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Sunday 11 October

Optics

Photon-efficient readout of optical cavity arrays via spatial heterodyne

Bridger McGimpsey and Matt Jaffe

Optical cavity arrays are an emerging tool for efficiently interfacing optical photons to quantum emitters for applications such as quantum computing. In this work, we demonstrate a metrology technique for such cavity arrays by interfering cavity array outputs against a tilted reference beam on a camera, constituting a spatial heterodyne. Both the amplitude and phase of each cavity's transmitted field can be extracted from the resulting images. Enabled by the improved scaling of heterodyne detection over intensity detection in the presence of technical noise, we demonstrate signal-to-noise ratio greater than one down to the single detected photon level, even in the presence of hundreds of noise equivalent photons. This readout technique holds promise for fast, non-destructive imaging of atomic qubits in cavity arrays by requiring fewer scattered photons while allowing the use of fast cameras with higher electronic readout noise.
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Optics · Cross-listed from astro-ph.IM

Occultation polarimetry as a probe of unresolved polarization

A. G. Tevzadze

Context: Low polarization in an unresolved source may reflect weak local polarization or spatial cancellation between strongly polarized regions. An occultation can break this spatial degeneracy by differentially sampling the source as the occulting boundary moves. Aims: We develop a general theoretical framework for occultation polarimetry and determine what information can be inferred directly from unresolved full Stokes light curves, without reconstructing a polarization image or prescribing a source model. Methods: For a stationary, spatially incoherent source undergoing monotonic occultation, we relate Stokes variations to the polarization sampled by an arbitrarily curved occulting boundary and derive an exact variance decomposition of the normalized Stokes vector. Results: The polarization deficit decomposes exactly into three non-negative contributions: local polarization deficit, mixing within limb samples, and mixing between their mean polarization states. The last is directly measurable and provides a sharp, model-independent lower bound on total spatial mixing. The associated covariance tensor further characterizes the direction and correlations of the resolved polarization variations, including those between linear and circular polarization. Finite sampling preserves the bound, which can be strengthened through complementary occultation trajectories. Conclusions: Occultation polarimetry provides a powerful observational technique for extracting quantitative, model independent constraints on spatial polarization mixing directly from unresolved Stokes light curves. It offers a means to reveal both the extent and the form of polarization structure otherwise inaccessible at the available angular resolution.
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Optics

Direct growth of crack-free stoichiometric silicon nitride on sapphire for wide-band photonics

Zhaohui Ma, Ashish Chanana, Zhiquan Yuan et al. (+5 more)

Low-loss stoichiometric silicon nitride on oxidized silicon has emerged as the major wide-band photonics platform for nonlinear and quantum photonics. These films, deposited by low-pressure chemical vapor deposition (LPCVD), are well known to have around 1000 MPa of residual tensile stress, which often leads to cracking when film thickness exceeds 400 nm. Although various stress-mitigation approaches can isolate or prevent cracking, this stress issue remains a major fabrication challenge. Low-residual-stress LPCVD stoichiometric silicon nitride on sapphire has also been reported and recently explored for photonics at telecommunication wavelengths. Here, we advance its development through systematic characterization, including thin-film stress analysis, ellipsometry and prism-coupling measurements of refractive index and loss, and swept-wavelength spectroscopy of fabricated photonic devices across a broad range of wavelengths. We demonstrate the direct growth of crack-free stoichiometric silicon nitride up to 2 {\mu}m thick with only 200 MPa of stress. Our fabricated devices show propagation losses of 0.35 dB/cm around 780 nm, 0.37 dB/cm around 1064 nm, and 0.25 dB/cm around 1630 nm. In addition, prism-coupling measurements indicate film losses below 1 dB/cm at wavelengths down to 500 nm. Our work highlights stoichiometric silicon nitride on sapphire as a promising wide-band photonics platform.
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All authors Zhaohui Ma, Ashish Chanana, Zhiquan Yuan, Khoi Hoang, Yiliang Bao, Daron Westly, Kartik Srinivasan, Xiyuan Lu

Optics

Nonperturbative optomechanics with thin, weakly reflective intracavity dielectrics

Andrew Laeuger and Nancy Aggarwal

Levitated dielectric sensors are often treated as perturbative probes of a pre-existing optical field. We show that this picture fails for a novel sensor geometry: a dielectric plate whose transverse extent captures the full optical mode. Even an optically thin sensor with modest refractive index can heavily restructure the intracavity fields, effectively partitioning a cavity into two subcavities with substantial cross-coupling and producing new optical resonances and trapping sites with properties which deviate from the standard intuition. Conventional perturbative expressions for the cavity frequency shift and optomechanical coupling depart from the exact solution at thicknesses as small as $\sim\lambda/(10n)$. Furthermore, cavity locking decreases the coupling and increases the trap stiffness by orders of magnitude, and the coupled subcavity structure permits appreciable optical cooling at zero detuning, a distinct behavior unique to this nonperturbative regime. These effects, sharing a common origin, establish a distinct regime of cavity optomechanics in which the sensor is no longer merely a probe of the cavity field, but an element that helps define it.
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Optics · Cross-listed from quant-ph

Non-Stationary Quantum Systems Associated with Stationary Scattering in One Dimension

