Optics
Spatial-Spectral Trade-offs in Metasurface-Based Snapshot Hyperspectral Imaging
Liam Fitzpatrick, Sean Molesky and Kai Wang
Snapshot hyperspectral imaging maps a spatial–spectral datacube onto a two-dimensional detector, with recoverability depending on the datacube sampling regime, the scene prior, and the optical encoding. We study this co-dependence with algorithmic recovery and optical design optimization in a differentiable metasurface model by varying the spatial–spectral ratio and comparing average-coherence, mutual-information, and end-to-end objectives. For compressed imaging with three bands, optimization of single-parameter dielectric pillars produces lens-like designs with overlapping wavelength-dependent point-spread functions across the objectives tested. End-to-end reconstruction can mask this collapse on restricted training distributions, showing that reconstruction fidelity depends jointly on the optical encoding and scene prior. For simple nano-pillar meta-atom geometries, the optimized singular-value spectrum deteriorates as the datacube becomes more spectrally dominated, whereas a relaxed model with independent complex transmission at each wavelength reduces this dependence. These results identify restricted wavelength-dependent transmission control in the pillar library as an important contributor to the observed spectral collapse. This motivates an illustrative local super-pixel spectrometer model in which spectral encoding is studied separately from global image formation under a plane-wave illumination approximation.
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Optics
Label-Efficient Generative Inverse Design and Design-Rule Discovery in Freeform Topological Photonics
Yuhan Zhang, Xin Xie, Bowen Song et al. (+3 more)
Topological photonic
crystals support robust, disorder-resilient light transport protected by their band-structure
topology, yet their design remains confined to a small set of
symmetry-defined templates. The surrounding freeform design space, where optimal performance and new functionality may reside, is difficult to access because of its high dimensionality and costly full-wave simulation needed for evaluating each candidate. % Here we report generative inverse design of freeform valley photonic
crystals. A label-free
diffusion prior learns the distribution of three-fold rotationally symmetric geometries from 7,689 unlabeled designs that cost 0.15~s each to produce, while a convolutional surrogate is trained on 1,666 full-wave band-gap simulations costing 4.28~min each, exploiting a 1,700-fold cost asymmetry. Across nine target band gaps up to $225~$meV, we generate and verify by full-wave simulation 270 valley photonic
crystal designs, reaching a mean absolute error of $1.4$–$6.7$~meV within the labeled range and retaining below $5.1\%$ fractional error at targets $25\%$ beyond its upper bound, while a label-conditioned
diffusion model trained on the same label data performs substantially worse. Beyond inverse design, the trained model functions as an instrument for discovering structure–property relations. At a target band gap where the labeled set contains only five designs, it generates hundreds, resolving
geometric trends that are statistically inaccessible in the training data and yielding interpretable rules for large-gap valley photonic
crystals. Our results establish surrogate-guided
diffusion as a label-efficient route to freeform topological-photonic design, and as a means of extracting design principles where physical intuition and simulation labels are both scarce.
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All authors Yuhan Zhang, Xin Xie, Bowen Song, Lixuan Chen, Liyue Shen, Hui Deng
Optics
Lasing Mode Control in ZnO Nanowires Coupled to TiO2 Nanopillars
Daniel Repp, Francesco Vitale, Raja Hoffmann et al. (+4 more)
Nanowire
lasers based on spectrally broad gain materials typically exhibit multimode emission, which limits their utility in applications requiring precisely defined spectral characteristics. In this study, we experimentally demonstrate the selective, narrow-band suppression of individual lasing modes in zinc oxide (ZnO) nanowire
lasers through near-field coupling to titania (TiO2) nanopillars. Our study is based on photoluminescence spectroscopy in the lasing regime, which is complemented by finite-difference time-domain simulations. We show suppression of longitudinal nanowire lasing modes by their resonant coupling to the whispering gallery modes in nanopillars of suitable size. In addition to spectral selectivity of the coupling, we reveal two distinct coupling regimes based on polarization matching between whispering gallery modes and nanowire waveguide modes. These findings demonstrate a promising approach towards engineering the spectral emission properties of nanowire
lasers through tailored photonic architectures.
