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Thursday 6 August

Optics

Abruptly autofocusing waves enter space-time

Nikolaos K. Efremidis and Demetrios N. Christodoulides

Whereas conventional Gaussian focusing gradually concentrates optical energy around the focal plane, abruptly autofocusing waves maintain a low peak intensity over most of their evolution before undergoing a sudden, high-contrast intensity surge at a prescribed focus. Since their introduction in 2010, their two-dimensional spatial realizations have enabled applications ranging from particle manipulation and material processing to terahertz generation and nonlinear optics. The recent work of Cao et al. marks the transition from (2+1)-dimensional spatial autofocusing to the full space-time domain through the experimental synthesis of spherical Airy wavepackets. This advance opens new opportunities for ultrafast structured light, tightly localized energy delivery, and nonlinear photonics.
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Optics

Transverse quantum-state characterization of programmable electron optics

Shengbo You, Paolo Rosi, Enzo Rotunno et al. (+6 more)

Programmable electron optics – electronically controlled phase plates – underpin proposals from dose-efficient phase imaging to shaped-electron X-ray sources, nearly all assuming a pure, fully coherent delivered wave whose purity has never been measured. Here we reconstruct the transverse density matrix of a microelectromechanical electrostatic spiral phase plate by mixed-state ptychography, from one four-dimensional STEM scan per state and without added hardware. The delivered beam is substantially mixed: its purity falls from approximately 0.47 to approximately 0.24 as the applied bias grows, inconsistent with a fixed lateral source-blur model, while the real-space coherence width stays near 1 nm. The same scans calibrate the device in situ, allow virtual orbital-angular-momentum sorting and, through a partial-coherence-aware transfer theory, indicate that purifying the output could improve dose efficiency roughly threefold. One acquisition thus becomes a quantum-state acceptance test for programmable electron optics, supplying the purity and coherence that emerging phase-plate and diffractive-imaging schemes assume but leave unquantified.
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All authors Shengbo You, Paolo Rosi, Enzo Rotunno, Alberto Roncaglia, Luca Belsito, Amir H. Tavabi, Rafal E. Dunin-Borkowski, Vincenzo Grillo, Philipp M. Pelz

Optics · Cross-listed from cs.CV

Engram-E2VID: Reference-Based Event-to-Video Reconstruction via Generative Activation of Appearance Engrams

Feiyu Ji, Xiang Li, Hao Ma et al. (+6 more)

Reference-based event-to-video reconstruction aims to recover target RGB frames from a reference frame and the event stream captured over the reference-to-target interval. Although events provide fine-grained temporal cues, they encode sparse and asynchronous log-intensity changes rather than absolute appearance, making faithful reconstruction intrinsically challenging. The central challenge lies in associating event-derived target-time structures with relevant appearance information from the reference frame, especially under complex motion and long temporal intervals. In this work, we propose Engram-E2VID, a structure-guided framework that reconstructs target frames through the generative activation of appearance engrams. Specifically, the reference frame is encoded into token-space appearance engrams, while the event stream and reference context are transformed into a target-time motion-structure scaffold that captures motion boundaries and event-induced structural changes. Within a one-step diffusion backbone, scaffold-derived structural tokens progressively interact with and activate relevant appearance engrams across layers. This token-space association allows target structures to access reference appearance without relying on direct pixel-wise correspondence, while the diffusion prior complements uncertain or newly revealed regions. Across three benchmarks, Engram-E2VID improves PSNR by up to 3.29 dB and reduces LPIPS by up to 0.08 over the strongest same-input baseline, while degrading more slowly as the reconstruction interval increases.
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All authors Feiyu Ji, Xiang Li, Hao Ma, Tianxiang Huang, Qingxin Lu, Mengqi Ji, Lei Han, Xiaokang Yang, Xiaoyun Yuan

Optics · Cross-listed from hep-ph

Net electron spin rotation in a plane-wave pulse: Holonomy set by the anomalous magnetic moment

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

We compute the spin rotation that survives after a relativistic electron has crossed a plane-wave laser pulse of finite duration. In the interaction picture built on the exact $g=2$ evolution, the Thomas-Bargmann-Michel-Telegdi equation becomes parallel transport by a connection with constant coefficients on the polarization plane, and the pulse enters only through the closed curve that the transverse vector potential traces there. The net rotation is the holonomy of that connection: an angle $-\frac{1}{2}a_e^2\mathcal{A}$ about the propagation direction, with $a_e=(g-2)/2$ the anomaly and $\mathcal{A}$ twice the signed area enclosed by the curve. That area is the spin angular momentum the pulse carries per unit area, so the rotation measures the helicity of the light. Reduction of the residual dynamics to a rotation coupled through the anomaly alone is an exact result of the 1960s [Ternov, Bagrov, and Klimenko, Sov. Phys. J. 11, 29 (1968); Bagrov and Gitman, The Dirac Equation and its Solutions (De Gruyter, Berlin, 2014), Sec. 5.3], which yields two closed-form cases; the area law is the general second order that those two cases bound. The same area governs the orientation memory of a neutral magnetic dipole [Oblak and Seraj, Phys. Rev. D 109, 044037 (2024)] with a coupling of order unity. For a charged electron on a Volkov orbit the coupling $g/2$ cancels identically, which suppresses the rotation by $1.3\times10^{-6}$ and leaves a channel with no $g$-independent part. We verify the cancellation at $g=2$ over 180 pulse configurations and the area law over 89 more. Finite focusing restores that part at second order in $1/kw_0$, and it exceeds the anomalous signal unless $w_0\gtrsim16\lambda$ at $\gamma=10$, or $270\lambda$ at $\gamma=1$.
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All authors N. S. Akintsov, A. P. Nevecheria, S. N. Andreev, Qing-Hua Qin