Ali Mostafazadeh and Alireza Shariati Joni

Stationary scattering admits a dynamical formulation in which the scattering data are extracted from the evolution operator for an effective non-stationary and non-unitary quantum system. This provides a mathematical method of solving scattering problems. We consider the possibility of realizing such a quantum system and relating the scattering information to outcomes of quantum measurements performed on it. To this end, we examine stationary scattering problems in one dimension where the scattering data consist of reflection and transmission amplitudes and the corresponding effective quantum system is a non-unitary two-level system. The states of this system identify points in a Bloch sphere $S^2$ and their evolution yields trajectories in $S^2$. Quantum measurements turn out to be capable of providing information about the reflection amplitudes. We identify configurations displaying reflectionlessness with situations where one or both of the poles of $S^2$ undergo cyclic evolutions. Spectral singularities and coherent perfect absorption correspond to dynamical spin flips which map one of the poles of $S^2$ to the other.
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Optics

Intrinsic Orbital Nernst Effect in Real Photonic Bands

Tao Zhu

We predict an intrinsic orbital Nernst effect in reciprocal photonic lattices with real Bloch modes. In the collisionless regime, a thermal gradient generates a transverse angular-displacement response although band angular moments and ordinary Berry curvatures vanish. The response is carried by angular-density dipoles formed through virtual mixing of distinct spatial modes. Their correlation with band velocity survives thermal averaging and is independently recovered from the angular-density readout of unitarily evolved wave packets. Two controls expose the mechanism: a fixed-generator two-level system has zero antisymmetric intrinsic response, and flattening the dispersion suppresses transport without changing the eigenstates. A canonical scalar Maxwell calculation realizes the effect through symmetry-selected virtual channels, even when one band dominates the thermal population. These findings establish an orbital-dipole mechanism for intrinsic thermal angular transport in real photonic bands.
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Optics

Tornado Wave-Encoded Point Spread Functions for Multi-Period Three-Dimensional Localization Imaging

Lai Chen, Rui Wang and Li-Gang Wang

Three-dimensional (3D) localization microscopy using rotational point spread functions (PSFs) is fundamentally challenged by limited axial range, poor PSF compactness, and depth-decoding ambiguity – particularly in dense specimens with heavy PSF overlap. To address these limitations, we introduce a 3D localization approach based on tornado wave (ToW)-PSFs, combined with a convolutional neural network (CNN) designed to decode continuous rotational patterns and resolve multi-period axial ambiguity. Our engineered PSF encodes the 3D position of each nanoparticle into a compact double-lobe pattern whose orientation rotates with axial position. This design yields a clean, well-defined structural evolution across an unprecedented 15 um axial range, with an average rotation rate of 21.8 degrees/um, ensuring robust long-range depth encoding. To recover coordinates from overlapping emitters, we systematically benchmark a conventional matching-pursuit (MP) algorithm against our CNN. While MP performs adequately in sparse scenes, the CNN demonstrates exceptional robustness in dense fields, achieving a 70.24% localization accuracy at 20 particles per image-substantially outperforming MP's 22.52% – while also significantly suppressing axial period-jump errors. Experimental validation on nanoparticles confirms reliable single- and multi-particle localization throughout the entire working range. Our results establish ToW-PSFs as a powerful and practical optical encoding strategy for high-density, extended-range 3D localization imaging.
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Optics

From Microresonator to Packaged Microcomb System: Fiber-Coupled Module and System Integration

Yudai Matsumura, Yoshihiro Makimoto, Tsutomu Mizuguchi et al. (+4 more)

We demonstrate a compact and robust soliton microcomb source designed for field-deployable operation. A directly fiber-coupled SiN microresonator was integrated with precise thermal control into a palm-sized module, reducing the footprint and volume by 16- and 81-fold, respectively. The module, together with the laser sources and optical amplifiers required for microcomb generation, was further integrated into a 19-inch rack-mounted enclosure, achieving system-level footprint and volume reductions of 2.3- and 3.7-fold, respectively. The packaged system achieved a 90% manual startup success rate and maintained continuous soliton operation for 18.8 days, while remaining operational under substantial temperature variations. A state-based automated startup scheme using discrete microcomb-state evaluation achieved single-soliton generation without manual intervention with success rates of 50% within 2 min and 60% within 3 min. Moreover, automated soliton initiation and sustained operation were demonstrated while the packaged microresonator module was directly subjected to random mechanical vibration. These results provide a practical platform for compact, robust, and field-deployable microcomb sources.
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All authors Yudai Matsumura, Yoshihiro Makimoto, Tsutomu Mizuguchi, Masayuki Higaki, Yu Tokizane, Naoya Kuse, Takeshi Yasui

Optics · Cross-listed from physics.flu-dyn

Local sensing of gas microflows using a levitated nanoparticle

Maxime Debiossac, David Grass, Daniel R. Ladiges et al. (+3 more)