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All authors Daniel Repp, Francesco Vitale, Raja Hoffmann, Isabelle Staude, Thomas Siefke, Carsten Ronning, Thomas Pertsch
Optics · Cross-listed from quant-ph
Bridging two families of non-Hermiticity: from non-reciprocal couplings to an imaginary potential using the Lanczos transformation
Li Ge
Two types of non-Hermiticity found in physical systems, i.e., non-reciprocal couplings and complex potentials, have gained considerable interest recently. The former leads to the non-Hermitian skin effect, while the latter gives rise to a range of non-Hermitian
symmetries such as parity-time ($PT$) and particle-hole
symmetries. Although these two non-Hermitian forms have been incorporated in the same models, so far they have been treated as distinct families of non-Hermiticity. In this work, we establish an isospectral mapping between them using the Lanczos transformation. More specifically, we show that a generalized Hatano-Nelson model $H$ with non-reciprocal and spatially varying couplings can be mapped to a tight-binding model $H_L$ with real symmetric couplings and an imaginary on-site potential. This result holds even when the original $H$ already has an imaginary potential and exceptional points. Our work provides a refreshed understanding of the connection between different forms of non-Hermiticity. It also offers an approach to obtaining an intuitive physical understanding of exceptional points in $H_L$ that are elusive in $H$. Finally, our findings also warrant a versatile approach to constructing non-Hermitian systems with a complex potential and a real spectrum, without $PT$
symmetry.
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Optics
A photonic integrated comb engine for ultracold quantum gases
Wei Sun, Xiaoying Yan, Jinbao Long et al. (+18 more)
Cold atoms underpin
quantum sensing, simulation and computation, but their coherent control demands highly stable optical fields whose generation, referencing and power scaling remain formidable integration challenges. While photonic integrated
circuits have yielded compact visible
lasers and high-$Q$ microresonators have enabled chip-scale optical frequency combs, these crucial technologies have largely remained functionally fragmented. Consequently, the coherent manipulation of ultracold
quantum gases using a fully integrated
laser-comb source has yet to be realized. Here we demonstrate a scalable, hybrid-integrated microcomb engine at 780 nm that seamlessly bridges frequency synthesis, atomic referencing and power amplification to achieve
quantum state control of a Bose–Einstein condensate. By self-injection locking of electrically driven III–V
lasers to high-$Q$ Si$_3$N$_4$ microresonators, we generate coherent platicon microcombs featuring 20- and 100-GHz mode spacings. Absolute referencing of the microcomb to an $^{85}$Rb transition actively suppresses long-term frequency drift from over 200 MHz to the 100-kHz level across 2,000 s. A selected comb tooth is subsequently injection-amplified to 102 mW, entirely preserving the microcomb's pristine coherence and stability. We utilize this synthesized field to construct an optical
lattice, drive coherent two-
photon Raman transitions, and prepare stationary
spin–orbit-coupled and Raman-
lattice states within an $^{87}$Rb condensate. By providing a synchronized optical grid, this atom-referenced microcomb can allow multiple optical-control channels to scale without a proportional multiplication of independent frequency references. Our work establishes a fully integrated frequency-synthesis architecture essential for realizing deployable, large-scale atomic
quantum systems.
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All authors Wei Sun, Xiaoying Yan, Jinbao Long, Sanli Huang, Zhixin Duan, Hao Tan, Zhenyuan Shang, Zeying Zhong, Jiahao Sun, Yue Hu, Shichang Li, Baoqi Shi, Yi-Han Luo, Shuyi Li, Chen Shen, Hanqing Liu, Xiangbin Su, Haiqiao Ni, Zhichuan Niu, Shengjun Yang, Junqiu Liu
Optics · Cross-listed from quant-ph
Decoherence Tuning in Voltage-Driven Plasmonic Cavities
Yuchen Wang, Oliver Tan and Norah M. Hoffmann
Strong light-matter coupling offers a powerful framework for modifying molecular structure, dynamics, and optical response, yet achieving this regime at the single-molecule level remains a central challenge. Scanning Tunneling Microscope Break Junctions (STM-BJ) provide a promising route by combining single-molecule addressability with extreme nanoscale field confinement. However, the metallic environment that enables such confinement also introduces substantial plasmonic and excitonic losses, raising the question of how strong coupling can be realized in a metal-molecule-metal junction. Here, we identify the voltage as the key control parameter. We show that the applied bias not only drives the formation of an interfacial
exciton through resonant charge transport but also suppresses its coupling to metallic loss channels. Simultaneously, the plasmonic cavity retains extreme mode confinement while the availability of modes is moderately tuned by voltage. Together, these results establish voltage-driven STM-BJs as electrically tunable single-molecule plasmonic cavities and open new routes for using the powerful STM-BJ toolbox, including
quantum transport, tracking chemical dynamics, optoelectronics, and molecular-scale
quantum control under strong light-matter coupling.
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Optics
Physical Fidelity of Wave-Based Inverse Problems under Broken Time-Reversal Symmetry
Haiyan Ou, Jiajia Duan, Edmund Y. Lam et al. (+1 more)
Modern coherent imaging commonly treats defocus interference as an undesirable artifact to be suppressed. Here, we show that this interference is instead a deterministic projection shadow associated with broken time-reversal
symmetry (TRS) under finite-aperture observation. The resulting non-
unitary observation operator imposes irretrievable information loss, making this shadow an unavoidable coherent residual. We demonstrate that suppressing this residual beyond the measurement support can yield physically inconsistent reconstructions by assigning unconstrained components within the null space, thereby disrupting the propagation of the reconstructed complex field. We term this failure mode physical overfitting and introduce the complex-field TRS residual metric, R_TRS(z). By using the measured axial
evolution of the projection shadow as a z-resolved physical reference, the metric extends fidelity assessment from two-dimensional (2D) detector-plane agreement to propagation-resolved three-dimensional (3D) complex-field consistency. These results establish a physical constraint on phase-space
retrieval and wave-based inverse reconstruction.