Optics

Spectrally flat and broadband doublepumped fiber optical parametric amplifiers

J. M. Chavez Boggio, J. D. Marconi, S. R. Bickham et al. (+1 more)

We study theoretically and experimentally spectrally flat and broadband double-pumped fiber-optical parametric amplifiers (2P-FOPAs). Closed formulas are derived for the gain ripple in 2P-FOPAs as a function of the pump wavelength separation and power, and the fiber non-linearity and fourth order dispersion coefficients. The impact of longitudinal random variations of the zero dispersion wavelength $\lambda_0$ on the gain flatness is investigated. Our theoretical findings are substantiated with experiments using conventional dispersion shifted fibers and highly nonlinear fibers (HNLFs). By using a HNLF having a low variation of $\lambda_0$ we demonstrate high gain and flat spectrum ($25 \pm 1.5\text{ dB}$) over $115\text{ nm}$.
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All authors J. M. Chavez Boggio, J. D. Marconi, S. R. Bickham, H. L. Fragnito

Optics

Dual-polarization control of broadband nonreciprocal thermal radiation by combining local and nonlocal metasurfaces

Shuang Xia, Mengqi Liu, Wenjian Wan et al. (+10 more)

Nonreciprocal thermal radiation offers a route to decouple spectral directional absorptivity and emissivity, thereby enabling new paradigms in thermal-photonic systems. However, in magneto-optical platforms, the intrinsic gyroelectric response generally confines observable nonreciprocity to transverse-magnetic (TM) polarization, while the transverse-electric (TE) response is absent. In this work, we experimentally demonstrate, for the first time, a local thermal metasurface strategy to activate TE-polarized nonreciprocity by creating artificial gyromagnetic response in a gyroelectric semiconductor platform. We further extend this mechanism to broadband dual-polarization operation employing a nonlocal thermal metasurface, which combines a resonator supercell with gradient-doped epsilon-near-zero magneto-optical multilayers. Pronounced absorptivity contrast is maintained over 22-27 {\mu}m for TE polarization and 19-27 {\mu}m for TM polarization. This platform provides a mechanism-based route to achieve broadband and dual-polarization nonreciprocal thermal absorption, opening new opportunities for advancing radiative energy-conversion devices.
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All authors Shuang Xia, Mengqi Liu, Wenjian Wan, Jialong Wang, Weihao Yang, Chaoran Wang, Huiqin Ma, Jun Qin, Hua Li, Yuan Wang, Lei Bi, Chengwei Qiu, Xiaobo Yin

Optics · Cross-listed from quant-ph

Generating two-mechanical mode entangled cat states, and steady-state entanglement, in cavity optomechanics in the presence of dissipation

Sanket Das and Jason Twamley

We investigate a dissipation-engineering approach to produce a phase-dependent collective-mode Schrödinger cat state involving two modes. Our model features a single cavity mode that interacts with two spectrally identical mechanical oscillators. Both oscillators are coupled through a phase-dependent hopping interaction. We demonstrate that by adjusting the phase of the phonon-hopping interaction, one can control the bipartite entanglement of the phase-dependent two-mode cat state during its generation. Additionally, our study reveals that phonon interactions act as a tunable parameter, enabling the manipulation of steady-state entanglement between the bare mechanical modes, even in the presence of environmental effects and thermal excitations. Our scheme provides a feasible approach for the phase-dependent multi mode non-Gaussian states preparation.
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Optics

Inverse mask design for interference lithography using automatic differentiable wave propagation

Chuntian Cao, Jangwoon Sung, Jack Griffiths et al. (+9 more)

Interference lithography (IL) is powerful for fabricating high-resolution periodic nanostructures, but designing masks to produce non-periodic patterns remains challenging. We introduce a gradient-based optimization framework for binary IL mask design using automatic differentiation. The forward model is implemented using the differentiable angular spectrum method (ASM). The inverse mask design is formulated as an optimization problem, where the mask logits are updated through backpropagation of the loss between the simulated field amplitude and the target pattern. We optimize a mask that reproduces a target pattern with only 0.1% isolated pixel-level defects, resolving features at half the mask pixel pitch. To scale mask optimization, we employ the shifted ASM, which partitions the mask into patches that are propagated independently and summed at the image plane. For a 3.84 mm$\times$3.84 mm mask, shifted ASM with 16 patches reduces peak GPU memory by 3.8$\times$ at only 1.3$\times$ runtime cost relative to standard ASM. With gradient checkpointing, peak memory is reduced by 7.4$\times$ at 2$\times$ runtime. Distributing across multiple GPUs further accelerates the optimization. This work establishes a physics-informed, machine learning-driven approach for IL mask design, moving a step further towards complex, non-periodic patterns. The source code is available at https://github.com/chuntian236/holography-optimization.git .
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All authors Chuntian Cao, Jangwoon Sung, Jack Griffiths, Yuan Gao, Xi Yu, Paul Baity, Nikhil Tiwale, Zhitian Shi, Juhong Ahn, Shinjae Yoo, Yong S. Chu, Chang-Yong Nam

