Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics Optics

physics.optics Watch Optics

Thursday 17 September

Optics

Frequency Attraction and Repulsion in Lasers with Complex Mutual Coupling

Amit Pando, Tomer Hacohen, Eran Bernstein et al. (+3 more)

We experimentally investigate laser synchronization under complex mutual coupling, featuring both dissipative and dispersive components. Using a reconfigurable digital degenerate cavity laser with precise control over system parameters, we show that complex coupling can induce both frequency attraction and repulsion, in contrast to common models of coupled oscillators. Furthermore, we show that these frequency shifts can be exploited to significantly enhance global synchronization in multi-laser arrays. Comparison with numerical and theoretical results indicate that amplitude dynamics of complex coupled lasers play an important role in the observed phenomena. Our results establish a versatile platform for exploring non-Hermitian physics and topological states in tailored laser networks.
Read the full abstract

All authors Amit Pando, Tomer Hacohen, Eran Bernstein, Victor Shelukin, Asher Friesem, Nir Davidson

Optics

Transient High-Harmonic Generation from Solids: From Spectroscopy and Control to Programmable Emission

Pieter J. van Essen, Torben Ham, Zhonghui Nie et al. (+1 more)

High-harmonic generation (HHG) from solids has emerged as a powerful probe of electronic structure and ultrafast dynamics in condensed matter systems. In this chapter, we review recent advances in solid-state HHG spectroscopy and control, with a focus on semiconductors and correlated materials. We discuss the theoretical foundations of HHG and summarize experimental approaches for extracting information from harmonic emission. HHG has been shown to be sensitive to a wide range of microscopic properties, including band structure, transition dipole moments, Berry phases, crystal symmetry, carrier populations, dephasing processes, and lattice dynamics. This sensitivity enables access to electronic and structural dynamics on femtosecond and attosecond timescales and has established HHG as a versatile spectroscopic tool. At the same time, the strong dependence of HHG on many coupled material and excitation parameters makes the emitted harmonics intrinsically difficult to associate with a single microscopic quantity. Rather than representing a limitation alone, this sensitivity also provides numerous pathways for control. We review how photoexcitation, multicolor driving fields, waveform engineering, and transient modification of material properties can be used to enhance, suppress, and shape harmonic emission. These developments position solid-state HHG not only as a spectroscopic technique, but also as a platform for programmable nonlinear optics with applications ranging from compact extreme-ultraviolet sources to super-resolution microscopy and ultrafast photonic devices.
Read the full abstract

All authors Pieter J. van Essen, Torben Ham, Zhonghui Nie, Peter M. Kraus

Optics

High-capacity computing with self-rectification nonlinear optical neural processor

Ruicheng Ma, Siyu Dong, Yuzhi Shi et al. (+14 more)

Artificial intelligence (AI) and neural networks have driven groundbreaking innovations across numerous disciplines. Optical computing offers the promise of unprecedented speed and energy efficiency in the post-Moore era; however, achieving efficient, practical nonlinear activation using all-optical approaches remains a challenge. Here, we present an optical nonlinear neural processing unit (ONNPU) that implements all-optical nonlinear activation through a self-rectification mechanism. The ONNPU architecture perfectly imitates the structure of digital neural networks, enabling seamless integration with the established deep learning ecosystem. We benchmark ONNPU across nine diverse tasks spanning decision, regression and generation, including accuracies of 98.07% on MNIST and 93.54% on Fashion-MNIST. When integrated into a 201-million-parameter Vision Transformer, ONNPU achieves 82.4% top-1 accuracy on full ImageNet classification (1,000 categories); when integrated into a 117-million-parameter decoder-only Transformer, ONNPU enables short-form story generation that outperforms GPT-2. By addressing more complex and diverse deep learning tasks, ONNPU paves the way toward practical optical machine intelligence, unleashing significant potential for high-performance optical computing.
Read the full abstract

All authors Ruicheng Ma, Siyu Dong, Yuzhi Shi, Yuchen Zhu, Hong Luo, Qiang Fu, Hadi Amata, Wolfgang Heidrich, Xiong Dun, Hongfei Jiao, Hui Zhang, Qinghua Song, Zeyong Wei, Zhanshan Wang, Ali Momeni, Romain Fleury, Xinbin Cheng

Optics

Power-Bandwidth Scaling of Resonantly Coupled Soliton Microcombs

Xinrui Luo, Kaixuan Zhu, Yuanlei Wang et al. (+8 more)

A soliton microcomb requires increasing pump power as its optical bandwidth is broadened. Resonant pumping through an auxiliary microresonator can reduce the power required to sustain a soliton, but simultaneously increases the power required for soliton formation. We show that this competition leads to optimal inter-resonator coupling, and the predicted minimum input pump power scales as the two-thirds power of the comb bandwidth, in contrast to the quadratic scaling under direct pumping. Experiments support the opposing power trends, providing a design rule for power-efficient, ultra-broadband soliton microcombs.
Read the full abstract

All authors Xinrui Luo, Kaixuan Zhu, Yuanlei Wang, Yinke Cheng, Haoyang Luo, Junqi Wang, Yiwen Yang, Zhenyu Xie, Bei-Bei Li, Qihuang Gong, Qi-Fan Yang