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All authors Haiyan Ou, Jiajia Duan, Edmund Y. Lam, Bingzhong Wang
Optics
Biorthogonality of Guided Modes in Non-Hermitian Electromagnetism
Amgad Abdrabou, M. A. Swillam, Şahin K. Özdemir et al. (+1 more)
Biorthogonality plays a central role in the analysis of non-Hermitian photonic systems, where modal expansions generally require both right and left eigenstates. While these concepts are straightforward within scalar and coupled-mode descriptions, their interpretation in the full vectorial Maxwell framework is less transparent. In particular, the standard electromagnetic modal orthogonality relation derived from unconjugated Lorentz reciprocity involves both electric and
magnetic fields and differs in form from the biorthogonality relations obtained from conventional adjoint-operator arguments. Here, we establish the connection between these two formulations for non-Hermitian waveguiding systems with gain and loss. Starting from the full vectorial electric-field wave equation, we formulate the guided-mode problem as a quadratic
eigenvalue problem in the propagation constant, construct its adjoint, and identify the corresponding left eigenmodes. We show that the left eigenmode is related to the complex conjugate of the backward-propagating electric-field mode and demonstrate that the resulting electric-field biorthogonal pairing is equivalent to the mixed electric–
magnetic field relation obtained from unconjugated Lorentz reciprocity. The framework also clarifies the electromagnetic meaning of modal normalization, its connection to self-orthogonality at exceptional points, and the recovery of conventional conjugated modal orthogonality in the lossless limit. These results provide a unified operator-theoretic interpretation of electromagnetic biorthogonality and Lorentz reciprocity and establish a direct connection between the left/right eigenstate
language of non-Hermitian physics and the reciprocity-based modal framework of classical electromagnetism.
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All authors Amgad Abdrabou, M. A. Swillam, Şahin K. Özdemir, R. El-Ganainy
Optics
Channel closing in strong-field photoemission from tip arrays
Leon Brückner, Jonas Heimerl, Constantin Nauk et al. (+1 more)
Ultrafast photoemission is a promising avenue for the development of petahertz electronics. For such devices, identifying the precise emission mechanism and quantifying the local field strength at the emission site are of utmost interest. While this information can be extracted from electron energy spectra or the scaling of the emission rate with peak intensity, such measurements are not always technically feasible and a clear interpretation of the results can be challenging. Here, we demonstrate channel closing as a precision gauge for the local enhanced optical nearfield strength. Channel closings originate from a field-induced upshift of the
vacuum level, which leads to a small decrease of the emission yield with increasing intensity. We report the first experimental observation of such channel closings in the photoemission rate from an array of nanometer-sharp gold tips. Our data are well matched by simulated yields, enabling us to precisely measure the local, field-enhanced optical nearfield at the tip array in situ. We expect this method to be a versatile diagnostic tool for the characterization of lightwave optoelectronic devices, as it suffices to measure currents only.
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All authors Leon Brückner, Jonas Heimerl, Constantin Nauk, Peter Hommelhoff
Optics
Theory of Airy-Beam Wavefront Sensing
Surya Kamal
A new wavefront sensing framework based on the interference of counter-accelerating Airy beams is presented. An engineered cubic phase function transforms a single Gaussian beam into two coherent Airy beams with opposite transverse accelerations, which self-recombine during free-space propagation to form an interference pattern encoding the aberrated incident wavefront. Numerical simulations demonstrate accurate recovery of the aberrated exit-pupil phase across the aberration sets considered, with a root-mean-square phase reconstruction error below $10^{-6} \mathrm{\;rad}$ for the aberration set shown and consistently low errors for the other sets, while maintaining accurate recovery in the presence of measurement noise. The approach eliminates collection optics and enables a compact wavefront-sensing architecture for applications where conventional interferometric systems are difficult to implement, including electron-optical systems, augmented and virtual reality systems.
