Nonlinear Optics and its Applications 2026

Climate change is one of the greatest and most urgent challenges of our time. If we want to keep the planet livable, greenhouse gas emissions must be net zero by 2050. Food production is responsible for up to a staggering 34% of greenhouse gas emissions. At the same time, our food production is highly sensitive to climate change and this is already having a major impact on the food system, such as crop failures due to extreme weather conditions. As a result, food security and food sustainability are top of mind. Technology can and will make the difference. The unprecedented convergence of AI, gene editing, DNA synthesis and biotechnology will revolutionize global industry, particularly in the agrifood domain. This presentation will show how optical sensing in general and photonic integrated circuits in particular are unique and indispensable technologies that provide solutions for farmers, food processing industry and consumers, and will help guide the transition of our food ecosystem to a more secure and sustainable industry. New tools in barns, in greenhouses, in orchards, in protein bioreactors and the accompanying digital twin AI technology will be shown.

Spectral imaging has long promised to uncover physiological and molecular information invisible to the human eye. Yet, despite decades of innovation, its translation into clinical routine has been slow. Beyond regulatory hurdles, challenges such as ill-posed inverse problems, data scarcity, and the demand for real-time analysis have repeatedly stalled progress. In this keynote, I will present recent breakthroughs at the intersection of computational biophotonics and machine learning that are reshaping the field. I will discuss how we combine spectral imaging with deep learning to achieve real-time tissue characterization in surgery and intensive care. Case studies will illustrate how spectral imaging can enable context-sensitive, clinically actionable support during interventions, transforming invisible spectral signatures into robust biomarkers. I will highlight not only our successes but also the failures that have shaped them. From spectral unmixing approaches that collapsed under distribution shifts to algorithms that failed spectacularly in the operating room, I will show how negative results became the foundation for new strategies. By dissecting what went wrong, we discovered how to adapt models across species and sensors, quantify uncertainty in predictions, and build validation frameworks that hold up under clinical reality. By putting the spotlight on failure—and how it fuels methodological innovation—I will argue that embracing negative results is the key to moving spectral imaging, powered by AI, from promise to practice. The future of the field may not depend on avoiding failure, but on failing better.

Nonlinear optics lies at the heart of classical and quantum light generation. Standard nonlinear crystals exhibit moderate second-order nonlinearities (χ(2) = 1-30 pm/V) but achieve high nonlinear conversion efficiencies due to their large thickness (millimeter/centimeter), limiting miniaturization. Here we realize ultracompact nonlinear structures based on non-centrosymmetric van der Waals (i.e., layered) materials, e.g., 3R-MoS2, which exhibit high nonlinearity (χ(2)~100 pm/V) and easy system integration, making them highly promising for frequency conversion over ultrathin pathlengths[1], entangled photon pair generation[2], and efficiency scaling with thickness of nonlinear processes like second harmonic generation (SHG)[3]. To achieve high efficiencies, comparable to bulk nonlinear crystals, we realize periodically-poled microscopic structures for quasi-phase matched up- and down-conversion [4], and nonlinear metasurfaces [5] which bypass phase-matching constraints. van der Waals periodically poled structures and nonlinear metasurfaces provide macroscopic nonlinear conversion efficiencies over microscopic thicknesses and open new pathways towards the realization of efficient, on-chip integrated nonlinear devices with ultracompact footprints, for generating and manipulating both classical and quantum states of light. References [1] C. Trovatello et al. "Tunable Optical Nonlinearities in Layered Materials" ACS Photonics 11, 2860-2873 (2024). [2] M. A. Weissflog et al. “A tunable transition metal dichalcogenide entangled photon-pair source” Nat. Commun. 15, 7600 (2024). [3] X. Xu et al. “Towards compact phase-matched and waveguided NLO in layered semiconductors” Nat. Photonics 16, 698-706 (2022). [4] C. Trovatello et al. "Quasi-phase-matched up- and down-conversion in PP layered semiconductors" Nat. Photonics (2025). [5] Z.H. Peng, M. Cotrufo et al. 3R-stacked transition metal dichalcogenide non-local metasurface for efficient second-harmonic generation. Nat. Photonics (2025).

We present a compact source of biphoton polarization-frequency entanglement realized by shaping the phase-matching function of a periodically poled KTP crystal. The source operates in a simple collinear setup using single-pass spontaneous parametric down-conversion and a dichroic or polarizing beam splitter. This robust and cost-effective configuration enables straightforward implementation outside the laboratory. We characterized the generated state using quantum state tomography across 16 polarization settings and a complementary method based on the symmetry of the joint spectral intensity. The polarization-entangled source exhibits strong nonclassical correlations, confirmed by violation of the Clauser-Horne-Shimony-Holt inequality and high visibility measurements in mutually unbiased bases.

Spontaneous parametric down-conversion (SPDC) presents a convenient method of producing highly correlated heralded entangled photon pairs for quantum applications and networking. Here, we report our results towards a fully optical-fibre-connected broadband Type-0 SPDC source at telecom wavelengths, utilising standard optical components and commercially available non-linear waveguides. Leveraging our array of efficient superconducting nanowire single photon detectors (SNSPDs) we obtained a CAR value (adjusted for probabilistic splitting) > 90000, a heralding efficiency of 58% and a g2h(0) < 0.001. To the best of our knowledge, these results are the best achieved to date considered across all these metrics in Zn-indiffused ridge waveguides. In addition to presenting our modelling and these results, we will also discuss our ongoing work in entanglement schemes.

Spatiotemporal optical vortices (STOVs) are structured light pulses that couple spatial and temporal degrees of freedom, carrying transverse orbital angular momentum (t-OAM). While their generation has been achieved in the visible and infrared regimes, extending STOVs into the extreme-ultraviolet (EUV) via high-order harmonic generation (HHG) enables new opportunities for ultrafast and nanoscale science. We present theoretical and experimental evidence of EUV-STOV generation driven by elliptical STOV beams and by spatio-spectral optical vortices (SSOVs), the spectral counterparts of STOVs. By analyzing the scaling of topological charge and t-OAM in STOV- and SSOV-driven HHG, we show that these quantities are not universally tied. Specifically, we demonstrate that HHG driven by SSOV fields yields EUV-STOV harmonics with non-scaling topological charge, enabling the synthesis of attosecond EUV-STOV pulses. These results open new avenues for controlling light topology in space and time during frequency up-conversion processes, with potential applications in ultrafast dynamics, nonlinear spectroscopy, and structured-light–matter interactions

We develop a theoretical framework for predicting spatial noise dynamics in multimode nonlinear photonics, which we experimentally demonstrate in multimode fibers. This insight enables us to show that by suitably engineering the optical field sent into the multimode fiber with a spatial light modulator we can strongly control and reduce the quantum noise at the output facet of the fiber.

This work presents a compact and alignment-free method for efficiently exciting higher-order modes (HOMs) in nonlinear optical fibers using 3D-printed metalens directly integrated on the fiber endface. The proposed metafiber platform uses dielectric nanostructures fabricated through 3D nanoprinting, offering robust performance, high reproducibility, and strong device integration within a small footprint. This approach allows stable coupling of broadband ultrashort pulses without bulky external optics. The integrated design supports efficient HOM excitation and soliton-based SCG, demonstrating a promising and scalable route toward compact, fiber-integrated light sources for nonlinear frequency conversion and broadband light generation.

We propose and experimentally demonstrate an integrated approach to suppress Kerr self-focusing by engineering the spatial dispersion of a medium using Laue-type photonic crystals. The photonic crystal, featuring longitudinally chirped and constant-period sections, was designed using a beam-propagation model and fabricated in a UV-fused-silica substrate by femtosecond direct laser writing with a Bessel beam. We characterized the structure by performing nonlinear transmission measurements and analyzing the evolution of the output beam profile as a function of the input pulse energy. Compared to a non-resonant reference structure and the bulk material, the dispersion-engineered photonic crystal successfully counteracts self-focusing, resulting in a 12% increase in the nonlinear absorption threshold. This work presents the first practical demonstration of nonlinearity management through spatial dispersion control in a monolithic photonic crystal, offering a new pathway to bypass the power-scaling limitations of nonlinear processes in solid-state materials.

We present XSOL, a new beamline for extreme soliton dynamics capable of generating terawatt-scale optical attosecond pulses and gigawatt-scale tunable vacuum-to-deep ultraviolet (VUV/DUV) pulses. Driven by 10 mJ, 40 fs pulses, the system utilizes gas-filled hollow-core fibres to achieve extreme pulse compression and frequency up-conversion. We report the generation of sub-cycle self-compressed pulses with ~1.3 fs duration and 2.1 mJ energy. We also demonstrate the generation of resonant dispersive waves tunable across the VUV/DUV range, achieving energies up to 170 µJ and durations of ~2.3 fs. Extending this platform, we also demonstrate the generation of single-cycle, millijoule-level radially polarised vector beams tunable down to 140 nm. These sources are fully characterised using advanced in-vacuum metrology, including TIPTOE for field-resolved measurements and transient-grating FROG employing new retrieval algorithms that incorporate dispersion effects. This work establishes a versatile, high-energy light source for next-generation strong-field physics.

Temporal cavity solitons (CS) in Kerr resonators offer a potential alternative to mode-locked lasers concerning the generation of ultracoherent pulse trains, guaranteeing high coherence between pulse trains and a highly coherent continuous wave lasers. In this work, we report the first experimental observation of single coherent picosecond pulses in a fiber active optical parametric oscillator driven in continuous wave.

This study presents the investigation of the previously scarcely explored high energy few-cycle post-compression regime. Experimental shortening of the 5 mJ, 830 nm and 7.7 fs pulse with a flat-top spatial profile was pursuit by nonlinear spectral broadening in a single 1 mm thick fused silica plate. The results show 3.8+0.20-0.11 fs (1.53 optical cycle) pulse duration with a 64 +2 -5 % relative peak power. The achieved spatial-spectral homogeneity was 97.1 %. The deformable mirror wavefront correction to the Strehl ratio of 0.88 was shown even in the presence of a strong nonlinear interaction. It was demonstrated that a simple numerical model can predict output spectral properties well. The presented research might enable the future generation of high energy and quality single-cycle super-octave pulses.