Local measurements of gas flow in microscale geometries remain challenging due to the difficulty of micromechanical sensors implantation. Here, we use a levitated nanoparticle as a minimally invasive probe to map, with high spatial resolution, both the local pressure and velocity gas flow for a canonical example - a micropipe subjected to a pressure gradient. This technique enables characterization of nonequilibrium gas transport across several flow regimes, from slip flow to free-molecular flow. We directly observe the emergence of a nonlinear pressure distribution at large pressure ratios and obtain agreement with kinetic-theory predictions and Direct Simulation Monte Carlo calculations. These results introduce levitated nanoparticles as powerful and reconfigurable probes for microchannel gas sensing, with applications in microtechnology, micro-chemistry, and bioengineering.
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All authors Maxime Debiossac, David Grass, Daniel R. Ladiges, John E. Sader, Markus Aspelmeyer, Nikolai Kiesel

Optics

Comparative Robustness of Mach-Zehender and Microring Photonic Matrix Multipliers Under Laser RIN and Thermal Drift

Andreas Falkenberg

Photonic matrix multipliers can accelerate neural-network inference, but their practical utility depends on how optical weight elements respond to source noise, thermal variation, and calibration error. This paper compares Mach-Zehnder modulator (MZM) and microring-resonator (MRR) implementations under laser relative-intensity noise (RIN), column-wise thermal/phase drift, and their joint action. Two CIFAR-10 classifiers - a compact four-layer CNN and ResNet-8 - are mapped to matched photonic multiply-accumulate chains using common source-distribution, detection, numerical, and calibration assumptions. Both architectures reproduce the same zero-perturbation baseline for each workload: 79.5% classification accuracy for the Small CNN and 70.0% for ResNet-8. Robustness is then evaluated using separate RIN-only and drift-only sweeps and a full two-dimensional RIN-drift grid, with dimensionless RMS perturbation levels extending from 0.5% to 20%. The analysis reports classification accuracy, class normalized confusion matrices, rolling-accuracy traces, one-dimensional robustness curves, and multidimensional response surfaces. Device equations and parameter definitions follow the models implemented in the QPI Labs Photonic Inference Simulator, with shared laser fluctuations propagated as correlated multiplicative noise and slow drift represented as a per-output-column perturbation of calibrated weights. All numerical results are generated from recorded experiment configurations and random seeds. The study provides a controlled system-level framework for comparing interferometric and resonant photonic weight elements while limiting conclusions to the implemented device models, perturbation ranges, calibration policy, and neural-network workloads.
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Optics · Cross-listed from cond-mat.mtrl-sci

Three-dimensional reconstruction of weakly scattering objects from single-defocus 4D-STEM data

Kousuke Ooe, Yufan Shen, Yuichi Shimakawa et al. (+2 more)

Three-dimensional (3D) atomic-structure analysis is of central importance in (scanning) transmission electron microscopy (STEM). STEM techniques to reconstruct 3D structure include tilt-series or defocus-series annular dark-field, best suited to heavier atomic species, and dynamical-scattering-model inversion applied to single-defocus four-dimensional (4D) STEM data, requiring computationally expensive post-experiment analysis. In this study, we propose a 3D-structure linear inversion (3D LINV) STEM algorithm, which enables a fast and direct reconstruction of 3D structures from a single-defocus 4D-STEM dataset. This method is based on solving linear equations relating the measured 4D-STEM data and the unknown 3D specimen potential under the thick weak phase object approximation. We show the capabilities of 3D LINV STEM through systematic 4D-STEM simulations across various observation parameters such as specimen thickness, partial coherence, and shot noise, and through an experimental demonstration of 3D structure reconstruction of a stacked freestanding membrane with atomic-scale lateral resolution and nanometre-scale depth resolution.
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All authors Kousuke Ooe, Yufan Shen, Yuichi Shimakawa, Daisuke Kan, Scott D. Findlay

Optics

Dual deconvolution multifocal fluorescence response matrix microscopy for aberration-free high-throughput super-resolution imaging

Sumin Lim, Sanghyeon Park, Tran Thinh Le et al. (+3 more)

Fluorescence response matrix imaging enables separate computational correction of excitation and emission aberrations through dual deconvolution, but single-focus acquisition requires a large number of camera frames, limiting its practical use. Multifocal excitation can accelerate acquisition by recording many illumination positions in parallel, but denser foci also increase inter-focus crosstalk, which can bias the estimated excitation and emission optical transfer functions and degrade aberration correction. Here, we introduce high-throughput aberration-free fluorescence response matrix imaging with adaptive multifocal illumination, in which the inter-focus spacing of the multifocal lattice is adjusted according to specimen-dependent crosstalk. A programmable digital micromirror device generates multifocal excitation lattices, and the resulting detector-resolved fluorescence responses are assembled into a two-coordinate fluorescence response matrix. Dual deconvolution separately estimates and corrects the excitation and emission optical transfer functions, and the aberration-corrected matrix is then combined in the spatial-frequency domain to reconstruct the aberration-free image. This strategy reduces the number of required camera frames by approximately three orders of magnitude, allowing response matrices with $\sim 10^6$ illumination positions to be acquired within seconds to a few minutes. The accelerated acquisition preserves the aberration-correction capability of dual deconvolution and achieves an estimated lateral resolution of $\sim$100 nm. Applied to heterogeneous mouse brain and kidney tissue, the method enables high-resolution, depth-resolved volumetric imaging while correcting specimen-dependent aberrations. Together, these results establish adaptive multifocal illumination as a practical route to high-throughput aberration-free fluorescence response matrix imaging.
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All authors Sumin Lim, Sanghyeon Park, Tran Thinh Le, Jin Hee Hong, Seokchan Yoon, Wonshik Choi