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Optics
Photonics-GCCE: group collaborative-competitive evolution multi-agent framework for universal and autonomous optical design
Weijie Xu, Ming Wang, Ruicheng Ma et al. (+20 more)
Large
language model (LLM)-empowered photonic
agents connect natural-
language intents to executable solvers, showing significant advantages over conventional optical design approaches. However, current multi-
agent frameworks operate within a collaborative paradigm without extrinsic selective pressure, which could inherit shared blind spots, converge prematurely, and fail to accumulate transferable experience for intricate tasks. Here, we introduce a group photonics collaboration-compete
evolution (GCCE) framework and its LLM instantiation, termed Photonics-GCCE. Two independent
agent groups pursue the same design target and undergo structured competitive evaluation across refractive-index fidelity, fabrication sensitivity, algorithmic adequacy, and physical consistency. Each group comprises a leader and three specialist
agents dedicated to materials, optimization, and code validation.
Agents refine their skills through competitive evaluation across design rounds. Benchmarking across six device categories against single-
agent and multi-
agent baselines shows that Photonics-GCCE elevates composite scores into the high 90s, improves fabrication robustness by 15 to 17 points, and reduces solver iterations to roughly 40 rounds. A representative quasi?BIC demonstration achieves a practically fabricable design with a quality factor of 13120. Our results demonstrate Photonics-GCCE as a general-purpose and closed-loop framework for autonomous optical design, capable of producing high-performance, fabrication-ready devices across diverse nanophotonic tasks.
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All authors Weijie Xu, Ming Wang, Ruicheng Ma, Zeyong Wei, Di Zhang, Jian Chen, Zining Wang, Sijun Hu, Linyuan Dou, Haoyu Li, Haigang Liang, Yijie Luo, Shuqiao Li, Qinghua Song, Huihui Zhu, Hongfei Jiao, Chao Liu, Ali Momeni, Zhanshan Wang, Yuzhi Shi, Romain Fleury, Cheng-Wei Qiu, Xinbin Cheng
Optics
Inverse-Designed Chiral Metasurfaces for Enhanced Helical Dichroism
Chia-Chun Pan, Yu-Hsi Chen, Munseong Bae et al. (+5 more)
Helical dichroism (HD), arising from the interaction between structured light carrying orbital angular momentum (OAM) and chiral matter, offers opportunities for enhanced chiroptical characterization at the subwavelength scale. Here, we employ inverse design to develop chiral metasurfaces tailored for enhanced HD under Laguerre-Gaussian (LG) beam illumination. The optimized planar structure exhibits a simulated HD around 115% at 800 nm for opposite OAM states, revealing the strong chiroptical response enabled by the inverse-designed geometry. The optimized metasurfaces were fabricated from Si$_3$N$_4$ and experimentally characterized using a custom-built optical system with controlled OAM excitation. A single chiral metasurface exhibited a maximum experimental HD up to 62% near 800 nm, demonstrating a strong OAM-dependent helical dichroic response from a single 6-micron-large chiral structure. Although the measured HD value is lower than the optimized simulation value, the experimental result validates the feasibility of inverse-designed chiral metasurfaces for structured-light chiroptics. These findings establish inverse design as an effective approach for engineering compact chiral nanophotonic structures with enhanced interactions with structured light, offering potential for miniaturized chiroptical sensing and OAM-resolved imaging.
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All authors Chia-Chun Pan, Yu-Hsi Chen, Munseong Bae, Haejun Chung, Dan Smith, Daniel Fan, Sejeong Kim, Ranjith R Unnithan
Optics
Order-Dependent Modification of High-Harmonic Generation by Quantum Dissipation and Lamb Shift
Xiangyu Zhang, Tong Wu, Xiang Li et al. (+5 more)
Many-body environments are conventionally incorporated into
quantum dynamics as heat baths, which induce a Lamb shift and
quantum dissipation. In the traditional picture, such environmental coupling is expected to induce suppression and broadening of spectral signals. In this letter, we investigate high-order harmonic generation (HHG) in a two-level system coupled to a heat bath via dipole-dipole interactions using the Lindblad master equation. It is found that the environmental effect does not simply suppress the harmonic efficiency. Instead, when the cutoff frequency of the coupling spectral density exceeds the energy-level spacing, the environment can actually enhance the harmonic yield. Further analysis reveals that this enhancement originates from intense level fluctuations induced by the Lamb shift. Meanwhile, the environmental influence exhibits a distinct dependence on harmonic order, manifesting clearly different behaviors for lower and higher harmonics. Our results challenge the common relaxation-time picture of uniform damping and establish a microscopic, order-dependent mechanism for environmental control of HHG, with direct implications for solid-state attosecond spectroscopy and
quantum material engineering.