Here we generate efficient high order harmonics with an IR driver focused down to the paraxial limit, using sub-µJ pulse energies and operating at a repetition rate of 2 MHz.

High-harmonic generation (HHG) in solids provides a compact route to extreme-ultraviolet (EUV) sources. In bulk materials, the high density strongly reshapes the driving laser pulse, affecting its intensity, spectrum, and temporal profile, which directly influences harmonic emission. We generate high-order EUV harmonics in MgO crystals up to the 31st order using few-cycle, 1550 nm light-pulses from a fiber laser, and study their spectra as a function of laser intensity, crystal orientation and thickness as well as its focal position. Observed correlations between infrared reshaping and harmonic spectra highlight the central role of nonlinear propagation in shaping EUV emission.

We present a compact, nonlinear compression scheme for generating multi-10-mJ femtosecond pulses in the short-wave infrared. For this purpose 2.0 ps pulses at 2.05 µm, from a 1 kHz Ho:YLF chirped pulse amplifier, are spectrally broadened due to self-phase modulation in CaF2. Subsequent compression using a pair of transmission gratings delivers 770-fs pulses with an energy of 41 mJ. The compression regime takes place below the onset of filamentation, resulting in an almost undisturbed beam profile. Post-compression is associated with a loss of 25%. Despite this, the resulting peak power is a remarkable 46 GW, the highest for 2-µm sub-ps sources.

Thin film lithium niobate (TFLN) has emerged as a leading platform for integrated photonics, combining frequency conversion with low-loss waveguides and electro-optic effects. These properties help to address key limitations of silicon-based material platforms, which rely on third-order processes and suffer from nonlinear photon absorption. While TFLN has proven effective in classical devices, its potential for scalable quantum photonic circuits remains marginal. Here, I will present a low threshold integrated optical parametric oscillator with a compact Bragg resonator. Then, I will show different type of periodic poling on chip for spontaneous parametric down conversion such as counter or back propagation convenient for high generation efficiency, single polarisation and high purity of photons.

We report the discovery of a higher-order spontaneous symmetry breaking (SSB) phenomenon in faticon structures within Kerr ring resonators. Faticons, formed by two interlocked counter-polarized field components, exhibit a distinctive dynamic interplay arising from an additional SSB that induces peak-power asymmetry between the components. This asymmetry drives a “chasing” interaction that accelerates or decelerates the composite pulse until a new steady propagation velocity is reached. The resulting change in velocity directly links to the degree of asymmetry, enabling controllable tuning of the round-trip time, repetition rate, and frequency-comb spacing. Furthermore, we demonstrate that such control can be externally induced through pump biasing, offering a direct route to engineered soliton dynamics in nonlinear resonators.

Optical bistability is a key nonlinear phenomenon that reflects the interplay between resonance detuning, cavity enhancement, and Kerr-induced refractive index changes. Observing and controlling bistability is a necessary step toward achieving stable parametric oscillation in integrated resonators. In particular, it provides the operating conditions and pump tuning strategies required for the generation of microcombs. In this work, we report optical bistability in Ge-based ring resonators, namely SiGe-on-Si and Ge-on-Si in the mid-infrared wavelength around 4 µm. This shows the high potential of Ge-based microresonators for mid-infrared broadband source generation, in particular for microcomb generation.

We investigate optical injection of a continuous-wave laser into a feedback-controlled Fabry–Perot cavity laser integrated on InP to study four-wave mixing for potential THz carrier generation. The injection induces equidistant FWM sidebands separated by a THz-range frequency offset with a side-mode suppression ratio exceeding 20 dB. Beat-note analysis with a narrow-linewidth reference laser reveals kHz-level linewidths for both the injected tone and FWM sidebands, confirming coherent operation.

We induce a third-order exceptional point (EP3) in an optical fiber using stimulated Brillouin scattering. The versatility of the approach allows to scan the parameter space and plot all three eigenvalue sheets, revealing cubic root dispersion and symmetry-induced structures such as lines of exceptional points of second order. Our work provides a new platform for studying exceptional points, with implications for enhanced sensors and optical nonlinearity for neuromorphic photonic systems. This fabrication-free approach paves the way for further research into non-Hermitian systems.

Reservoir computing (RC) with physical devices offers an energy efficient method for analog computing. It is specifically suited for tasks where nonlinearity as well as memory is needed. Here we investigate time series forecasting tasks using semiconductor lasers with optical self-feedback. If the data is injected and detected within a time-multiplexed setup, one physical node is sufficient. Due to the delay, the laser is able to emit complex emission patterns in time that correspond to dynamics in a high dimensional phase space. We discuss that by tuning internal system timescales, feedback-delay, and input-schemes, the dynamic response of the laser can be changed in a controlled manner to meet the specific RC task requirements. Further, non-rational ratios between input clock cycle and delay lead to more complex internal coupling topologies and improve the short term memory of the RC setup.

Photonic systems are emerging as a compelling alternative to electronic computing, offering unmatched parallelism, energy efficiency, and speed. Recent advances demonstrate that nonlinear optical platforms, such as highly nonlinear fibers and semiconductor lasers, can be configured as physical neural networks, leveraging their intrinsic physics for computation. Here, we characterize two photonic platforms: highly nonlinear fiber (HNLF) and vertical-cavity surface-emitting lasers (VCSELs). Using metrics like dimensionality (independent degrees of freedom) and consistency (reproducibility), we show how input power and physical parameters shape computational capacity. HNLF achieves up to 100 principal components and 87% MNIST classification accuracy, outperforming linear baselines. VCSELs reveal similar dependencies, with performance scaling laws analogous to classical AI. These findings highlight photonics’ potential to revolutionize computing architectures and introduce relevant application agnostic metrics.

We demonstrate the generation of ultrashort pulses in a fiber amplifier covering the L (1560-1625 nm) and U (1625–1675 nm) telecommunication bands by utilizing nonlinear effects and machine learning algorithms. The research details the development and optimization of an ultrafast nonlinear fiber amplifier based on Erbium-Ytterbium co-doped double-clad fiber with a small core (3.8 μm). This fiber design enables amplification in the normal dispersion regime, which is typically unavailable in this spectral range, and increases sensitivity to nonlinear effects. The setup allows us to produce a broadband output spectrum through nonlinear effects and the characteristic redshift of the normal dispersion regime. A programmable optical filter is placed at the amplifier input, allowing control over the spectral phase and shape of the initial pulse. Machine learning algorithms are used to iteratively modify the input pulse and evaluate the output to achieve the most optimal results.

Excitability, at the core of the spiking activity of neurons and cardiac cells, is defined by the all-or-none response to external perturbations. Artificial spiking neurons appear as promising candidates for efficient analogue computing or on-demand source of optical pulses. Meanwhile optomechanical systems are applied as microwave to optics interface for potential quantum computing and time-frequency reference. Here, we demonstrate spiking neuron behavior for a GHz gallium phosphide nano-electro-optomechanical crystal integrated on a silicon circuitry. We prepare the mechanical system close to the locked-unlocked transition thanks to on-chip electrodes and observe clear signatures of the saddle-node on invariant circle behavior. We demonstrate further the control of excitable pulses and characterize typical associated properties such as temporal summation or refractory periods important features in an analog computing framework. Our device, scalable to a large number of systems on a single photonic chip, could lay the foundations for distributed analogue optomechanical computing.

The propagation of ultrashort optical pulses in fibres is governed by the Nonlinear Schrödinger Equation (NLSE), whose numerical integration remains computationally expensive for high-dimensional applications. Traditional solvers such as the Split Step Fourier Method are accurate but limited by step-size constraints and scaling complexity. In response to these drawbacks, machine learning methods have emerged as promising alternatives to act as surrogate propagators. Specifically, deep neural networks offer robust capabilities for learning patterns and predicting solutions of nonlinear differential equations. Despite their performance, these methods are inherently limited due to sensitivity to noise and error accumulation over long sequence prediction tasks. In this work, we present a generative surrogate model for the NLSE based on denoising diffusion probabilistic models (DDPMs). Diffusion models have recently shown remarkable capability in learning complex physical distributions and reconstructing missing information from partial or noisy data. Our framework learns the spatiotemporal evolution of the optical field from simulated NLSE datasets, predicting the full-field intensity and phase from partially masked intensity inputs. Using a U-Net backbone within the diffusion process, the model generates physically consistent propagation maps across varying soliton numbers, capturing the nonlinear interplay between dispersion and self-phase modulation. We benchmark the DDPM against a deterministic U-Net trained under equivalent conditions and show superior generalisation to out-of-distribution nonlinear regimes and masked inputs. Quantitative evaluation using standard metrics confirms that the diffusion-based surrogate accurately reproduces the nonlinear dynamics of ultrashort pulse propagation. This work highlights the potential of diffusion models as fast, data-driven solvers for complex photonic partial-differential equations and paves the way to the application of generative models to the prediction of nonlinear optical phenomena.

Stimulated Brillouin scattering couples optical and acoustic waves with applications for signal processing, narrow-linewidth lasers, and environmental sensors. Traditional Brillouin interactions in waveguides are fixed in frequency by momentum conservation for backward scattering, and by the geometrically determined cutoff frequencies for forward scatting. Alternatively, a wide new range of frequencies become accessible with Forward InterModal coupling to the Fundamental Acoustic Modes (FIM-FAM) in waveguides with more than one optical mode. With FIM-FAM, record Brillouin coupling strengths and ultranarrow linewidths become available as well as qualitatively new behavior such as phonon self-interference. This talk will review recent investigations of FIM-FAM including ultranarrow linewidths in fiber tapers, tunable record-performance RF filters, as well as strong FIM-FAM interactions in integrated silicon nitride devices.

