Nonlinear Optics and its Applications 2024

I will explore various facets of photonic quantum systems and their application in photonic quantum technologies. Firstly, I will focus into quantum foundations and by discuss quantum interference, a key element in photonic quantum technologies. I will highlight how the distinguishability and mixedness of quantum states influence the interference of multiple single photons – and demonstrate novel schemes for generating multipartite entangled quantum states. I will then address photonic quantum computing, specifically focusing on the building blocks of photonic quantum computers. This includes the generation of resource states essential for photonic quantum computing. I will then shift to photonic quantum networks, covering both their hardware aspects and showcasing quantum-network applications that extend beyond bi-partite quantum communication. Lastly, I will outline how photonic integration facilitates the scalability of these systems and discuss the associated challenges.

Joining the rich photophysics of organic light-emitting materials with the exquisite sensitivity of optical resonances to geometry and refractive index enables a plethora of devices with unusual and exciting properties. Examples from my team include biointegrated microlasers for real time sensing of cellular activity and long-term cell tracking, as well as the development of photonic implants with extreme form factors and wireless power supply that support thousands of individually addressable organic LEDs and thus allow optogenetic targeting of neurons deep in the brain with unprecedented spatial control. Very recently, by driving the interaction between excited states in organic materials and resonances in thin optical cavities into the strong coupling regime, we unlocked new tuning parameters which may play a crucial role in the next generation of TVs and computer displays to achieve even more saturated colour while retaining angle-independent emission characteristics.

In my talk, I will discuss recent progress in applying the concept of Fisher information to the problem of estimating system parameters in complex scattering environments, such as inside or behind a disordered medium [1,2,3,4]. Interestingly, such tools can also be successfully applied to artificial neural networks, in particular to define the performance limit of a network in extracting information from a complex system. [1] Maximum information states for coherent scattering measurements, D. Bouchet, S. Rotter, and A. P. Mosk, Nature Physics 17, 564 (2021). [2] Optimal control of coherent light scattering for binary decision problems, D. Bouchet, L. M. Rachbauer, S. Rotter, A. P. Mosk, and E. Bossy, Phys. Rev. Lett. 127, 253902 (2021). [3] Invariance property of the Fisher information in scattering media, M. Horodynski, D. Bouchet, M. Kühmayer, and S. Rotter, Phys. Rev. Lett. 127, 233201 (2021). [4] Continuity equation for the flow of Fisher information in wave scattering, J. Hüpfl, F. Russo, L. M. Rachbauer, D. Bouchet, J. Lu, U. Kuhl, and S. Rotter, arXiv:2309.00010

In the context of separation estimation between two incoherent point sources, it has recently been shown that an optimal measurement strategy, which saturates the quantum Cramer-Rao bound, involves the use of spatial mode demultiplexing method (SPADE). To realize mode selective measurement required for SPADE, we propose a new approach based on sum frequency generation (SFG). The conversion of infrared light coming from two incoherent point sources is performed in a periodically-poled lithium niobate (PPLN) crystal by mean of a spatially shaped pump laser. By analyzing the converted images obtained with pump beams shaped as Hermite-Gaussian (HG) modes, we demonstrate the mode-sorting capabilities of this system. Our experiment, shows that our measurement method can estimate separations in sub-Rayleigh regime with improved accuracy compared to the traditional direct imaging method.

Structured light are fields which are spatially shaped in its properties such as its amplitude, phase, or polarization. This spatial variation enables light to carry interesting features including orbital angular momentum, complex energy flow structures, singularity configurations, and more. We will discuss how these features make structured light a cutting-edge tool in various areas, ranging from singular and quantum optics to nanophotonics. Exploring its capabilities, we will present the customization of light down to the nanoscale and its application for advanced imaging of nanoemitters as well as quantum cryptography.

We review recent works in optical signal shaping and advanced characterization techniques within the framework of nonlinear fiber propagation. Specifically, we focus on the development of characterization methods based on the dispersive Fourier transform to monitor incoherent spectral broadening processes with enhanced resolution and sensitivity. In this framework, we also discuss recent studies of modulation instability in a noise-driven regime. Paired with suitable optical monitoring techniques, we show that controlled coherent optical seeding can be leveraged via several machine learning approaches to tailor and optimize incoherent spectral broadening dynamics.

Our research focuses on optimizing optical femtosecond pulses for nonlinear optics, addressing challenges in fiber-based systems with dispersion and nonlinearity. Utilizing spectral phase control and optimization algorithms like particle swarm and simulated annealing, we fine-tune a complex phase mask for desired pulse shapes. Our method involves custom phase-profile optimization via spectral-domain phase modulation to compensate for nonlinear effects in pulse delivery. Using a chirped femtosecond source, operating at 1550nm, and a fiber amplifier, our implemented optimization scheme produces near-transform-limited pulses after propagation in polarization-maintaining fiber. This approach accommodates diverse pulse durations, showcasing the effectiveness of off-the-shelf programmable components with optimization algorithms in nonlinear optics and optical signal processing applications.

Deep learning has emerged as a powerful tool for solving complex problems in a wide range of domains. The success of deep learning can be attributed to several factors, including the availability of massive datasets, the increasing computing power of modern hardware, and the development of efficient algorithms. Still, In the modern era of information and communication technologies, the demand for faster and more efficient data transmission has driven researchers to explore novel approaches to enhance communication systems, among them is the optical approach for such a problem. In our lab, we develop a fully optical deep learning network that is based on high order spatial mode, and the ultrafast nonlinear four wave mixing interactions inside multimode fibers. We exploit the optical nonlinear interactions between waves for developing a deep learning network that is faster than any electronic based network. In this study, we present the algorithm we developed and the theoretical implementation of such network. In addition, we demonstrate our ability to decompose and classify ultrafast signals, such as temporal modes combinations, which are typically undetectable by standard devices,

We apply the machine learning technique of dominant balance analysis to study nonlinear and dispersive pulse propagation in optical fibre. We show results for different cases including: the emergence of modulation instability from noise; fundamental and higher-order soliton propagation; soliton-dispersive wave generation; Raman soliton and supercontinuum dynamics; optical wavebreaking; the generation of Riemann wave shocks. For all cases, we show how we can automatically distinguish regions of dominant interactions where different nonlinear and dispersive terms combine to drive the propagation dynamics.