Wednesday 5 August

Optics

High Spectral Energy Density All-Fiber Nanosecond Pulsed 1.7 $\mu$m Light Source for Photoacoustic Microscopy

Seongjin Bak, Sang Min Park, Yuon Song et al. (+7 more)

We present a high spectral energy density all-fiber nanosecond pulsed 1.7 $\mu$m light source specifically designed for photoacoustic microscopy (PAM). The system targets the first overtone absorption of C-H bonds near 1720 nm within the near-infrared-III (NIR-III) window, where lipids exhibit strong optical absorption and tissues benefit from reduced scattering and high permissible fluence. To achieve narrow linewidth, high pulse energy, and high pulse repetition rate (PRR), we developed a master oscillator fiber amplifier architecture based on stimulated Raman scattering. A 1589.80 nm Raman pump and a custom-built narrow-linewidth Raman seed laser were employed to generate spectrally pure 1719.44 nm pulses with an approximately 0.10 nm linewidth. The proposed light source delivers nanosecond pulses of approximately 5 ns with high pulse energy of at least 2.2 $\mu$J and tunable PRRs up to 300 kHz, resulting in a spectral energy density of approximately 22 $\mu$J/nm, which is significantly higher than that of conventional 1.7 $\mu$m light sources. The performance of the NIR-PAM system was validated through resolution testing with a 1951 USAF target, demonstrating a spatial resolution of approximately 4.14 $\mu$m and an axial resolution of approximately 85.5 $\mu$m. Phantom imaging of CH$_2$-rich polymer films and ex vivo lipid-rich biological tissues confirmed the system's high spatial fidelity and strong contrast for lipid-specific structures. This compact, stable, and spectrally refined light source with high spectral energy density can offer an effective solution for high-resolution, label-free molecular imaging and represents a promising platform for clinical photoacoustic imaging applications involving lipid detection and metabolic disease diagnostics.
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All authors Seongjin Bak, Sang Min Park, Yuon Song, Jeesu Kim, Tae Won Nam, Dong-Wook Han, Chang-Seok Kim, Soon-Woo Cho, Brett E. Bouma, Hwidon Lee

Optics · Cross-listed from astro-ph.IM

Comparative analysis of fiber Bragg grating filter losses inscribed by continuous wave UV and femtosecond-IR lasers for astrophotonics

Aashia Rahman, Ria G. Krämer, Abani Shankar Nayak et al. (+8 more)

Fiber Bragg grating (FBG) filters have been demonstrated as promising components in astrophotonic instrumentation for near-infrared ground-based observations. Given the photon-starved nature of astronomical applications, it is critical to minimize insertion losses across astrophotonic components. In addition to the insertion loss (IL) introduced by specialty fibers and inscription techniques, FBGs exhibit cladding mode (CM) losses. In this work, we studied the loss characteristics of five filter lines in three photosensitive fibers, i.e., a low-numerical-aperture (NA) fiber, a high-NA bend-insensitive fiber, and a cladding-mode-suppressed (CMS) fiber, and in a non-photosensitive fiber, SMF-28. The filters were inscribed using two phase mask-based illumination methods: a continuous wave ultraviolet (UV) laser with a complex phase mask allowing for multi-channel filters, and a femtosecond infrared (fs-IR) laser with phase mask integrated shaping apertures for spectral profile control. Our results show that UV-inscribed gratings in high-NA bend-insensitive fiber yield the lowest CM losses ($\approx$ 0.5 dB) among photosensitive fibers, but exhibit the highest IL (4.6 dB), and FBGs in non-photosensitive SMF-28 fiber, inscribed with fs-IR, achieve the lowest IL (< 0.05 dB) with a comparatively higher CM loss (0.93 dB). To reduce the high IL in high-NA fiber, we explored tapering and bridging methods and report that bridging reduces IL by $\sim$ 3 dB. We show that both filter platforms remain viable for integration into an astrophotonic system, with IL below 1 dB. Finally, we propose a compact bridge-fiber scheme with the potential to further reduce IL to below 0.5 dB while reducing the number of bridging fibers and, consequently, the number of splice junctions by 50%.
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All authors Aashia Rahman, Ria G. Krämer, Abani Shankar Nayak, Julius Göhring, Piyamas Choochalerm, Anna Maria Weiß, Samuel L. Döpfner, Tim Schleifer, Kalaga Madhav, Martin M. Roth, Stefan Nolte

Optics

Overcoming Scattering in High-Cell-Density Tomographic Volumetric Bioprinting Using Computational Light Optimization

Qianyi Zhang, Felix Wechsler, Viola Sgarminato et al. (+2 more)

Tomographic volumetric additive manufacturing has emerged as a transformative 3D printing technology for rapidly fabricating complex geometries. It offers significant advantages for bioprinting due to its contactless and short process time (a few tens of seconds). However, the presence of high cell densities ($>10^7$ cells mL-1) in bioresins introduces substantial light scattering, which degrades printing resolution and fidelity, hindering the fabrication of biologically relevant microstructures such as vascular channels and cavities. To address this challenge, we utilize a computational patterning framework leveraging physically based inverse rendering to optimize light delivery in scattering environments. This method iteratively refines tomographic projections by simulating light-matter interactions in cell-laden hydrogels, enabling precise compensation for scattering effects. Experimental results demonstrate that our approach achieves 500 ${\mu}m$ diameter vascular channels at $2*10^7$ cells mL-1. Furthermore, we integrate this computational method with refractive index matching strategies, reducing scattering artifacts by minimizing optical mismatch between cells and the hydrogel matrix, enabling printing at $4.1*10^7$ cells mL-1. The compatibility of these dual strategies enables unprecedented print fidelity in turbid bioresins. This advancement expands the scope of tomographic volumetric additive manufacturing for engineering functional tissues with intricate microarchitectures.
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All authors Qianyi Zhang, Felix Wechsler, Viola Sgarminato, Christophe Moser, Riccardo Rizzo