Saturday 10 October

Optics · Cross-listed from quant-ph

Monogamy of quantum steering in exciton–cavity optomechanical system

Hamza Harraf, Mohamed Amazioug and Rachid Ahl Laamara

In this work, we study a theoretical scheme to investigate the monogamy of quantum steering in a hybrid exciton–cavity optomechanical (EOM) system. Within the Gaussian-state formalism, we quantify the steerability among the exciton, photon, and mechanical modes in both the steady-state and dynamical regimes. We establish and verify CKW-type monogamy inequalities for Gaussian steering and demonstrate that the distribution of bipartite steering among the three modes can be controlled through the system parameters. We further examine the influence of thermal noise and temporal evolution on the steering properties and the corresponding monogamy relations. Our results show that increasing the temperature generally suppresses the strength of Gaussian steering and modifies the degree of steering sharing imposed by the CKW-type monogamy relations. In contrast, in the dynamical regime, the steerability can increase with evolution time over suitable temporal windows, indicating that the transient dynamics can be exploited to enhance quantum correlations. These results highlight the potential of hybrid exciton–optomechanical platforms for controllable quantum correlations and provide a promising route toward the generation and manipulation of multipartite quantum resources.
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Optics · Cross-listed from cond-mat.mtrl-sci

Interfacial Coupling Reshapes Nonlinear Polarization in a Spin-Defect van der Waals Heterostructure

Lena Dalifoski, Eveline Mayner and Poonam Singh

Van der Waals heterostructures offer a direct route to couple an optically active layer to a two-dimensional spin sensor, yet their coherent nonlinear response at interfaces remains poorly resolved. Here, we use polarization-resolved second harmonic-generation imaging to resolve four distinct regions of a hexagonal boron nitride (hBN) -based heterostructure, native hBN, neutron-irradiated hBN containing negatively charged boron vacancies (VB-), PbI2 and their complete overlap. The detected intensity scales quadratically with incident power, consistent with a dominant second-order optical process. Polarization scans show that adding PbI2 transforms the distorted VB- SHG anisotropy into a predominantly fourfold response with a sixfold stronger SHG than native hBN alone. This non-additive nonlinear response occurs in the same layer architecture also shown to enhance defect photoluminescence, linking spin-defect sensitization to an interface-modified effective second-order susceptibility.
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Optics

Observation of quadrature-dependent unidirectional flow of light

Jamison Sloan, Eran Lustig, Louise Schul et al. (+5 more)

Unidirectional transport of light is a central capability in photonics, enabling critical functionalities such as isolation and routing. Ordinarily, this directionality depends on the mode of light, but not its phase. In this work, we experimentally demonstrate phase-dependent unidirectional transport of light for the first time. Specifically, we realize a system where conjugate quadratures of an optical field decouple and propagate in opposite directions. Our all-optical approach uses multiple pump frequencies in a high-$Q$ nanophotonic micro-resonator to achieve Hamiltonian programming through Kerr nonlinearity. Even though we rely on optical nonlinearity, our approach is not limited to any minimal power requirement on the signal. We demonstrate the ultimate limit of this by measuring the effect of quadrature-dependent transport on vacuum fluctuations. Our approach unlocks a fundamental new capability for controlling light, and can enable previously inaccessible regimes of phase-sensitive directional amplification, sensing, and routing.
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All authors Jamison Sloan, Eran Lustig, Louise Schul, Trung Kien Le, Melissa A. Guidry, Daniil M. Lukin, Shanhui Fan, Jelena Vučković

Optics

Resonant dispersive wave emission: a route toward few-cycle, tunable strong-field drivers in the visible

Martin Gebhardt, Joleik Nordmann, Nikoleta Kotsina et al. (+4 more)

Intense ultrafast lasers are the backbone of strong-field physics and enable table-top scale applications of coherent high-photon energy radiation through high-harmonic generation (HHG). Using short-wavelength drivers in HHG promises highly efficient conversion into the extreme ultraviolet, but short pulse durations are essential to this approach. We generate multi-GW peak power, sub-10 fs pulses in the visible with broad spectral tunability (220–752 nm) by harnessing soliton dynamics in large-core, gas-filled capillary fibers for high-energy resonant dispersive wave emission. This establishes the potential of resonant dispersive waves as a new class of driving lasers for HHG and strong-field physics in addition to widespread applications in ultrafast spectroscopy.
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All authors Martin Gebhardt, Joleik Nordmann, Nikoleta Kotsina, Michael Heynck, Teodora Grigorova, Christian Brahms, John C. Travers

Optics · Cross-listed from quant-ph

Partial-coherence weak measurement of polarization qubits with a temporal pointer: theory and experiment