Optics

Broadband transverse mode directional couplers using partial Euler bends

Airin Antony, Daniel Peace and Jacquiline Romero

Transverse modes beyond the fundamental mode are increasingly being explored to increase information capacity in both mode-division multiplexing and high-dimensional quantum information processing. The ability to combine and separate these modes at arbitrary ratios over a broad bandwidth is central to these applications. Motivated by the lower bending loss and intermodal crosstalk of partial Euler bends in multimode waveguides, we develop a geometric framework based on partial Euler bends for broadband power coupling between the first two transverse electric modes on a silicon-on-insulator platform. Our methodology uses a hybrid of eigenmode expansion and finite-difference time-domain methods. Our designs feature a mode (de)multiplexer, as well as unbalanced couplers (2/3 and 1/3 splitters). The simulated 1-dB bandwidths of our directional couplers range from $101$ nm to $134$ nm. The best-performing fabricated mode (de)multiplexer has a measured 1-dB bandwidth of $90$ nm, a conversion efficiency of $94.0\%$ and crosstalk below $-18$ dB at $1550$ nm. Our results validate the use of partial Euler bends for broadband transverse mode directional couplers and provide a general framework for their design.
Read the full abstract

Optics

Mo2TiC2Tx MXene Saturable Absorption for Neural Networks on a Chip

Shadad Watad, Aviad Katiyi, Bar Favelukis et al. (+5 more)

MXenes have attracted considerable interest for integrated nonlinear photonics owing to their broadband optical response and chemical tunability, yet investigations have focused predominantly on Ti-based compositions, leaving the nonlinear potential of double-transition-metal MXenes largely unexplored. Here we quantify the nonlinear optical response of the double-transition-metal MXene \ce{Mo2TiC2T_x} and demonstrate its functionality as a waveguide-integrated nonlinear activation element for neuromorphic photonics. Z-scan measurements at \SI{800}{\nano\metre} reveal strong saturable absorption in films of two different thicknesses, yielding effective nonlinear absorption coefficients ($\beta_\mathrm{eff}$) between approximately $-2.69\times10^{3}$ and $-0.88\times10^{3}$ \si{\centi\metre\per\giga\watt}, with the nonlinear response decreasing at higher excitation intensities. The extracted nonlinear absorption is approximately one order of magnitude larger than that reported for \ce{Ti3C2T_x} MXene under comparable conditions. We integrate an ultrathin \ce{Mo2TiC2T_x} MXene layer onto a silicon rib waveguide to realize a compact nonlinear optical activation function, which, when implemented in a neural-network emulator, achieves $98.39\%$ classification accuracy on the MNIST benchmark. This work expands the MXene material platform beyond Ti-based compositions and establishes double-transition-metal MXenes as promising candidates for high-performance integrated nonlinear photonic and neuromorphic computing technologies.
Read the full abstract

All authors Shadad Watad, Aviad Katiyi, Bar Favelukis, Muhammad Sharif Uddin, Anupma Thakur, Maxim Sokol, Babak Anasori, Alina Karabchevsky

Optics

Aberration sensing in fluorescence microscopy using quantum correlations

Shay Elmalem, Shaurya Aarav, Allard K. F. Hübler et al. (+2 more)

Widefield fluorescence microscopy is an essential biological imaging tool, yet its penetration depth is fundamentally restricted by tissue-induced aberrations. Correcting these requires precise characterization of the point spread function (PSF), but existing wavefront sensing techniques rely either on often-unavailable guide stars, or on computationally heavy indirect phase retrieval methods, that could struggle in low-contrast regions. Here, we show that the PSF can be mapped directly and non-invasively by exploiting quantum correlations between photons. Standard fluorophores inherently exhibit photon antibunching, effectively acting as sources of “missing” photon pairs. By capturing these correlation statistics across a wide field of view using a single-photon avalanche diode (SPAD) array imager, we extract the local PSF autocorrelation directly from the fluorescence emission itself. This approach bypasses the limitations of classical intensity measurements, requiring no iterative or complex numerical optimization. We demonstrate widefield direct PSF retrieval in a second or less, paving the way for real-time operation. By translating quantum optical concepts to conventional fluorescent probes, this technique provides a robust, direct pathway to deep-tissue adaptive optics in life sciences.
Read the full abstract

All authors Shay Elmalem, Shaurya Aarav, Allard K. F. Hübler, Hugo Defienne, Dan Oron

Optics · Cross-listed from cs.LG

Learning-Based Reconstruction of Optical Properties in Bilayered Media from Single-distance Time-Resolved Reflectance Measurements

Caterina Amendola, Giulia Maffeis, Lorenzo Buffoni et al. (+8 more)

The inverse problem of reconstructing optical properties, specifically absorption and scattering coefficients, in layered biological media from time-domain reflectance measurements remains a significant challenge for traditional analytical models. Inverse solvers based on the diffusion equation often struggle with structural heterogeneity, frequently yielding poor accuracy for superficial absorption and deep-layers scattering. In this work, we propose a machine learning framework as an alternative approach to reconstruct the optical properties of a bilayered medium, benchmarking its efficiency and accuracy against model-based algorithms. To overcome the intrinsic approximations of diffusion theory and inverse reconstruction, we generated a robust synthetic dataset of forward DTOF using exact Monte Carlo simulations at multiple source-detector distances. A machine learning pipeline was then trained on this dataset and validated against state-of-the-art model-based reconstruction methods. Besides the significant reconstruction speed-up, the machine learning approach achieves higher accuracy than model-based inverse solvers, further providing an estimate of the parameter space dimensionality without requiring any a priori information about the number of layers in the investigated geometry. Further enhancements in the reconstruction accuracy can be expected in future extensions of this work, by training the pipeline over multiple DTOF curves from the same medium, in a joint multi-distance reconstruction approach.
Read the full abstract

All authors Caterina Amendola, Giulia Maffeis, Lorenzo Buffoni, Lorenzo Chicchi, Francesco Coghi, Duccio Fanelli, Raffaele Marino, Fabrizio Martelli, Riccardo Paoli, Lorenzo Pattelli, Lorenzo Spinelli

Optics

Rapidity-Coupled Spin Dynamics in Pulsed Laser Fields from Physics-Informed Neural Networks