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All authors Xiangyu Zhang, Tong Wu, Xiang Li, Jianshi Lu, Zhe Yang, Chao Yu, Shicheng Jiang, Ruifeng Lu
Optics
A native signed incoherent photonic matrix core on thin-film lithium niobate supporting in situ backpropagation
Yuan Ren, Yong Zheng, Ruixue Liu et al. (+2 more)
Artificial intelligence workloads increasingly demand computing architectures combining high throughput, energy efficiency, and physical scalability. Here we present a signed incoherent optical
matrix multiplier on thin-film lithium niobate that natively supports signed inputs and weights. We demonstrate closed-loop in situ backpropagation on a 16 X 16 photonic core, including forward computation, nonlinear operations, error propagation, and gradient computation. Measured physical outputs directly participate in optimization, thereby incorporating actual device responses and nonidealities into training. The core achieves 8-bit multiplication and 10-bit accumulation precision across 256 channels, maintains 10-bit accuracy in tiled 256 X 256
matrix computation, and further executes
Transformer linear operations in a BERT-mini workload. This work presents a fundamental, scalable building block that addresses key limitations in practical optical computing, thereby opening avenues for large-scale, high-efficiency photonic neuromorphic systems.
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All authors Yuan Ren, Yong Zheng, Ruixue Liu, Min Wang, Ya Cheng
Optics
Shift-register synchronization of dual-wavelength pulse trains in resonators with quadratic nonlinearity
Stepan Bogdanov, Anastasiya Bednyakova and Sergei K. Turitsyn
Self-organization of nonlinear waves underpins phenomena ranging from hydrodynamic pattern formation to optical frequency-comb generation. We introduce and numerically demonstrate a shift-register synchronization mechanism for pulse trains in quadratic nonlinear resonators. The synchronized state persists despite substantial group-velocity mismatch through continuous parametric energy exchange, resulting in deterministic discrete pulse shifts after each cavity round trip. Nonlinear parametric interaction modifies the effective walk-off, allowing the pulse trains to satisfy the shift-register synchronization conditions. The proposed mechanism reveals a previously unexplored synchronization regime in quadratic resonators and provides a route toward multicolour frequency combs, optical
memories, and ultrafast photonic information processing.
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Optics
All-Dielectric Ceramic 3-D Printed Unidirectional Leaky-Wave Antenna at mm-Wave Frequencies
Guillaume François, Masoud Sakaki, Henrik Jansen et al. (+3 more)
An all-dielectric leaky-wave
antenna, radiating unidirectionally at broadside without the use of a metallic ground plane, is designed and manufactured. It operates in the 70-90 GHz frequency range with a design broadside frequency of 77 GHz. The design process makes use of the theory of photonic bandgaps to position a -1 harmonic at the broadside frequency on the second Bragg-condition point. The structure is then modified to close the bandgap and to simultaneously guarantee maximum total field coupling to the relevant radiating harmonic, ensuring radiation unidirectionality. The
antenna is manufactured with an Al2O3 ceramic printing process, demonstrating its manufacturing potential for complex low-loss high-frequency structures. Simulations agree well with measurements, with the main deviation being a 1 GHz frequency shift that could be reproduced in simulation. The
antenna prototype shows a scanning range of -18{\deg}-22{\deg} and gain values above 23 dBi. More than 85 % of the radiation power is radiated unidirectionally at broadside, with simulations showing potential to attain 98 %.
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All authors Guillaume François, Masoud Sakaki, Henrik Jansen, Amar Al-Bassam, Niels Benson, Dirk Heberling
Optics · Cross-listed from cs.AI
SHRAV: State-Hypothesis-Reason-Action-Verify Framework for Physical Modeling and Inverse Design
Ziheng Guo and Yang Bu
Physical modeling and inverse design require computation that can continue from reusable state. We introduce SHRAV, an architecture-independent computational framework organized around State, Hypothesis, Reason, Action, and Verify. Its central mechanism is a state-continuation core with declared reuse boundaries and explicit roles for learned
evolution and numerical quantities. Forward configurations evolve predictive state and read out physical responses; inverse-design configurations additionally generate target-directed modifications and consume evaluator feedback. Electromagnetic world-model studies are mapped to forward configurations, with selected readout and reuse diagnostics reported here. Computational lithography demonstrates an inverse-design configuration: four fixed-weight design updates improve thresholded aerial-image intersection-over-union from 0.5313 to 0.8153 under independent scalar-pupil replay, with a maximum absolute IoU difference of approximately 0.000824 between predictor estimates and independent replay.
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Optics
Thouless Pumping of Wave Action in Photonic Time Crystals
Minwook Kyung, Younsung Kim, Kyungmin Lee et al. (+3 more)
A topological pump transports a conserved quantity. Yet temporal modulation exchanges energy with the field, so the transported quantity must be identified from Maxwell's equations. Here we connect band
topology to the temporal displacement of conserved Maxwell wave action in a photonic time
crystal. The temporal Wannier function of an isolated positive-action band carries unit action with zero net energy flux, and its temporal center is a Berry polarization. Over one adiabatic cycle, that center shifts by the band Chern number: one
cell for a rigid translation and two for a two-tone cycle within a single band.