Optical phase information is fundamental to sensing, imaging, and telecommunication. Conventional phase recovery techniques rely on interferometric setups with reference arms or computationally demanding algorithms. This work presents a reference- and algorithm-free method for local and distributed phase recovery using weak nonlinear effects in optical fibers. By operating in low-power regimes, self-phase modulation maps input phase directly to measurable spectral intensity. The approach achieves linear correlation (Pearson correlation ≈ 0.98) between input phase and output spectrum using standard fiber components in a fully fiber-integrated setup. Simulations of phase-encoded images and experimental validation using a waveshaper and dispersive Fourier transform measurements at 80 MHz demonstrate real-time, distributed phase retrieval. These results highlight nonlinear fibers as a compact platform for fast, reference-free phase sensing.

We have developed a novel, low-noise 1.85 μm femtosecond (fs) pump delivering 58 fs pulses at 210 mW, with a 40 MHz repetition rate and a low relative intensity noise (RIN) of 0.41%. We identified two elliptical-core, polarisation-maintaining ZBLAN fibres with core dimensions of 6.7×2.7 μm and 8.9×4.1 μm that exhibit all-normal dispersion in the region of interest. By pumping these fibres with the 1.85 μm source, we generated an ultra-low-noise supercontinuum (SC) in the 6.7×2.7 μm core fibre, spanning 1.500–2.251 μm at the −40 dB level, with a minimum RIN of 0.22% at 1.7 μm. The SC from the 8.9×4.1 μm core fibre spans 1.465–2.297 μm at the −40 dB level, with a minimum RIN of 0.36% at 2.0 μm. To achieve higher peak power, the 58 fs pulses were soliton-compressed to sub-10 fs durations. The resulting pulse was coupled into the 6.7×2.7 μm fibre, producing an ultra-low-noise SC spanning 0.771–2.724 μm, with a measured RIN as low as 0.21% at 2.1 μm.

We demonstrate a novel polarization-maintaining all-normal dispersion photonic crystal fiber (PM-ANDi PCF) engineered for femtosecond pumping at 1030 nm, enabling ultra-stable and highly coherent supercontinuum generation from 650 to 1300 nm. Polarization control is achieved through an innovative two-hole design that replaces traditional stress rods, offering simplicity and robustness. Numerical and experimental studies reveal excellent noise performance, with relative intensity noise below 0.5% and phase fluctuations under 15 mrad. This new PM fiber platform provides a powerful tool for ultrafast metrology, coherent optical synthesis, and broadband light sources requiring exceptional stability and polarization control.

Optical microfibers (OMFs) exhibit strong field confinement and dispersion highly dependent on their diameter, making them excellent platforms for controlling nonlinear optical effects. We investigate the tuning of intramodal four-wave mixing (FWM) through diameter control of silica OMFs. Numerical modeling shows that an OMF with a 6.57 µm diameter has a zero-dispersion wavelength near 1064 nm, with predicted anti-Stokes FWM sidebands spanning 715–960 nm for diameters between 6.0 and 8.9 µm. Experimentally, OMFs fabricated from SMF28 fibers using the heat-brush technique demonstrate FWM tunability from 960 nm down to 717 nm as the diameter varies from 9.0 µm to 6.1 µm, corresponding to a detuning up to 137 THz. A total wavelength tunability exceeding 250 nm is thus achieved with only 3 µm diameter variation. Numerical simulations based on the nonlinear Schrödinger equation show good agreement with experiments, confirming efficient and controllable far-detuned FWM generation in OMFs.

The spectral coherence of supercontinuum generation in polarization-maintaining all-normal-dispersion photonic crystal fibers (PM-ANDi PCF) is investigated using a combined experimental and numerical approach. We quantify stochastic phase noise driven by pulse-energy fluctuations and evaluate spectrally resolved intensity-to-phase transfer coefficients across the generated bandwidth. The measured stochastic phase noise approaches the theoretical interferometric limit imposed by shot noise, and the intensity-to-phase transfer coefficients show excellent agreement with predictions from nonlinear propagation theory. These analyses reveal the underlying noise mechanisms and confirm the excellent coherence properties of the resulting supercontinuum, highlighting its suitability for applications requiring low-energy and high repetition rate supercontinuums.

Quantum-enhanced imaging is an emerging area of research with relevance to a wide variety of application areas, including transport, gaming, environmental research, and security and defence. This subject encompasses a range of techniques and utilizes a number of developing quantum technologies. Time-resolved single-photon imaging approaches have been used to reconstruct high-resolution three-dimensional images, including challenging scenarios such as imaging through atmospheric obscurants and clutter. Critically, this approach has been extended to imaging in turbid underwater conditions. In the past, image reconstruction often proved to be time-consuming due to the inherent computational complexity, however advances in algorithms and hardware have allowed examples of “real-time” reconstruction of moving targets. Single-photon imaging has been used in demonstrations of moving target identification and human activity recognition with the aid of artificial intelligence approaches. Alternative single-photon imaging approaches, such as ghost imaging, will also be discussed.

I will present the PIXEurope Pilot Line, a recently started 400MEuro initiative under the Chips JU, that aims at developing and transferring advanced photonic integrated circuit (PIC) technologies and processes. Through Open Access, PIXEurope will support end-users in increasing the readiness level of their products. I will also present some technologies, leveraging PICs, that were developed at ICFO and transferred to spin-offs, now commercializing quantum random number generators, cryptography systems and phase imagers. Biography: Valerio Pruneri is an ICREA Professor and Corning Inc. chair, leading the Optoelectronics group at ICFO. He is also the Director of PIXEurope Pilot Line. Previously he worked for Avanex, Corning, Pirelli, and the University of Southampton. With his groups in academia and industry, he has developed technologies for the photonic, photonic integration, and quantum. He is inventor in more than 70 granted or pending patent families, leading to numerous industrial collaborations and the creation of four spin offs, Quside, Sixsenso, Luxquanta and Shinephi.

Squeezed states of light are a key resource for quantum sensing, communication, and information processing, enabling measurements beyond the shot noise limit. However, generating highly squeezed and correlated quantum light in fiber-based platforms remains a challenge due to dispersion management, Raman noise, and limited control over nonlinear interactions. Here we demonstrate a temporal optical parametric oscillator based on a time-lens in a temporal 2f configuration. The cavity compensates multiple dispersion orders mismatch between the pump and the generated waves, maintaining temporal overlap throughout the nonlinear interaction and thereby enabling enhanced parametric gain and efficient cascading over a broad pump range. We observe high-brightness signal and idler generation with strong temporal correlations, and extract up to 9.2dB of two-mode squeezing, exceeding previously reported squeezing levels in fiber-based optical parametric oscillators. By comparing with conventional optical parametric oscillators and amplifiers, we show that the temporal configurations achieve significantly higher efficiency in generating bright correlated photon pairs. Our results establish temporal Fourier cavities as a powerful and efficient platform toward high-performance continuous-variable quantum light sources in Kerr nonlinear platforms.

Temporal optics arises from the analogy between spatial diffraction of light in free space and temporal dispersion of pulses in dispersive media, enabling the development of advanced temporal devices such as time-lenses. In this work, we present a cascade time-lens configuration utilizing a cascade four-wave mixing (FWM) process, theoretically developed and experimentally demonstrated, analyzed distinctly in both Fourier and imaging configurations. These analyses of the cascade time-lens significantly simplify experimental setups, providing comprehensive characterization of ultrafast optical signals. Such capabilities are relevant for applications in ultrafast optics, optical communications, signal processing, and quantum measurement technologies.

In this work, we present a combined experimental–theoretical investigation of tungsten ditelluride (WTe₂), a type-II Weyl semimetal in the transition-metal dichalcogenide family, structure, optical properties, and preliminary harmonic generation response using ultra-short laser pulses. High-quality WTe₂ single crystals were lab-grown by chemical vapor transport and characterized by Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Density functional theory (DFT) and time-dependent DFT (TDDFT) were employed to compute the dielectric function and optical absorption spectra to investigate the crystal’s anisotropic responses. Moreover, the DFT and TDDFT computational results were compared against experimental results, which show excellent agreement. Our combined study offers a comprehensive picture of WTe₂’s electronic structure and its linear and nonlinear optical responses, underscoring its potential for industrial applications.

The development of multifunctional nanomaterials is central to advancing light-based technologies through enhanced optical performance and versatility. In this study, nickel oxide (NiO) nano-thin films were synthesized via spray pyrolysis and subsequently modified by microwave (MW) irradiation to tailor their third-order nonlinear optical (NLO) properties. The role of MW-induced surface and structural modifications was systematically investigated, and the NLO modifications induced in the MW-irradiated NiO nano-thin films were analyzed under picosecond, nanosecond, and continuous-wave (CW) laser excitations. Z-scan analyses under CW excitation revealed pronounced reverse saturable absorption (RSA) with an enhanced nonlinear absorption coefficient of ~10⁻¹ m/W, attributed to sequential two-photon absorption, excited state absorption, and free-carrier absorption processes in the MW irradiated nano-thin films. Fluence-dependent third harmonic generation (THG) studies using nanosecond excitation demonstrated that 400 W-MW irradiated films achieved higher efficiency at elevated fluence, whereas films irradiated at 640 W and 800 W maintained strong responses even at lower fluence regimes. These trends highlight the influence of MW-induced defect states on carrier dynamics. Further investigations using the Maker fringe technique under picosecond excitation confirmed the angular dependence of THG intensity in MW-irradiated NiO nano-thin films and revealed enhanced excitation–relaxation dynamics within the lattice. The third-order nonlinear susceptibilities reached values of 8.46 ×10⁻²¹ m²/V² (480 W) and 8.06 ×10⁻²¹ m²/V² (800 W), surpassing those of pristine samples. Overall, the findings demonstrate that MW irradiation provides an effective strategy to engineer defect-mediated pathways and significantly enhance nonlinear optical responses in NiO nano-thin films. This approach deepens the understanding of MW-nanomaterial interactions and establishes a pathway toward the rational design of advanced NLO materials.