N. S. Akintsov, A. P. Nevecheria, S. N. Andreev et al. (+1 more)

Carrier-envelope-phase (CEP) stabilized few-cycle pulses make the sub-cycle field structure a control parameter for laser-driven polarized electron sources, yet spin solvers for such pulses are rarely tested against exact results. We show that for an electron initially at rest in a linearly polarized plane-wave pulse the rest-frame polarization angle follows the instantaneous vector potential, $\Sigma = 2\arctan(a_x/2) + a_e a_x$ with $a_e$ the electron anomaly: the net rotation vanishes for every CEP, while the peak intra-pulse angle varies over the CEP by 3.02 degrees for a two-cycle and by 0.22 degrees for an eight-cycle pulse. The result follows from the Volkov orbit in longitudinal and transverse rapidities. We use it to validate a light-front reference integrator and a physics-informed neural network trained only on the light-front equations, which reaches $4\times10^{-5}$ in the spin sector and carries over to elliptical polarization, for which no closed-form solution is known. This gives validated tools for CEP-resolved spin dynamics in intense fields.
Read the full abstract

All authors N. S. Akintsov, A. P. Nevecheria, S. N. Andreev, Qing-Hua Qin

Optics

Voltage-Current-Emission Framework of Time-Resolved Electroluminescence

Hui Bao, Longjia Wu, Yanan Guo et al. (+3 more)

Time-resolved electroluminescence has been a central methodology in the development of LED devices. However, it still lacks quantitative theoretical descriptions of time-resolved electroluminescence. By combining the equivalent circuit models of semiconductor devices and the carrier dynamics of electroluminescence processes, we here developed a Voltage-Current-Emission framework to illustrate time-resolved electroluminescence from the pulse voltage as input, to injection current and finally generate electroluminescence as output. The features of different LED devices can be quantitatively interpreted, confirming the universal applicability across LEDs with different materials and device structures. Importantly, the curves of time-resolved electroluminescence can be simulated to quantitatively describe the dynamics of current and carriers of LED operation. In all, the Voltage-Current-Emission framework offers theoretical guidance for achieving advanced LED devices for AI technology.
Read the full abstract

All authors Hui Bao, Longjia Wu, Yanan Guo, Jianchang Yan, Ying Wang, Haizheng Zhong

Optics

Limits on the free-space group velocity of optical wave packets incorporating angular dispersion. Part~II, non-differentiable angular dispersion: tutorial

Layton A. Hall and Ayman F. Abouraddy

In Part~I of this tutorial, we showed that introducing angular dispersion (AD) into a collimated optical pulse allows for tuning the wave packet group velocity in free space. In principle, the group velocity can take on arbitrary values, whether superluminal, subluminal, or even negative. However, any significant deviation of the group velocity from $c$ (the speed of light in vacuum) necessitates propagation at large angles with respect to the optical axis in the non-paraxial regime. In Part~II of this tutorial, we describe the recent discovery of a new form of AD we refer to as `non-differentiable AD', which circumvents the limits imposed by conventional (differentiable) AD. Non-differentiable AD does not refer to an AD profile that is discontinuous, contains a kink, or features a singularity. Rather, a non-differentiable AD profile is continuous, smooth, and is differentiable everywhere except for one wavelength at which the derivative is not defined. We show that salutary features follow from this non-differentiability with respect to tuning the group velocity of a pulsed beam in free space; namely, significant deviations in the group velocity away from $c$ are achievable in the paraxial regime while remaining free of group-velocity dispersion and all higher-order dispersive effects. This tutorial presents an outline of these recent results for tuning the group velocity of a wave packet via non-differentiable AD, connecting them with the corresponding results associated with conventional AD – as outlined in Part~I. Moreover, we show that non-differentiable AD undergirds the unique characteristics of propagation-invariant space-time wave packets, thus unifying a large swathe of results in a single conceptual framework.
Read the full abstract

Optics

Limits on the free-space group velocity of optical wave packets incorporating angular dispersion. Part~I, conventional angular dispersion: tutorial

Layton A. Hall and Ayman F. Abouraddy

A plane-wave optical pulse travels in free space at a group velocity $c$ (the speed of light in vacuum) measured along its propagation axis. It is sometimes thought that spatially structuring the field in free space reduces the group velocity below $c$ because – intuitively – the oblique wave vectors undergirding the wave packet increase the average group delay. Here we show that spatiotemporally structuring a pulsed optical beam (or wave packet) can yield – in principle – arbitrary group velocities in free space in contradistinction to this commonly held intuition. We devote our attention here to pulses endowed with angular dispersion (AD) where the propagation angle is wavelength dependent. This class of wave packets is particularly pertinent because their group velocity is constant over the transverse field profile and along the propagation axis, thereby yielding an unambiguous group delay. However, significant deviation of the AD-induced group velocity in free space from~$c$ inevitably requires a large numerical aperture that lies deep in the non-paraxial regime, and such wave packets experience AD-induced group-velocity dispersion. The formulation presented here captures a broad range of results, connecting them in a single framework. In Part~II of this tutorial, we describe recently identified `non-differentiable AD' (associated with propagation-invariant space-time wave packets) that helps circumvent the limits associated with conventional (differentiable) AD as outlined here.
Read the full abstract

Optics

Automatic Optical Alignment Using Projective Geometry

Bowen Li, Lukas Palm, Xin Wei et al. (+5 more)

