Peer Revenue Publish or profit

Papers

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

Physics Physics Optics

physics.optics Watch Optics

Monday 5 October

Optics

Digital confocal imaging in holographic optical coherence tomography at high space-bandwidth product

N. P. Klooster, S. A. Thakur, F. Zeisberger et al. (+4 more)

Full-field Fourier-domain optical coherence tomography (FF-FD-OCT) enables rapid volumetric imaging but lacks the confocal gating inherent to point-scanning OCT. By acquiring volumes under multiple oblique illuminations, a digital confocal volume can be synthesized in post-processing, a technique originally developed within the framework of reflection matrix imaging (RMI). Existing implementations, however, are often time-domain, off-axis, or use a Michelson interferometer, which reduces sensitivity, speed and the usable space-bandwidth product (SBP). Here, we present an oblique-illumination FF-FD-OCT system in a Mach-Zehnder configuration. This setup enables optimal use of SBP, providing up to a fourfold increase in effective acquisition throughput. In addition, we pose the scattering and aberrations as an overdetermined system, allowing a closed-form solution of an alternating least squares problem. The resulting iterative optimization is equivalent to the state-of-the-art closed-loop accumulation of single scattering (CLASS) algorithm. We demonstrate the setup and reconstruction method in lens tissue, a PSF phantom, a USAF target, and a model eye. The resulting digital confocal volumes provide locally optimized focusing and detection quality, and show improved resolution and signal-to-noise ratio (SNR) compared to conventional FF-FD-OCT. The technique combines the advantages of FF-FD-OCT and confocal OCT while mitigating the limitations of both approaches.
Read the full abstract

All authors N. P. Klooster, S. A. Thakur, F. Zeisberger, J. R. Hagen, S. Eggert, U. Najar, D. Hillmann

Optics · Cross-listed from gr-qc

Cherenkov Bursts are Memory Steps

Jann Zosso, Guangzi Xu and Vitor Cardoso

We show that the familiar Cherenkov burst from a finite superluminal charge track can be understood as a pair of interfering electromagnetic memory transitions. Endpoint accelerations of the track produce opposite memory steps in the transverse vector potential, such that the corresponding finite-frequency radiation is universally fixed, below the endpoint-acceleration-scale, by the memory amplitude and the time for which the temporary memory offset persists. As the Cherenkov direction is approached, the memory amplitudes grow while their separation in observer time shrinks, until the two vector-potential steps overlap and their divergent contributions cancel into a finite Cherenkov burst. This perspective opens the door to using the Askaryan effect as a setting in which individual macroscopic memory transitions may be resolved, providing a new experimental arena for memory-linked infrared physics.
Read the full abstract

Optics

Continuous-wave 148.4-nm generation in top-seeded solution-grown strontium tetraborate

Yanzhang Wu, Peng Yang, Lingfeng Yan et al. (+6 more)

We report an implementation of continuous-wave (CW) vacuum-ultraviolet (VUV) generation at 148.4 nm by single-pass second-harmonic generation of 296.8 nm light in strontium tetraborate (SBO). At an incident fundamental power of approximately 580~mW, we estimate a VUV output power of approximately 1.7 nW at the crystal exit. The crystal is grown by the top-seeded solution growth method and operated in a helium-filled chamber. The quadratic power dependence observed under vacuum, together with its strong suppression in air, supports the identification of the generated second harmonic. We further characterize the dependence of the VUV signal on beam position, incidence angle, polarization, and crystal temperature, providing practical guidance for SBO-based CW VUV sources for nuclear spectroscopy and clock applications.
Read the full abstract

All authors Yanzhang Wu, Peng Yang, Lingfeng Yan, Qi Xiao, Jiahong Li, Juxian Li, Beichen Huang, Zhiwei Jiao, Shiqian Ding

Optics

Symmetry Control in Coupled Quantum Cascade Ring Lasers

DOMINIK SCHOCK, ANNA INVERNICI, MICHAEL JAIDL et al. (+5 more)

Optical frequency combs with fast tunability are essential for integrated spectroscopy and sensing. However, achieving such functionality in the terahertz regime presents a significant challenge. This work introduces a novel approach that exploits supermode symmetry control in terahertz lasers. By electrically manipulating the gain ratio between coupled concentric ring lasers, we selectively excite symmetric and antisymmetric supermodes, allowing frequency tuning and spectral modulation across different frequency regimes and operation modes. Moreover, simultaneous lasing of both supermodes results in a reduced total integrated dispersion, widening the comb locking range. Supported by matrix formalism and numerical simulations, this work demonstrates the potential of symmetry control for enhanced electro-optic modulation, opening new avenues for on-chip spectroscopy and sensing applications.
Read the full abstract