Optics · Cross-listed from eess.IV

AI-based single-shot structured-light depth reconstruction for real-time laparoscopic surgical guidance

Wayne Wonseok Rodgers, Xiangyi Le, Seonghoon Jang et al. (+5 more)

Significance. Accurate intraoperative depth perception is important for autonomous and semi-autonomous robotic laparoscopic surgery. Conventional fringe projection profilometry can achieve millimeter-scale accuracy but often requires multi-shot acquisition, digital-micromirror-device projection, and projector-camera synchronization, complicating integration into compact laparoscopic systems. Aim. To develop a synchronization-free, single-shot depth-sensing platform using a passive LED-illuminated binary mask and a VQ-VAE prior with a custom U-Net depth head. Approach. A compact projection module was coupled to one channel of a dual-channel laparoscope, while the second channel imaged the fringe-illuminated target. A Zivid 3D camera acquired reference depth for 722 paired phantom images. Zivid depth maps were reprojected into the SSLE image frame for supervised training and evaluation. The VQ-VAE encoded each input into a discrete latent representation, and a latent-space U-Net predicted depth without a separate mask-prediction branch. Results. Using a fixed train/validation/test split, the proposed model achieved an MAE of 3.70 mm, AbsRel of 0.0326, delta=1.1 accuracy of 0.962, and delta=1.1^2 accuracy of 0.970. It achieved lower MAE than the dual U-Net MaskNet + DepthNet baseline and outperformed off-the-shelf monocular depth models in MAE, AbsRel, and threshold accuracy. The pipeline operated at 26.0 Hz over 301 consecutive frames on an NVIDIA A100 GPU. Conclusions. The LED-illuminated binary-pattern platform with latent-space depth reconstruction enables synchronization-free, video-rate endoscopic depth estimation. Results demonstrate Zivid-referenced phantom reconstruction without an explicit segmentation stage, while emphasizing the importance of dataset size and SSLE-Zivid calibration accuracy.
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All authors Wayne Wonseok Rodgers, Xiangyi Le, Seonghoon Jang, Shuwen Wei, Justin Opfermann, Michael Kam, Axel Krieger, Jin U. Kang

Optics

Mask-free fast patterning of organic light-emitting diode pixels using laser-assisted close-space sublimation

Subhamoy Sahoo, Jain Jose, Mani R et al. (+8 more)

Existing patterning processes for organic light-emitting diode displays offer micrometer-scale precision but are constrained by long processing times for large-area substrates. In this work, we study a fast growth method for patterned organic film deposition, aimed at applications including active-matrix organic light-emitting diode displays. The approach employs a specially engineered donor substrate in a close-space sublimation configuration combined with laser heating. The donor substrate incorporates spatially patterned absorber and reflector layers that enable selective, one-step or two-step transfer of organic material onto a receiver substrate. We analyze the optical response and heat-transfer dynamics that govern the selective transfer mechanism and demonstrate precise pixel patterning with micrometer-scale spatial fidelity. The reliability and practical applicability of the method are validated by fabricating light-emitting diode devices by using this rapid transfer process and benchmarking their performance against devices produced via conventional vacuum thermal evaporation. The resulting devices exhibit comparable optoelectronic performance, confirming the robustness and technological relevance of the proposed strategy for scalable fabrication of patterned organic light-emitting diodes for display application.
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All authors Subhamoy Sahoo, Jain Jose, Mani R, Arghya Saha, Kanimozhi V, Dhruvajyoti Barah, R. Bairava Ganesh, Amitava Majumdar, Jayeeta Bhattacharyya, G Rajeswaran, Debdutta Ray

Optics

Photonic-chip-based generation of sub-100-femtosecond optical frequency combs

Weiqiang Xie, Zhengshun Lei, Zeyu Xiao et al. (+8 more)

Sub-100-fs optical pulses and frequency comb sources have been revolutionizing a wide range of applications, from ultrafast optical science to optical frequency standard and measurement. To date, the leading techniques for generating such pulses in practical systems rely on tabletop mode-locked lasers, which inherently suffer from high system complexity, limited long-term reliability, and pronounced environmental sensitivity. Meanwhile, driven by advances in photonic integration, chip-scale approaches have sought to realize miniaturized pulse sources. However, simultaneously achieving sub-100-fs duration, ideal pulse shape, and a broadband flat-topped spectrum remains a significant challenge. Here, we address these challenges by combining two key photonic chip technologies: TFLN EO modulators for picosecond seed pulse generation, and highly nonlinear optical loop mirrors (NOLM) based on AlGaAsOI nanowaveguides for efficient temporal pulse cleaning and spectral broadening. In theoretical simulation and experiment, we show that for an input seed pulse centred at ~1550nm, a single-stage AlGaAs NOLM with a loop length of 1cm can produce flat-topped, nearly tenfold spectral broadening and over tenfold compression of pulse width, and more than 10dB suppression of pulse pedestals. Using initial EO comb pulses with ps-level durations at repetition rates of 10-20GHz, we demonstrate photonic-chip-enabled pulses with an unprecedented duration of 55fs and a flat-topped comb spectrum whose 10dB optical bandwidth exceeds 90nm. Our results highlight the remarkable potential of photonic chip technologies to realize high-repetition-rate, miniaturized sub-100-fs optical pulse generators with the prospect of superior stability and operability. The demonstrated photonic-chip-based sub-100-fs optical frequency comb sources may establish a new paradigm for both scientific research and practical applications.
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All authors Weiqiang Xie, Zhengshun Lei, Zeyu Xiao, Yudi Zhao, Xing Zou, Wenqi Wei, Zihao Wang, Ting Wang, Jianjun Zhang, Bofang Zheng, Yikai Su