Shane P. Gervais and Lambert Giner

Weak measurement has proven useful for metrology, for probing quantum paradoxes, and for the direct measurement of quantum states. Weak measurements of polarization qubits with temporal pointers provide a direct route to weak-value characterization, including in regimes where the pointer is only partially coherent. We derive a closed-form expression for the post-selected temporal shift that interpolates between the incoherent and coherent (ideal) weak-measurement limits through a single parameter $\nu$, the pointer visibility. The expression is experimentally tested for a range of polarization states spanning three trajectories corresponding to rotations about the principal axes of the Poincaré sphere. Two of the trajectories provide parameter-free benchmarks, with the real part of the weak value following $\cos^2\theta$ and $1/2$. In contrast, the weak value along the third trajectory is sensitive to incoherence and is well described by the single-parameter partial-coherence model, from which a reduced pointer visibility is obtained. Time shifts are extracted from the smoothed derivative of the pulse leading edge with internal calibration, reaching few-picosecond precision on 10 ns optical pulses using commercial components. The same apparatus also gives qualitative access to the imaginary quadrature through the frequency centroid, showing that temporal weak measurements remain accessible and quantitative in partially coherent pulsed systems.
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Optics

Ultra-low-loss Ta2O5 waveguide for integrated nonlinear photonics

Xiaotong Zhang, Shuxuan Guo, Ruixuan Yi et al. (+8 more)

Integrated nonlinear photonics demands waveguides that simultaneously offer ultra-low-loss, relatively strong nonlinearity, and tight mode confinement. Tantalum pentoxide (Ta2O5) is attractive for this purpose because it combines a broad transparency window, relatively strong third-order nonlinearity, and favorable thick-film growth characteristics. In tightly confined Ta2O5 waveguides, however, enhanced interaction between the optical mode and etched sidewalls makes scattering loss an important limitation for achieving high Q anomalous-dispersion resonators. Here, we mitigate this confinement-scattering trade-off in pure Ta2O5 waveguides using a fabrication flow based on the Damascene concept. The resulting microring resonators (MRRs) with a cross-section of 1.6 {\mu}m x 0.85 {\mu}m exhibit intrinsic quality factors exceeding 4.0 x 106, corresponding to propagation losses below 10 dB/m, while maintaining anomalous dispersion suitable for bright dissipative Kerr soliton operation. Using these resonators, we generate a coherent bright single-soliton microcomb with a repetition rate of 108.32 GHz. Under optimized dual-pump operating conditions, the platform further exhibits an experimentally accessible single-soliton window spanning 7.5 GHz, indicating a large detuning tolerance for soliton operation; this broad operating window is consistent with the relatively weak thermo-optic response of Ta2O5. Thermal-bistability analysis further indicates that the residual scattering loss is comparable to the material-absorption loss, rather than dominating the loss budget. These results demonstrate that low optical loss, tight mode confinement, and dispersion engineering suitable for soliton formation can be jointly achieved in a pure Ta2O5 platform, providing an ultra-low-loss platform foundation for integrated nonlinear photonic devices and more complex chip-scale nonlinear photonic systems.
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All authors Xiaotong Zhang, Shuxuan Guo, Ruixuan Yi, Zheze Shi, Like Shui, Long Huang, Leiran Wang, Yang Wang, Junling Qu, Wenfu Zhang, Xuetao Gan

Optics · Cross-listed from cs.NI

Stackelberg Game with Multi-Agent Transformer for ISRS-Aware Resource Re-optimization in Multi-Band Optical Networks

Jiaxin Liu, Rentao Gu, Miao Zhu et al. (+3 more)

The rapid expansion of generative AI is driving computing infrastructures toward interconnected AI data centers. Multi-band optical networks have become the backbone of such connectivity. To accommodate increasingly dynamic traffic demands, these networks require continual resource re-optimization to improve resource utilization and reduce service blocking. However, multi-band transmission amplifies inter-channel stimulated Raman scattering(ISRS), inducing nonlinear coupling among services. This coupling complicates re-optimization, as local adjustments perturb the global power profile, creating interdependent optimization decisions across services. Moreover, the nonlinear interactions vary with the subset of services selected for re-optimization, and inappropriate selection may reduce re-optimization effectiveness or diminish achievable benefits. To address these challenges, we propose a Stackelberg Game with Multi-Agent Transformer (SG-MAT) approach for ISRS-aware resource re-optimization. SG-MAT employs a leader-follower structure, in which the MAT-based follower models nonlinear coupling and generates coordinated channel reallocations, feeding the utilization improvements to the leader. Using this feedback, the leader identifies critical service subsets, approximating a Stackelberg equilibrium to guide global decisions and enabling consistent and efficient re-optimization. Simulation results show that SG-MAT achieves the highest utilization improvement and reduces the blocking ratio by approximately 30% under moderate traffic loads, with computational complexity comparable to benchmarks.
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All authors Jiaxin Liu, Rentao Gu, Miao Zhu, Zeguang Zou, Hui Li, Yuefeng Ji

Optics

Selective spatiotemporal mode-locking in multimode Mamyshev oscillators

Changfeng Wang, Jia Liu, Yutai Zhao et al. (+6 more)