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All authors Minwook Kyung, Younsung Kim, Kyungmin Lee, Hee Chul Park, Moon Jip Park, Bumki Min
Optics
Programmable and scalable on-chip WDM processing platform enabled by cascaded FSR-free resonators
Boshu Sun, Haojie Zhu, Ying Sun et al. (+17 more)
Wavelength-division multiplexing (WDM) is pivotal for expanding the capacity and functionality of photonic systems, from communications to computing. However, on-chip implementation for broadband operation is fundamentally limited by the narrow free spectral range (FSR) and inefficient drop transmission of conventional optical microcavities. Here, we transcend this limit with a scalable integrated WDM processing platform based on cascaded dual-sided coupled Fabry-Pérot add-drop resonators. This unit achieves a record-large FSR-free bandwidth (> 300 nm) and low insertion loss (< 0.5 dB), while enabling independent manipulation of monochromatic light in both the wavelength and intensity domains. Leveraging these performances, we architect programmable cores with up to 20 channels in a single bus waveguide to demonstrate application versatility by configuring as: a high-capacity on-chip WDM communication fabric (2.4-Tbps single-link WDM transmission and O-to-C-band multi-subband (de)triplexing), a reconfigurable optical processor (broadband and hitless wavelength-selective switching), and a parallel computing accelerator (theoretically capable of 1.28-TOPS convolution operations, 16-channel modulation). This work establishes a unified and versatile WDM processing platform that bridges high-speed optical communication with in-line computing, charting a scalable and backward-compatible path toward petabit-per-second-class links and hundreds of TOPS of on-chip computation, resolving a critical bottleneck for next-generation photonic systems.
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All authors Boshu Sun, Haojie Zhu, Ying Sun, Kunhao Lei, Zijia Wang, Kangjian Bao, Weiqi Lu, Yuhao Fang, Yuting Ye, Danyang Hao, Qingyan Deng, Zequn Chen, Yingchun Wu, Maoliang Wei, Wei Cao, Xu Sun, Qicheng Zhang, Hongtao Lin, William Shieh, Lan Li
Optics
Magnetic Lifting of BIC Symmetry Protection Enables Nonreciprocal Beam Steering and Angular Information Encoding
Chengrui Zhang, Zijing Xianyu, Chufan Zhou et al. (+9 more)
Symmetry-protected bound states in the continuum (SP-BICs) offer exceptional optical confinement but remain nonradiative. Here, we demonstrate that magnetically lifting their protecting
symmetry enables nonreciprocal beam steering with intrinsic angular information encoding. In a magneto-optical photonic
crystal slab, an in-plane
magnetic field converts an SP-BIC into a radiative quasi-BIC and, together with vertical dielectric asymmetry, continuously displaces the associated band extremum away from the Gamma point. The steered beam exhibits two independent locking relations: its wavelength is locked to the elevation angle, while its polarization orientation is locked to the azimuthal angle. These relations embed complementary spectral and polarization information into the scanning beam, providing additional sensing channels for multidimensional
LiDAR. Moreover, the nonreciprocal dispersion gives different resonance frequencies at opposite wave vectors, supporting resonant emission at +k while back-reflected light at the same frequency is off resonance at -k, opening a route to intrinsic self-isolation and reduced optical feedback. These findings establish a unified framework connecting
magnetic beam steering, angular information encoding, and nonreciprocal feedback suppression, with prospects for compact reconfigurable light sources and integrated optical engines.
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All authors Chengrui Zhang, Zijing Xianyu, Chufan Zhou, Qi Jiang, Shengxuan Si, Wanli Xue, Ji Wu, Haoming Zhong, Jiaqi Zhang, Hanqi He, Edoardo Charbon, Zhiyu Wang
Optics
Spectral Lock-in Detection for High-Sensitivity Spectroscopy
Szu-An Tsao, Joseph J. Hwang and Mona Jarrahi
The ability to recover weak signals without sacrificing their spectral information is central to precision spectroscopy, yet conventional lock-in detection achieves noise rejection at the expense of spectral dimensionality and ultimately imposes a trade-off between detection bandwidth and sensitivity. Here, we introduce spectral lock-in detection, a versatile framework that extends lock-in noise rejection independently to every resolved component of a broadband spectrum. By separating the fast-time coordinate encoding spectral information from the slow-time coordinate carrying temporal modulation, the measured waveform is spectrally resolved before demodulation, enabling each frequency channel to be independently detected and integrated. We show analytically that, for spectrally stable signals, the signal power in each spectral channel remains invariant, while the noise power ideally decreases by 10 dB per decade of integration time, enabling spectral features buried beneath the instantaneous noise floor to emerge without loss of frequency information. We experimentally validate this framework in both phase-incoherent heterodyne terahertz spectroscopy and phase-coherent terahertz time-domain spectroscopy, demonstrating more than six orders of magnitude of sensitivity enhancement across the spectrally resolved channels. Because spectral discrimination is performed computationally on the acquired waveform, the approach requires neither sequential spectral scanning nor additional spectral-selection, multichannel-detection, or interferometric hardware. Spectral lock-in detection therefore provides a broadly applicable route to enhancing sensitivity across diverse spectroscopic platforms and frequency regimes, opening new opportunities for high-sensitivity, information-rich measurements across the electromagnetic spectrum.