All authors DOMINIK SCHOCK, ANNA INVERNICI, MICHAEL JAIDL, MIRIAM GIPARAKIS, SASCHA PREU, AARON M. ANDREWS, JURAJ DARMO, KARL UNTERRAINER

Optics

Extraordinary Optical Spin Hall Effect in 2D Exciton Emission in Open Cavities

Kunal Banerjee, Ben Johns, Nitin Yadav et al. (+2 more)

Open cavities are emerging as a promising platform for studying light-matter interactions. A lossy open cavity couples to an atomic monolayer, resulting in parabolic dispersive emission at room temperature. Here, light-matter interaction is weak, and the dispersion arises from a phenomenon known as dark strong coupling. The bright 2D exciton rapidly decays through the cavity mode, leaving behind spin-dark excitons of the 2D lattice, thereby undergoing symmetry breaking. Further, mapping the polarisation dependence in the k-space reveals spin-orbit interaction in the coupled system. A synthetic spin-orbit Hamiltonian is constructed to extract the effective contributions of Rashba- and Dresselhaus-type interactions in the open cavity. The system shows a clear evolution of the spin-orbit effect at room temperature. Here, emission is polarisation-sensitive, yielding high degrees of linear and circular polarisation. This is one of the simplest configurations for studying photonic spin-orbit coupling, in which an atomic monolayer provides Rashba and Dresselhaus coupling constants of 24 eV Å, and ~10^5 eV Å^2, respectively. Therefore, an open cavity platform is promising for polarisation-sensitive measurements and device applications.
Read the full abstract

All authors Kunal Banerjee, Ben Johns, Nitin Yadav, Anil Shaji, Jino George

Optics

Electro-Optical Metalens for Near-Surface Cooling of a Levitated Particle

Pedro Rosso Gomez, Bruno Melo, Adeel Afridi et al. (+3 more)

Advanced levitation optomechanics in the quantum regime requires sophisticated quantumengineered protocols operating at shorter length and time scales, demanding an increasing control over both optical and electrical potentials. Integrated chip-scale platforms offer a natural route toward such control. Here, we demonstrate optical levitation in vacuum using a miniaturized hybrid electro-optical metalens. Motion control is achieved using a high numerical aperture metalens combined with electrical active feedback using planar electrodes, enabling cooling to low phonon occupations. Reheating measurements enable us to rule out any significant influence from electric field noise; an encouraging result for the future development of on-chip levitation platforms operating close to surfaces. This compact integrated platform facilitates the precise manipulation and control of levitated nanoparticles while laying the ground toward exploiting the full capacity of metaoptics to engineer complex optical potentials, marking a significant step forward in technologies for quantum levitation optomechanics.
Read the full abstract

All authors Pedro Rosso Gomez, Bruno Melo, Adeel Afridi, Mohamed Sabry Mohamed, Nadine Meyer, Romain Quidant

Optics

Spatial delocalization of cold oscillators in hollow-core fibers

Soumya Chakraborty, Pardeep Kumar, Gordon K. L. Wong et al. (+2 more)

Trapped particles in hollow-core fibers enable long-range sensing, though advanced control of their in-fiber motion, such as multimodal cooling and squeezing, remains challenging. Here, we present optical interference-based adaptive techniques for controlling the motion of a fringe-trapped silica nanoparticle inside a fiber. After feedback-cooling its axial and radial motion, we induce axial delocalization (position anti-squeezing) via two complementary approaches. First, non-adiabatic fringe suppression expands the position variance by 11.83 ($\pm$0.7) dB to that of the initial cold-state while retaining Gaussian statistics. Second, multi-pass particle positioning at dark fringes increases the delocalization to 13.23 ($\pm$0.5) dB relative to the cold-state's variance via dark inverted optical potentials, in agreement with our Wiener stochastic model. Stronger delocalization produces non-Gaussian states of motion. Unlike prior inverted-trap implementations, our method requires neither auxiliary optical traps nor charged particles in Paul traps. Our results demonstrate fringe-trapped particles in hollow-core fibers as a versatile platform for long-range sensing and macroscopic quantum physics.
Read the full abstract

All authors Soumya Chakraborty, Pardeep Kumar, Gordon K. L. Wong, Claudiu Genes, Nicolas Y. Joly

Optics · Cross-listed from quant-ph

A robust framework for the comprehensive characterisation of parametric down-conversion sources