Spatiotemporal mode-locking (STML) in multimode fibers introduces spatial degrees of freedom for ultrashort pulse generation, yet flexible manipulation of transverse mode compositions within multimode solitons remains challenging. Here, we propose a spectrum-to-mode mapping strategy in multimode Mamyshev oscillators (MOs) to selectively synchronize specific transverse modes through synergistic cross-phase modulation and offset spectral filtering. Meanwhile, four-wave mixing acts to stabilize intermodal phase relationships, facilitating selective STML characterized by diverse mode compositions with matched group velocities. Spatiotemporal solitons containing the pure LP01 mode, degenerate LP11 modes, or LP02+LP21 composite modes are selectively realized and mapped across the parameter space spanned by intracavity gain and filter detuning. Furthermore, intracavity collisions between coexisting mode groups with disparate group velocities are demonstrated to enable dynamic mode selection. Beyond the simulation of six modes in graded-index multimode fibers, selective STML is also demonstrated in MOs based on step-index multimode fibers and fibers supporting more transverse modes, confirming the generality of our approach. This strategy offers a versatile and robust pathway for transverse mode regulation and provides new insights into full dimensional structured light manipulation in multimode ultrafast fiber lasers.
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All authors Changfeng Wang, Jia Liu, Yutai Zhao, Ran Xia, Wenjun Ni, Chunyong Yang, Xiahui Tang, Gang Xu, Perry Ping Shum

Optics

Near-focus intensity evolution of spatiotemporal optical vortex pulses and consequences for their nonlinear upconversion

Titouan Gadeyne, Vartika Vishnoi and Thierry Ruchon

Spatiotemporal optical vortex (STOV) laser pulses are attracting attention for their puzzling transverse orbital angular momentum (OAM) and propagation properties, which could determine their future applications. While the characteristic reshaping of their space-time envelope upon diffraction from the focal plane to the far-field is now well-established, the evolution of their intensity as they propagate has not been studied quantitatively, despite growing interest for their use in nonlinear optics and strong-field physics. Here, we explore experimentally and analytically the focusing dynamics of STOVs produced by a pulse shaper, and evidence a substantial longitudinal shift between the coordinate at which a circularly-symmetric STOV forms and that at which the pulse reaches its peak intensity. To illustrate some practical consequences for applications, we experimentally demonstrate how the yield of second-harmonic generation can consequently be maximized several Rayleigh lengths beyond the plane where the circular STOV really occurs. These results signal careful characterization of spatiotemporal pulses as a requisite for nonlinear optical experiments, and pave the way for finer control of complex laser drivers for light-matter interactions.
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Optics

Maximal Axion Optical Chirality Enabled by Degenerate Quasibound States in the Continuum

Chang-Yin Ji, Chong Wang, Jiafang Li et al. (+1 more)

Axion quasiparticles introduce magnetoelectric coupling in topological materials, yet their optical signatures are intrinsically weak, severely limiting experimental detection and practical exploitation. Here, we demonstrate maximal optical chirality of axion quasiparticles by coupling them with degenerate quasibound states in the continuum (qBICs). By integrating three-dimensional topological insulators (3DTIs) with achiral photonic crystal slabs (PCSs), we reveal that axion quasiparticles induce an effective Zeeman effect that lifts the degeneracy of achiral qBICs in PCSs, splitting them into two nondegenerate high-Q chiral qBICs with maximally opposite chirality. These result in a more than 10^3- and 200-fold increase in the polarization conversion efficiency and Faraday rotation angle, respectively, compared to the intrinsic chiroptical response of bare 3DTI films. Moreover, circular dichroism and nonreciprocal optical responses are revealed as new key signatures for probing axion quasiparticles in 3DTI-PCS coupled systems. Our results provide a definitive route for observing axion quasiparticles and topological physics, while establishing a promising platform for controlling optical polarization, spin, phase, and nonreciprocal responses.
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All authors Chang-Yin Ji, Chong Wang, Jiafang Li, Yugui Yao

Optics · Cross-listed from physics.atom-ph

Interpretation of chirality imprinted on photoelectron momentum spectra by three-dimensional light fields

Junxin Yuan, Yuhong Li, Fei Li et al. (+9 more)

Synthetic three-dimensional (3D) light fields provide a new route to imprinting chirality on achiral matter through light–matter interaction. Although previous work has numerically demonstrated that chirality can be imprinted on the photoelectron momentum spectrum of atoms, a transparent analytical physical picture that links the structure of the driving field to the chirality of the spectrum is still an open question. Here, using frequency-domain theory based on nonperturbative quantum electrodynamics (QED), we demonstrate that this chirality originates from coherence between adjacent quantum transition channels. We further find that a symmetry transformation introduces into the coherence term a symmetry-breaking phase shift ($\Phi_{\mathrm{SBPS}}$), which can be tuned by varying the laser-field parameters to preserve or break the corresponding symmetry in the spectrum. Once all such symmetries are broken, the momentum spectrum becomes chiral. In particular, for the noncollinear two-color 3D light field considered here, the spectrum is chiral for even $f=\omega_2/\omega_1$ and achiral for odd $f$. Our results provide a microscopic interpretation of chirality imprinting and establish a framework for predicting and controlling chiral electron wave packets with synthetic 3D light fields.
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All authors Junxin Yuan, Yuhong Li, Fei Li, Jinkai Zhang, Shiyang Zhong, Hao Teng, Yujun Yang, Yingchun Guo, Zhiyi Wei, Jing Chen, Xiaojun Liu, Bingbing Wang

Optics

A Portable Optical Frequency Comb with Low Repetition-Rate Drift Based on "Optical Cubes"