Aligning and maintaining complex optical beam paths is a central challenge across experimental science, because it is a high-dimensional task with strong cross-coupling between controls, often in systems with limited physical access. We present an automated hardware-software framework that resolves this alignment challenge using low-cost, retro-fittable motorized mounts driven by projective-geometry models and a photodiode-fed optimizer. A compact forward model describes the beam path to paraxial order with only the physical mirror angles left free, so it can be rapidly ($\sim$ms) numerically inverted to return the required mirror angles for a desired beam trajectory. A photodiode-fed optimizer then fine-tunes this geometric starting point, and converged mirror settings are tabulated for retrieval in milliseconds and actuation in seconds. We experimentally demonstrate the performance of this approach on a retro-reflected lattice atom-transport system, yielding improvements in both speed and precision over manual alignment. This framework reduces the manual effort required to align complex beam paths, enables programmable optical control in experiments with limited physical access, and enhances the scalability of complex optical architectures.
Read the full abstract

All authors Bowen Li, Lukas Palm, Xin Wei, Marius Jürgensen, Zeyang Li, Yiming Cady Feng, Abhishek V. Karve, Jon Simon

Wednesday 16 September

Optics · Cross-listed from physics.med-ph

Retinal hazards and glare from space mirrors

Salvador Bará

Projects of orbital mirrors reflecting sunlight towards Earth raise reasonable concerns regarding photochemical and thermal retinal hazards and detrimental effects on visual performance (disability glare). This paper addresses these issues based on some current eye safety and glare standards. Telescopic observations of single mirrors appear to pose a significant risk of photochemical retinal hazard. The risk is higher for vulnerable populations. Unaided eye viewing of a mirror keeps the retinal risks low, both photochemical and thermal; however, disability glare may be unacceptably high, affecting awareness and response in critical visual operations. The simultaneous presence of several mirrors in the visual field of the observer, seen with the unaided eye or through optical instruments, will significantly increase all types of hazards. The kind and severity of their combined effects will depend on the angular distance between them. Additional information is needed to evaluate the effects of the transient flashes of light during mirror slewing operations.
Read the full abstract

Optics

Time-resolved topology of aperiodically driven systems

Justin T. Cole, Christina Jörg, Terry A. Loring et al. (+1 more)

Topological phases of periodically driven systems are commonly classified through Floquet Hamiltonians, whose definition relies on a repeated driving cycle. However, this framework breaks down for systems whose realized evolution is aperiodic or nonlinear, even when robust topological phenomena appear to persist. Here, we introduce an evolution-history spectral localizer framework that classifies Chern topology directly from a system's finite-time unitary evolution operator. The method produces a time-resolved local Chern marker and an associated local gap, allowing topology and its protection to be tracked during the actual dynamics of a driven system. We demonstrate this approach in quasiperiodically driven and nonlinear photonic models, where it identifies transient topological protection, its subsequent loss, and the recovery of topology after nonlinear excitations disperse. The developed framework provides a route for analyzing driven photonic systems whose topological behavior depends on finite-time dynamics rather than an idealized Floquet cycle.
Read the full abstract

All authors Justin T. Cole, Christina Jörg, Terry A. Loring, Alexander Cerjan

Optics · Cross-listed from quant-ph

Observing and evading quantum back-action on a kilogram-scale oscillator

Begüm Kabagöz, Eric Oelker, Dhruva Ganapathy et al. (+203 more)

Continuous quantum displacement measurements are fundamentally limited by a trade-off between readout imprecision and measurement back-action, constrained by the Heisenberg uncertainty principle. In the Laser Interferometric Gravitational-Wave Observatory (LIGO), these two quantum noise components dominate much of the observation band, making it an excellent testbed. We induce a sub-Hz-linewidth optomechanical mode by trapping the differential motion of the 40-kg mirrors in a band where radiation-pressure back-action dominates the motion. Engineering the quantum state entering the dark port creates correlations between imprecision and back-action that partially cancel their contributions, reducing observed motion near resonance by ~47%. A framework resolving the imprecision, back-action, and correlation terms identifies the origin of this suppression. These results demonstrate quantum back-action evasion and quantum reservoir engineering in a macroscopic optomechanical system.
Read the full abstract