Denis A. Kopylov, Michael Stefszky and Christine Silberhorn

Reliable verification of squeezed-light sources is essential for photonic quantum technologies. High-dimensional quantum optical networks demand single-mode, pure squeezed states which, in principle, can be generated through careful engineering of parametric down-conversion-based (PDC) sources. However, due to the imperfections of optical components, the generated state is never pure and commonly contains internal mode structure. Existing characterisation techniques, based on either joint spectral intensity or normalized second-order correlation functions, work under the assumption that the probed state is pure, and therefore can result in incomplete or misleading assessment of the source quality. Here, we develop a device-agnostic characterisation framework for PDC-based sources with distinguishable signal and idler fields. Treating the source as a black box producing a mixed multimode Gaussian state, we find a lower bound for the state purity, which can be experimentally determined via mode-unresolved measurements. Our approach enables a holistic assessment of realistic squeezed-light source quality without requiring a detailed model of the nonlinear device and its surrounding optical network, providing practical benchmarks for optimizing sources for state-of-the-art quantum applications.
Read the full abstract

Optics

Time frequency distributions of Optical sources (II): externally modulated semiconductor lasers

José Capmany

We extend a time frequency framework previously developed for directly modulated lasers to external modulation of the continuous wave output of a 1550 nm DFB laser described by Langevin rate equations. Four modulators are considered an InP electro absorption modulator, a LiNbO3 dual drive Mach Zehnder modulator, a dual parallel Mach Zehnder modulator and a silicon carrier depletion modulator
Read the full abstract

Optics

Time frequency distributions of optical sources (I): directly modulated semiconductor lasers

Jose Capmany

We develop a time frequency framework for the dynamics of directly modulated semiconductor lasers in which the optical field obtained from the singlemode rate equations is represented by distributions of Cohen class. Closed form small signal solutions are derived for RC filtered square current pulses and for sinusoidal modulation, including the exact chirp to power ratio with gain compression and spontaneous emission and a line expansion of the Wigner distribution of the sinusoidally modulated field. Kernels satisfying two known conditions return the laser chirp as the first conditional moment.
Read the full abstract

Optics · Cross-listed from physics.med-ph

The FetalSenseM V2: a wearable and wireless, multi-wavelength NIRS device for continuous monitoring of placental oxygenation and metabolism

Luca Giannoni, Frederic Lange, Musa Talati et al. (+9 more)

We present here the FetalSenseM V2 (FSM V2), a wireless and wearable, multi-wavelength, NIRS device, based on LED illumination at six NIR wavelengths (782, 800, 818, 830, 848 and 888 nm). It utilises two sources located on the flexible wings of the sensor body, and three photodiodes placed symmetrically in its centre at 1 cm from each other. The configuration provides two sets of three source-to-detector distances (SDS) at 3, 4 and 5 cm. FSM V2 allows estimation of dynamic, relative changes in placental concentrations of HbO2, HHb and oxCCO. At the same time, the dual set of SDS also enables the use of multi-distance algorithms, such as spatially-resolved spectroscopy (SRS) and Dual Slope (DS), for estimating placental oxygen saturation (PlO2). FSM V2 is the first example of a new generation of wearable NIRS devices, paving the way for smart and advanced monitoring of placental health at bedside. The FSM V2 was successfully validated on a bench-testing, metrological platform based on optical phantoms, as well as against a gold-standard, time-domain (TD) NIRS system, before moving to preliminary examples of clinical application and usability on pregnancy monitoring trials at University College Lon-don Hospital (UCLH), conducted as part of an in vivo proof-of-concept study.
Read the full abstract

All authors Luca Giannoni, Frederic Lange, Musa Talati, Uzair Hakim, Darshana Gopal, Angelos Artemiou, Niccole Ranaei-Zamani, Olivia Newth, Sarah Johnson, Maeve McGaughey, Subhabrata Mitra, Ilias Tachtsidis

Optics

Advances in the Vacuum Magnetic Birefringence measurement using a pulsed Foil Coil

Enzo Rodriguez Alvarez, Jonathan Agil, Julien Billette et al. (+3 more)

In this paper, in the framework of the Biréfringence Magnétique du Vide (BMV) experiment, we present our current apparatus in detail and we discuss its critical points. We also report the results obtained using specially designed pulsed coils called Foil Coils. Our novel measurement of the vacuum linear magnetic birefringence constant is $K_{VMB} < 1.7 \cdot 10^{-21}~\text{T}^{-2}$ at a confidence level of 68$\%$, which is an improvement with respect to our previous 2014 measurement.
Read the full abstract

All authors Enzo Rodriguez Alvarez, Jonathan Agil, Julien Billette, Jérôme Béard, Rémy Battesti, Carlo Rizzo

Optics

Tunable low-phase-noise terahertz synthesis using a fiber-interferometer-referenced optical frequency comb and an EDFA-integrated Vernier cavity