The guided transmission of optical waves is critical for light-based applications in modern communication, information processing and energy generation systems. Traditionally, the guiding of light waves in structures such as optical fibers has been predominantly achieved through the use of total internal reflection. In periodic platforms, a variety of other physical mechanisms can also be deployed to transport optical waves. However, transversely confining light in fully dielectric, non-periodic and passive configurations remains a challenge in situations where total internal reflection is not supported. Here we present an approach to trapping light that utilizes the exotic features of Lagrange points—a special class of equilibrium positions akin to those responsible for capturing Trojan asteroids in celestial mechanics. This is achieved in arrangements in which optical Coriolis forces induce guiding channels even at locations where the refractive index landscape is defocusing or entirely unremarkable. These findings may have implications beyond standard optical waveguiding schemes and could also apply to other physical systems such as acoustics, electron beams and ultracold atoms.

Temporal optics revolutionize the field of ultrafast detection with time-lens and time-stretch schemes. We developed a temporal interferometer that enables us to measure ultrafast phase shifts. With this interferometer, we measured phase shifts of correlated beams traveling in different temporal trajectories. This allows us to demonstrate the Aharonov-Bohm effect in the time domain. We developed the theoretical basis of this temporal Aharonov-Bohm effect and showed it in experimental measurements. In the talk, we will explain this effect, describe the experimental setup, and show the results.

We experimentally show an optoacoustic memory based on Brillouin scattering with one order of magnitude higher storage time that retrieves amplitude and phase information after 120ns. We increase the intrinsic phonon lifetime of a highly nonlinear fiber by a factor of six by cooling the fiber down to 4.2K. We demonstrate the performance enhancement of optoacoustic memory by measuring the amplitude and phase information of an initial data pulse and its corresponding retrieved readout pulse using direct and double homodyne detection. Furthermore, we present the influence of different cryogenic temperatures between 4.2K and 20K on the optoacoustic memory and compare the results with continuous-wave measurements. In conclusion, our work can not only accelerate photonic computing but also advance other applications of stimulated Brillouin scattering that require long phonon lifetimes, such as optoacoustic filters in microwave photonics. In addition, the presented long-lasting sound wave optoacoustic memory is compatible with active acoustic refreshment technique potentially leading to all-optical coherent memory beyond 1 μs.

By investigating the nonlinear propagation of Bessel beams (BBs) in a photorefractive crystal, we demonstrate their ability to induce complex 3D waveguides with up to 9 outputs by one single diffracting BB or two counterpropagating (CP) BBs. By tuning the parameters such as the beam size, applied electric field, and input beam power, our platform enables all-optical control of output intensity levels and numbers. Besides, the spatiotemporal dynamics are investigated in the case of CP BBs, revealing the threshold value of nonlinearity for time-periodic, quasi-periodic, and turbulent dynamics with spatially localized instabilities. Finally, the continuous modulation of the orbital angular momentum is realized, and an expanded modulation range is discussed in both stationary and dynamic regimes. These results hold promise for all-optical switches, dynamical optical components, and OAM-based components for all-optical networks.

Optical whispering gallery mode (WGM) type microresonator devices provide ultra-high Q factors and have a multitude of sensing applications. Microbubble resonators are a type of WGM device with a hollow shell and thin wall that can contain the sensing material, isolating it from the environment, and can still hold a high Q factor. In this work, a microbubble resonator was filled with a water solution of magnetospirillum bacteria - a type of magnetotactic bacteria with a unique ability to align with an external magnetic field. The alignment of such bacteria in the direction of magnetic field lines results in a change in the effective refractive index of the microbubble resonator, detectable as a shift in the WGM resonance wavelength. This enables us to determine the presence and properties of the bacteria. Our results indicate that the microbubble WGM resonator device can also work as a versatile platform for bio-sensing applications.

Spiking neural networks are a class of artificial neural networks maintaining a strict analogy to brain-like processing. I’ll show a new hardware approach in which semiconductor microcavities in strong light-matter coupling regime can operate as optical spiking neurons. We demonstrated the intrinsic property of exciton-polaritons to resemble the Leaky Integrate-and-Fire spiking mechanism. Polaritons when pumped with a pulsed laser exhibit leaky-integration due to relaxation of the excitonic reservoir, threshold-and-fire mechanism due to transition to polariton condensate, and resetting due to stimulated emission of photons. Our approach provides means for energy-efficient ultrafast processing of spike-like laser pulses at the level below 1 pJ/spike.

Silicon one-dimensional optomechanical cavities offer a cost-effective and highly scalable solution for the study and implementation of non-linear phenomena. By modifying the refractive index of silicon through thermal or free-carrier effects, it becomes possible to optically drive these resonators into a state of high-amplitude and coherent self-sustained mechanical oscillation. The nonlinearity stemming from this amplification mechanism provides significant adaptability in adjusting the frequency of mechanical resonators, enabling experiments such as injection locking, synchronization, and the study of chaotic dynamics. In this work, we show different novel configurations for the synchronization between mechanical flexural modes of silicon nanobeams and their locking to an external reference signal. The results hold great promise for applications in the distribution of clock signals in future photonic integrated circuits, as well as for establishing extensive networks of optomechanical resonators for studying complex non-linear dynamics.

We consider a resonator with two optical modes, excited with counter-propagating light of equal intensities. Recently, it was shown that the natural symmetry of this optical system can lead to spontaneous symmetry breaking of its steady states. We show that this symmetry property also applies to chaotic attractors, leading to different types of self-switching oscillations. We demonstrate that transitions between such attractors occur when the system exhibits a Shilnikov bifurcation. We employ a dynamical system approach to identify distinct switching behaviors as characterized by symbolic information and associated Shilnikov bifurcations.

In this work, we experimentally demonstrate, for the first time that the PR crystal can reduce the group velocity of a light pulse at 1310 nm at room temperature. The performances of the slow light, including the time delay and the fractional delay, are analyzed as a function of several parameters, such as the intensity, the duration, and the polarization of the input pulse.

we investigate experimentally the phenomenon of intra-envelope four-wave mixing in optical fibers. This phenomenon arises when two lasers, having nearly identical central frequencies, interact by four wave mixing process with each other. As a result, new spectral components are created within the existing spectra. We successfully isolate these components using a third laser through a multi-heterodyne detection process.