Optics

Freeform super-oscillatory optics for CMOS-integrated THz super-resolution imaging

Jin Chen, Liang Gao, Hao Guo et al. (+5 more)

The diffraction limit fundamentally constrains the spatial resolution of far-field imaging systems. While near-field techniques can circumvent this limit, their inherently short working distances (WD) severely restrict practical applications. Super-oscillatory lenses (SOLs) offer a far-field alternative; however, conventional SOLs are plagued by discrete operating wavelengths, low efficiencies (below 5%), and formidable trade-offs among numerical aperture, chromatic aberration, and depth of focus (DOF). Here, we introduce a nonlocal, nonlinear-curvature mechanism to design a freeform SOL that achieves ultrabroadband (0.3 to 1 THz), achromatic super-resolution focusing with an unprecedented efficiency of 44%. Operating at a 9 mm WD, the lens maintains a consistent sub-diffraction full-width at half-maximum (FWHM) of around 0.45 wavelength alongside an extended DOF of around 10 wavelengths. By integrating a compact 65-nm CMOS oscillator-radiator array, we establish an advanced imaging platform capable of resolving complex 2D and 3D sub-millimeter features (down to 0.15 mm). Readily scalable to the optical regime via two-photon lithography, this freeform SOL paradigm paves the way for next-generation, high-performance integrated photonics.
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All authors Jin Chen, Liang Gao, Hao Guo, Zhi Chao Chen, Kang Jie Lin, Kam Man Shum, Ka Fai Chan, Chi Hou Chan

Optics · Cross-listed from physics.chem-ph

Time-resolved THz Stark spectroscopy of molecules in water

Elnaz Zyaee, Vladislav Slama, Seyyed Jabbar Mousavi et al. (+3 more)

Stark spectroscopy is a powerful method for probing molecular dipole moment changes, charge transfer dynamics, and polarizability under applied electric fields. Time-Resolved Terahertz Stark Spectroscopy (TRTSS), which employs intense single-cycle terahertz (THz) pulses to induce transient Stark shifts, overcomes key limitations of conventional approaches. Unlike static or low-frequency fields, THz pulses oscillate much faster than typical molecular rotation times, effectively preventing dipole reorientation and enabling measurements in solutions at ambient conditions. Here, we extend TRTSS to molecules dissolved in water, the most important polar solvent for chemical and biological systems and report the first demonstration of Stark spectroscopy in water at room temperature. Using Malachite Green and Methyl Orange as model systems, we observe clear THz-induced spectral modulations, demonstrating that TRTSS can successfully reveal THz Stark responses even in highly polar, hydrogen-bonded environments. Measured signals exhibit a combination of linear (dipole-driven) and quadratic (polarizability-driven) Stark effects in both systems, consistent with time-dependent density functional theory (TD-DFT) calculations. Comparison with TD-DFT further suggests that conformational effects can influence the extracted Stark parameters in solvated molecules.
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All authors Elnaz Zyaee, Vladislav Slama, Seyyed Jabbar Mousavi, David Rohrbach, Ursula Rothlisberger, Thomas Feurer

Optics

Universal Function Approximation via Diffractive Optical Processors: Physical Limits, Error Bounds, and Learnability

Md Sadman Sakib Rahman, Che-Yung Shen and Aydogan Ozcan

We present a unified theoretical framework connecting classical universal approximation theory, Fourier-feature approximation, and diffractive optical processors. We show that phase-encoded diffractive processors implement finite Fourier-feature expansions whose mathematical completeness follows from Fourier/Stone-Weierstrass arguments, while their physical realizability is governed by finite coefficient synthesis through optimized spatially varying coherent point-spread functions (PSFs). Our analyses derive approximation-error bounds that separate Fourier truncation, PSF-synthesis, input phase error, optical hardware, readout, and noise contributions; establish scaling relationships linking approximation complexity to optical degrees of freedom and input/output space-bandwidth products; derive photon-budget and throughput limits imposed by photon statistics; formulate finite-class statistical learnability bounds for phase-quantized diffractive function approximators; and analyze the impact of spatially incoherent illumination. We further analyze coherent optical cascadability and show that quadratic feature expansion through coherent mixing and optical readout provides a mechanism for enhanced representation while remaining fundamentally distinct from the depth-separation results established for digital neural networks. Our analyses provide a rigorous theoretical foundation for diffractive nonlinear function approximation and establish quantitative relationships among mathematical expressivity, optical hardware resources, statistical learning, and physical performance limits, thereby offering general design principles for large-scale analog optical computing systems.
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Optics