All authors Begüm Kabagöz, Eric Oelker, Dhruva Ganapathy, Nergis Mavalvala, Vivishek Sudhir, Vladimir Bossilkov, Joseph Betzweiser, Valery V. Frolov, Anamaria Effler, Adam Mullavey, Lisa Barsotti, Evan D. Hall, Peter Fritschel, R. Abbott, I. Abouelfettouh, R. X. Adhikari, A. Ananyeva, S. Appert, S. K. Apple, K. Arai, N. Aritomi, S. M. Aston, M. Ball, S. W. Ballmer, D. Barker, B. K. Berger, D. Bhattacharjee, G. Billingsley, S. Biscans, C. D. Blair, N. Bode, E. Bonilla, A. Branch, A. F. Brooks, D. D. Brown, J. Bryant, C. Cahillane, A. Calafat, S. R. Callos, H. Cao, E. Capote, F. Clara, J. Collins, C. M. Compton, G. Connolly, R. Cottingham, D. C. Coyne, R. Crouch, J. Csizmazia, A. Cumming, L. P. Dartez, D. Davis, N. Demos, E. Dohmen, K. L. Dooley, J. C. Driggers, S. E. Dwyer, A. Ejlli, T. Etzel, M. Evans, J. Feicht, R. Frey, W. Frischhertz, M. Fuentes-Garcia, P. Fulda, M. Fyffe, B. Gateley, T. Gayer, J. A. Giaime, K. D. Giardina, J. Glanzer, E. Goetz, R. Goetz, A. W. Goodwin-Jones, S. Gras, C. Gray, D. Griffith, H. Grote, T. Guidry, J. Gurs, J. Hanks, J. Hanson, M. C. Heintze, A. F. Helmling-Cornell, N. A. Holland, D. Hoyland, H. Y. Huang, Y. Inoue, A. L. James, A. Jamies, R. Jaume, A. Jennings, W. Jia, D. H. Jones, S. Karat, S. Karki, M. Kasprzack, K. Kawabe, N. Kijbunchoo, P. J. King, J. S. Kissel, K. Komori, A. Kontos, R. Kumar, K. Kuns, M. Landry, B. Lantz, M. Laxen, K. Lee, M. Lesovsky, F. Llamas Villarreal, M. Lormand, H. A. Loughlin, R. Macas, M. MacInnis, C. N. Makarem, B. Mannix, G. L. Mansell, R. M. Martin, K. Mason, F. Matichard, N. Maxwell, G. McCarrol, R. McCarthy, D. E. McClelland, S. McCormick, T. McRae, F. Mera, E. L. Merilh, J. R. Mérou, F. Meylahn, R. Mittleman, D. Moraru, G. Moreno, M. Nakano, T. J. N. Nelson, A. Neunzert, J. Notte, J. Oberling, T. O'Hanlon, R. Oram, C. Osthelder, D. J. Ottaway, H. Overmier, W. Parker, O. Patane, A. Pele, H. Pham, M. Pirello, J. Pullin, V. Quetschke, K. E. Ramirez, K. Ransom, J. Reyes, J. W. Richardson, M. Robinson, J. G. Rollins, C. L. Romel, J. H. Romie, M. P. Ross, B. I. Rotimi, K. Ryan, T. Sadecki, A. Sanchez, E. J. Sanchez, L. E. Sanchez, R. L. Savage, D. Schaetzl, M. G. Schiworski, R. Schnabel, R. M. S. Schofield, E. Schwartz, D. Sellers, T. Shaffer, R. W. Short, D. Sigg, B. J. J. Slagmolen, C. Soike, S. Soni, V. Srivastava, L. Sun, D. B. Tanner, M. Thomas, P. Thomas, K. A. Thorne, M. R. Todd, C. I. Torrie, G. Traylor, A. S. Ubhi, G. Vajente, J. Vanosky, A. Vecchio, P. J. Veitch, A. M. Vibhute, E. R. G. von Reis, J. Warner, B. Weaver, R. Weiss, C. Whittle, B. Willke, C. C. Wipf, J. L. Wright, V. A. Xu, H. Yamamoto, L. Zhang, M. E. Zucker

Optics

Correlation geometry and topology of structured optical beams

Jyrki Laatikainen and Olga Korotkova

Correlation geometry and topology in a random, scalar beam carrying Orbital Angular Momentum (OAM) in $L$ modes are shown to be linked to the real and imaginary parts, respectively, of its orbitalization matrix (OM). The OM is obtained by filtering the cross-spectral density in the polar Fourier basis at a given cross-section and radius for each pair of OAM indices. The symmetric real part of the OM has the diagonal canonical form, specifying the ellipsoid-like correlation geometry of the beam. The skew-symmetric imaginary part of the OM has the Darboux canonical form, enabling decomposition into $N\leq L/2$ mutually orthogonal circulation states and $L-2N$ trivial circulation-free states, mutually orthogonal and $L-2N$ trivial circulation states thereby defining the $N$-dimensional orbitalization torus associated with the correlation topology of the beam. The canonical forms are then used to define the degrees of linear and circular orbital anisotropy and stability, and the degrees of linear and circular orbitalization, in analogy with corresponding quantities in 2D and 3D polarization theory. These results demonstrate the emergence of fundamentally new correlation structures in random multimode OAM-carrying light, not accessible in lower-dimensional systems and absent in the deterministic limit.
Read the full abstract

Optics · Cross-listed from quant-ph

Liouvillian exceptional points in the emergence of quantum synchronization

Carlos Ortega Taberner, Rosalind E. Cotton and Paul R. Eastham

The coupling between self-sustained oscillators, such as lasers or polariton condensates, leads to different steady-states in different regimes. Weak coupling allows the oscillators to behave independently, with different frequencies and uncorrelated phases, while stronger coupling can produce synchronization. In classical or semiclassical theories transitions between these steady-states correspond to changes in the topology of the phase space attractors and occur at generalized exceptional points. We investigate the corresponding changes in a quantum theory of coupled lasers or condensates. We show how the different steady-state regimes of the classical limit give rise to distinct forms for the spectra and eigenmatrices of the slow modes of the Liouvillian. By following the spectral flow between the different regimes we show that the synchronization transition is controlled by cascades of exceptional points in these slow modes, protected by a generalized PT symmetry. Our results show how singularities of the quantum Liouvillian control the different dynamical regimes, and give rise to experimental signatures of the synchronization transition which remain well-defined in the few-particle regime dominated by quantum effects.
Read the full abstract

Optics

Dual-comb generated in single thin-film lithium niobate microrings

Renhong Gao, Qifeng Hou, Xinzhi Zheng et al. (+12 more)

Dual-comb technology has emerged as an essential tool for high-precision spectroscopy, real-time ranging, and high-sensitivity sensing. Integrating dual-comb sources into a single microresonator would substantially reduce pump power, footprint, system complexity, and cost, yet this remains a significant challenge. Here, we demonstrate, for the first time, integrated dual-comb generation in a single thin-film lithium niobate (TFLN) microring, under single continuous-wave laser pumping. Rather than regarding TFLN's strong Raman nonlinearity as detrimental, as conventionally viewed, we harness it constructively. By engineering the dispersion of TFLN microrings, we leverage the fundamental and first-order transverse-electric mode families with loaded Q factors exceeding 5X10^6, comparable repetition rates, and suitable dispersion profiles, and bridge them through stimulated Raman scattering (SRS) processes. Pumping a first-order mode at 1551.28 nm initially excites both Stokes and anti-Stokes SRS in the fundamental mode family at low thresholds, and subsequently produces two independent, spectrally separated combs at a pump power of 320 mW via direct Kerr and Raman-assisted Kerr effects, respectively. The two combs span broad bandwidths, exhibit repetition rates of ~102 GHz with a slight difference of ~624 MHz, and do not merge spectrally. The broadest spectrum spans 654 nm, and the Raman-Kerr comb has a 3-dB bandwidth exceeding 29 nm. Further characterization confirms that the comb lines exhibit low phase noise, with an intrinsic linewidth of 410 Hz. This work establishes a robust pathway for on-chip dual-comb generation in a single-laser pumped microring, significantly advancing dual-comb systems toward simplified architectures, enhanced robustness, and scalable integration, while accelerating their practical deployment.
Read the full abstract