Functionalized diamondoid clusters exhibit extreme nonlinear optical properties in powder form. With their nonlinearity enabling continuous-wave driven white-light generation is possible. However, powders inherently introduce scattering and other grain size dependent effects, rendering them undesirable for optical applications.

This work examines the tunable nonlinear optical properties of Mn-doped NiO thin films modified by microwave (MW) irradiation. MW exposure induces structural and optical changes that enable controlled adjustment of second- and third-order nonlinearities. Under femtosecond excitation, films irradiated for 8–10 min show the strongest THG due to optimized defect structures and rapid dipole interactions. Nanosecond excitation yields maximum THG for the 10-min film, while picosecond angle-resolved THG peaks for the 2-min sample, highlighting regime-dependent dipolar and thermal effects. SHG, dominated by surface symmetry breaking and lattice distortions, is significantly enhanced only for 10-min irradiation. Z-scan results confirm pronounced third-order nonlinearities. Overall, MW engineering enables dynamic tuning of nonlinear responses for advanced photonic applications.

We introduce a simple yet powerful unsupervised learning approach that lets light “cluster itself.” By analyzing only temporal intensity profiles—without phase or spectral data—centroid-based clustering reveals hidden regimes of nonlinear pulse propagation in optical fibers. Distinct features such as soliton compression, pulse splitting, and optical wave breaking emerge naturally from the data. Even with drastically reduced sampling, the method retains strong physical interpretability. This data-driven framework provides a new, intuitive lens to explore complex nonlinear dynamics and paves the way for machine-learning–assisted discovery in photonics and beyond.

Optical fibre-based extreme learning machines (ELMs) are a powerful physical platform for unconventional computing in photonics. Recent experiments have demonstrated ELM operation using both anomalous-dispersion supercontinuum generation and normal-dispersion wave-breaking. Building on our previously reported generalized nonlinear Schrödinger equation (GNLSE) based numerical pipeline, we present the first numerical study of polarization-dependent effects in fibre ELMs using coupled vectorial GNLSEs with Raman, self-steepening, and higher-order dispersion. We investigate MNIST classification accuracy versus input polarisation and readout strategies in both dispersion regimes. Our results reveal how polarisation coupling influences ELM performance, providing insight for designing polarisation-sensitive nonlinear fibre computing platforms.

We present a proof of concept that the nonlinear two-photon absorption (2PA) signal obtained by open-aperture single-beam Nonlinear Ellipse Rotation (NER) measurements can be used to determine the linear chirp and the temporal duration of ultrafast laser pulses. This is done by taking into account the change in signal magnitude caused by 2PA as a function of the pulse propagation within materials with known group velocity dispersion (GVD). NER measurements are carried out in two optical glasses from Schott, SF6 and LaSF-N30, using femtosecond laser pulses at different wavelengths and with distinct initial chirps and temporal durations. The results obtained by NER are consistent with the ones simultaneously obtained by the nonlinear refraction signal and by a commercial GECO Autocorrelator from Light Conversion.

Compounds exhibiting excited-state intramolecular proton transfer (ESIPT) display remarkable photophysical properties such as significant Stokes shifts and environment-sensitive emission. We investigated the linear and nonlinear photophysics and ultrafast excited-state dynamics of a 2-(2′-hydroxyphenyl)benzoxazole derivative, HBO-EEMN, in DCM, ACN, and MeOH. HBO-EEMN shows strong one-photon absorption in the UV–Vis and a two-photon absorption cross-section of ~24 GM at 800 nm, nearly solvent-independent. Excitation to S₁ yields dominant emission from the Keto tautomer, with anionic contribution in ACN and multispecies emission in MeOH (Enol, Keto, and Anion). Excitation to S₂, however, favors Enol emission. Quantum-chemical calculations suggest that this behavior stems from vibrational cooling, which prevents proton transfer at higher excitation energies. Femtosecond transient absorption measurements reveal an ESIPT timescale of ~0.3 ps, followed by vibrational and solvation relaxation over tens of picoseconds. In MeOH, a new excited-state absorption appears after ~10 ps, attributed to an anionic species, highlighting the solvent’s influence on proton-transfer dynamics.

We study the origin and stability of parametrically driven cavity solitons (PDCSs) in Kerr resonators in the presence of bichromatic pumping. PDCSs arise through parametric four-wave mixing and they sit atop a rapidly oscillating fringe background which emerges due to the beating between the two pump frequencies. We perform a detailed bifurcation and stability analysis based on path-continuation techniques, which allows us to discover that stable multipeak PDCSs do also exist and that they organize in a slanted snaking kind of bifurcation structure. Moreover, we show the emergence of breather dynamics and the presence of drift instabilities.

We consider long-haul optical fiber transmission using multi-solitons obtained via the Hirota bilinearization of the integrable nonlinear Schrödinger equation. We propose a neural-network-based receiver that demodulates the degrees of freedom in Hirota multi-solitons, including the eigenvalues in the nonlinear Fourier transform. We demonstrate transmission over optical links with in-line amplification across 1000 km, achieving 5 bits per eigenvalue per real dimension, and bit-error rates as low as 1e-4. Our results show that the spectral amplitudes of multi-solitons can be accurately modulated and used to carry additional information over long distances.

Dirac and Weyl semimetals exhibit discrete band degeneracies, whereas nodal line semimetals (NDLS) possess a one-dimensional closed loop degeneracy in momentum space. In non-Hermitian systems, the symmetry-protected nodal line is replaced by an exceptional line. In this study, we have conducted experiments that demonstrate the presence of concentric exceptional lines within an atomic vapor system that possesses anti-PT symmetry. Additionally, we have also shown the topological phase transition on these exceptional lines by defining a Z_2 topological index, originating from the spectral topology of the system exhibiting a positive nonlinear refractive index. These findings position our system as a prime candidate for an all-optical exceptional-line semimetal, which has immense applications in quantum gate preparations and sensing.

The advancement of quantum optical technologies depends on the transition to integrated chips based on quantum photonic elements. Significant part of research is focused on integrated quantum sources, for example, Kerr frequency combs. There are two main challenges – selecting materials with high nonlinear efficiency and developing the fabrication process suitable for these materials. Organic materials have large nonlinear coefficient values, which creates opportunities for lower power device fabrication. Polymers are compatible with other material photonic platforms, and they can be simply integrated through wet-coating methods, which is crucial for heterogeneous platform development. Here we show fabrication process and optical properties of Kerr frequency combs made with novel glass forming organic materials in host-guest systems. The results show that these materials have large third-order Kerr coefficient. Two types of designs were tested – spiral waveguides and frequency combs with ring resonators. Optical losses and in-device nonlinearities of fabricated structures were characterized.

We demonstrate a novel method for generating a dense optical frequency comb by coupling a standard Fabry-Perot laser diode with a high-Q SNAP microresonator. Unlike conventional self-injection locking, which seeks single-mode operation, our approach leverages the unique, dense axial mode spectrum of the SNAP resonator. This enables stable, simultaneous locking of the laser to multiple axial modes. We report, for the first time, the generation of a stable axial comb with a mode spacing of ~2.4 GHz (19.2 pm), attributed to four-wave mixing within the laser's gain medium. This simple, compact architecture offers a new path toward multi-wavelength sources for sensing and microwave photonics.

We used narrow-linewidth 1560.492-nm and 1076.956-nm single-frequency MOPA fiber lasers to produce 637.2-nm red laser efficiently via single-pass Sum-Frequency Generation (SFG) with PPLN crystal. The cavity-enhanced Second-Harmonic Generation (SHG) with BBO crystal was utilized to produce the frequency-tunable narrow-linewidth watt-level 318.6-nm UV laser. Red Pitaya modules based on FPGA were employed to lock the SHG cavity with BBO crystal to 637.2-nm red laser via PDH locking scheme, and also lock the 1560.492-nm MOPA fiber laser to Rubidium-87 D2 transition via single-pass PPLN frequency doubling to 780.246 nm and Rubidium polarization spectroscopy. We achieved 318.6-nm UV laser with more than 2 Watts output and its linewidth is < 10 kHz. Using the 318.6-nm UV laser system, we have realized the single-step Rydberg excitation from the ground state 6S1/2 to the Rydberg state nP3/2 (n = 70~100) of cesium atoms in hot atomic vapor cell and laser cooled and trapped in a MOT. The background DC electric fields were measured experimentally via cold Rydberg atoms’ Stark effect. To avoid random localized electric fields which come from the self-ionization of Rydberg atoms, the Rydberg weakly-dressed ground state of cold cesium atoms will be prepared via 318.6-nm UV laser and will be employed to detect weak DC electric fields via Ramsey interferometer. Refs: [1] JOSAB, 33 (2016) p.2020; [2] Opt. Express, 25 (2017) p.22510; [3] IEEE J. Sel. Topics Quant. Electr., 26 (2020) 1600106; [4] J. Quant. Opt., 31 (2025) 011001 (in Chinese); [5] Opt. Express, 33 (2025) p.7081

We experimentally establish a nonlinear optical extension of the Van Cittert-Zernike theorem, unveiling a direct mapping between near-field source intensity at the fundamental frequency and far-field coherence at the second harmonic. By frequency doubling an incoherent source, we show that the spatial structure of a fundamental beam can be inferred from its harmonic coherence. The theorem is demonstrated for two cases: an incoherent Gaussian pump yielding a Gaussian-correlated second harmonic, and a ring-shaped pump producing a Bessel-correlated one. By varying the crystal length and engineering its nonlinear coefficients, we further control the coherence evolution within the nonlinear medium. These results extend the Van Cittert-Zernike framework into the nonlinear regime.

Integrated photonics platforms are having an increasing impact in many quantum optical applications, due to their ease of cascading sequential operations while simultaneously scaling to large component numbers. In order to maintain performance fidelity as the complexity of these photonic circuits increases, it is inevitable that these circuits will be implemented with foundry fabrication. Traditional photonics foundry platforms, originating in classical datacom applications, have typical waveguide thickness of 0.22µm, which significantly enhances surface absorption and roughness induced scattering effects on propagating optical fields. Given the critical importance of loss for quantum information applications, here we consider the generation of photon pairs in a low-loss, thick (3µm) silicon foundry platform, and explore the associated nonlinearity-loss-footprint tradeoffs, with a view towards understanding the optimal silicon thickness for resonator based photon pair sources.

