate substrate, enabling continuous tuning of the gap geometry through macroscopic bending. In the flat state, the resonant transmission exhibits only a weak dependence on the incident THz field strength. Upon bending, increasing the incident field strength induces pronounced resonance suppression accompanied by saturation of the voltage developed across the nanogaps. This nonlinear response is consistent with the opening of a field-dependent tunneling conduction channel through the mechanically narrowed PMMA barriers. Simmons-model calculations illustrate the strong increase in tunneling current density and the associated dissipative gap response as the local gap width approaches the few-nanometer regime. These results establish mechanical deformation as a macroscopic means of controlling tunneling-mediated THz nonlinearities in flexible metasurfaces.
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All authors Dasom Kim, Dukhyung Lee, Young-Mi Bahk, Dai-Sik Kim

Optics · Cross-listed from cond-mat.mes-hall

Rydberg excitons in core-shell nanostructures I. Optical properties

Sylwia Zielińska-Raczyńska, Gerard Czajkowski and David Ziemkiewicz

Optical properties of Cu$_2$O-metal core-shell nanostructures containing Rydberg excitons are examined. Calculations of electron and hole eigenfunctions and eigenenergies are used to calculate exciton energy and its dependence on system geometry and dimensionality. The limits of very small and very large structures are discussed, making the results applicable to low principal quantum number excitons as well as to Rydberg states. The Real Density Matrix Approach method is used to calculate the optical properties of the studied systems.
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Optics

Topological characterization of a reconfigurable synthetic-frequency SSH lattice on an integrated lithium-niobate platform

Hiep Xuan Dinh, Armandas Balčytis, Guanghui Ren et al. (+3 more)

Synthetic frequency dimensions provide a powerful and highly reconfigurable platform for topological photonics. However, experimentally identifying their topological phases remains challenging because these systems do not naturally provide well-defined boundaries or readily accessible edge-state signatures. Here, we realize a reconfigurable Su-Schrieffer-Heeger (SSH) lattice in a synthetic frequency dimension using an integrated thin-film lithium-niobate photonic molecule and directly measure its topology. Electro-optic coupling between staggered resonator supermodes enables independent control of the effective intra-cell and inter-cell hopping strengths, enabling dynamic switching between trivial and non-trivial topological phases on the same chip. We validate the transition through two independently derived bulk topological invariants: direct retrieval of Zak phase from time-resolved synthetic-dimension band-structure spectroscopy; and extraction of the winding number using mean-chiral-displacement method from site-resolved steady-state measurements. Both approaches consistently identify the topological transition and agree closely with theoretical predictions. Our results demonstrate experimentally accessible, boundary-independent methods for characterizing topology in synthetic-frequency lattices. More broadly, the integrated and dynamically reconfigurable photonic platform provides a scalable framework for bulk topological characterization and programmable topological photonic systems.
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All authors Hiep Xuan Dinh, Armandas Balčytis, Guanghui Ren, Mei Xian Low, Arnan Mitchell, Thach G. Nguyen

Optics

Topological Optical Frequency Combs

Rujiang Li and Wenfu Zhang

Optical frequency combs (OFCs) are revolutionary light sources characterized by discrete and equally spaced spectral lines, and they have found widespread applications in metrology, spectroscopy, and communications. In the early stages, OFCs were realized using mode-locked lasers. With advancements in the fabrication of high-quality factor ($Q$) microresonators and the increasing demand for miniaturized and integrable photonic chips, microresonator-based OFCs, commonly referred to as microcombs, have been developed. Although early studies of microcombs primarily focused on single microresonators or a few resonators, a significant breakthrough occurred in 2021 when it was theoretically predicted that light propagating in the topological edge channel of an array of ring resonators could generate nested frequency combs known as topological OFCs. Since then, the field of topological OFCs has progressed rapidly, with experimental observations made in 2024. This Perspective will introduce the history of OFCs, placing particular emphasis on the emergence and development of topological OFCs, as well as exploring the research challenges and opportunities associated with them.
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Optics · Cross-listed from physics.app-ph

Multiplexing approaches to thermoradiative signatureless communications

Valerii Radchenkov, Peter J. Reece, Stephen P. Bremner et al. (+2 more)