Masayuki Higaki, Yoshiaki Nakajima, Yu Tokizane et al. (+4 more)

demonstrate a frequency-tunable, low-phase-noise terahertz (THz) synthesizer based on a fiber-interferometer-referenced optical frequency comb (OFC), an erbium-doped fiber amplifier (EDFA)-integrated Vernier cavity, and dual optical injection locking (OIL). The Vernier cavity converts the densely spaced modes of a fiber OFC with a repetition frequency of approximately 100 MHz into a filtered comb with gigahertz-scale effective mode spacing, facilitating selective single-mode OIL. Intracavity and extracavity EDFAs in the Vernier cavity enable a side-mode suppression ratio exceeding 70 dB. Independent control of the Vernier-cavity free spectral range and the OFC repetition frequency provides flexible Vernier filtering conditions for selecting master modes for dual OIL. Two selected comb modes are transferred to injection-locked optical carriers and photomixed in a uni-traveling-carrier photodiode to generate continuous-wave THz signals. Frequency-tunable THz generation is demonstrated at 230, 267, and 320 GHz. At 267 GHz, a signal-to-noise ratio exceeding 70 dB and a measured phase noise of -95.7 dBc/Hz at a 10-kHz offset are obtained; the phase-noise measurement is limited by the local-oscillator system. The proposed architecture provides a fiber-based approach to frequency-tunable, low-phase-noise THz synthesis by combining an optical-reference-based OFC with flexible Vernier-assisted comb-mode selection.
Read the full abstract

All authors Masayuki Higaki, Yoshiaki Nakajima, Yu Tokizane, Kwangyun Jung, Ryosuke Nakamura, Naoya Kuse, Takeshi Yasui

Optics · Cross-listed from physics.atom-ph

Bifurcation of laser-dressed band extrema in solids under intense low-frequency fields

Alexander Flegel, Liang-Wen Pi, Liang-You Peng et al. (+1 more)

We show that an intense low-frequency laser field can qualitatively modify the local extremal structure of an interband energy gap in a crystal. Using an instantaneous laser-dressed basis obtained from the nonperturbative diagonalization of the multiband crystal Hamiltonian, we derive a quartic normal form for the dressed gap near a high-symmetry point. At a critical field, the quadratic part of this normal form changes sign, and the gap experiences a bifurcation: a single symmetric minimum splits into two symmetry-related minima separated by a local maximum. We identify the microscopic origin of this bifurcation by decomposing the quadratic part into a homogeneous Stark contribution and a field-modified band-curvature contribution. The latter originates from the multiband redistribution of interband polarizations and provides the mechanism for the field-induced change of the gap extrema. A realization for the Kronig–Penney model demonstrates the same bifurcation at multiple high-symmetry points and for different interband gaps. As an illustration of its spectral consequences, we show that the bifurcation gives rise to an additional van Hove feature in the instantaneous interband susceptibility above the absorption edge. Our results establish a general mechanism by which strong-field dressing modifies the local geometry of the electronic spectrum.
Read the full abstract

All authors Alexander Flegel, Liang-Wen Pi, Liang-You Peng, Mikhail Frolov

Optics

Scatter-free perfect reflection in multichannel monolithic high-contrast gratings: direct–indirect Fourier-harmonic interference and dimensionality of the solution set

Sun-Goo Lee and Wook-Jae Lee

Monolithic high-contrast gratings (MHCGs) can exhibit scatter-free perfect reflection despite open higher-order substrate diffraction channels, but the underlying mechanism has not been fully clarified. Using a Fourier-harmonic description, we show that all open higher-order channels in the high-index substrate can be simultaneously extinguished through destructive interference between the radiation fields generated by the direct and indirect source contributions. By contrast, the zeroth-order transmission vanishes when the modulation-induced zeroth-order field interferes destructively with the background transmitted field of the incident wave. Together, these cancellations yield unit zeroth-order reflectance in lossless MHCGs. The near invariance of the internal field harmonics accounts for the remarkable stability of these conditions against changes in the substrate refractive index. We further show that the number of symmetry-compatible open channels determines the generic codimension of the perfect-reflection solution set. Depending on the number of independent design parameters relative to this codimension, the solutions form continuous curves, appear as isolated points, or are generically absent. Introducing an additional geometrical parameter restores isolated perfect-reflection solutions when an additional diffraction channel opens. The same cancellation mechanisms and channel counting apply to both TE and TM polarizations.
Read the full abstract