We explore ultrafast quasi-phase-matching (QPM) in resonance-enhanced microstructured fibers for generating higher-order dispersive waves. By modulating waveguide dispersion through nanofilm coatings, we investigate sideband formation using numerical simulations and proof-of-concept experiments. The study combines modeling and experimental feedback to optimize fiber and excitation parameters, enabling tunable dispersive-wave generation. These findings contribute to the development of broadband light sources for ultrafast photonics and spectroscopy.

The advancement in nonlinear optics has drawn interest to organic materials because of their significant third-order nonlinearity. Host-guest polymer materials containing organic dyes with high nonlinear efficiency have been employed to form nonlinear optical elements, including ring resonators and directional couplers. To determine the optimal geometries of the systems, COMSOL Multiphysics was employed to perform physically accurate numerical simulations. Our results show the potential of organic nonlinear materials for enabling compact, efficient, and versatile optical signal processing devices.

We investigate theoretically and experimentally the nonlinear dynamics of degenerate optical parametric oscillators (DOPO) in a silicon nitride microring resonator driven by two tunable lasers. Our results provide a comprehensive understanding of DOPO operation and stability, with implications for the development of compact and reliable photonic devices.

We reveal that bifurcations occurring at the limits of optical bistability and the onset spontaneous symmetry breaking in Kerr ring and Fabry-Pérot resonators correspond to exceptional points in an analogous linear non-Hermitian system. This insight enables new approaches for controlling nonlinear photonic devices, integrated photonics, optical computing, and frequency comb generation.

Aluminum nitride (AlN) thin films were deposited on glass substrates and analyzed for their potential in integrated nonlinear photonics. The material features a wide bandgap (6.2 ± 0.05 eV), an infrared refractive index of 2.00 ± 0.05, and full CMOS compatibility, making it well-suited for on-chip devices. AFM and Raman spectroscopy confirmed a uniform morphology and amorphous structure with a thickness of approximately 350 nm. The nonlinear optical response, examined through the nonlinear elliptical polarization rotation (NER) technique, showed a third-order nonlinearity approximately fifteen times higher than fused silica, confirming AlN’s potential for efficient integrated photonic applications.

We demonstrate dissipative Kerr soliton (DKS) generation and near-zero-dispersion solitons in gallium phosphide (GaP) photonic-crystal Fabry–Perot (PC-FP) resonators driven by subharmonic optical pulses from an electro-optic frequency comb. The high refractive index and χ(3) nonlinearity of GaP enable broadband dispersion engineering with compact, high-Q cavities. Our devices, operating at 20 and 55 GHz free spectral ranges, support large-scale integration with over 200 resonators per chip. In the 55 GHz device, we observe subharmonic Kelly sidebands originating from strong dispersion and periodic soliton perturbation, consistent with simulations of a pulse-driven Lugiato–Lefever equation. Further dispersion broadening produces oscillatory integrated-dispersion profiles, giving rise to unconventional coherent structures. In 20 GHz resonators, we observe high-order near-zero-dispersion solitons with temporal oscillations and dispersive-wave emission induced by dispersion oscillations rather than zero-dispersion crossings.

The finite-difference time-domain (FDTD) method is widely used to solve Maxwell’s equations, but most commercial and research-grade FDTD software relies on implicit iterative solvers to handle optical nonlinearities—a computationally demanding process. Recent advances introduced an explicit FDTD approach for dispersive media with optical nonlinearities, based on a nonlinear generalization of the Lorentz dispersion model [1]. In this work, we present a simplified explicit implementation of the generalized Lorentz model in the weakly dispersive limit (ω ≪ ω₀), specifically designed for transparent Kerr media. We achieve an efficient and scalable framework for simulating the generalized nonlinear Schrödinger equation in complex structures, such as stratified media. We validate this method through two applications: the propagation of femtosecond pulses in silicon and the behavior of a Kerr Gires–Tournois interferometer, a promising platform for generating Kerr frequency combs. [1] C. Varin et al., Computer Physics Communications, 222, (2018)

Third-order nonlinear optical properties are crucial for modern photonics and optoelectronics, as they define a material’s response to intense electromagnetic fields and enable applications such as frequency comb generation, white-light continuum, and all-optical modulation in photonic integrated circuits (PICs). While silicon photonics dominate current PICs, silicon’s weak nonlinear response has driven interest in more efficient materials. Organic compounds have emerged as promising candidates due to their high molecular polarizability, structural tunability, and low-cost synthesis. In present contribution we are applying higher-order HRS or third harmonic scattering (THS) to obtain  values of novel organic materials. Using a tunable femtosecond laser (1200–1600 nm), THS signals were recorded with narrow-band filters or a monochromator and analyzed via internal or CS₂-based external referencing. Results from THS were compared with γ values obtained independently by the Z-scan technique.

Expanding nonlinear optics in optical fibers to multimode fibers has allowed for observing and learning about significantly more complex phenomena, while also enabling control over processes like beam self-cleaning, supercontinuum generation, and soliton formation. Implicit in all of these investigations is the eventual development along nonlinear propagation of high-dimensional fields that are structured in space and time. In our work we consider the same physical system, i.e. a graded-index multimode fiber, but with input fields that already have their own space-time structure. In doing so we gain a much more explicit control over the highly nonlinear interactions, and can observe new effects such as multimode domain wall locking and especially a new form of multimode solitons, and trains of such solitons. We will discuss the formation and properties of these new nonlinear optical structures and the implications.

We propose a hollow ring-core fiber (RCF) design, optimized to enhance efficiency for the nonlinear process, such as four-wave mixing and parametric amplification. This structure provides improved spatial modal overlap between the fundamental (HE₁₁) and higher-order (TE₀₁) modes, while simultaneously reducing the effective mode area compared to step-index fibers and solid RCFs. The central air-hole confines the optical fields within the ring region increasing modal overlap and intensity, thereby improving nonlinear interactions. Our analysis at 1550 nm using mixed-mode phase matching (TE₀₁ as pump and idler, HE₁₁ as signal) demonstrates that the optimized hollow RCF exhibits enhanced f-factor values, supporting efficient photon-pair generation. Although the present study has been carried out for GeO2-doped fibers, this approach is extendable to other materials such as ZBLAN, enabling mid-infrared nonlinear photonics and photon-pair generation.

The development of on-chip pulse compression is fundamental for fully integrated optical systems, and applications in ultrafast physics, metrology and non-linear optics. The optimization of this process to unlock the possible used of integrated semiconductor lasers as the seed of nonlinear phenomena is pivotal for applications. We present here a process based on the use of an optimization methods to determine a nearly-free-form waveguide profile along light propagation towards high efficiency on-chip pulse compression capped with the availabilities of integrated light sources.

In previous studies on laser harmonic generation in plasma and solids, we have developed a beat-wave approach to laser harmonic generation, in which all Fourier spectra take the form of regular grids [1–3]. In this paper, we extend our model to the nonlinear optical response of isotropic chiral media driven by locally chiral light [4–7], in which the tip of the electric-field vector draws a chiral Lissajous figure in time. As in our earlier work on laser-solid interactions [1], the medium is represented by a zero-frequency (DC) driving mode. We show how an enantio-sensitive DC mode can be derived from the interaction of synthetic chiral light with a chiral medium. The beating between this DC mode and the EM fields then leads to a regular harmonic spectrum with alternating chiral and achiral modes. We will derive the criteria for these modes to overlap in Fourier space, so they can combine to yield enantio-sensitive interference patterns or line intensities. Finally, we will apply our framework to a variety of existing results [4–7] to validate its predictions. [1] R. Trines et al., Nature Communications 15, 6878 (2024). [2] R. Trines et al., Proc. SPIE PC13347, PC133470H (2025); https://doi.org/10.1117/12.3043381 [3] R Trines et al., arXiv:2507.08635 (2025). [4] D. Ayuso et al., Nature Photonics 13, 866 (2019). [5] D. Ayuso et al., Nature Communicaitons 12, 3951 (2021). [6] N. Mayer et al., Nature Photonics 18, 1155 (2024). [7] J. Vogwell et al., Science Advances 9, eadj1429 (2023).

Photonic-based Extreme Learning Machines (ELMs) offer promising opportunities for fast and energy-efficient computing. Here we use the recently implemented generalized nonlinear Schrödinger equation simulation framework to systematically study fiber-based ELM performance exploring the impact of dispersion, nonlinearity, encoding, and different noise sources. By analyzing both numerical simulation and experimental data, we relate classification accuracy to correlations between output supercontinuum spectra and embedded information with a specific focus on physics governing the complex nonlinear dynamics in optical fibers. Our results highlight the rich parameter space determining fiber-based ELM performance and provide insight into the limits, optimization strategies, and practical implementation of these systems.

We report the experimental observation of Oscillating Turing Rolls (OTRs)—a new exact periodic solution of the Lugiato–Lefever equation (LLE)—in compact Si₃N₄ microring resonators with 23 μm radius (FSR = 1 THz) and strong dispersion (D₂/2π = 49 MHz). The small cavity size makes the spatial period comparable to the resonator length, enabling observation of pure temporal intermittency. Using optical and electrical spectrum analyzers, we capture intracavity power oscillations with 0.25 ns resolution. As pump power increases, the OTR region expands, showing switching between single- and double-period oscillations for different detunings, followed by a chaotic modulation-instability regime. We further observe intermittency, characterized by periodic switching between regular and chaotic dynamics over microsecond-to-second timescales, marking the transition to fully developed optical chaos.