Integrated optical phased arrays (OPAs), fabricated in advanced silicon-photonics platforms, enable manipulation and dynamic control of free-space light in a compact form factor, at low costs, and in a non-mechanical way. This talk will highlight our work on developing OPA-based platforms, devices, and systems that enable chip-based solutions to high-impact problems in areas including augmented-reality displays, LiDAR sensing for autonomous vehicles, optical trapping for biophotonics, 3D printing, and trapped-ion quantum engineering.

We demonstrate integrated optical continuous-travelling-wave parametric amplifiers that significantly surpass the amplification bandwidth of traditional Erbium-Doped Fiber Amplifiers. Using a 5.55-cm-long integrated gallium phosphide waveguide, we achieve up to 35 dB of parametric gain in the small-signal regime, and more than 10 dB of off-chip net gain in the wavelength window spanning approximately 140 nm and centered at 1550 nm, with the maximum value of net gain reaching 25 dB. This is, to our knowledge, the first demonstration of such a large and broadband continuous-wave net gain in a photonic integrated waveguide.

A thermo-electrical imprinting process has been employed to induce second-order optical nonlinear (SONL) response in amorphous sodo-niobate optical thin films. By characterizing the geometry and the magnitude of the SONL response, a key aspect of thin film’s poling mechanisms compared with bulk glasses was established. This lies in the appearance of a charge accumulation at the film/substrate interface, described by the Maxwell–Wagner effect. A way to minimize this effect was then proven by promoting an induced built-in static field in the plane of the film using a microstructured electrode. A SONL susceptibility as high as 29 pm/V was measured, and its geometry and location were controlled at the micrometer scale. This work paves the way for the future design of integrated nonlinear photonic circuits based on amorphous inorganic poled materials.

The possibility of using photonic crystals to counteract the spatial Kerr effect, thus suppressing filamentation is shown. Tuning the photonic crystal geometry and projecting to the appropriate Bloch mode branch allows fine control of the spatial dispersion. Chirped photonic crystals can be engineered with such geometry that the designed diffraction compensates for nonlinear focusing, suppressing beam filamentation. The designed chirped photonic crystals have been fabricated in fused silica and experimental measurements show that they exhibit the necessary enhanced diffraction.

We show that hexagonal boron nitride (hBN), a two-dimensional insulator supports tunable excitons in the near and middle ultraviolet if subjected to an external superlattice potential. Our calculations predict that as we increase the strength of the potential, the gap reduces, and the anisotropy of the dispersion is enhanced. Consequently, the binding-energies of the excitons decrease, leading to a red-shift of the excitonic levels. We also observe that the absorption is reduced when we change the polarization from along the periodicity of the potential to perpendicular to it, with the system acting as an optical polarizer. As we reduce the gap, the characteristic frequency range for which we can excite exciton-polaritons red-shifts as well. These modes behave quite differently from pristine hBN in extreme cases where the anisotropy of the system grows indefinitely. In this way, by tuning the potential, we can manipulate the excitonic and sub-gap optical properties of hBN.

In nonlinear physics, the fundamental soliton has drawn significant attention due to its pivotal role in dynamic systems. Its remarkable property lies in maintaining shape and resilience when interacting with other nonlinear waves. We explore this phenomenon in the context of single-mode optical fibers, employing the one-dimensional nonlinear Schrödinger (1D-NLSE) equation, which yields distinct bound states of solitons. Our research focuses on the spatio-temporal dynamics within these bound states, demonstrating our ability to manipulate soliton velocity. We compare our findings with an Inverse Scattering Transform (IST) spectrum perturbation theory, decomposing the signal into solitonic components. Our experiments employ a Recirculating Optical Fiber Loop system and homodyne interferometric methods, enabling full characterization of the initial complex field. Our results showcase the robustness of the IST perturbation theory, even in the presence of perturbative higher-order effects

A recent method called gain-through-filtering has been proposed, which enables tuneable repetition rate OFC generation in passive driven fibre cavities based on a filter induced modulation instability process in the normal dispersion regime. We show that the introduction of the Erbium-doped fiber amplifier further enables controlling of the overall cavity finesse, lowering the input power threshold of the comb formation and enhancing the energy transfer to higher order comb lines.

We have developed a novel and highly-sensitive distributed measurement technique for characterizing supercontinuum generation along a tapered silica optical fiber. Based on a confocal microscope, this method involves a far-field point-by-point Rayleigh scattering analysis along the waveguide, providing micrometer spatial resolution and high spectral resolution. This non-destructive and non-invasive technique enables the observation of each step of supercontinuum generation along the fiber taper. This includes cascaded Raman scattering, four-wave mixing, and dispersive wave generation. We present the spatial nonlinear dynamic that is not accessible with standard spectral analyzers.

In the passive Kerr cavities, the period-2 dynamics of the sidebands, i.e., repeating periodically every two cavity roundtrips, has been analytically predicted and experimentally observed since the 90s. The period-doubling continuous waves have also been reported. We show that the modulational instability analysis on the period-doubling continuous waves, using two coupled Ikeda maps, unveils a novel period-4 modulation patterns, which are experimentally accessible.

In this investigation, we conducted a study on the amplification of ultra-low repetition rate pulses, specifically in the 0.5 to 16 MHz range, utilizing gain-managed nonlinear techniques. The research was centered around the implementation of a 1064 nm all-polarization-maintaining fiber mode-locked laser, which was seeded with an acoustic-optical pulse picker to regulate the pulse repetition rate. This experimental approach significantly enhanced the nonlinear pulse propagation effects across various pulse repetition rates at 1064 nm, offering new insights into the dynamics of GMN amplification in ultra-low repetition rate regimes.

In this work, we theoretically investigate the nonlinear light dynamics in dual-core fiber passive-driven resonators. Utilizing coupled Ikeda maps and Lugiato-Lefever equations, we analyze bistability and modulation instability, unveiling notable differences from single-core fiber cavities. Specifically, we highlight the difference in modulation instability maximum gain frequency between supermodes. Our discoveries pave the way for multicore fibre cavity experimental setup design, and modelling.

