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.

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.

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.

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.

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.

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.

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

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.

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 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 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.

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.

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 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.