Optics

Constraints on the Origin of Universal $1/f^2$ Photon-Count Spectra at Baseband

Malvin Carl Teich and Steven B. Lowen

A series of 11.6-d-duration photon-counting experiments, employing a broad variety of light sources with different statistical properties and optical spectra, were carried out over a 1.5-yr period. All of the photon-count spectra at baseband followed a common $1/f^2$ form over the frequency range $1 \times 10^{-6} \leqslant f \leqslant 5 \times 10^{-4}$ Hz, corresponding to a timescale range $33$ min $ \leqslant T_f \leqslant 11.6$ d, where $T_f \equiv 1/f$. The lower and upper timescale limits were established by the photodetector noise floor and the duration of the individual experiments, respectively. Unlike ordinary Brownian motion, all of the measured photon-count sample paths exhibited irregular long-timescale fluctuations, with durations ranging from hours to days. It has been established that the photon-count spectra cannot plausibly be ascribed to fluctuations of the current, voltage, or temperature of the source or the detector, nor to technical sources of noise associated with the optical system or local environment. Although the physical origin of the photon-count fluctuations remains unresolved, several heterodox hypotheses are set forth. From a statistical point-of-view, the photon counts appear to follow a doubly stochastic Poisson process with a slowly varying random intensity. Analogous experiments that rely on ionizing radiation and direct-conversion solid-state radiation detectors are proposed.
Read the full abstract

Sunday 4 October

Optics

Calibration-Free Broadband Reconstructive Spectrometer based on Conical Phase Modulation

Junrui Liang, Zhongming Huang, Yanting Guo et al. (+6 more)

Reconstructive spectrometers (RSs) shift spectral analysis from hardware-heavy dispersion to encoding-decoding schemes. In the speckle-based RSs, spectra are encoded into disordered intensity patterns and then recovered algorithmically. However, characterizing such spectral-encoding transmission matrices (TMs) typically demands empirically complex calibrations, which rely on expensive tunable light sources to generate known wavelengths. In this work, we demonstrate a fully calibration-free RS that leverages conical phase modulation from an axicon. The target spectra are encoded into a Bessel-form intensity profile, enabling computational construction of a deterministic TM and thus completely removing the need for optical calibration. With this computer-generated TM, broadband spectral reconstruction is experimentally achieved across a 650 nm range (1050-1700 nm)–nearly three times the bandwidth of existing calibration-simplified RSs–while a spectral resolution of 2.9 nm remains comparable to that of these counterparts. Compared with an RS requiring optical calibration for equivalent performance, our solution achieves an approximate 36-fold cost reduction.Unlike most speckle RSs, the axicon RS requires no fixed input polarizer, further enhancing energy efficiency and simplicity through polarization-insensitive operation. To the best of our knowledge, this is the first reported experimentally calibration-free RS, featuring superior simplicity, practicality, and cost-effectiveness for practical applications.
Read the full abstract

All authors Junrui Liang, Zhongming Huang, Yanting Guo, Jun Ye, Yanzhao Ke, Jun Li, Jiangming Xu, Jinyong Leng, Pu Zhou

Optics

Spin-orbit-induced gauge field and spin Hall effects in quasi-paraxial fluids of light

Caroline Stier and Nicolas Cherroret

We show that quasi-paraxial fluids of light propagating in nonlinear Kerr media naturally experience an effective gauge field arising from the intrinsic spin-orbit interaction of light encoded in Maxwell equations. By deriving the leading nonparaxial corrections to the nonlinear Schrödinger equation governing the fluid evolution, we find that, for circularly polarized beams, these corrections generate an effective Lorentz force that modifies the fluid dynamics. Remarkably, the corresponding gauge field is not externally imposed but self-consistently generated by the fluid itself, with its sign controlled by the light helicity and its magnitude governed by the spatial variations of the nonlinear refractive index. We illustrate the physical consequences of this gauge field in two configurations: the chiral deformation of normal and superfluid flows past an obstacle, accompanied by a transverse spin Hall force, and the cumulative precession of an optical wave packet trapped in a focusing fluid.
Read the full abstract

Optics

Surface-pinned nonsingular topologically charged defects in nanoplasmonics

Michael I. Tribelsky and Vladimir V. Ternovski

We discuss surface-pinned, topologically charged, nonsingular defects (SD) in light scattering by a plasmonic object. They follow from exact Maxwell boundary conditions and are purely topological—unaffected by surface forces. At optical frequencies, in (quasi) 2D, they appear in the electric and Poynting vector fields for $H^{(z)}$ polarization, not for $E^{(z)}$. Exact solutions for a circular cylinder reveal topological charge-conserving bifurcations involving SDs with bulk singularities or SDs alone, and contraction of defect regions under loss.
Read the full abstract

Optics

Photonic architectures for synthetic chiral light-driven chiral sensing

Alexander Löhr, Justas Terentjevas, Patricia Vindel-Zandbergen et al. (+6 more)