Optical cavities with nonlinear elements and delayed self-coupling are widely explored candidates for photonic reservoir computing (RC). For time series prediction applications that appear in many real-world problems, energy efficiency, robustness and performance are key indicators. With this contribution I want to clarify the role of internal dynamic coupling and timescales on the performance of a photonic RC system and discuss routes for optimization. By numerically comparing various delay-based RC systems e.g., quantum-dot lasers, spin-VCSEL (vertically emitting semiconductor lasers), and semiconductor amplifiers regarding their performance on different time series prediction tasks, to messages are emphasized: First, a concise understanding of the nonlinear dynamic response (bifurcation structure) of the chosen dynamical system is necessary in order to use its full potential for RC and prevent operation with unsuitable parameters. Second, the input scheme (optical injection, current modulation etc.) crucially changes the outcome as it changes the direction of the perturbation and therewith the nonlinearity. The input can be further utilized to externally add a memory timescale that is needed for the chosen task and thus offers an easy tunability of RC systems.

Programmable photonic circuits manipulate the flow of light on a chip by electrically controlling a set of tunable analog gates connected by optical waveguides. Light is distributed and spatially rerouted to implement various linear functions by interfering signals along different paths. A general-purpose photonic processor can be built by integrating this flexible hardware in a technology stack comprising an electronic monitoring and controlling layer and a software layer for resource control and programming. This processor can leverage the unique properties of photonics in terms of ultra-high bandwidth, high-speed operation, and low power consumption while operating in a complementary and synergistic way with electronic processors. This talk will review the recent advances in the field and it will also delve into the potential application fields for this technology including, communications, 6G systems, interconnections, switching for data centers and computing.

Molybdenum disulfide (MoS2) dots have potential applications as optical limiter and beam modulators. In this work, MoS2 quantum dots (QDs) prepared via the solvothermal method are studied for their broadband nonlinear optical (NLO) response. The as-prepared dots are few layers thick with lateral size distribution of 2-8 nm. The photoluminescence spectra show dependence on incident pump wavelength. Tunable femtosecond laser based z-scan technique shows reverse-saturable absorption and self-defocusing behavior. The direct bandgap in visible region achieved via quantum confinement effect enhances the NLO response of QDs. The mechanisms of two photon absorption along with thermal nonlinearity have been found to be operating in the system.

Strong coupling of an optical mode with the organic materials paves the way for understanding the light matter interactions. With the existence of this hybrid light-matter state, many properties of the material, including the optical nonlinearities are enhanced significantly. However, the measurements in former works are only focused on some specific nonlinear optical phenomenons, this limits their generality in other nonlinear optical processes. In our work, we strongly coupled the Frenkel excitons of J-aggregate cyanine molecules (TDBC) to an optical mode in a Fabry-Perot cavity, and measured the nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of the coupled system via Z-scan technique. Under the polaritonic state, those coefficients can be enhanced more than 2 orders of magnitude compared with that for the bare molecule film. In addition, the temporal response of the coupled system shows 120 fs, which has promising applications in ultrafast optical switching. This finding makes it possible to study the effect of strong coupling on a series of n2, β-related nonlinear optical phenomenons.

We study the transmission of the Nonlinear-optical loop mirror (NOLM) with strict polarization controlled and polarization-imbalanced as an optical filter. The NOLM is composed of a loop of two SMF-28 optical fiber sections of 150 meters of equal length twisted same ratio (7 turns/meter) in a clockwise and anticlockwise direction, canceling the linear birefringence. We use a coupler 50/50 and a quarter-wave retarder (QWR) as a polarization controller (PC). Adjusting the PC angle, it is possible to have maximum or minimum transmission and change the polarization in the OFSI, converting the linear polarization into elliptical polarization. We use a rectangular sign for input that was amplified, therefore, the noise also was amplified. The results show that NOLM can recover the original signal. However, the temporal results show that NOLM can filter the noise of low radiation, allowing us to recover the original signal.

we use the fourth-order Runge–Kutta and fast Fourier transform-based spectral analysis to study the power spectrum of the phenomena of multi-periodicity, crenelated, mixed-mode oscillations, and chaos when the values of the bandwidth and the cubic-nonlinear term (CNT) of the filter vary in the cubic-nonlinear optoelectronic oscillator (CN-OEO). On the one hand, when the high and low cut-off frequencies are sufficiently far apart, it is numerically proved that the presence of the CNT reveals the frequency combs generation with a free spectral range equal to the inverse of the time delay. Likewise, the width of the central peak narrows with the increase of the CNT, showing that the system becomes more and more selective in terms of oscillation frequencies. On the other hand, when the cut-off frequencies are sufficiently close, harmonic and sub-harmonic frequencies are recorded. In either case, CN-OEO displays oscillations whose frequencies remain greater than those of an OEO.

We are exploring an optoelectronic oscillator featuring a Colpitts oscillator in its electrical path. The Colpitts oscillator generates high-frequency electrical signals and exhibits dynamical behaviors such as periodic and bursting oscillations which can be easily monitored using a potentiometer. Inserting the Colpitts oscillator in the optoelectronic oscillator, we put forward the interaction between optical nonlinearity and electronic nonlinearity to obtain complex dynamical behaviors. The temporal dynamics of the system with and without delayed feedback are investigated experimentally. It is shown that a wide variety of periodic and chaotic states can be excited and that there is an amplification of the signal frequencies. In particular, bursting, chaotic bursting, and chaotic pulse-package oscillations with slow-fast temporal dynamics are experimentally observed in the system.

Nonlinear optical phenomena of the Floquet engineering with doping mechanism with optically active materials could be a preferable choice to exploit in quantum information process. The defect tolerance and easy band-gap manipulation with cost effective synthesis makes them suitable candidate for this observation. Although, these are quick degradable, but our recently published work clearly showed the enhancement of CsPbI3 nanocrystal's stability up to one month in low humidity environment. Here, we have demonstrated simultaneously observation Optical Stark and Block Siegert effect in Cu-doped CsPbI3 nanocrystals by incorporating helicity-resolved pump-probe experiment. We have observed prominent excitonic shift in co and cross-polarization of pump-probe at very small detuning. Interestingly, we found that theoretical description of established two-level system must be modified with addition modification in detuning and Rabi frequency to consider fast rotating to explain the features.

Linear spectrophotometric transmittance measurements are widely used for basic photophysical characterizations of dissolved molecular species e.g. for determining the value of molar extinction coefficient. However, such measurements usually require prior information about the molar concentration of the studied chromophores, which in many cases such as e.g. genetically-encoded species, is not readily available. Here we demonstrate that by using high-accuracy measurement of small intensity-dependent changes induced in the sample transmittance due to high peak intensity femtosecond pulses we are able to provide estimates of the extinction coefficient without prior knowledge of the concentration.