We investigate the anisotropy of high-harmonic generation (HHG) in zinc selenide (ZnSe) under varying mid-infrared laser intensities. Even and odd harmonics show out of phase rotational dependence, with even orders exhibiting greater consistency. The shift in angular dependence with increasing intensity indicates interband and intraband interplay and the influence of ZnSe’s anisotropic band structure. These findings highlight how crystal symmetry and electronic anisotropy shape intensity dependent solid-state HHG dynamics.

Metal–organic frameworks (MOFs) are versatile platforms for optical and optoelectronic applications due to their tunable crystal structure, porosity, and photophysical properties. Their capacity as ultrathin light sources and nonlinear optical (NLO) crystals offers new opportunities for miniaturized photonic devices. First, ultrathin light sources based on 2D MOFs were achieved via mechanical exfoliation of lanthanide-based MOF (Ln-MOF) nanosheets. Reducing thickness from 500 to 13.5 nm enhances photoluminescence (PL) 10–50 fold, while temperature variation (7–300 K) induces an additional 10–20-fold nonlinear increase. These effects demonstrate scalable, robust MOF nanosheets as ultrathin light sources and optical sensors. Second, at the microscale, a non-centrosymmetric MOF microcrystal supports broadband, multi-wavelength coherent light generation. Second- and third-order nonlinearities enable simultaneous sum-frequency and cascaded processes spanning 350 nm with 7–32 coherent peaks and a quality factor up to 180. Together, these results show that rationally designed MOFs (from nanosheets to microcrystals) provide highly efficient, tunable platforms bridging fundamental photophysics and practical optoelectronic applications , going beyond conventional nonlinear optics.

We demonstrate on-chip supercontinuum generation using dual-wavelength pumping in a nonlinear photonic integrated circuit fabricated from high-index doped silica glass. Femtosecond pulses at 1040 nm and 1560 nm interact through cross-phase modulation and temporal reflections, producing broadband spectra that exceed those from single-pump excitation. Temporal reflections arise when the 1040 nm pulse interacts with a soliton-like index barrier at 1560 nm, generating far-detuned dispersive waves that extend the continuum. Experiments and simulations show excellent agreement with phase-matching theory. These results represent the first demonstration of dual-pump supercontinuum generation on a chip and highlight temporal reflections as a key mechanism for bandwidth control in integrated nonlinear photonics.

The two-electron problem is always nontrivial due to electron–electron repulsion. Beyond real atoms, attention has turned to artificial atoms, namely quantum dots, two or more electrons confined at a semiconductor interface. The confinement potential varies from parabolic potential, Gaussian potential, symmetric double well potential, to rectangular well potential. Incorporating an anharmonic term into the harmonic potential for two-electron quantum dots is a significant advancement. Recently, we studied such confinement through anharmonic potentials. In these works, we investigate the effect of the two-electron quantum dots in an anharmonic potential under a uniform strong magnetic field along the Z-axis.

We study second-harmonic generation (SHG) in silicon nitride (SiN) waveguides integrated with a monolayer of MoS2. We introduce a full vectorial–tensorial nonlinear model that captures the χ(2) response of the 2D material and the vectorial nature of the guided modes. The model reveals a key role played by the electric-field components along the waveguide axis, especially for nonlinear modal interactions with TM modes. We observed SHG in a SiN waveguide phase-matched for the TE0 → TM2 modal interaction, integrated with a 110 μm MoS2 monolayer whose armchair direction forms a 1.7° angle relative to the waveguide axis, successfully validating our model.

We developed a perturbative approach for the resolution of nonlinear scattering electromagnetic problems for arbitrary polarizations and incident angles. The modeling of the scattering of light by nonlinear materials leads, even for a monochromatic source, to a system of coupled nonlinear partial differential equations. Two main approaches are commonly employed to solve these equations. The first consists in directly solving the coupled nonlinear system through iterative methods; however this approach is very time-consuming. The second approach relies on perturbation theory. Assuming that the field amplitudes are sufficiently small, the coupled nonlinear system can be decoupled into a set of linear equations that are solved sequentially. In this work, we generalize this approach to the n-th order for the full system of nonlinear equations describing light scattering in the harmonic domain, and compare it in several test cases with the solution obtained from a previously reported iterative approach.

Kerr cavity solitons—the time-domain counterparts of Kerr frequency combs—have driven advances from chip-scale optical clocks to low-noise microwave generation. While most studies focus on single-mode resonators, multimode vectorial systems enable richer dynamics. We report two-dimensional spontaneous symmetry breaking in vectorial cavity solitons supported by orthogonal polarization modes. Under symmetric pulsed pumping, the solitons exhibit mirror-asymmetric polarization intensities and symmetry-broken temporal positions through cascading pitchfork bifurcations. Polarization- and temporal-symmetry breaking arise independently, with the latter explained by a vectorial perturbation model. These results reveal new dynamical degrees of freedom in Kerr resonators and broaden control of vectorial states of light.

K. Giannaris1, S. Rincon-Celis2, Y. Pellegrin3, F. Odobel3, F. Sauvage4, S. Haacke2, D. Brida1 1. Department of Physics and Materials Science, University of Luxembourg, 162A avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg 2. Université de Strasbourg – CNRS, IPCMS, CNRS, 23 rue du Loess, 67100 Strasbourg, France 3. Nantes Université – CNRS, CEISAM, UMR 6230, 44000 Nantes, France 4. Université de Picardie Jules Verne – CNRS,LRCS, 15 Rue Baudelocque, 80000 Amiens, France In this work we are investigating the ultrafast photo-induced processes relevant for the function and power conversion efficiency (PCE) of transparent near-infrared dye-sensitized solar cells. The cell design consists of a semiconducting (SC) layer (TiO2 or Al2O3), on which the dye molecules (pyrrolopyrrole cyanine TB336) are covalently bound, and an electrolyte for the charge regeneration of the dyes [1]. To study the complex dynamics that lead to photocurrent we use an advanced implementation of Two-Dimensional Electronic Spectroscopy (2DES), with sub-7fs pump pulses spanning the TB336 absorption spectrum (650-850 nm), and white-light probing (400-900 nm). This technique can therefore distinguish precisely the cation generation efficiency of monomers and dimers, respectively. First results indicate an unexpected red-shift of the action spectrum of cation generation, as compared to the total absorption spectrum of the cells. Future experiments will verify this finding for solar cells with different dye concentrations. [1] T. Baron et al., Angew. Chem. Int. Ed. 61, e202207459 (2022) [2] M. Kurucz et al., ChemPhotoChem, 8, e202300175 (2024)

Self-referencing is the integral part of an optical frequency division, the process that bridging the gap between optical and RF domains. However, the most common material for octave-spanning microcomb generation, Silicon Nitride (SiN), lacks the intrinsic second-order non-linearity to produce the second-harmonic required for self-referencing. This issue can be overcome by employing a photo-induced effect, which has been successfully demonstrated in SiN microresonators, but this poses the question if the doubled signal comply to high metrological standards of optical clocks. In our work we show that it is possible to achieve a decent relative frequency stability at 1e-15 level in a SiN-based microring, which corresponds to the state-of-the-art miniaturized atomic frequency references requirements.

Continuous-wave laser sources in the 290–320 nm multi-Watt regime are of great importance for driving quantum clocks and scaling quantum computers based on Rydberg states of certain trapped atoms or ions. Current second-harmonic cavities are not suited for combining these power and wavelength requirements. Using a resonant fourth-harmonic generation approach with a Raman fiber amplifier and a new cavity design, we demonstrate up to 4.7 W of power at 302 nm with no signs of degradation over 500 h.

We demonstrate nonlinearity-induced orbital coupling and superposition that enable vortex OAM generation and robust transport through a Kagome-based disclination, thanks to the nonlinear bandgap and dual-topological protection inherent to the lattice structure.

We report on the self-organization and the coherence transition dynamics during the establishment of mode-locking in a Mamyshev Oscillator. The Mamyshev oscillator consists of two offset filters and gain fibers in a cascaded arrangement. Light experiences periodic gains and spectral losses along the cavity, which can induce Faraday Instability even in the normal dispersion regime. Our simulation results show that there are two operational regimes of Mamyshev Oscillator. In the self-pulsating regime, the wavelength separation of the two offset filters is relatively small and the gain is relatively large. Laser mode-locking can initiate spontaneously without the need for external seeds. However, in the seed-driven pulsating regime, the separation of the two filters is relatively large, the mode-locking cannot self-start without an external seed. The numerical results show that there exist two distinct coherence transition pathways during the buildup of mode-locking in this regime. One is the coherence annihilation pathway, in which the seed coherence is lost during the mode-locking process. The other is the coherence memory pathway, in which the seed coherence can be preserved. In the coherence memory regime, we demonstrated synthesized dissipative soliton molecules and all-optical bit storage. All experimental results show that the seed-phase coherence remains intact in the coherence memory regime. Conversely, the phase coherence undergoes complete degradation in the coherence annihilation regime.

We demonstrate unidirectional operation of a solid-state ring laser using differential parametric gain with a single pump source for both the laser and the nonlinear mixing process. A tunable single-frequency tapered diode laser (775 – 810 nm, 1.7 W) pumps a 10 mm long Nd:YVO₄ crystal, while difference-frequency generation in a 20 mm long PPLN crystal between the single-frequency pump diode and the 1064 nm laser reinforces co-propagating photons, enabling unidirectionality. This doubles unidirectional output power and maintains single-frequency operation, verified by Fabry–Perot measurements. The idler is tunable from 3250 – 3430 nm with up to 5 mW output power. This approach offers a compact, cost-effective route to mid-IR sources.

Through high harmonic generation as a sensitive probe for electronic and structural properties we investigate the charge density wave phase transition of TiSe2. At temperatures below 100 K anisotropy in the non-linear response emerges and is identified via our developed mean-field model as an asymmetric atom displacement from directional CDW strength.