All authors Renhong Gao, Qifeng Hou, Xinzhi Zheng, Bin Li, Guanghui Zhao, Yingnuo Qiu, Xinke Xing, Boyang Nan, Yixuan Yang, Saisai Sun, Kunpeng Jia, Zhenda Xie, Jintian Lin, Shining Zhu, Ya Cheng

Optics · Cross-listed from quant-ph

Filter-Free Indistinguishable Photon Generation from Continuous-Wave-Driven Integrated Microresonators

Ruiyang Chen, Sicheng Zeng, Yuan Chen et al. (+6 more)

Quantum networks require scalable photon sources combining narrow linewidth, high efficiency, and high indistinguishability. Microresonator photon-pair sources are promising candidates, yet a source-only description based on the joint spectral amplitude (JSA) predicts near-zero Hong-Ou-Mandel (HOM) interference visibility between photons generated by independent, CW-driven microresonators. In this work, we show that the observed HOM interference is not determined by the JSA alone. By combining finite-time detection with cavity-enhanced spontaneous four-wave mixing, we characterize a detector-conditioned heralded state governed by the idler-photon detection window. We further demonstrate that independently optimizing the idler and signal detection windows allows both heralded-photon indistinguishability and intrinsic heralding efficiency to approach unity, without spectral filtering or complex source engineering. Utilizing integrated high-$Q$ silicon nitride microresonators, we achieve HOM visibilities of 0.992(8) and 0.942(12), without background subtraction, at fourfold count rates of 4.5(3) and 12.2(6) Hz, respectively. Our work establishes CW-driven high-$Q$ microresonators as a robust and scalable platform for quantum-network primitives.
Read the full abstract

All authors Ruiyang Chen, Sicheng Zeng, Yuan Chen, Sanli Huang, Zeying Zhong, Zhen Chen, Xue Bai, Yi-Han Luo, Junqiu Liu

Optics · Cross-listed from quant-ph

Giant-atom-mediated photon blockade

C. Cui, W. Y. Hu, Y. Q. Ji et al. (+3 more)

Photon blockade is a phenomenon where the presence of system nonlinearity causes the output to consist of single photons, which has been extensively studied in point atom systems, but it is barely explored in giant atom ones. In this paper, we propose giant atom-mediated photon blockade scheme based on two cavities and three cavities systems with driving field applied to the first cavity. We show that simultaneous unconventional photon blockades (UPBs) can not occur in the point atom system (the atom coupling only to the leftmost cavity) due to there always existing a cavity to have a single path. In contrast, the spatially extended nature of giant atom enables coupling to multiple cavities and allows for the introduction of a phase and coupling strength. Consequently, simultaneous UPBs in multiple cavities can be obtained due to the multipath destructive interference. Moreover, by manipulating the detuning, we observe simultaneous conventional photon blockades (CPBs) in multiple cavities. Finally, we study simultaneous two-photon blockades (2PBs) in point atom multiple cavities system.
Read the full abstract

All authors C. Cui, W. Y. Hu, Y. Q. Ji, H. T. Cui, Yan-Hui Zhou, H. Z. Shen

Optics

350-GHz-Band 4 by 4 RTD Monostatic Radar Array for Sequential Multidirectional Ranging

Li Yi, Ryoma Nakamura, Shota Ito et al. (+6 more)

Terahertz (THz) sensing offers significant potential for nondestructive evaluation, imaging, and metrology, but the cost and complexity of existing systems remain barriers to practical deployment. This letter presents a compact 4 by 4 monostatic radar array based on a single-RTD-per-pixel architecture, in which each resonant tunneling diode (RTD) functions as both a bias-tunable oscillator and a self-mixing detector. The RTD elements are sequentially addressed through a low-frequency switching network and share the same baseband control and readout electronics. A shared 3D-printed dielectric lens maps the RTD elements to spatially separated sensing directions. We experimentally verify the operation of all array elements and demonstrate sequential multidirectional ranging using four selected elements, followed by preliminary 16-pixel THz imaging. By combining self-mixing at each pixel with low-frequency selection and shared optics, the array avoids a separate THz receiver chain for each pixel and provides a compact architecture for electronically addressable THz sensing and imaging.
Read the full abstract

All authors Li Yi, Ryoma Nakamura, Shota Ito, Yousuke Nishida, Koji Terumoto, Toshihisa Maeda, Bryce Chung, Yunbin Jiang, Daniel Headland

Optics

Multi-contrast wide-field mid-infrared photothermal imaging

Anooj Thayyil Raveendran, Cornelia Reuter, Samir F. El-Mashtoly et al. (+2 more)