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Optics · Cross-listed from quant-ph
A 75-mL intrinsically stable atom-filtered laser enabling deployable quantum devices
Zijie Liu, Zheng Xiao, Zhiyang Wang et al. (+10 more)
Numerous
quantum devices require
lasers strictly locked to atomic transitions. Atom-filtered
lasers (AFLs) are considered a leading candidate for
quantum device
laser sources due to their ability to self-align to atomic transitions. However, the sub-GHz sharp transmission spectra of conventional atomic filters impose constraints on both
laser miniaturization and output stability. Herein, we demonstrate a micro Faraday anomalous dispersion optical filter ({\mu}FADOF) operating within the extreme hyperfine Paschen-Back regime, generating a 7.5 GHz flat-top transmission window. By integrating this filter, the miniaturization bottleneck of the AFLs is overcome, achieving a 30-fold volume reduction to a compact package volume of 75 mL. Simultaneously, investigations into the optical self-feedback characteristics of the {\mu}FADOF reveal a stable operating regime, where the optical self-feedback of the atomic filter acts as a stabilizing mechanism, enabling the
laser to achieve a power instability of 9 x 10^-6 at 1 s and 3.2 x 10^-5 at 8400 s. The optical frequency standard based on this 75-mL AFL achieves a further improvement in long-term frequency stability to 3 x 10^-13 at 10000 s and maintains turn-key operation under environmental shocks, highlighting the critical role of this
laser in the development of deployable
quantum devices.
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All authors Zijie Liu, Zheng Xiao, Zhiyang Wang, Xiaolei Guan, Xiaomin Qin, Suyang Wei, Hongtian Song, Baoshuai Wang, Jia Zhang, Xiaopeng Xie, Tiantian Shi, Anhong Dang, Jingbiao Chen
Optics
Boundary singular scattering enables coherent perfect absorption and lasing without resonators
Letian Yu, Xu Zheng, Cesare Soci et al. (+2 more)
Scattering singularities are features conventionally associated with resonant scattering bodies, which correspond to the zeros and poles of a scattering
matrix, and manifest as coherent perfect absorption and lasing respectively. Here, we show that they can emerge solely from an interface, eliminating the need for any resonant body. We introduce boundary singular scattering, whereby an interface between two non-Hermitian media supports coherent perfect absorption, lasing, or both. Despite these singular responses, the two adjoining media are in parity-time (PT)-unbroken phases, with entirely real bulk spectra. This phenomenon originates from a singular boundary mode-matching condition unique to non-Hermitian systems, not from any underlying resonant modes. We demonstrate it experimentally in a programmable synthetic photonic
lattice, and show coherent switching between perfect absorption and lasing by controlling only the relative phase of the incident beams. The same mechanism further generalizes from mirror-symmetric interfaces to asymmetric interfaces with dissimilar bulk dispersions. Our work establishes boundaries as a previously unexplored origin of scattering singularities, opening a resonator-free route to coherent perfect absorption, lasing, and other singular wave phenomena.
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All authors Letian Yu, Xu Zheng, Cesare Soci, Y. D. Chong, Baile Zhang
Optics
Anisometric Dielectric Snowman-Particle Provides Improved Control Over Photonic Hook
Yu. E. Geints, I.V. Minin and O.V. Minin
A novel efficient method for controlling photonic hook (PH) with an anisotropic dielectric microparticle dimer in the snowman-particle configuration is introduced and numerically justified. In contrast to existing schemes that rely on structured illumination, partial shielding, or complex morphologies, the proposed anisometric geometry utilizes a simple and easily manufacturable form composed of two partially overlapping cylinders. The finite element method was employed to study how the degree of asymmetry, spatial rotation, and optical properties of the upper particle (the head of the snowman-particle) affect the bending angle and maximum intensity of PH. For the first time, it has been demonstrated that adjusting these parameters allows for the deliberate switching between single and double PH modes, as well as controlling the direction and
curvature of the hook, including the fragmentation of the focal area. This approach offers high efficiency in utilizing incident radiation, simplicity in fabrication, and broad tunability of PH characteristics. The findings pave the way for the development of compact near-field optical devices, such as optical traps, high-resolution microscopes, sensors, and tools for surface microstructuring.