Efficient second harmonic generation requires phase matching. Precise phase matching is achieved at a fixed incidence angle with respect to the optical axis of the birefringent crystal, for a given frequency. Phase mismatch depends linearly on the incidence angle in the vicinity of the phase matching point. In the spatial domain, the linear phase mismatch corresponds to the walk-off of the interacting beams. We show that the periodic modulation of the refractive index of the nonlinear material (both in the transverse and longitudinal directions, on a wavelength scale) can modify the angular dispersion of interacting waves. This can alter phase-matching characteristics and can affect the beam walk-off. In an ideal case, this can result in phase matching over a finite angular range, eliminating or significantly reducing walk-off effects. This can ultimately enhance the efficiency of second-harmonic generation, particularly when working with narrow beams.

In this work, we experimentally study the nonlinear optical behaviour of a pre-created alloy nanoparticle using a high-repetition rate femtosecond laser source for photonic applications. The alloy nanoparticles have been created using the second harmonic generation of the Nd: YAG laser

It is known, that well above the generation threshold random fiber laser radiation is characterized with wide spectrum, representing continuous set of spectral components. At the same time, just above the threshold generation possesses a higher degree of coherency, consisting of a discrete number of localized modes, each with a certain lifetime of about 1 ms. We study – both experimentally and by means of numerical simulation – in detail the statistical manifestation of the transition process between these two states. We demonstrate the clear analogy between exponential grown of energy in the spectral mode of a single-mode laser and increase of spectral modes number in the random fiber laser, and emphasize the role of nonlinear interactions in this process.

Neuromorphic photonic processors need synaptic elements that are ultra-compact, low-loss, broadband, and non-volatile. We present and numerically validate a 2×2 slot directional coupler (DC) whose silicon slot region is symmetrically clad with the phase-change material (PCM) Sb₂Se₃. In our concept, the PCM forms the inner rails of the DC while the outer rails are standard Si waveguides; toggling Sb₂Se₃ between amorphous and crystalline states perturbs the super-mode splitting and flips the bar/cross transfer, enabling non-volatile weight programming. The PCM geometry is inspired our prior work on optimal transitions between different substrate materials in heterogeneous Photonic Integrated Circuits, which we adapted here to minimize scattering at the Si/PCM interfaces. Design proceeded from eigenmode/FDE analysis to 3D FDTD. Super-mode extraction was used to set an initial coupling length, then the full device was optimized in FDTD. The stand-alone coupler achieves an active length as short as 2.3 µm, yielding a footprint suited for high synapse density. Across the 1500–1600 nm band the transmission on the selected output remains ≥ 0.80 with weak wavelength dependence (flat within a few percent in our sweeps), while the non-selected port stays near zero, giving >10 dB simulated extinction without additional phase trimming. The short length directly translates to low propagation loss and relaxed phase-error sensitivity. To assess system-level feasibility, we simulated meshes of up to 15 such DC building blocks and executed basic matrix operations. We emulate programming by assigning the measured complex refractive indices of Sb₂Se₃ in its amorphous and crystalline states; switching the PCM flips each DC between bar-dominant and cross-dominant states. The meshes show numerically stable behavior for representative linear transforms, with performance limited primarily by insertion loss of passive sections and (possibly in future fabricated versions) by mesh calibration and not by bandwidth. Because the device is broadband around 1550 nm and non-volatile, it avoids continuous bias power typical of thermo-optic or carrier-based weights. These characteristics make it a promising reconfigurable building-block for dense neuromorphic PIC inferences.

We report the experimental results of high repetition rate pulse train generation obtained from injection of initially modulated continuous wave into the fiber with longitudinally decreasing anomalous dispersion. As a result, we observed the stable sub-picosecond pulse trains with repetition rate ranging from 100 to 300 GHz and optical spectrum width up to 80 nm at -20 dB level. On the basis of comparison of experimental results with numerical simulations, a method for clarifying the parameters of dispersion profile of the fibers is proposed.

The study provides a joint numerical and experimental analysis of how saturable absorber positioning affects the performance of a polarization-maintaining (PM) soliton fiber laser mode-locked due to a SESAM. Our simulations identify a specific optimal region within the cavity where precise SESAM placement facilitates stable single-pulse operation at increased gain levels, effectively suppressing background noise and delaying multi-pulse transitions. These results are validated by an Er-doped PM fiber laser experiment, showing enhanced pulse energy and spectral width. This approach offers a robust strategy for optimizing soliton lasers, with significant implications for advanced short-wavelength infrared (SWIR) systems, (especially for Tm- and Ho-doped fiber lasers).

Carbon fiber reinforced polymer (CFRP) is an ideal material for manufacturing critical components such as orthopedic surgical instruments, robotic end-effectors for surgery, and personalized surgical navigation tools, owing to its exceptional specific strength, stiffness, and fatigue resistance. Conventional machining methods are prone to microcracks and interfacial delamination, making it difficult to meet stringent medical standards. Femtosecond laser technology, with its superior "cold machining" characteristics, serves as a core technique for processing CFRP. However, the significant anisotropic thermal conductivity of carbon fibers in CFRP limits the precision of femtosecond laser machining. Therefore, this study primarily focuses on the influence of femtosecond laser parameters on axial and radial thermal conduction in CFRP. The research findings reveal that high scanning speeds can effectively mitigate thermal conduction differences caused by carbon fiber anisotropy, providing theoretical guidance for the application of femtosecond laser machining in high-end medical fields.

Introduced about 25 years ago, the optical frequency comb has made routine the counting and synthesis of the oscillations of light on the femtosecond time scale. As such, it is an essential component of all optical clocks and time-transfer systems with precision at the 18th digit. The coherent microwave-to-optical capabilities of frequency combs extend to wide-ranging applications in fundamental and applied spectroscopy, the synthesis of microwaves with ultra-low phase noise, and the discovery of planets orbiting distant stars. In practically all these cases, optical frequency combs have been employed as classical sources of laser light. Here, a new avenue of research involves the development of squeezed optical frequency combs, and the use of such quantum combs for enhanced metrology. This talk will provide an overview of the state-of-the-art of both classical and quantum frequency combs and highlight their use in the most impactful applications.

We investigate a silicon microresonator with tunable Hermitian and non-Hermitian coupling between the counterpropagating modes, enabled by integrated phase shifters for intensity and phase control. Phase tuning allows control of nonlinear behaviors such as bistability, self-pulsing, and transitions between stationary and quasi-stationary states. The system shows strong path dependence: forward and backward phase sweeps over the same 2π range produce different responses, indicating memory effects arising from nonlinear light–matter interaction and non-Hermitian coupling. Modeling links these features to a global bifurcation involving saddle-node annihilation and a distant limit cycle. The DRUM (Dynamically Reconfigurable Unified Microresonator) provides a reconfigurable platform for complex nonlinear dynamics relevant to neuromorphic and optical information processing.

Kerr frequency combs (microcombs) arise when a continuous-wave laser couples into an optical microresonator, generating evenly spaced, coherent lines through Kerr nonlinearity, dispersion, and dissipation. While most studies rely on anomalous dispersion, requiring thick waveguides and non-standard fabrication, we explore microcomb generation in the normal-dispersion regime using CMOS-compatible silicon nitride (SiN) resonators. Two approaches are demonstrated: (1) pumping with electro-optic sidebands synchronized to the resonator’s free spectral range (FSR), and (2) employing photonic crystal resonators with engineered dispersion perturbations for spontaneous comb emergence. Both designs use compact 20 GHz-FSR spiral resonators on 350 nm-thick SiN, achieving intrinsic quality factors up to 10 million. This work establishes a scalable, foundry-compatible platform for normal-dispersion microcombs with potential extension into the visible spectrum.

A whispering-gallery microbubble resonator stands out for its hollow structure, offering numerous applications in sensing and in situ light-matter interactions. Offering ultrahigh Q-factors, these resonators also exhibit a dense mode spectrum, with mode mixing and interference effects that limit sensing potential. In this work, we isolated selected modes of such a dense spectrum by writing geometric filters on the resonator outer surface using focused ion beam milling. Next, to recover the Q-factor, we milled submicron-sized holes near the equator to provide mode spatial confinement. Furthermore, we demonstrated pressure sensing (without modal interference) using these precision modified resonators and obtained good sensitivities, on par with our previous works, confirming their potential. The mode-selection capabilities and precise fabrication methods discussed in this work may be useful for controlling intermodal interactions.

We introduce a compact all-fiber dual-color femtosecond laser delivering synchronized 1.55 µm and 1.03 µm pulses, where the 1 µm branch is formed through dispersive-wave emission in PM-HNLF pumped by sub-30 fs pulses. Using a high-sensitivity balanced cross-correlator, we achieve the first sub-femtosecond timing-jitter characterization between the dispersive wave and pump pulses in a fiber-integrated system. The exceptional stability of this dual-color source unlocks new capabilities for mid-IR DFG, ultrafast pump–probe microscopy, and attosecond-level synchronization in advanced accelerator and photon-science facilities.

Ultrafast sciences and technologies are founded on the principles of ultrashort-pulse nonlinear optics. Until now, their discrete and bulky nature has hindered the utilization of their vast functionalities for many applications, ranging from sensing to computing and quantum information processing. In the past few years, nanophotonic lithium niobate (LN) has emerged as one of the most promising platforms for integrated photonics, characterized by strong quadratic nonlinearity. In this talk, I will present recent experimental progress in the realization and utilization of ultrafast nonlinear devices in nanophotonic LN, which outperform their table-top counterparts. These advancements include intense optical parametric amplification, ultrafast ultra-low-energy all-optical switching, few-cycle vacuum squeezing, ultrafast laser mode-locking, ultrabroadband coherent light sources, and generation of two-cycle pulse. I will also discuss ongoing efforts toward the miniaturization of ultrafast technologies and the development of chip-scale ultrafast nanophotonic circuits in both the classical and quantum regimes.

Thin-Film Lithium Niobate (TFLN) makes the material’s wide transparency window and high nonlinearities accessible for tightly confined nanowaveguides. In our study, the second order nonlinearity is harnessed in a 600nm thick X-cut LN via quasi phase-matched operation. Low loss nanowaveguides are fabricated via Reactive Ion Etching and periodic poling is obtained by electric field inversion thanks to electrodes patterned on both sides of the waveguides. Poling is then monitored by Piezoresponse Force Microscopy. Second Harmonic Generation with a normalized conversion efficiency over 3000%/W/cm² is demonstrated.