Using mid-infrared emission from semiconductor devices for covert communications remains a relatively unexplored and yet promising opportunity. The phenomenon of negative luminescence allows for a method of signatureless covert communications where the net infrared emission of an emitting optoelectronic device is balanced to be identical to the ambient thermal background. In this work we provide a practical demonstration of covert data transfer over a thermoradiative channel with data rates up to 100 kbps. In addition, we demonstrate several additional multiplexing techniques that make the proposed thermoradiative communications method more secure against interception by achieving zero instantaneous optical emission, while remaining detectable if a sufficiently spatially or spectrally discerning observation is utilised. Finally, we discuss various application scenarios in which the proposed methods can be used to achieve secure signatureless communications.
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All authors Valerii Radchenkov, Peter J. Reece, Stephen P. Bremner, Nicholas J. Ekins-Daukes, Michael P. Nielsen

Optics

Metasurface-integrated VCSEL designed for polarization control in optical Ising machines

Wenjie Chen, Zifeng Yuan, Hong-Lin Lin et al. (+4 more)

The orthogonal polarization states of vertical-cavity surface-emitting lasers (VCSELs) can be used to describe candidate solutions to the Ising Hamiltonian, which is useful for solving quadratic unconstrained binary optimization problems. However, the natural anisotropy of VCSELs tends to overly favor one polarization state, which impedes the system from working as desired. In this work, we have designed and fabricated a metasurface, which may lead to a VCSEL with reduced undesired anisotropy. By changing the geometric size of nano-structures in the metasurface, the polarization state of the output light can be altered. Based on the injection-locking theory and spin-flip model, we numerically show that VCSELs with lowered anisotropy are more easily affected by the injection locking needed in Ising systems. Additionally, we numerically study the evolution of a 3-bit VCSEL-based Ising system and verify that the computational accuracy of the photonic Ising machine can be improved to more than twice that of its counterpart with higher anisotropy.
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All authors Wenjie Chen, Zifeng Yuan, Hong-Lin Lin, Luo Qi, Jiaru Chu, Aaron Danner, Yuhang Chen

Thursday 17 September

Optics

RTLViT: real-time lensless reconstruction with a lightweight vision transformer

Leyla A. Kabuli, Vasilisa Ponomarenko and Laura Waller

Mask-based lensless imagers capture measurements using simple, compact hardware and recover images using a reconstruction algorithm. The reconstruction algorithm affects the image quality, inference speed, and computational requirements of the imaging system, often trading off image quality against computational efficiency. Advancing toward integrated lensless imagers, where encoding and reconstruction occur within a single device (e.g., a mobile phone), requires a fast, high-quality, and practical reconstruction method. We introduce the Real-Time Lensless Vision Transformer (RTLViT), a lightweight, purely data-driven reconstruction architecture for high-quality and real-time lensless reconstruction. With only 1.09 million learnable parameters, RTLViT provides higher-quality reconstructions than both real-time baselines and substantially larger attention-based architectures, including improvements of up to 3.46 dB in peak signal-to-noise ratio over architectures with $15 \times$ more learnable parameters. We demonstrate that RTLViT maintains high-quality reconstructions across a wide range of training dataset sizes and two different mask designs (lenslets and a diffuser). Finally, we implement real-time reconstruction with RTLViT on laptops and smartphones, supporting future integrated lensless imagers for real-time applications.
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Optics

Generation of Stable Peak-Power Similaritons through Gain-Managed Nonlinearity

Haoyuan He, Maksim Kozlov, Alexander Gabriel Loehr et al. (+3 more)

Fiber lasers and amplifiers offer attractive alternatives to conventional solid-state systems. However, generation of high-energy ultrashort laser pulses in fibers faces challenges due to the complex interplay of multiple nonlinear effects arising due to pulse confinement within a small fiber core and also limitations imposed by the gain bandwidth of the available active fibers. The discovery of self-similar amplification and gain-managed nonlinear amplification (GMNA) pulse propagation regimes in fibers with normal dispersion suggests that these challenges can be turned into an advantage. Here we show that pulses generated in the GMNA regime are, in fact, the realization of the idealized similariton-type pulses in realistic fibers with limited gain bandwidth. Our analytical and numerical results show how one should shape the fiber gain as a function of propagation length to achieve constant peak power similariton-like pulses with steadily increasing energy, the pulse bandwidth exceeding the gain bandwidth, and the nearly linear frequency chirp allowing for efficient pulse compression to its Fourier limit. Absent Raman nonlinearities, these pulses can reach $\mu$J level energies in standard single-mode fibers, representing a tenfold increase in pulse energy compared to the best currently available nonlinear amplifiers. Our results have significant implications for the fundamental understanding of nonlinear wave dynamics and for the advancement of fiber laser technology, supporting the reliable generation of high-energy pulses for practical use in areas such as micromachining, metrology, and bioimaging.
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All authors Haoyuan He, Maksim Kozlov, Alexander Gabriel Loehr, Peng Gao, Misha Ivanov, Pavel Sidorenko