Molecular chirality gives rise to left- and right-handed enantiomers whose balance underpins biochemical function. Deviations from this enantiomeric excess are promising biomarkers of disease. Despite its importance, rapid and sensitive detection of enantiomeric excess in trace amounts of small chiral molecules remains an outstanding challenge. Synthetic chiral light introduces new opportunities for chiroptical spectroscopy, with the potential to enhance light-matter interactions by several orders of magnitude. Here we propose a new class of photonic architectures for synthetic chiral light, in which photonic structures generate, guide and optimize chiral light-matter interactions. As a first realization, we show that hollow dielectric waveguides support phase-matched propagation of multicolor fields enabling coherent accumulation of the enantio-sensitive nonlinear response over centimeter-scale distances. By combining microscopic quantum-response simulations with Maxwell's equations, we predict that incident pulse energies of around 1 uJ produce hundreds of picojoules of third-harmonic emission from only picomole quantities of carvone gas at 50 mbar over just 2 cm of propagation, with enantio-sensitive contrast approaching 5%. Phase-resolved Fourier analysis isolates a background-free chiral signal exhibiting the maximum possible dichroism of 200%. Beyond efficient chiral sensing, photonic architectures for synthetic chiral light establish a scalable platform for integrated nonlinear chiral spectroscopy, molecular fingerprinting based on ultrafast electron dynamics, and topologically robust chiroptical observables.
Read the full abstract

All authors Alexander Löhr, Justas Terentjevas, Patricia Vindel-Zandbergen, Aude Rodriguez, David Ayuso, Laura Rego, Serguei Patchkovskii, Misha Ivanov, Olga Smirnova

Optics

Integrated robust universal linear optics based on white-boxed multi-plane light conversion

Xin-Yu Song, Lan-Tian Feng, Pan Gong et al. (+3 more)

The integrated universal linear optical processor realized via multi-plane light conversion (MPLC) features low hardware complexity and high fabrication robustness, suitable for diverse photonic processing tasks. However, the lack of validated calibration protocols limits its universality and potential. Here, we propose a machine-learning-based calibration method and verify it using an eight-mode silicon photonic processor composed of interleaved multiport directional couplers and phase-shifter arrays. We characterize coupler transfer matrices and current-phase responses of individual phase shifters. To validate the robustness, we demonstrate its universality with Haar-random unitary matrices at wavelengths of 1500, 1550, and 1580 nm, and under partial phase-shifter deactivation. With this white-boxed device, we also demonstrate high-dimensional quantum gates and quantum reservoir computing for handwritten digit classification. Our work advances integrated MPLC-based universal linear optics and paves the way for large-scale, fabrication-robust, broadband hardware for classical and quantum photonic information processing.
Read the full abstract

All authors Xin-Yu Song, Lan-Tian Feng, Pan Gong, Yu-Yang Ding, Guang-Can Guo, Xi-Feng Ren

Optics

Deep learning enables large-scale inverse design of free-form metasurfaces

Viktor A. Lilja, Khosro Zangeneh Kamali, Mikael Käll et al. (+1 more)

Metasurfaces are ultrathin optical elements that control light through carefully engineered structures smaller than the wavelength of light, enabling compact devices with functionalities that are difficult to achieve with conventional optics. However, exploiting their full design freedom over large areas has been prohibited by the large computational cost of repeated electromagnetic simulations required for inverse design. Here we introduce a physics-tailored deep-learning surrogate model that exploits the locality and symmetries of electromagnetic interactions to generalize from small-scale simulations to metasurfaces orders of magnitude larger. The model captures nonlocal interactions while predicting optical fields more than four orders of magnitude faster than the conventional electromagnetic solver it is trained on, enabling gradient-based topology optimization under arbitrary illumination. We validate the approach through the inverse design and experimental realization of free-form metagratings with diffraction angles up to 75 degrees, as well as a millimeter-scale free-form holographic metasurface more than 1,000 wavelengths across and comprising 1.6 billion degrees of freedom. By decoupling the scale of electromagnetic simulation from the scale of inverse design, our approach enables system-scale free-form photonic devices that retain nanoscale design freedom.
Read the full abstract

All authors Viktor A. Lilja, Khosro Zangeneh Kamali, Mikael Käll, Philippe Tassin

Saturday 3 October

Optics

Efficient Light Trapping Strategy in Solar Cells via Vertically Disordered Perovskite Nanowires

Sina Salimian and Nicklas Anttu

In this work, we investigated the absorption of light in perovskite nanowires (PrvNWs) for application as active layer in a solar cell. Specifically, we simulated PrvNWs with a random position inside the pores of an AAO membrane. The results demonstrate that this vertical disorder can boost light absorption, up to 28% in terms of short-circuit current, in comparison to the corresponding ordered PrvNW array. This performance boost is due to a combination of light trapping and anti-reflection effect. Thus, our findings suggest that vertically disordered PrvNWs can have a much better performance than ordered arrays. Also, we showed that it is not necessary to aim for a very narrow length distribution in the nanowires, easing the fabrication requirements.
Read the full abstract

Optics

Phase-matching in high-order harmonic generation with a plasma-reshaped driving field