Wide-field mid-infrared photothermal (MIP) imaging enables high-speed, chemically specific imaging at sub-micrometer spatial resolution through several possible contrast mechanisms, including scattering change, fluorescence modulation, and phase change. Each mechanism offers distinct advantages, yet existing wide-field MIP instruments have typically been limited to a single contrast mechanism so far, requiring a dedicated instrument for each. Here, we introduce a switchable multi-contrast wide-field MIP microscope that allows the photothermal readout mechanism (based on scattering-, fluorescence-, or quantitative phase imaging (QPI)) to be matched to the sample and imaging conditions. We characterize the spectral fidelity and signal-to-noise (SNR) ratio of each mechanism using 5 \mu m polystyrene (PS) beads, and the effective spatial resolution using 300 nm PS beads. Scattering- and fluorescence-based detection achieved a sub-500 nm measured point spread function full width at half maximum, while QPI-based detection reached approximately 900 nm but provided up to 26-fold higher SNR than scattering. We further demonstrate imaging across a range of samples, including A549 cells in buffer, mouse lung tissue section, bacteria, and SU8 polymer at 1.4 and 5 \mu m thickness, with a field of view exceeding 200 \mu m. Comparison across these samples shows that each contrast mechanism offers distinct trade-offs in resolution, sensitivity, and applicability, guiding readout-strategy selection by sample type. These results establish a flexible, switchable multi-contrast platform for wide-field MIP imaging, with broad applicability across polymer and biological samples.
Read the full abstract

All authors Anooj Thayyil Raveendran, Cornelia Reuter, Samir F. El-Mashtoly, Jürgen Popp, Christoph Kraft

Optics

Topological photonic cavities based on dissimilar Bragg gratings

Alejandro Sánchez-Sánchez, José Manuel Luque-González, Gauthier Krizman et al. (+12 more)

Topological photonic cavities offer a powerful route to robust optical confinement and enhanced light-matter interactions. Interface states that emerge at the boundary between one-dimensional periodic structures with distinct topological phases, enable cavities with ultra-small mode volumes and intrinsic protection against disorder. Existing implementations typically create the trivial and topological phases by redefining the unit cell on either side of the cavity, so that both periodic structures share the same band structure. This constraint limits design flexibility and the range of accessible devices. Here we introduce a fundamentally different strategy for realizing topological cavities based on combining periodic waveguides with distinct band structures. By exploiting bandgap closing and band inversion in Bragg gratings, we independently control the topological phase and bandgap width of each structure. We experimentally realize silicon topological cavities formed by two different Bragg gratings without period shifting, and observe topological modes despite significant differences between the two gratings. Our results establish a new route to topological photonic cavity design, demonstrating that band inversion between dissimilar Bragg gratings enables cavity formation beyond symmetric constraints and provides a mechanism to engineer optical confinement via mirror asymmetry.
Read the full abstract

All authors Alejandro Sánchez-Sánchez, José Manuel Luque-González, Gauthier Krizman, Dorian Oser, Paula Nuño Ruano, David González-Andrade, David Medina Quiroz, Samson Edmond, Alejandro Ortega-Moñux, Jens H. Schmid, Pavel Cheben, Laurent Vivien, Iñigo Molina-Fernández, J. Gonzalo Wangüemert-Pérez, Carlos Alonso-Ramos

Optics · Cross-listed from quant-ph

Optical Quantum Computing

Hamza Hasnaoui, Leonardo Limongi, Taira Giordani et al. (+5 more)

Under the label of optical quantum computing, there are a variety of protocols and experiments that use the quantum properties of light to achieve a computational advantage over classical computing machines. In this review, we describe some of the main implementations, which differ in the type of encoding and in how the computation is performed, whether using gates or cluster states. For each protocol, we describe advantages and challenges with an overview of the experimental results obtained, summarized in tables. Because of the great relevance achieved in this field, there is a section dedicated to non-universal quantum computation with photons, where boson sampling, variational quantum eigensolvers, and quantum machine learning applications are described. The aim is to give the reader the broadest overview of the applications where photons and their quantum properties play a key role in computation.
Read the full abstract

All authors Hamza Hasnaoui, Leonardo Limongi, Taira Giordani, Beatrice Polacchi, Alberto Quaranta, Martino Bernard, Fabio Sciarrino, Mirko Lobino

Optics

Wavelength-Multiplexed Nonlinear Computing with a Single-Layer Diffractive Optical Processor

Yongkang Cheng, Che-Yung Shen, Yuntian Wang et al. (+2 more)

Diffractive optical processors provide a promising platform for high-throughput, low-latency analog computing by exploiting engineered wave propagation to transform optical fields. However, implementing nonlinear mappings in optical hardware remains challenging. Here, we introduce a wavelength-multiplexed encoding-and-decoding (E+D) diffractive processor that exploits multiple illumination wavelengths to enhance the nonlinear function-approximation capability of a compact single-layer diffractive architecture, without cascading multiple diffractive layers or increasing the trainable degrees of freedom. Under sequential wavelength scanning, each wavelength-detector channel implements a distinct nonlinear function at the output of the diffractive processor. Numerical simulations using 100 wavelength channels and 10,000 spatial detector regions at the output of the diffractive processor demonstrate the implementation of one million distinct nonlinear functions through wavelength multiplexing. We also demonstrate a simultaneous multiwavelength illumination configuration in which the E+D diffractive processor performs wavelength-division multiplexing and nonlinear function approximation concurrently. This multiwavelength illumination configuration is experimentally validated by optically implementing 64 distinct nonlinear functions under simultaneous illumination at eight wavelengths from 495 to 635 nm. Through numerical simulations and visible-light experimental demonstrations, our results indicate that this wavelength-multiplexed nonlinear function approximation framework provides a scalable route toward compact, high-capacity diffractive processors for large-scale analog optical computing and optical information processing.
Read the full abstract

All authors Yongkang Cheng, Che-Yung Shen, Yuntian Wang, Shiqi Chen, Aydogan Ozcan