Optics · Cross-listed from cs.CV

Image-Derived PM10 Estimation in Cattle Feedlot Using Machine Learning: Addressing Concentration Ranges Beyond Existing Digital Imaging Methods

Sirapoom Peanusaha, Greg B. Ferguson, K. Jack Bush et al. (+2 more)

Affordable dust monitoring remains a pressing need for the cattle feedlot industry, yet camera-based PM estimation, despite its growing body of research in urban air quality settings, has not been evaluated under the extended concentration ranges characteristic of intensive livestock operations. This study developed an image-based approach using contrast panel features and machine learning to estimate PM10 concentrations in a commercial cattle feedlot, where hourly average PM10 ranged from 250 to 1,000 ug/m^-3 and instantaneous concentrations reached 5,000 to 20,000 ug/m^-3. Grayscale images were captured during the evening dust peak period, and features including panel contrast, black and white panel pixel values, and overall image brightness were extracted. The model also incorporated recent past values from preceding images and solar zenith angle as predictors. Among the candidate models evaluated, XGBoost achieved the highest predictive performance, with an R^2 of 0.792 and a median absolute error of 103 ug/m^-3. Feature importance analysis revealed that (a) panels positioned farthest from the camera contributed most strongly to predictions and (b) that black panel pixel values were more sensitive than white panel values to changes in PM10 concentration. Prediction accuracy during the sunset transition, which coincides with the onset of the feedlot evening dust peak, remains an area for further refinement. These findings demonstrate the feasibility of image-based PM10 estimation across PM concentration ranges substantially exceeding those reported in prior urban studies and provide practical guidelines for future deployment in feedlot environments.
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All authors Sirapoom Peanusaha, Greg B. Ferguson, K. Jack Bush, Peiyang Li, Brent W. Auvermann

Optics

Phase-Flow Topology of Bound States in the Continuum

Nikolai A. Vlasov, Varvara P. Panurchenko, Ravshanjon Kh. Nazarov et al. (+3 more)

Control of topological charges of bound states in the continuum (BICs) is essential for advanced topological photonics. A rigorous theoretical framework for understanding the formation of these charges is therefore necessary for further progress in this field. However, conventional multipolar formalism often fail to predict the topological charge when no single multipole dominates the mode. To address this fundamental issue, we present a rigorous dynamical systems framework for describing formation of topological charges. This attitude provides a direct link between polarization vortex and the local structure of the vector polarization field. Within the proposed framework, we challenge the established identification of the topological charge with the Hopf index of the dominant multipole and demonstrate the significant role played by derivatives of the multipolar coefficients in determining the charge. Our theoretical framework is validated within semi-analytical multipolar decompositions and full-wave numerical simulations of periodic dielectric metasurfaces. Furthermore, we show how the symmetry of the unit cell influences the local structure of the polarization field around BIC and identify the necessary conditions for the formation of high topological charges. Our findings provide a more rigorous basis for analysing BICs' topological properties, paving the way for advanced applications in topological photonics.
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All authors Nikolai A. Vlasov, Varvara P. Panurchenko, Ravshanjon Kh. Nazarov, Stanislav S. Baturin, Ekaterina E. Maslova, Zarina F. Kondratenko