Gaspard Beaufort, Venus Poulain, Melvin Redon et al. (+13 more)

The transition from titanium-sapphire to ytterbium-based laser technology enables turnkey implementations of high-order harmonic generation (HHG) setups at high repetition rates, opening up new applications, e.g., in semiconductor metrology. This, however, requires exploring and understanding the impact of new experimental conditions. Here, we study HHG in neon over the spectral range 8-17 nm with high spectral resolution, using a post-compressed ytterbium laser. Our measurements reveal a large pulse-energy- and pressure-dependent spectral shift, spanning more than two harmonic orders. The femto-chirp of the harmonic emission combined with the blueshift of the fundamental field allows us to relate the observed spectral shifts to the temporal window of harmonic generation, which is determined by phase-matching. To understand these dynamics, it is essential to consider the reshaping of the driving laser field inside the plasma, despite the low driving intensity and long pulse duration. We introduce an on-axis phase-matching description that captures these effects and reproduces the experimental and simulated trends. These results demonstrate the central role of plasma-induced laser reshaping in phase-matching of HHG, which should be accounted for when optimizing sources in a multi-parameter landscape.
Read the full abstract

All authors Gaspard Beaufort, Venus Poulain, Melvin Redon, Robin Weissenbilder, Elisa Appi, Filip Salbrink, Saga Westerberg, Aimee J. Ross, Sylvianne Roscam Abbing, David P. O'Dwyer, Yin Tao, Per Eng-Johnsson, Cord L. Arnold, Anne L'Huillier, Peter Smorenburg, Anne-Lise Viotti

Optics · Cross-listed from astro-ph.IM

Vector field dark matter search with Sagnac interferometer

Yuki Inoue, Quynh Lan Nguyen and Ippei Obata

We present the first calculation showing that a material-asymmetric Sagnac speed meter can improve quantum-noise-limited sensitivity to $B-L$ vector dark matter by nearly two orders of magnitude over a Fabry–Perot Michelson position meter at the low-mass end of the band. We introduce material contrast into a dual-ring interferometer to probe composition-dependent $B-L$ forces and compare the two configurations at equal incident power, input-mirror transmissivity, and cavity round-trip length. For sapphire mirrors and a one-week benchmark, the quantum-noise-only median expected $95\%$ CL upper limit reaches $1.2\times10^{-27}$ at $m_A=4.1\times10^{-14}\,\mathrm{eV}/c^2$ ($10\,\mathrm{Hz}$), a factor-$57$ improvement. This band-edge forecast assumes negligible classical noise; sensitivity at $10\,\mathrm{Hz}$ is not established for a realizable suspension and isolation system. The material-induced displacement is essentially identical in both configurations, with the gain arising from reduced low-frequency quantum backaction. These results identify speed-meter readout as a promising route to lower-mass vector-dark-matter searches.
Read the full abstract

Optics · Cross-listed from quant-ph

Symmetry resolved entanglement in Schwinger pair production

Wajid Joyia, S.M. Al-Marzoug and Amaria Javed

We study the charge resolved structure of the pairwise mode entanglement produced by the Schwinger effect. Using the $U(1)$ electric charge of quantum electrodynamics, we decompose the entanglement of the reduced density matrices of momentum modes into individual charge sectors, applying the symmetry resolved entanglement entropy to the pure bipartition reductions and the charge imbalance resolved negativity to the mixed particle-antiparticle pair. For a constant electric field we obtain closed form results for every mode pairing, with all field dependence controlled by the single pair production probability $|\beta|^2=e^{-\pi\mu}$. For the particle, particle and antiparticle antiparticle pairs the entanglement entropy within each charge sector is field independent, so that the field acts only by redistributing statistical weight among the sectors; for the mixed particle antiparticle pair the populated sector additionally carries a field dependent entropy. The vacuum created pair is the richest case: its resolved negativity is distributed over three imbalance sectors and is transported from one sector to the next as the field increases, the sectors contributing equally only at the critical field. The entanglement across a fixed momentum bipartition, by contrast, is frozen at its initial value because pair creation conserves the sector charge. Symmetry resolution thus refines the total entanglement measures into a sector resolved picture, exposing where in charge space the entanglement of the Schwinger mechanism resides and how the electric field moves it, information beyond that contained in the total measures or in particle number distributions.
Read the full abstract

Optics

Nondestructive 3D Quantification of the Magnitude and Extent of Indentation-Induced Densification in Glass

Sang-min Lee, Dohyeon Lee, Juheon Lee et al. (+2 more)