Design of a thermal loading resilient optical enhancement cavity for operation at 515 nm for X-ray production through inverse Compton scattering in an energy recovery linac

Alice Renaux, Aurelien Martens, Yann Peinaud et al. (+5 more)

A fast and simple method to optimize a high-power optical enhancement cavity is proposed. It is applied to a four-mirror bow-tie cavity operating at 515 nm, which is to be implemented within the PERLE ERL for the production of X-rays through inverse Compton scattering. The optimized figure of merit is the expected X-ray photon rate. Thermal loading is carefully evaluated, giving also a path towards very high average power operation in infrared. One shows that photon rates exceeding 10^11 per second at average energies above 280 keV in apertures of a few miliradians are within reach. For easier comparison with existing Compact X-ray sources providing high rates of photons, the performance of the proposed design is also evaluated for a system delivering infrared laser pulses. It is shown that a source delivering more than 10^13 photons per second is achievable with this design, an unprecedented performance for existing Compton X-ray sources. The design procedure employed here can be easily applied to other applications of high-power high-finesse optical cavities.
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All authors Alice Renaux, Aurelien Martens, Yann Peinaud, Ronic Chiche, Kevin Dupraz, Marie Jacquet, Daniele Nutarelli, Fabian Zomer

Optics

Photogalvanic second harmonic generation in Si3N4 for 1 Hz level on-chip metrology and spectroscopy

Andrei Diakonov, Roy Zektzer, Xiyuan Lu et al. (+2 more)

The coherent photogalvanic (PG) effect induces an effective $\chi^{(2)}$ nonlinearity in natively $\chi^{(3)}$ silicon nitride integrated photonics, unlocking pathways toward chip-scale precision spectroscopy and optical clockworks via second harmonic generation (SHG). While quasi-phase-matched PG-SHG using spatially varying internal electric fields offers tuning flexibility, it is often accompanied by pump-power- and detuning-dependent frequency offsets. Here, we investigate whether direct phase-matching—utilizing an intermodal scheme that generates a spatially uniform electric field—can support metrologically compatible SHG. By comparing the fundamental and doubled optical frequencies in a silicon nitride microresonator, we test the preservation of the (2:1) frequency ratio in directly phase-matched PG-SHG. We observe a frequency offset of $< 1\mathrm{~Hz}$, contrasting with previous limitations in quasi-phase-matched configurations. Furthermore, we measure a residual fractional frequency instability of $2\times 10^{-15}$ at $1\mathrm{~s}$, averaging down to the $10^{-16}$ level at $1000\mathrm{~s}$, with multi-hour deviations remaining below $1\mathrm{~Hz}$. These results establish directly phase-matched PG-SHG as a robust, metrologically compatible route to effective $\chi^{(2)}$ functionality, combining sub-Hz frequency-ratio fidelity and high coherence on a mature integrated platform for optical clockworks, self-referencing, and precision spectroscopy.
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All authors Andrei Diakonov, Roy Zektzer, Xiyuan Lu, Kartik Srinivasan, Liron Stern

Optics

All-Optical Field-Resolved Spectroscopy With Interferometric Nonlinear Cross-Correlations

Felix Ritzkowsky, Gian Luca Dolso, Benjamin Mazur et al. (+2 more)

Direct time-domain measurements of electric fields enable sub-cycle spectroscopy of light-matter interactions, but established techniques such as electro-optic sampling are constrained in their bandwidth by gate-pulse duration and phase-matching limitations. Alternative approaches have emerged in recent years based on asymmetric interferometric nonlinear cross-correlations with highly nonlinear media, and have demonstrated, for example, the field-resolved study of exciton ensembles. However, these nonlinear cross-correlation-based techniques have been benchmarked almost exclusively by self-referenced pulse characterization rather than by their quantitative spectroscopic performance, and all-optical approaches have received less attention than those based on direct charge emission. Here we extend all-optical asymmetric interferometric cross-correlation to higher nonlinearities in sub-wavelength films and demonstrate field-resolved spectroscopy of the free-induction decay of two ro-vibrational bands of ambient water vapor with a performance comparable to state of the art electro-optic sampling. The measurement spans 190 THz of bandwidth (80 THz to 270 THz) with sub-500 GHz spectral resolution, a spectral intensity dynamic range of six orders of magnitude, and a field-strength noise floor of 100 kV per meter. We anticipate the rapid adoption of here presented all-optical sampling to many experimental settings and a broad impact beyond the ultrafast optics research community as it is drastically simplified in comparison to ionization based techniques and allows the translation of electro-optic-sampling-level sensitivity into higher frequency ranges not previously accessible by conventional tools.
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All authors Felix Ritzkowsky, Gian Luca Dolso, Benjamin Mazur, Matthew Yeung, Phillip D. Keathley