Optics

Physics-aware hyper-reduction for full-vector photonic waveguide mode solvers

Daniel Rodríguez-Guillén and Lorena Velázquez-Ibarra

Photonic waveguide design often requires repeated full-vector Maxwell eigenmode solves over wavelength and geometry, where the subpixel smoothing needed at dielectric interfaces makes operator assembly a substantial part of the cost. We present a physics-aware hyper-reduction framework for accelerating this assembly. The method exploits an exact affine dependence of the discrete operators on the locally sampled inverse-permittivity tensor, and chooses its strategy from how a parameter acts on the interface cells. We demonstrate two regimes. In wavelength sweeps at fixed geometry, tensor values change on a fixed set of cells, and proper orthogonal decomposition with matrix discrete empirical interpolation reproduces the operators from few snapshots. In moving-boundary sweeps, interface information relocates across the grid, and event-driven dynamic local sampling updates only the coefficients a geometric step changes, reproducing full assembly exactly. These results show that operator assembly can be reduced by more than an order of magnitude without approximating the moving boundary, shifting the cost of a photonic mode sweep to the eigensolver.
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Optics

Volumetric Evanescent Edge Coupling for Fiber-to-Chip Optical I/O

Hamdy Elshehaby, Omar Bakheet, Mohamed A. Swillam et al. (+1 more)

Scaling optical input/output for co-packaged optics is limited by the fiber-to-chip interface. Conventional edge coupling offers low loss and broad bandwidth but confines channels to a single row along the chip facet. On the other hand, surface couplers are either narrowband or difficult to fabricate with high yield and, importantly, compete with back-end metal routing. In this work, we introduce volumetric edge coupling, in which the chip edge is structured in three dimensions so that optical coupling can occur over a two-dimensional region rather than along a single line, providing a route toward interfacing multiple waveguides with multiple cores of a multicore fiber while preserving optical access from the chip perimeter. We investigate a single-channel realization based on total-internal-reflection (TIR)-mediated evanescent coupling through the 54.7$^\circ$ sidewall of a KOH-etched silicon cavity, with the coupling profile shaped by a wedged buried-oxide ridge. Finite-difference time-domain simulations predict a peak coupling efficiency of 88% (-0.56 dB) at 1550 nm and a 1-dB bandwidth of 86.45 nm spanning the C-band. The design further exhibits a vertical alignment tolerance of approximately $\pm$2 $\mu$m, weak sensitivity to transverse offsets up to 5 $\mu$m, and a $\pm$0.8$^\circ$ 1-dB angular tolerance. The reflected optical field also provides a potential alignment signal, offering a path toward reduced active alignment overhead in future multicore implementations.
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All authors Hamdy Elshehaby, Omar Bakheet, Mohamed A. Swillam, Mohamed Elkabbash

Optics

A Simplified Model for Linear Mode Coupling in Multimode Fibers with Experimental Assessment

Paolo Carniello, Filipe M. Ferreira, Fabio A. Barbosa et al. (+2 more)

We propose a novel surrogate model for linear coupling in graded-index multimode fibers that is computationally more efficient than existing models, and can be tuned through a single measurable parameter. The model is benchmarked numerically and experimentally on a 90-polarization-mode fiber.
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All authors Paolo Carniello, Filipe M. Ferreira, Fabio A. Barbosa, Ming-Jun Li, Norbert Hanik

Optics

Quantum Battery Enhancement via Degenerate Optical Parametric Amplifier and Common Reservoirs

Y. Y. Yang, H. N. Liu, Gangcheng Wang et al. (+2 more)

We investigate a nonreciprocal quantum battery in which the charger and battery share one or two common reservoirs, with the charger driven by a degenerate optical parametric amplifier (DOPA). Reservoir-mediated dissipative interactions enable directional energy transfer, while the DOPA provides additional parametric am plification. We show that, in the stable below-threshold regime, the DOPA can enhance the battery energy and average charging power, with the nonlinear gain and pump phase providing effective control of the charging dynamics. Further optimization of the dissipative-coupling asymmetry improves the stored energy. These fea tures persist for both single- and two-common-reservoir configurations, demonstrating a tunable strategy for enhancing open-system quantum-battery charging.
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All authors Y. Y. Yang, H. N. Liu, Gangcheng Wang, T. Z. Luan, H. Z. Shen

Optics

High-order correlations and ultrafast Wigner negativities in bright-squeezed-vacuum-driven high-harmonic generation

Sebastián de-la-Peña, Heiko Appel, Marcelo F. Ciappina et al. (+2 more)