The advancement of modern communication systems has sparked significant interest in the creation of optical signal processing devices. To create such devices, we can use third-order nonlinear optical effects, for example, Kerr effect that is essential for optical device development. The main challenge is selecting materials with high nonlinear efficiency. Organic materials have attracted more scientific interest in last years, due to their large nonlinear coefficient values. Here we show nonlinear optical properties of novel derivatives of push-pull azobenzene, that were functionalized with pentafluoro phenyl groups to enhance the nonlinear response. These materials can form glassy thin films without a host material, thus simplifying the device fabrication processes. In this work nonlinear optical properties of solutions with these materials were measured by z-scan method, irradiating the solutions with a tunable femtosecond laser. Our results show that these materials are efficient enough to be used in optical device fabrication.

This study presents an innovative method to perform spatiotemporal characterization of ultrashort pulses. It combines compressive sensing structured illumination with spatial light modulators for spatial characterization and fringe-resolved autocorrelation for point-to-point temporal characterization. The approach incorporates intelligent sampling using the reduced Scramble-Hadamard basis, making a generalization of single pixel images for coding of the ultrashort pulse characterization and advanced computational imaging techniques involving specialized reconstruction algorithms such as Nesta using the TV standard to fully collect the initial structure, demonstrating that it is possible to realize the measurement in a shorter time.

Two-photon absorption (2PA) transitions play a key role in many photonic applications, where 2PA spectral features for organic fluorophores are often due to electronic-vibrational (vibronic) transitions. While quantum-chemical calculations excel at modeling electronic 2PA transitions, success in predicting vibronic properties remains limited. This is in part due to high computational costs of evaluating 2PA tensor derivatives required for Herzberg-Teller (HT) vibronic interactions, especially if carried out across full vibrational coordinate space of the chromophores. Here, we present a novel cost-effective approach to model HT vibronic 2PA spectra by using the latest version of FCclasses3 code combined with judicious pre-selection of symmetry-adapted vibrational subspace. We apply this method to a C2h inversion-symmetric diketopyrrolopyrrole, where the 2PA spectrum is dominated by HT terms. Our results validate the experimental 2PA spectra and polarization ratio, confirming two-photon HT coupling is dominated by Bu-symmetry modes. However, nominally-forbidden features near the electronic-origin appear significantly larger than HT coupling permits, suggesting additional phenomena.

Exploring optical analogues with paraxial fluids of light has been a subject of great interest over the past years. Despite many optical analogues having been created and explored with these systems, they have some limitations that usually hinder the observation of the desired dynamics. Since these systems map the effective time onto the propagation direction, the fixed size of the nonlinear media limits the experimental effective time, and only the output state is accessible. In this work, we present a solution to overcome these problems in the form of an optical feedback loop, which consists of reconstructing the output state and then re-injecting it again at the entrance of the medium through the utilization of Spatial Light Modulators. This technique enables access to intermediate states and an extension of the system effective time. The results presented in this work pave the way for observing new dynamics with paraxial fluids of light.

We report the generation of optical frequency combs in fiber Fabry-Perot resonators operating in the normal dispersion regime. Thanks to the compact design and the easy coupling of the resonator, switching waves can be generated in an all-fiber experimental setup employing a pulsed pumping scheme. The influence of dispersion is thoroughly discussed, revealing the potential to create a frequency comb spanning a 15 THz bandwidth through the utilization of a flattened low dispersion cavity. The experimental results are in good agreement with the theory and the numerical simulations.

The pursuit of inducing second-order optical nonlinearity (SONL) in amorphous materials such as silica glasses has been explored. However, the induced SONL response was very weak compared to crystalline materials. Recently, the induced χ _xxx ^(2) of sodium-doped Nb2O5 thin film has demonstrated a remarkable value of 29 pm/V through patterned thermal poling technique. Here, we employ numerical simulations to design the electro-optic (EO) modulator based on induced nonlinearity in sodium-doped Nb2O5 waveguides (strip and rib). With the optimal modulator configuration, we can achieve V _π L of 20 V.cm for strip waveguide and 40 V.cm for rib waveguide. Additionally, the incorporation of a 600 nm SiO2 top cladding enhanced the modulation efficiency nearly two-fold for rib (19 Vcm) and to a lesser extent for strip (17 Vcm). With its robust induced SONL response, wide transparency and practical fabrication feasibility, sodium doped Nb2O5 waveguides emerge as a compelling candidate for high-performance EO modulators.

Triamino-heptazines (TAH's) comprise the fundamental building blocks of graphitic carbon nitride, an alluring material with promising applications in optoelectronics. However, the core D3h molecular symmetry enforces a forbidden lowest-energy excited singlet state, making it a challenge to characterize via conventional spectroscopy. Here, we measure one- and two-photon absorption spectra of an acidic form of triamino-heptazine, 3H-TAH, and use reversible acid/base titration to further probe the symmetry of the low-energy transitions in aqueous solution, which suggests the molecular structure is dimelem. Two-photon absorption reveals two distinct low-energy transitions in acidic conditions, both of which are one-photon forbidden. The lowest energy state additionally becomes one-photon allowed in basic conditions. Spectroscopic changes can be described according to chromophore symmetry switching, with C3h, D3h, or Cs point group symmetry in respective acidic, neutral, or basic environments.

A multimode optical fiber supports the excitation and propagation of a singular, pure optical mode. This mode, characterized by a field pattern that adheres to the boundary conditions, remains constant throughout the length of the fiber. When two such pure optical modes, moving in opposite directions, are initiated, they could interact via the stimulated Brillouin scattering (SBS). In this study, we introduce an analytic theoretical framework to describe the SBS interactions between two counterpropagating optical modes, each selectively excited in an acoustically uniform multimode optical fiber. Using a weakly guiding step-index fiber model, we have formulated an analytical expression that maps the spatial distribution of sound field amplitude within the fiber core. Furthermore, we have investigated the characteristics of the SBS gain spectra, particularly focusing on the interactions between modes of varying orders. Through this approach, we aim to provide comprehensive insights into the sound propagation phenomena associated with SBS in multimode optical fibers, highlighting their unique influences on the SBS gain spectrum.