Optics

Quantum optoelectronics in semiconductor solar cell materials and devices

Xi Liu and Wenxi Fang

We analyze the integration of quantum optical phenomena, such as cavity quantum electrodynamics (CQED), Fabry Perot resonances, and strong light-matter coupling, into the design and engineering of next generation photovoltaic systems. We examine how these phenomena can be harnessed through photonic structures including optical cavities, plasmonic materials, and metasurfaces to improve light trapping, absorption, and carrier dynamics in future solar cell devices. Specific focus is given to semiconductor materials such as perovskites, organics, transition metal dichalcogenides (TMD), cadmium telluride (CdTe), and silicon. For perovskite solar cells, we analyze device architectures, interfacial engineering with hyperbranched polymers, and additive optimization using molecular dopants and nanosheets to enhance film morphology and stability. We further examine laser-based metrology for thin-film characterization and coherent spectroscopy techniques involving frequency combs and high-harmonic generation. The paper also shows how machine learning (ML), combined with density functional theory (DFT), accelerates material screening and performance prediction for next-generation solar cell absorbers. These developments demonstrate how quantum optoelectronic design principles are transforming photovoltaic research and enabling higher efficiency, stability, and functionality in solar energy devices.
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Tuesday 4 August

Optics

Analysis of Nonlinear Phase Noise in Coherent Fiber-Optic Systems Based on Phase Shift Keying

Shiva Kumar

Analytical expressions for the phase variance in a nonlinear fiber optic system based on phase-shift keying are developed. The Gauss-Hermite functions are used as the orthogonal basis to represent the noise field. Number of degrees of freedom (DOF) to accurately model the phase variance is estimated. The amplifier noise excites higher order Gauss-Hermite noise modes and the nonlinear mixing of a signal pulse and higher order Gauss-Hermite noise mode leads to new noise fields which enhance the nonlinear phase noise. The higher order noise modes propagate linearly and enhance the linear phase noise if the matched filter is not used at the receiver. Analytical expression for the optimum launch power is developed taking into account the linear and nonlinear phase noise.
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Optics · Cross-listed from quant-ph

An optical-fibre-integrated buffer for packet-switched quantum networks

Daniel Spegel-Lexne, Joakim Argillander, Martin Clason et al. (+5 more)

Packet-switched quantum networks require buffers that can delay qubit payloads while routing information is read out in real time. Previous approaches have not provided this functionality in a fully fibre-integrated architecture compatible with telecom infrastructure. Here we demonstrate an optical-fibre-integrated buffer, based on a recirculating loop and a fibre storage line, in which the storage time of a polarisation-encoded qubit payload is determined by readout of an attached packet header. The key component behind this achievement is an ultra-low-loss poled fibre phase modulator, which provides fast, polarisation-insensitive switching directly in fibre and allows header and payload to be processed within the buffer. We demonstrate storage and retrieval of polarisation-encoded qubit payloads for storage times up to 47 $\mu$s, with an average quantum bit error rate of 1.8% together with stable operation over several hours. These results establish a practical fibre-based architecture for packet-level quantum network buffering that can easily integrate into the current telecommunication infrastructure opening up new paths for deployment of the quantum internet.
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All authors Daniel Spegel-Lexne, Joakim Argillander, Martin Clason, Åsa Claesson, Kenny Hey Tow, Gustavo Lima, João M. B. Pereira, Guilherme B. Xavier

Optics

Structured light under turbulence

Guilherme S. Barros, Lucas C. Céleri, Antonio Zelaquett Khoury et al. (+3 more)

Structured light has emerged as a promising resource for high-capacity and secure free-space optical communication, where atmospheric turbulence remains a major source of signal degradation. In this work, we investigate the resilience of different transverse mode structures of an optical beam with respect to the random action of turbulence. A spatial light modulator (SLM) is programmed to apply amplitude and phase modulation corresponding to the desired transverse mode, which is then transmitted through a turbulent medium emulated by a second SLM. Laguerre-Gauss, Hermite-Gauss, and Airy beams are investigated through the resulting intensity distributions measured with a camera. Different figures of merit are used to evaluate and compare the resilience of these modes.
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All authors Guilherme S. Barros, Lucas C. Céleri, Antonio Zelaquett Khoury, André L. S. Santos Junior, Rafael M. Gomes, Guilherme L. Zanin

Optics · Cross-listed from math.AP

Refraction laws in spatio-temporal media

Cristian E. Gutiérrez and Eric Stachura

We study the time-dependent Maxwell system, formulated in the sense of distributions, for electromagnetic waves propagating through media with temporal and spatial material interfaces. Under explicit trace and regularity assumptions on the permittivity and permeability, we derive the jump conditions produced by temporal discontinuities and by subsequent spatial interfaces. These conditions are used to obtain generalized Snell laws for the wave vectors generated by temporal splitting, reflection, and transmission. We also derive the associated amplitude equations and organize them as a finite-dimensional linear system for a space-time slab geometry. Finally, we provide an explicit oblique-incidence example. Our approach does not impose a smooth-field ansatz and allows material parameters that need not be constant away from the interfaces.
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Optics

Can crystal symmetry reshape ENZ photonics?: Opinion

Mario G. Silveirinha

Over the last decade, epsilon-near-zero (ENZ) photonics has been driven by the search for lower losses and stronger nonlinear responses. Here, I ask a different question: can crystal symmetry also be used to shape the ENZ response? I focus on low-symmetry conductors, where the geometry of the electronic states can produce electric currents that are not present in ordinary Drude materials. These currents may enable polarization-dependent gain, nonreciprocal effects, and ultrafast nonlinearities controlled by symmetry and an external bias. I suggest that such materials may be useful for active and time-varying nanophotonics.
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Optics

Modulation in degree of cross-polarization at Young's interferometer illuminated by non-uniformly polarized electromagnetic fields