Zhendong Chen, Hanbo Xu, Ruoao Yang et al. (+6 more)

We demonstrate a compact, fully stabilized, all-polarization-maintaining (all-PM) Er:fiber optical frequency comb (OFC) implemented on a silica optical-cube platform. The optical comb module, including the oscillator, amplifier, spectral-broadening stage, 780-nm frequency-doubling branch, and f-to-2f interferometer, occupies a volume of 0.88 L. Without active temperature control, the free-running repetition frequency exhibits a peak-to-peak excursion of 75 Hz over 10 h, corresponding to 0.375 ppm. Under the same laboratory conditions, this excursion is 6.2 times smaller than that of a mechanically mounted non-PM reference comb. The amplified pulses are compressed to 94 fs and spectrally broadened in a PM highly nonlinear fiber. A coherent-population-trapping-based chip-scale atomic clock is employed for the first time as the radio-frequency reference for comb locking, thereby reducing the footprint of the microwave-reference subsystem. The resulting in-loop, optical-frequency-normalized tracking instability reaches 6.03E-17 at 1 s and 2.57E-18 at 10,000 s. These results demonstrate a compact comb architecture with reduced sensitivity to environmental perturbations, providing a practical route toward portable optical atomic clocks.
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All authors Zhendong Chen, Hanbo Xu, Ruoao Yang, Tianyu Liu, Hongshuo Wu, Duo Pan, Zhigang Zhang, Jianjun Wu, Jingbiao Chen

Friday 9 October

Optics

Fast local field calculation in cascaded coupled systems

Isam Ben Soltane, Romain Asso and Matthieu Davy

Computing the field within a sub-unit of cascaded systems is a recurring problem in wave physics. It is central to gradient-based inverse design, in situations where only a region of the system is modified while the rest remains fixed. Standard approaches either resimulate the entire cascade at every change, or require a detailed characterization of every surrounding sub-system. Both become impractical when many design iterations are needed. Here, we introduce a hybrid method combining the $S$-matrix approach, which propagates fields through cascaded systems, with the Green's function method, which gives the field generated by a source within a characterized system. In this approach, the sub-systems surrounding the region of interest need only be characterized once, after which the local field can be recomputed rapidly for any new configuration. We validate the method on a disordered lossy waveguide, finding excellent agreement with finite-element simulations. We also demonstrate its efficiency on a disordered multimode cavity, where it achieves a fifty-fold speed-up over full-wave simulation and reduces a wideband focusing calculation from eleven hours to ten minutes. This approach opens the way to fast, iterative field calculations in complex systems coupled to their environment, with direct applications to inverse design and wideband wavefront-shaping.
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Optics

Definition of Multi-Parameter Super-Resolution for Optical Telescopes

Peter Menart, Seungman Choi and Zubin Jacob

Super-resolution techniques in microscopy are opening new frontiers in biology, and super-resolution for telescope imaging may provide similar benefits for astronomy and space domain awareness. Telescope super-resolution techniques such as multi-plane light conversion and photonic lanterns have been inspired by the ability of mode sorting measurements to extract classical Fisher information closer to the quantum bound than standard telescope imaging. Fisher information analyses for super-resolution imaging systems commonly consider the case of imaging point sources, but often only consider estimating a small subset of the parameters. Furthermore, there has been no demonstration of an estimation algorithm with performance that follows the limit set by the Fisher information when all point source parameters are considered. We provide a framework for defining and analyzing super-resolution using the classical and quantum Fisher information for the multi-parameter estimation problem and demonstrate an algorithm that can achieve the classical Fisher information bound for all the parameters simultaneously.
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Optics · Cross-listed from cond-mat.mtrl-sci

Precursor stoichiometry controls dopant structure, defect chemistry, and valence in Mn-doped ZnGa$_2$O$_4$ nanocrystals

Mátyás M. Rudolf, Gábor Bortel, Nikoletta Jegenyés et al. (+5 more)

The luminescence of doped nanocrystals is usually optimised through the activator; here we show that the host cation ratio is an equally decisive, and largely overlooked, design variable. Mn-doped ZnGa$_2$O$_4$ nanocrystals (Mn:Zn = $4\times10^{-4}$) were grown hydrothermally at nominal Zn/Ga ratios between 0.30 and 0.75 (stoichiometric: 0.50) and post-annealed at 400–1100$^\circ$C, and the resulting composition–temperature matrix was mapped by X-ray- and UV-excited luminescence, EPR, Rietveld-refined X-ray diffraction, Raman spectroscopy and SEM. The as-grown crystals are phase-pure spinel at every composition and accommodate their off-stoichiometry internally as a point-defect inventory, reflected in a 0.4% variation of the lattice parameter; on annealing, the excess gallium is exsolved as $\beta$-Ga$_2$O$_3$ in amounts set by the solution composition. The Mn$^{2+}$ emission separates into two optima, near-stoichiometric crystals annealed at 400–600$^\circ$C and Zn-excess crystals annealed at 1100$^\circ$C, the latter being twice as bright under X-ray excitation. Under X-ray and 365~nm excitation the two optima are separated by a minimum at 800$^\circ$C that coincides with a collapse of the Mn$^{2+}$ EPR population and has no counterpart in the Raman linewidths, identifying transient, defect-compensated oxidation of the dopant rather than lattice degradation as its origin. The most Zn-rich composition shows neither Mn$^{2+}$ nor Mn$^{4+}$ emission at any annealing stage, whereas its trace Cr$^{3+}$ emission is strong, indicating that Mn is rejected already during growth. Solution stoichiometry therefore acts on two levels, dopant capture and native-defect inventory, while annealing controls dopant valence and lattice order. The brightest high-temperature phosphor is thus not the nominally stoichiometric one, but the composition whose excess is consumed on its way to stoichiometry.
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All authors Mátyás M. Rudolf, Gábor Bortel, Nikoletta Jegenyés, Árpád Jakab, László Bencs, Ferenc Simon, Adam Gali, Dávid Beke