Dipicolinic acid (DPA), bound to calcium (Ca), is a main component of bacterial endospores. Complexation of DPA with lanthanide ions, particularly Terbium (Tb), allows for rapid detection of DPA via monitoring of the lanthanide luminescence, with applications spanning from cell imaging to contamination and biohazard detection, to sterilization control. Here we present time-resolved luminescence of Tb(DPA) complexes upon UV excitation at 266 nm. Our data directly monitor the luminescence dynamics and speak for a rise of the luminescence on a sub-50 ns time scale, which is more than 1000 times faster than previously reported, and raise questions about the details of the energy transfer process in these complexes and the states involved. The results are relevant for both, the design of more sensitive detection schemes for Tb-DPA fluorescence, and for the design of novel Tb-based luminescence probes or novel fluorescence probes working as FRET acceptors of Tb energy.

Broadband Coherent anti-Stokes Raman Spectroscopy (BCARS) is explored as a rapid, label-free method for detecting microplastics in drinking water. It offers significant advantages over current methods like visual inspection, FTIR, spontaneous Raman spectroscopy, and gas chromatography, in terms of sensitivity, speed, and non-destructiveness. BCARS can identify particles as small as a micron and differentiate between plastic types through chemical analysis. This method, much faster than spontaneous Raman spectroscopy, uses a dual excitation technique for probing Raman spectra. The study demonstrates BCARS' efficacy with a mixture of polystyrene and Poly(methyl methacrylate) microbeads, highlighting its potential in microplastic detection and environmental monitoring.

Sideband injection locking, whereby a secondary continuous-wave laser is injected in the spectral wing of a Kerr comb, enables all-optical control of the repetition rate and offset frequency. We derive the scaling laws of such systems and show excellent agreement with experimental and numerical results, with opportunities for all-optical stabilization of microresonator frequency combs.

Bistable coupled systems can exhibit nonlinear waves. Domino waves represent a straightforward example of nonlinear waves in everyday life. Domino waves are observed in extended bistable chains in which a domino has two stable equilibria; vertical and horizontal. These elements are coupled reciprocally. Namely, if one exchanges the role of emitter and receiver, the observed propagation is the same. Nonetheless, there is no knowledge of the impact of non-reciprocal coupling on the propagation of nonlinear waves. Based on an experiment using a liquid crystal light valve (LCLV) with optical feedback, nonreciprocal nonlinear wave propagation can be studied in a one-dimensional chain discrete model. The use of a spatial light modulator and an optical feedback loop enables us to control the initial conditions and non-reciprocal coupling, respectively. The nonlinear waves spatiotemporal evolution and velocities are also characterized. A discrete model of the bistable system is derived using a tight binding like approach for the LCLV with non-reciprocal optical feedback. Numerical simulations of the non-reciprocal coupled bistable systems fairly agree with experimental observations.

Electron-hole liquid (EHL), is a nonequilibrium macroscopic state of matter arising due to the strong correlations among charge carriers, above a critical density and below a temperature, which has recently been found in many semiconducting materials like TMDCs, and halide perovskites. However, the lasing behaviour induced by the EHL state is still unknown. In this paper, we reported that this EHL state is able to produce broadband and sizable optical gain with dual amplified spontaneous emission (ASE) bands. Two kinds of the ASE band are successfully observed at 4K: the Biexciton band and EHL band with their respective threshold fluence of 25 μJcm−2 and 200 μJcm−2. At room temperature, this dual behaviour vanished due to the large contribution of non-radiative recombination. We believe that the formation of EHL also stimulates other macroscopic quantum phenomena such as superfluorescence.

We report on the experimental and numerical studies exploring dynamical processes of soliton birth and annihilation of solitons in the laser ring cavity. The specific purpose of the research is focused on the exact control of the pulse repetition rate of a harmonically mode-locked fiber laser. We have demonstrated that the birth of a new pulse occurs from the soliton background (i.e., from the dispersive waves) through its shaping to the soliton or from the existing pulse through its splitting. The injection of external continuous wave (CW) allows one-by-one change of the number of solitons in the laser cavity thus enabling the fine-tuning of the pulse repetition rate. We present new experimental observations of the laser transition dynamics associated with the changes of the soliton numbers and give clear insight into the possible physical mechanisms responsible for these effects.

The work unveils a hybrid scenario of dissipative localised structures combining two independent types of soliton solutions in extended nonlinear systems. We show the hybridisation of these two well established soliton formation mechanisms in Kerr cavities with periodic non-Hermitian modulations, resulting in a novel scenario that embodies the properties of both formation mechanisms. The hybridisation blends the properties of anomalous and normal dispersion regimes in a normal dispersive cavity and allows the stabilisation of new families of frequency combs associated to stable solitons, molecules and patterns. Moreover, it introduces unexpected mechanisms for real-time and reversible manipulation of frequency combs.

(INVITED) The field of nonlinear optics (NLO) has been continuously growing over the past decades, and several NLO data tables were published before the turn of the century. After the year 2000, there have been major advances in materials science and technology beneficial for NLO research, but a data table providing an overview of the post-2000 developments in NLO has so far been lacking. Here, we introduce a new set of NLO data tables listing a representative collection of experimental works published since 2000 for bulk materials, solvents, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and THz NLO materials. In addition, we provide a list of best practices for characterizing NLO materials. The presented data tables and best practices form the foundation for a more adequate comparison, interpretation, and practical use of already published NLO parameters and those that will be published in the future.

Polycrystalline silicon germanium (SiGe) core fibers offer great potential as flexible nonlinear platforms. Compared to Si core fibers, the SiGe material offers high nonlinear coefficients, extended mid-infrared wavelength coverage, and the possibility to tune the bandgap and index of refraction through varying the Ge composition. Here SiGe core fibers (10% Germanium) were fabricated using the molten core drawing (MCD) method, followed by CO2 laser irradiation. The transmission properties of the fibers were subsequently improved further using a fiber tapering method, to tailor the core diameter and enhance the crystallinity. The resulting tapered SiGe fiber had linear losses of 2.31 dB/cm at 1550 nm and 4 dB/cm at 2500 nm, significantly lower than previous reports. Nonlinear characterization of the fibers reveals that the nonlinear coefficients are higher than standard Si core fibers, as expected due to the introduction of germanium.