Optics · Cross-listed from physics.ao-ph

Tropospheric Ozone Formation Potential and Related Design Considerations for Radiative Coolers

Jyothis Anand, Piero Di Carlo, Eleonora Aruffo et al. (+2 more)

Recently, radiative coolers have been widely explored for reducing cooling loads or lowering temperatures in buildings, and at urban scales as a heat-mitigation measure. However, the potential impacts of radiative cooler deployment on the chemical composition of the atmosphere remain largely unexplored. A defining feature of recently-designed radiative coolers is their high ultraviolet (UV) reflectance, which is required for sub-ambient cooling under strong sunlight. Yet, wide adoption of such UV-reflective radiative coolers could substantially increase the UV actinic flux in the atmosphere above. This, in turn, may affect tropospheric ozone concentrations, particularly in urban atmospheres with high NOx concentrations. Here, as a case study, we use a 0-dimensional photochemical box model, constrained by field measurements of meteorological conditions and chemical concentrations in the urban environment of Houston, Texas, to explore the potential impact of the widespread use of UV-reflective radiative coolers on ozone concentrations. Our calculations show that complete deployment of radiative coolers may increase tropospheric ozone levels by as much as 30% during specific meteorological conditions in Houston. Informed by the wavelength-dependent modelling results, we propose specific designs, namely pigmented radiative coolers with different UV reflectances, and UV-absorptive visible-reemitting fluorescent radiative coolers, that could minimize negative ozone formation while retaining appreciable cooling performance. Our results motivate further study on the effects of widespread deployment of radiative cooling designs like superwhite roof paints on air quality, and materials that simultaneously minimize adverse photochemical impact and maximize cooling performance.
Read the full abstract

All authors Jyothis Anand, Piero Di Carlo, Eleonora Aruffo, Paul E. Ohno, Jyotirmoy Mandal

Optics

On imaging capabilities of the Imaging and Medical beamline at the Australian Synchrotron

T.E. Gureyev, K.M. Pavlov, C.J. Hall et al. (+6 more)

Several propagation-based and analyser-based X-ray phase-contrast imaging experiments with over 100 m between the imaged objects and the detector were carried out at the Imaging and Medical beamline (IMBL) of the Australian Synchrotron. These experiments were aimed at characterization of possible phase-contrast imaging setups at IMBL. Effects of the beam divergence, polychromaticity and X-ray source size on the contrast and spatial resolution of images were evaluated quantitatively in different imaging scenarios. The results of this work will be used for improving the existing and developing new imaging capabilities at the beamline. Applications to X-ray phase-contrast tomography of biomedical samples, particularly for medical breast cancer imaging, are briefly discussed.
Read the full abstract

All authors T.E. Gureyev, K.M. Pavlov, C.J. Hall, A. Maksimenko, D. Pelliccia, D.M. Paganin, A.W. Stevenson, A. Entezam, H.M. Quiney

Optics

Environmental qualification and performance of a CubeSat-scale dual optical frequency comb payload for space applications

Stephanie D. Leifer, Matthew J. Kelley, Natalie Walsh et al. (+23 more)

We report the environmental qualification and performance of CombSat, a dual optical frequency comb payload designed for deployment on a 12U CubeSat in low Earth orbit. The payload integrates two self-referenced, 200 MHz hybrid fiber-waveguide frequency combs, a narrow-linewidth optical reference, a heterodyne beat detection unit, and FPGA-based control electronics in a total mass of 8.3 kg and volume of 5.7 L, and nominal power consumption of 21W. We describe the mechanical, thermal, and radiation-tolerant design features of the system and present the results of random vibration, storage temperature cycling, and thermal-vacuum testing conducted in accordance with NASA's General Environmental Verification Standard. We show that key comb performance metrics including oscillator and amplifier output power, frep, fCEO, and fopt signal-to-noise ratios, and integrated phase noise, remain within specification after environmental exposure, and we discuss observed failure modes and design modifications that improved robustness. These results demonstrate that compact, low power, fully stabilized, autonomous dual-comb systems can be engineered and qualified for spaceflight on CubeSat platforms, providing a path forward for future low-cost comb-based space applications.
Read the full abstract

All authors Stephanie D. Leifer, Matthew J. Kelley, Natalie Walsh, Ziba Shahriary, Paul Steinvurzel, Chrissy Fortuna, Geoffrey Maul, Adam Darley, Ian Coddington, Laura C. Sinclair, Ariel Berman, Victor Chin, Henry Timmers, Kevin Knabe, Jason Pinon, Andrew Attar, Cole Smith, Cyrus Bry, Davis S. Kun, Stan Stanev, Nicole Thai, Bennett Sodergren, Daniel Deveraux, Grant Capan, Will McIntyre, Manas Choure

Tuesday 15 September

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

A semiconductor photon-pair source based on a polariton cascade

Karol Kawa

We present a theoretical study of a semiconductor photon-pair source based on a radiative cascade enabled by a permanent exciton dipole. The source consists of a GaAs quantum dot placed between a metal nanoparticle and a mirror. The dot exciton and the localized electromagnetic mode mix to form upper and lower polaritons. Without a permanent dipole, a symmetry separating states with even and odd excitation numbers forbids photon emission between the polaritons. Separation of the mean electron and hole positions gives the exciton a permanent dipole and breaks this symmetry. The upper polariton can then emit an idler photon as it decays to the lower polariton. The lower polariton can emit a signal photon as the system returns to its ground state. Using an effective model, we calculate the probability that a prepared upper polariton emits both photons through the metal antenna. We also analyse fluctuations in the emitted photon counts and correlations between the two emission channels. The calculation establishes an operating principle for assumed emitter properties and optical loss rates. Whether the device can be built and its photon correlations measured remains open.
Read the full abstract