Optics

Spatial Nonlocality from Finite Extinction Ratio in BOTDR over Heterogeneous Fiber Links

Giannis Poulopoulos, Constantinos Haliotis, Panagiotis Toumasis et al. (+1 more)

Finite extinction ratio in pulse-modulated Brillouin optical time-domain reflectometry (BOTDR) produces residual inter-pulse Brillouin backscatter outside the nominal pulse gate. We model and experimentally quantify this effect as spatial nonlocality in a heterogeneous fiber link and define the spectral contamination ratio (SCR) as the contaminating Brillouin-band power normalized to the local Brillouin-band power. Measurements were performed using a 1.2 km standard single-mode fiber (SMF) followed by 0.1 km of dispersion-compensating fiber (DCF), whose separated Brillouin frequency shifts allow section-to-section leakage to be resolved spectrally. At 20 m spatial resolution, increasing the extinction ratio from 18.5 to 33.0 dB reduced the SMF-band contamination in the DCF gates from -5.3 to -14.8 dB. Over the 16-33 dB range, the SCR showed fitted slopes of -1.064 and -1.246 dB/dB for the two contamination directions. These results quantify finite-ER-induced spatial nonlocality and provide a link-specific metric for extinction-ratio selection in BOTDR.
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All authors Giannis Poulopoulos, Constantinos Haliotis, Panagiotis Toumasis, Hercules Avramopoulos

Optics

Statistical Optical Replication and Mixing of Spatial Information across Wavelengths

Wanting Hou, Wei Liu, Hong-Chao Liu et al. (+2 more)

Accessing and combining the spatial information carried by light at different wavelengths is important for linking structured-light encoding with spectrally distinct detection channels. Here, we introduce a correlation-enabled linear-optical framework for cross-wavelength imaging, bidirectional replication, and spatial information mixing. Shared random holographic modulation establishes correlations between nondegenerate optical fields, allowing spatial information to be retrieved from joint intensity fluctuations. In the demonstrated replicator, a spatial pattern encoded at one wavelength is read out in the detection coordinates of another through intensity correlations. Selecting diffraction-order pairs produces correlation kernels containing either the product or the conjugate product of two input field envelopes. These operations reproduce the spatial algebra underlying sum- and difference-frequency generation, while the optical fields retain their original carrier frequencies. The theory accounts for wavelength-dependent propagation and coordinate scaling, linking the input structures to observable correlation patterns. Together, these results establish a common framework for cross-wavelength spatial information processing through engineered optical correlations and joint detection.
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All authors Wanting Hou, Wei Liu, Hong-Chao Liu, Zhiyuan Ye, Jun Xiong

Optics

PhySeqNet: physics-informed fluorescent foci detection for BARseq spatial transcriptomics

Neha Goswami, John Hover, Renae Galluccio et al. (+4 more)

BARseq enables spatially resolved gene-expression profiling across intact tissue, but its sensitivity depends on accurate detection and decoding of dense fluorescent rolonies. Existing spot-calling approaches can be conservative where signals overlap, while supervised deep learning is limited by the lack of reliable manual ground truth in real tissue images. Here we present PhySeqNet, a physics-informed deep learning framework for annotation-free fluorescent foci detection in BARseq. PhySeqNet trains U-Net detectors entirely on semi-synthetic images generated from an instrument-matched optical model combined with real sample-free experimental noise, and is integrated into pyBARseq, a modular Python pipeline for BARseq analysis. PhySeqNet achieved high detection performance on held-out simulated data across wavelength bands. On real tissue images, where ground truth is unavailable, we evaluated detections by forward-model reconstruction: PhySeqNet with conservative barcode-aware non-maxima suppression (NMSB) achieved higher reconstruction fidelity (NCC and MS-SSIM) than the BarDensr single-shot estimator, tuned classical spot detectors, and a pretrained deep-learning detector. In the analyzed brain section, PhySeqNet with NMSB yielded a median of 51 counts per cell versus 47 for BarDensr, with a similar number of genes detected per cell. The recovered transcripts produced spatial expression patterns qualitatively consistent with Allen MERFISH reference data and preserved cell-type composition after scANVI label transfer. These results show that physics-informed simulation can train practical, annotation-free detectors that improve BARseq sensitivity without disrupting downstream biological interpretation.
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All authors Neha Goswami, John Hover, Renae Galluccio, Yichen Wu, Huiqing Zhan, Xiaoyin Chen, Anthony M. Zador