The damage threshold of femtosecond laser mirrors is critical in the construction of femtosecond laser systems. Therefore, we developed a uniform and efficient test method for femtosecond mirrors for the most relevant laser wavelengths of 266 nm,400 nm, 800 nm and 1030 nm and tested various broadband metal and metal-dielectric hybrid mirrors. With this, damage threshold values as high as 1 J/cm2 were observed for laser pulses with pulse lengths between 70 and 90 fs.

We propose an X-cut LiNbO3 non-linear waveguide based on a thin film membrane. The structure allows second harmonic generation by birefringence phase matching between the two fundamental modes TE00 (SHG) and TM00 (Pump) at telecom wavelength. We demonstrate a competitive conversion efficiency compared to a quasi-phase-matched configuration with the advantage of a broadband response of 100nm and high manufacturing tolerance.

We investigate stimulated Raman scattering (SRS) and supercontinuum (SC) generation in a high-index doped silica glass integrated waveguide under various pumping wavelengths and input polarization states. New Raman peaks, different from fused silica, were observed at 48 THz and 75 THz, respectively. We also show that nearly flat SCs were generated from 700 nm until 2400 nm when pumping in the anomalous dispersion regime (at 1200 nm, 1300 nm, and 1550 nm), while narrower SCs were generated when pumping in the normal dispersion regime at 1000 nm. We further investigated the impact of TE/TM polarization modes of the integrated waveguide on SC generation and found a very good agreement with numerical simulations of the modified nonlinear Schrödinger equation.

We investigate pumping nonlinear interactions in multi-mode waveguides with focused laser pulses that contain space-time correlations. This allows for the different modes of the waveguide to be excited with different temporal envelopes. Established nonlinear processes in standard multi-mode graded-index fibers, such as beam self-cleaning or supercontinuum generation, could be significantly affected or even controlled by such novel initial conditions. We will introduce precisely how to introduce such initial conditions and show numerical results of parameter scans of different space-time couplings and relate them to more standard cases. We will also discuss implications for experiments, and analouges in other waveguide platforms, such as vortex fibers or integrated photonic waveguides.

Lately, there has been a renewed attention to the study of multimode signals and their ultrafast interactions. One fascinating phenomenon in this field is known as nonlinear multimode dispersive waves. These waves are frequently observed and hold significant applications across diverse physical systems. While the single-mode case of these waves has been widely researched, the multimode scenario remains relatively unexplored. Understanding and studying nonlinear multimode dispersive waves holds great significance in predicting and analyzing wave phenomena within many systems. In our lab, we developed multimode time lens, which can measure the temporal and spatial dynamics of signals inside multimode fibers. We study the interactions of multimode dispersive waves, in both frequency and time domain. We use the multimode time lens we developed to image and analyze the temporal dynamics between the different spatial modes, as well as the modes coupling over time and the energy transfer between them. In this talk, we will present our measurement system in details and describe our novel results on multimode dispersive waves interactions.

We investigate an original approach for the generation of unequally spaced frequency combs using (2) –(3) nonlinearities in multimode graded-index (MM-GRIN) fiber. In a preliminary step, the MM-GRIN fiber (50 µm of core diameter and 125 μm of cladding diameter) is optically poled with a Nd:YAG sub-nanosecond microchip laser at 1064 nm. As a results, a double periodical inscription of a complex second order non-linearity χ(2) grating was led. The resulting χ(2) inscription allows the generation of second harmonic wave (SH) from a supercontinuum obtained in the infrared domain under the Raman and soliton propagation actions. We then detect the generation of various irregularly spaced spectral peaks surrounding the original SH (532 nm) at the fiber output allowing harmonic generation on more than 100 nm in the visible domain.

We focus our experimentally and numerical investigation of weak nonlinear light propagation in various aperiodic Mathieu lattices optically induced in the photorefractive medium using our advanced one-pass experimental setup. We demonstrate the transitional dimensionality of discrete diffraction within such radial-elliptical Mathieu photonic lattices. We control the shape of discrete diffraction distribution over the combination of the radial direction with the circular, elliptic, or hyperbolic through adjustments of beam order, characteristic structure size, and ellipticity of the Mathieu beams used for the photonic lattices generation. By varying the input beam position, we investigated the transition from one-dimensional to two-dimensional diffraction, and we observed the most prominent discrete diffraction along the crystal's anisotropic direction.

Recently, spontaneous parametric down-conversion (SPDC), leading to the generation of entangled photons, has been implemented in ultrasmall sources: subwavelength layers, metasurfaces, even nanoantennas. The lifted constraint of phase matching gives to SPDC even more freedom than to classical effects like harmonic generation or frequency conversion. The reason is that SPDC, as a spontaneous effect, is stimulated by quantum vacuum fluctuations, which populate all modes uniformly. In my talk I will show examples of SPDC in ultrathin samples, demonstrating very broad spectral and angular width, extremely high degrees of continuous-variable entanglement, tunable polarization entanglement, and orders of magnitude enhancement of photon pair production rate due to the geometric resonances of dielectric metasurfaces.

Squeezed states of light represent a key resource for the implementation of several quantum communication and computation protocols, for fundamental tests of quantum mechanics, as well as to improve the precision of measurements beyond the standard quantum limit. We report the observation of squeezing in the intensity difference of twin beams generated by cascaded nonlinear processes in a single optical resonator: a primary process of second harmonic generation of the pump laser triggers an optical parametric oscillation, giving rise to two parametric modes around the pump frequency. A reduction of noise up to −5.0 ± 1.3 dB is achieved with respect to the standard quantum limit. Demonstration of twin-beam correlations in our cascaded system paves the way to extensive investigations of its exclusive nonclassical properties. In fact, the complex interactions between the two nonlinear processes produce a variety of nonclassical effects that are not accessible to each single nonlinear process, such as multipartite entanglement, of paramount importance for the development of advanced quantum protocols.

Interferometers are highly sensitive measurement devices that map phase changes into intensity changes. Those classical interferometers have a sensitivity limit that cannot be beaten by classical approaches. Quantum interferometers can surpass that shot-noise limit and improve the sensitivity by employing squeezed states of light and destructive interference of the noise. We developed and demonstrated a temporal quantum interferometer by utilizing two time-lenses in a 4f configuration. We achieved three advantageous in addition to the improved sensitivity of quantum interferometers; The first one is obtaining high temporal resolution by applying time lenses. The second is simultaneously measuring interference in time and frequency domains in single shot measurement. Third, our ultrafast temporal quantum interferometer is sensitive to the phase derivative and can detect ultrafast phase changes.