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Optics
DNNsolver: Accurate and Efficient Deep Learning Modeling of Polarization-Sensitive Diffractive Neural Networks
Shuyi Wang, Hong-Bo Sun and Linhan Lin
Diffractive neural networks (DNNs), composed of cascaded diffractive layers, offer a promising platform for high-speed optical computing. However, accurate and efficient modeling of high-density, polarization-sensitive DNNs remains challenging. Conventional model based on thin element approximation (TEA) fails to capture electromagnetic coupling within layers, while full-wave simulations such as finite-difference time-domain (FDTD) methods are computationally expensive. Here, we propose DNNsolver, a deep learning-based electromagnetic surrogate model that learns the scattering response of diffractive layers. By predicting the scattering
matrix rather than source-dependent output fields, DNNsolver decouples the incident wavefront from the model and could be applied to arbitrary input fields. A local scattering kernel and sliding-window strategy further allow efficient modeling of DNNs with arbitrary spatial sizes. For single diffractive layer under random speckle illumination, DNNsolver achieves an average mean squared error (MSE) of 0.0095 and about 10^6-fold speedup compared with FDTD simulations. DNNsolver is further applied to the optimization of a trilayer polarization-multiplexed image classifier, which exhibits better agreement with FDTD simulations than its TEA-based counterpart. Our work provides an accurate and efficient framework for the design and optimization of high-density, polarization-sensitive DNNs.
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Optics · Cross-listed from physics.flu-dyn
Measurement of Nanoscale Surface Disturbances on Liquid Jets Using the Mie Scattering Method
Dingwei Zhang, Qiyou Liu, Hu Sun et al. (+3 more)
The Plateau–Rayleigh instability of
liquid jets governs a wide range of natural and industrial processes. While the classical linear stability theory accurately predicts disturbance growth rates and dominant wavelengths, it cannot quantify the amplitude and frequency spectrum of nanoscale initial surface disturbances. This critical missing information prevents accurate forecasting of breakup lengths and droplet generation. Conventional optical imaging is constrained by the diffraction limit and lacks the capability to resolve such nanoscale surface fluctuations. Here we introduce a Mie-scattering-based measurement technique to characterize nanoscale surface disturbances on
liquid jets. The method employs a thin
laser sheet to illuminate the jet, with scattered light captured at designated azimuthal observation angles. Based on Lorenz–Mie theory, we develop an inversion
algorithm incorporating cosine similarity and cross-correlation to reconstruct jet surface disturbances from measured scattering fringes, achieving a sub-nanometer resolution for detecting diameter variations, with an overall measurement precision limited by a background noise floor of 0.18 nm RMS. Comparative analyses of forward and rainbow scattering signals further confirm that the surface disturbances become axially symmetric as the amplitude reaches a few nanometers, and thus satisfies the assumptions of the scattering model. Synchronous validations against high–speed imaging and scanning electron microscopy corroborate the quantitative accuracy of our scattering method. Applied in the near-nozzle region, the technique identifies two intrinsic signatures of initial perturbations:
stochastic pulse-like fluctuations and low-frequency oscillations.
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All authors Dingwei Zhang, Qiyou Liu, Hu Sun, Qingfei Fu, Bingqiang Ji, Lijun Yang
Optics
High-power visible laser via injection locking to a photonic integrated circuit optical parametric oscillator
Daniel Pimbi, Zhiquan Yuan, Ashish Chanana et al. (+4 more)
Kerr photonic integrated
circuit optical parametric oscillators (PIC OPOs) provide a promising platform for coherent visible-light generation, offering broad wavelength accessibility and low frequency noise for applications in
quantum information processing, precision metrology, spectroscopy, and sensing. However, achieving large fiber-coupled output powers and high conversion efficiency remains challenging, impacting the practical deployment of these sources. Here we demonstrate optical injection locking of a commercially available visible Fabry-Pérot (FP)
laser diode to a PIC OPO, realizing a hybrid
laser that combines the complementary strengths of nonlinear frequency conversion with those of
semiconductor laser technologies. Using 25 $\mu$W of injected PIC OPO signal, we generate coherent visible-light at 635 nm with a fiber-coupled output power of $\approx$ 40 mW and side-mode suppression ratio $\gtrsim$ 36.3 dB. The injection-locked FP
laser faithfully inherits the low frequency noise characteristics of the PIC OPO signal, achieving a frequency noise floor of 714 Hz$^2$/Hz. We further demonstrate $\gtrsim1$ GHz wide locking bandwidths that enable stable injection locking without active PIC OPO stabilization, together with coarse wavelength tunability over 6 nm while preserving both high output power and spectral purity. Our results establish optical injection locking with nonlinear light sources as a compelling option for coherent, high-power, and wavelength-agile integrated coherent visible sources.
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All authors Daniel Pimbi, Zhiquan Yuan, Ashish Chanana, Usman A. Javid, Xiyuan Lu, Jordan Stone, Kartik Srinivasan