High-harmonic generation (HHG) is a prototypical strong-field process in which intense light drives matter to emit radiation at integer multiples of the driving frequency. Extending HHG into the quantum-optical regime offers new opportunities to probe and control strongly nonlinear light-matter interactions using nonclassical states of light. Yet describing this regime requires a fully quantum treatment of the correlated electron-photon dynamics, which becomes computationally challenging for broadband, strongly squeezed fields. Here we solve the quantum-electrodynamical dynamics of a two-level system driven by bright squeezed vacuum in a converged multimode Hilbert space. Both the driving field and emitted harmonics are fully quantized, with the light-matter interaction treated nonperturbatively. This enables direct access to the multimode quantum state and its higher-order correlations beyond semiclassical sampling or perturbative descriptions. We show that squeezed-vacuum driving produces harmonic emission with qualitatively distinct second- and third-order photon correlations compared with coherent excitation. Moreover, back-action from the driven emitter strongly reshapes the incident squeezed field, generating pronounced Wigner-function negativities that evolve on attosecond timescales. Our results establish a fully quantum framework for broadband strong-field dynamics with squeezed light and provide a route to predicting and interpreting quantum-HHG experiments and their extension to more complex emitters.
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All authors Sebastián de-la-Peña, Heiko Appel, Marcelo F. Ciappina, Ofer Neufeld, Angel Rubio

Optics

Path-Integrated Polarization Rotation Signatures in Subsea Networks: Cable Geometry Effects in 2023 Turkey Earthquakes

Mohammad M. Hosseini, Miquel Masanas, Giuseppe Parisi et al. (+5 more)

We analyze polarization data streamed from a commercial coherent transponder, used in MedNautilus link, during 2023 Turkey earthquakes. We show how earthquake features and cable geometry fundamentally govern the optical polarization response, taking the first steps for detailed interpretation in designing fiber-based seismic sensing systems.
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All authors Mohammad M. Hosseini, Miquel Masanas, Giuseppe Parisi, Wesley Braga Melo, Alberto Marullo, Danilo Decaroli, Sergei K. Turitsyn, Antonio Napoli

Optics · Cross-listed from quant-ph

Noise-Robust Quantum State Characterization for Remote State Preparation with Deep Learning

Bo Tang, Zixuan Liao, Hao Li et al. (+9 more)

Quantum communication underpins secure information processing and scalable quantum networks. In particular, remote state preparation (RSP) enables efficient quantum state transfer, but accurately estimating target states under complex noise remains challenging. Here, we propose a Transformer-based Quantum State Characterizer (TQSC) model for noisy RSP experiments. Our model reconstructs experimentally prepared pure and mixed photonic polarization states from noisy measurements in complex scattering environments, while its attention patterns provide physically grounded insights into correlations among the measured observables. The method achieves a mean estimator-target fidelity exceeding 99.999% under complex scattering and dynamic Gaussian noise, while its robustness and generalization are further examined using Qiskit-simulated Bloch-ball states. Furthermore, in a practical MNIST image transmission task with held-out states, the decoded bit error rate is reduced from 50.34% to zero after TQSC post-processing. The TQSC model enables accurate tomographic characterization under dynamic noise and provides physically grounded post-hoc insights, holding promise for intelligent quantum information processing applications.
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All authors Bo Tang, Zixuan Liao, Hao Li, Yilin Yang, Jiani Lei, Zengya Li, Jing Qiu, Zhaohui Dong, Zhengyang Mao, Yuanhua Li, Yuanlin Zheng, Xianfeng Chen

Optics

Characterization of spatially inhomogeneous chirp in ultrashort multielectron beams via femtosecond hole burning

Yuichi Tachibana and Yuya Morimoto

Direct observation of the temporal-energy structure of pulsed electron beams is crucial for beam-driven light generation and time-resolved microscopic imaging. In this study, we characterized the spatially non-uniform time-energy structure in multi-electron ultrashort pulses exhibiting significant space-charge effects. By combining spectral hole burning originating from the photon-induced near-field electron microscopy (PINEM) effect with angle-resolved energy analysis, we observed time-energy correlations at each beam angle. Applying this method to 37-keV pulses containing up to 17 electrons per pulse, we determined energy spread and chirp rate, which vary by up to 100% and 40%, respectively, across the entire beam. These findings highlight the importance of characterizing multi-electron pulses with spatial or angular resolution and suggest the utility of spatially modulated light for the shaping of high-flux pulsed electron beams.
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