Rajneesh Joshi and Gyaprasad

The degree of cross-polarization (DoCP) and the electromagnetic degree of coherence (EM DoC) of an electromagnetic beam are investigated at the observation points for incoherent and non-uniformly polarized, i.e., different degree of polarization with respect to space at the two pinholes in Young's interference experiment. We note that DoCP at the observation plane can be expressed as the average value of the degree of polarization at the pinholes of Young's interference experiment. The present study also verifies that the DoCP is a two-point generalization of the DoP. Additionally, EM DoC at observation points can be controlled by DoP at pinholes. The findings may be useful for classical ghost imaging, lensless imaging, and the study of Stokes correlations.
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Optics

Joint spectral characterization of SPDC photon pairs near 2 $\mu$m in (Al)GaAs-on-insulator waveguides

Alexandre Z. Leger, Emil Z. Ulsig, Samuel E. Fontaine et al. (+8 more)

Integrated photon-pair sources are a core component of chip-based quantum computing, communication, and metrology. Although such sources have been demonstrated at conventional telecom wavelengths, the 2 $\mu$m band remains comparatively less explored, despite offering advantages for free-space quantum communication, low-loss transmission in emerging fiber networks, and integration with silicon photonic platforms. In this paper, we demonstrate spontaneous parametric down-conversion (SPDC) in straight GaAs- and AlGaAs-on-insulator waveguides. This platform offers strong second-order nonlinearity and geometry-tunable dispersion, which are advantageous for efficient on-chip pair generation. Measurements of the joint spectral intensity and heralded second-order correlation function show broadband emission around 2 $\mu$m with strong spectral anti-correlations. To our knowledge, this is the first direct joint-spectral characterization of an integrated SPDC source in this wavelength regime.
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All authors Alexandre Z. Leger, Emil Z. Ulsig, Samuel E. Fontaine, Dileep V. Reddy, Eric J. Stanton, Lynden K. Shalm, Richard P. Mirin, Martin J. Stevens, J. E. Sipe, Nicolas Volet, Deny R. Hamel

Optics

Self-Focusing Control for Depth-Precise Wafer Slicing of 4H-SiC in Femtosecond Laser Processing

Dong Hee Kang, Jaeseung Lim, Mishfaqur Rahman et al. (+4 more)

4H-SiC has emerged as a third-generation chip material because its superior thermal conductivity and high breakdown field enable the material to achieve high power density and higher switching frequencies in power-electronics applications. As chip architectures evolve toward 3D and heterogeneous integration, the mechanical and thermal design space tightens while yield risks grow. In particular, advanced packages require mid-process wafer thinning to < 100 $\mu$m to shorten interconnects and control thermo-mechanical stress. Femtosecond laser slicing for 4H-SiC wafers offers a non-contact processing approach to produce thin layers with low defects, while strong optical nonlinearities obscure the relationship between the laser parameters and the resulting slicing quality. Here, we systematically investigate Kerr-induced self-focusing using a femtosecond laser in 4H-SiC slicing by combining experiments, a semi-empirical analytical model, and numerical ray optics simulations. We demonstrate that the interplay between pulse energy and processing depth governs the self-focusing behavior, which directly correlates with post-separation surface texture parameters and separation stress, thereby linking nonlinear beam propagation to slicing quality. Based on this relationship, we define a processability map in the pulse energy with self-focusing depth space over a normalized irradiance background. Analytically, the model extends the Marburger formula to focused beams by replacing the power ratio with a normalized irradiance. Ray optics simulations capture the geometric features at the self-focusing point and are validated against experimental observations. Within physically defined thresholds, the processability map directly connects laser parameters to separation stress and surface texture metrics, providing practical guidance for depth control beyond trial-and-error.
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All authors Dong Hee Kang, Jaeseung Lim, Mishfaqur Rahman, Seongheum Han, Jae-Hak Lee, Seungman Kim, Jihoon Jeong

Optics

AFLOW-EMERALD: ElectroMagnetic modes EngineeRing in Advanced LayereD materials

Stefano Campanaro, Luca Bursi, Nicholas H. Anderson et al. (+2 more)

Layered and periodically patterned heterostructures underpin advanced optical, photonic, and plasmonic (meta)materials, whose rational design demands electromagnetic solvers that are both numerically robust and tightly linked to the underlying material properties. Here, we present AFLOW-EMERALD (ElectroMagnetic modes EngineeRing in Advanced LayereD materials), an open-source, modular, Python-based computational framework for simulating electromagnetic wave propagation in finite and periodic layered (meta)materials. Built around a unified object-oriented architecture, AFLOW-EMERALD combines a numerically stable scattering-matrix method with plane-wave expansion and extends to rigorous coupled-wave analysis for laterally patterned structures such as gratings. The software computes optical spectra, spatial field distributions, and photonic band structures, including complex-k dispersion in lossy, dispersive media. A streamlined YAML workflow allows users to seamlessly import dielectric function datasets from experimental, literature, or first-principles sources. Owing to its modular design, AFLOW-EMERALD is readily extensible and suitable for integration into computational materials-design pipelines, providing a practical platform for the coupled material-geometry engineering of dielectric photonic crystals, plasmonic multilayers, hyperbolic metamaterials, and more complex architectures supporting, e.g., surface and volume plasmon-polariton modes.
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All authors Stefano Campanaro, Luca Bursi, Nicholas H. Anderson, Stefano Curtarolo, Arrigo Calzolari