We present a new guiding mechanism in which light confinement is achieved entirely through nonlinear interaction, without any change in the refractive index of the medium. By spatially modulating the second-order nonlinearity to form a narrow, periodically poled strip within an otherwise monodomain KTP crystal, we realize dual-wavelength guiding that is all-optically controlled by the pump beam. The mechanism is based on the sum-frequency generation process and is analogues to spin transport across magnetic domain walls, where the signal and idler fields form an effective pseudo-spin whose guiding behavior depends on their relative phase. We experimentally demonstrate these concepts in several guiding configurations, including a pseudo-spin slab waveguide, directional coupler, and Y-splitter, enabling robust control of frequency-superposition states. Our findings pave the way for numerous waveguiding hallmarks within a single nonlinear crystal and open new possibilities for integrated and quantum photonics.

As optical communication technologies move toward fully light-based architectures, unconventional beams offer new opportunities for advanced control of light propagation and information processing. Airy beams, in particular, are notable for their self-bending trajectories and resistance to diffraction. In this study, we explore how these beams evolve nonlinearly when propagating through optically induced photonic lattices with defects. By conducting a detailed analysis, we show that the interplay between beam parameters, lattice design, and nonlinear effects governs the number, position, and intensity of the resulting output channels. Our investigation reveals that fine adjustments of these factors allow not only the creation of multiple stable output pathways but also control over their spacing. These insights underscore the relevance of defect-tailored lattices combined with Airy beam excitation for optical routing and interconnects, contributing to the development of adaptable all-optical processing systems.

In this presentation, we will discuss a novel probabilistic photonic computing platform based on polarization symmetry-breaking in a nonlinear Kerr resonator. Driven by picosecond pulses, the system utilizes a period-2 operating regime to generate symmetry-protected bias-free binary states encoded in intensity, bypassing the need for complex phase stabilization of DOPO-based Ising machines. The platform is highly versatile: without feedback, it functions as a MHz-speed random-number generator; with a DC bias, it produces probabilistic bits with a sigmoidal response; and with measurement-based feedback, it emulates Ising-model dynamics. Experimental results demonstrate its ability to successfully find ground-state configurations for combinatorial problems.

We experimentally uncover abnormal synchronization patterns in a breathing-soliton fiber laser, extending far beyond the classical Arnold’s tongues. By tuning intracavity loss, we map the synchronization between breathing frequency and cavity repetition rate, uncovering unexpected leaf-like and ray-like structures with internal holes—signatures of quasi-periodic dynamics. Supported by numerical modeling, these results provide the first experimental evidence of long-predicted complex synchronization geometries. Our findings establish breathing-soliton lasers as a versatile platform for exploring nonlinear synchronization in photonics and open new routes to control, stabilize, and harness dynamic behaviors in ultrafast optical systems.

An imaging system with a single lens imposes a quadratic phase on the optical field. Usually, we can neglect it when measuring intensity, since our sensors are not sensitive to this phase. For certain signal processing applications we may need to remove this phase. In our lab, we develop temporal imaging systems which image signals in time, similar to a lens in space. Therefore, temporal imaging systems also exhibit quadratic phase on the output signal. To cancel this quadratic phase, we designed a double-lens microscopy system that enables chirpless temporal magnification of the input signal. It can be used for adjusting the temporal width of entangled photons – making them temporally indistinguishable. Or for measuring optical decaying signals in active-dispersive medium with complex β_2, (the temporal equivalence of spatial evanescent waves). This system also has a larger temporal aperture compared to a single time-lens, assuring no loss of frequencies at the output.

We have designed and developed a reverse Electro-Optic Modulator (EOM) based time-lens. Our setup enables radio-frequency (RF) signal modulation driven by an optical input, effectively performing a temporal Fourier transform on the RF signal. In this research, we numerically simulate and experimentally demonstrate the dynamics of such lens. Owing to the unique design of our lens, we further demonstrate that the lens can operate as a quantum element, by sending a squeezed pump as the optical input.

We present a new class of optical resonator: the temporal optical parametric oscillator (temporal OPO) which is a cavity constructed around a time-lens in a 2f configuration, enabling light to oscillate not in space, but in time. Unlike conventional OPOs, the temporal OPO exhibits roundtrip Fourier transforms, mapping time into frequency and vice versa, giving rise to a cascade of novel nonlinear effects. We explore the generation of soliton pairs under negative dispersion, enabled by effective dispersion inversion, and observe ultrafast oscillatory dynamics driven by nonlinear polarization mode dispersion. The temporal OPO combines parametric gain, dispersion control, and spectral–temporal feedback, offering a rich platform for exploring high-speed dynamics, soliton interactions, and time-frequency duality in nonlinear optics. This work opens the door to temporally-engineered resonators with potential applications in ultrafast signal processing, temporal spectroscopy, and optical computing.

Although the development of ultraviolet (UV) frequency combs has been accomplished 20 years ago [1, 2], it was only very recently that the ultraviolet spectral region has been conquered by dual comb spectroscopy (DCS) [3-7]. DCS combines broad spectral coverage with frequency comb precision, fast measurement speeds and high spectral resolution. However, as frequency combs mainly emit in the infrared region, frequency up-conversion into the UV is still required for UV DCS. This makes UV DCS challenging: the conversion efficiency scales with pulse energy and hence increases with shrinking pulse repetition rates. On the other hand, DCS favors high repetition rates for stable conditions during the pulse interferometry. In this conference contribution, the most recent projects of the Coherent Sensing Group at TU Graz aiming at UV frequency comb generation and DCS will be presented. The efforts advancing dual comb spectroscopy include different comb systems with different repetition rates and the extension into the vacuum ultraviolet via nonlinear methods such as high harmonic generation. Intermediate steps recently enabled dual comb spectroscopy in real time and in the field for atmospheric sensing of nitrogen dioxide with an unprecedented temporal resolution of one second [8, 9]. References: [1] C. Gohle et al., “A frequency comb in the extreme ultraviolet", Nature 436, 234 (2005). [2] R. Jason Jones et al., Phys. Rev. Lett. 94, 193201 (2005). [3] B. Xu et al., “Near-ultraviolet photon-counting dual-comb spectroscopy”. Nature 627, 289 (2024). [4] K. F. Chang et al. „Multi-harmonic near-infrared–ultraviolet dual-comb spectrometer”, Opt Lett 49, 1684 (2024). [5] J. J. McCauley et al., “Dual-comb spectroscopy in the deep ultraviolet. Optica 11, 460 (2024). [6] A., Muraviev et al., Optica 11, 1486 (2024). [7] L., Fürst et al. “Broadband near-ultraviolet dual comb spectroscopy”. Optica 11, 471 (2024). [8] A. Eber et al., “Streaming self-corrected dual-comb spectrometer”, Optics Letters, 33, 35314 (2025). [9] A. Eber et al., Coherent field sensing of nitrogen dioxide. Opt Express 32, 6575 (2024). [10] A. Eber et al., NIR/VIS DCS comparing high and low repetition rate regimes, arXiv:2509.02159 (2025).

We demonstrate a hybrid turnkey Kerr microcomb laser achieving single-soliton operation with 100 GHz free spectral range and 300 nm bandwidth, overcoming the integration and power limitations of previous microrod-based and wide-FSR hybrid systems. This performance, achieved in a single-soliton regime using an anomalous dispersion silicon nitride (Si₃N₄) microresonator integrated into a fibre Fabry-Perot cavity, marks a significant advancement in hybrid OFC generation. The resulting 64 comb lines, spanning the entire C-band above the -20 dBm level, deliver an average output power of 17 mW in single-mode fibre

We demonstrate generation of an octave-spanning soliton frequency comb in a single 15 GHz silicon nitride racetrack resonator pumped by picosecond pulses synchronized to the cavity repetition rate. The soliton state is achieved with 600 mW of average pump power. Euler bends with adiabatically varying curvature suppress higher-order spatial modes, producing a smooth spectrum with dual dispersive waves. Long directional couplers and low-loss fabrication enable strong high-frequency coupling, allowing efficient extraction of higher-order dispersive waves without precise dispersion engineering. The generated comb spans 24.7 THz (12 fs pulse duration) and contains approximately 8,800 lines, including 4,500 within a 3 dB bandwidth—representing, to our knowledge, the largest number of comb lines reported from a single microresonator.

Soliton microcombs with low repetition rates are highly desirable for applications such as optical clocks, broadband communications, ultrafast ranging, and precision spectroscopy, yet they remain difficult to realize due to the strong thermal instability in long-cavity microresonators. Dual-mode pumping has emerged as an effective method to mitigate thermal effects, but in long-cavity devices the mismatch in coupling conditions between the primary and auxiliary modes limits its applicability. Here, we introduce a robust solution that leverages engineered inter-modal coupling in racetrack microresonators to efficiently couple pump power into the auxiliary mode. Using a high-Q (>10 M) silicon nitride device, we demonstrate deterministic, thermally accessible single-soliton generation at a 33-GHz repetition rate. This approach provides a simple and broadly applicable pathway for reliable low-repetition-rate soliton microcomb generation.

Pure-quartic cavity solitons are an emerging class of dissipative Kerr solitons that are promising for various applications including telecommunications. They form in passive cavities under the balance of negative quartic dispersions and Kerr nonlinearity, as well as loss and parametric gain. Using a generalized Lugiato Lefever equation, we numerically investigate dynamics of pure-quartic cavity solitons. We observe the spontaneous emergence of uniformly spaced solitons, perfect soliton crystals (PSC), out of temporal chaos. These perfect crystals break into soliton molecules as detuning is increased. We use a strain analogy to quantify the stability of these PSCs and behaviour of temporal patterns in the soliton existence regime. Our results interpret such behaviours, could be closely linked with the enhanced soliton-soliton interactions, mediated via oscillatory tails of pure quartic solitons.