We develop an ultrathin source of two-photon polarization Bell states based on an InGaP nonlinear metasurface. The metasurface facilitates a local optical resonance with a tailored angular dispersion, enabling the generation of polarization-entangled photon pairs through spontaneous parametric down conversion. This opens new possibilities for practical applications of integrated metasurfaces in advanced quantum technologies.

Sub-micron tapered fibers have been proposed to be a suitable platform for the implementation of third-order spontaneous parametric down conversion (TOSPDC). Through a full theoretical treatment of all terms contributing to the expected triplet generation rate we gain new insights into the polarization dependence of the TOSPDC efficiency. For a circular pump polarization, the triplet polarization state is fully determined as a consequence of angular momentum conservation. On the other hand, different polarizations are possible in the case of linear pump polarization. We can utilize these results for the design of optimal coincidence detection measurements with improved signal-to-noise ratio.

Precision astronomical spectroscopy is vital for seeking life beyond Earth and often relies on detecting very small wavelength shifts over years. Precision of these instruments are ensured by regular wavelength calibration and laser frequency combs stabilized with frequency standards have recently emerged as suitable sources. In this work, we demonstrate wavelength calibration of an astronomical spectrograph in ultraviolet spectrum below 400 nm. This is achieved using second- and third- order nonlinear effects in thin-film, periodically poled lithium niobate waveguides with an infrared electro-optic comb generator at 18 GHz.

Continuous-wave (CW) laser-driven integrated Kerr microresonators enable broadband optical frequency combs with high repetition rates and low threshold power, in a compact footprint. A drawback of such microcombs is the low conversion efficiency from the pump laser to the comb lines, which is often in the few percent range or below. Here, complementing previously demonstrated approaches to increase conversion efficiency, we demonstrate a novel approach that leverages a chip-based rare-earth (Tm3+)-doped optical gain medium to boost the pump-to-comb conversion efficiency by more than one order of magnitude. Importantly, the gain medium does not require an additional pump laser, but recycles residual pump light from the Kerr-comb: the CW pump of the Kerr-comb (1610 nm) coincides with the pump wavelength of the on-chip gain medium, allowing unconverted pump power to be absorbed and transferred to the comb lines within gain window (1700 - 1900 nm). This enables a new class of highly efficient Kerr-combs for applications e.g. in data centers and optical computing.

We report the generation of a stable and broadband optical frequency comb featuring 28 THz bandwidth, sustained by a single 80 fs cavity soliton recirculating in a fiber Fabry-Pérot resonator. This large spectrum is comparable to frequency combs obtained with microresonators operating in the anomalous dispersion regime. Thanks to the compact design and the easy coupling of the resonator, cavity solitons can be generated in an all-fiber experimental setup with a continuous wave pumping scheme.

So far, dissipative temporal solitons in a laser with a saturable absorber have been studied mainly in the context either of Haus's master equation or of the cubic-quintic complex Ginzburg-Landau equation. We present here a study based on an equation which includes saturation of the amplifier via a cubic approximation and saturation of the absorber at all orders. The equation describes well a system where both gain and absorption are fast, the laser is close to threshold, the unsaturated absorption is small, and the saturation intensity of the amplifier is much larger than that of the absorber. The model is appropriate for fast semiconductor lasers, such as quantum cascade lasers, since it encompasses the relevant phase-amplitude coupling via the linewidth enhancement factors of the gain and absorption media. Our study shows the crucial role played by these factors in the transition from cw emission to various types of pulsed emission, including dissipative temporal solitons.

Complete phase stabilization of a chip-integrated self-injection-locked microresonator frequency comb is presented for the first time. We utilize recently demonstrated synthetic-reflection self-injection locking to guarantee deterministic access to single soliton microcomb. The microcomb offset frequency is phase-locked via the diode current to an external optical reference, while the repetition rate is phase-locked via a micro-heater to an RF oscillator. Both locks only require low-voltage, CMOS-compatible signals. This demonstration paves the way for metrological-grade chip-integrated optical frequency comb sources.

This study presents a method to achieve cascaded phase locking among three adjacent sub-combs by injecting a tailored frequency comb into a multi-wavelength laser (MWL). Leveraging the nonlinear dynamics of the MWL under a narrow-band comb injection, our research demonstrates that the injection of a narrowband comb with an extra tone results in a multiplied comb fully phase-correlated with the re-generated comb. By adjusting the frequency of the extra tone, we achieve cascaded phase locking for the mode which is not directly affected by the injection. This approach offers a roadmap for extending phase-locking capabilities across higher frequency offsets, potentially reaching a few THz.

This study investigates the nonlinear effects on signal integrity in 16-QAM optical communication systems by focusing on received signal distributions without noise interference. Utilizing GPU-based simulations and analyzing ``triplets'' of consecutive signal points, we uncover that nonlinear interactions generate distinctive patterns in signal behaviour, challenging the adequacy of standard Gaussian models. Our analysis employs the Gaussian Mixture Model (GMM), revealing that multi-component models offer a more accurate representation of signal distributions, highlighting the complexity of nonlinear effects. This research not only enhances our understanding of signal behaviour under nonlinear conditions but also paves the way for future investigations into improving optical communication system design and reliability.

This article introduces an innovative procedure integrating chromatic dispersion compensation (CDC) and sliding window methodology for ongoing signal processing in optical communications. Our strategy notably elevates the precision and effectiveness of Nonlinear Fourier Transform (NFT) processing, culminating in superior system operation and heightened transmission capabilities.

We report on the results of experimental and numerical studies enabling deep insight into the physical mechanisms underlying the super-mode noise suppression in harmonically mode-locked (HML) fiber laser using the resonant continuous wave (CW) injection. In particular, we have proved experimentally that the supermode noise suppression effect is available only with the CW injected to the long-wavelength side of laser spectrum. Injection to the opposite side destroys the HML operation regime and leads to the formation of tight soliton bunch. Our numerical simulations confirm these specific features. To get the result, we have simulated phase-locking between the CW and a single soliton. Then, the developed model has been applied to the laser cavity operating multiple pulses in the presence of the gain depletion and recovery mechanism responsible for harmonic pulse arrangement. We clearly demonstrate how the CW injection accelerates or destroys the HML process enabling the generation of additional inter-pulse forces.