Vickers hardness characterizes resistance to indentation but does not distinguish the magnitude of local densification from the volume of glass affected. Here, low-coherence holotomography reconstructs three-dimensional refractive-index (RI) images of Vickers-indented fused silica, borosilicate, and soda-lime glass across applied loads and nominal dwell times. Analysis of RI changes using the Lorentz-Lorenz relation quantifies densification, while segmentation measures the spatial extent of the densified region. Cracks are observed within the same reconstructed RI images. Densified volume increased with load even when peak densification plateaued, and glasses with similar hardness showed different densification responses. Longer nominal dwell times were associated with larger volumes above fixed RI thresholds and comparatively small changes in peak densification. Joint analysis of densification and crack morphology thus characterizes subsurface indentation damage beyond hardness alone. Densification is quantified as an optical estimate under the Lorentz-Lorenz assumptions; residual stress, polarizability, and reconstruction can also affect RI.
Read the full abstract

All authors Sang-min Lee, Dohyeon Lee, Juheon Lee, Herve Hugonnet, YongKeun Park

Optics

Robust Optical Pulling of Plasmonic, Chiral, and Dielectric Nanorods in Single and Cluster Configurations Using Hyperbolic Metamaterials

Md. Al Amin Chy, Md. Ajijul Haque Sakib Opu, Md Fujael Ahmed et al. (+2 more)

Optical manipulation enables the control of microscopic particles using light and has become an active area of research in recent years. One particularly interesting aspect is the possibility of generating optical pulling forces with hyperbolic metamaterials (HMMs), which leads to unusual light-matter interactions. In this work, the pulling response of plasmonic, chiral, and dielectric nanorods is studied on an HMM substrate. The system is illuminated by a time-harmonic, plane-polarized laser beam propagating along the +Z to -Z direction. The analysis is carried out under two different configurations. In the first case, plasmonic, chiral, and dielectric nanorods are arranged in a heterogeneous cluster over the HMMs and analyzed for the optical force response under three environmental conditions: fully immersed in water, partially immersed (half air-half water), and fully in air. Full-wave simulations reveal that in all three environments, all the objects (plasmonic, chiral, dielectric) nanorods consistently experience an optical pulling force at the 1E(-20)N scales for clustered configuration. In the second case, each nanorod type was independently placed on the same HMMs substrate within a full-air medium and investigated their force behaviors, while the plasmonic experience 100 times more than others for the single setup, which is 1E(-19)N ranges. Like the case of the cluster, three nanorods alone demonstrate a stable optical pulling force, also getting the pulling force with the variation of length, radius, and distance between them, which makes this optical setup more practical. Plasmonic behavior changes a lot with the arrangement of the nanostructures. On the other hand, dielectric nanorods are affected more by their length than their position. In our results, optical pulling appears for all the nanorods even with a simple HMM structure...
Read the full abstract

All authors Md. Al Amin Chy, Md. Ajijul Haque Sakib Opu, Md Fujael Ahmed, Rashedul Albab, Md. Janibul Alam Soeb

Optics

Bidirectional schlieren imaging using dual-LED illumination and a lens aperture as a knife-edge

Vimod Kumar and Manish Kumar

In this letter, we demonstrate that employing the Lens Aperture as a Knife-Edge (LAKE) with two identical LEDs has the distinct advantage of obtaining schlieren images along two cutoff orientations. It is possible to control LED brightness to obtain a desirable weighted sum of both horizontal and vertical schlieren cutoff images on each camera frames. Powering the LED sources by an affordable and programmable Arduino board enables a rapid switch between the horizontal and vertical schlieren cutoff that is exactly synced to the camera frames, resulting in crosstalk-free schlieren image sequence. Furthermore, with a little postprocessing, this monochrome image series can be easily transformed into a colorful sequence of bidirectional schlieren images.
Read the full abstract

Optics

Temporal Branched Flow of Light

Weifeng Ding, Chaokai Yang, Zhaoying Wang et al. (+1 more)

Branched flow of light arises when spatially correlated disorder folds families of rays into caustics. Here, we demonstrate a temporal analog in the retarded-time coordinate of an optical pulse in a waveguide, where branched flow becomes hyper-dispersive. Retardation during pulse propagation induces spatiotemporal correlations that break propagation reciprocity and imprint a trajectory memory. This nonreciprocity enables unidirectional temporal branched flow with no spatial counterpart. A memory model is developed combining ray-density and phase fluctuations with single-ray dynamics in a memory cell. The model reveals competition between fluctuation-induced focusing and destruction, which yields nontrivial diagrams of propagation regimes with distinct dispersion scalings. For a 532-nm pulse in a $\mathrm{LiNbO_3}$ fiber, we predict that refractive-index disorder induced by active modulations or quantum vacuum fluctuations can produce first caustics on meter-to-kilometer scales, offering routes to experimental observation and to sensing ultra-weak fluctuations.
Read the full abstract

All authors Weifeng Ding, Chaokai Yang, Zhaoying Wang, Fanglin Bao