Conference Agenda

We will present how widely used techniques such as autoencoders can be used to perform phase noise characterization of optical frequency combs. Optical frequency comb is an optical source that produces evenly spaced frequency lines. It is considered as a frequency ruler and has diverse applications in: frequency referencing, grid synchronization, optical communication, calibration for spectrographs e.g.

Classifying chestnuts as healthy or diseased remains a complex challenge in quality assessment. In our study, we use THz imaging to determine accurately the health status of chestnuts. Through innovative spectroscopic analysis, we explore the potential of three distinct unsupervised data analysis techniques: Principal Component Analysis (PCA), k-Means Clustering, and Agglomerative Clustering. Compared to traditional analysis methods, our findings unveil the remarkable ability of these methods to differentiate between healthy, diseased and in an intermediate state chestnuts, even when concealed beneath the peel. This research not only advances our understanding of quality control in chestnut production but also highlights the potential of THz imaging in agricultural applications.

Deep neural networks based on physics-driven learning make it possible to train neural networks with a reduced data set and also have the potential to transfer part of the numerical computations to optical processing. The aim of this work is to develop the first deep holographic microscope device incorporating a hybrid neural network based on the plane-wave angular spectrum method for dynamic image autofocusing in microscopy applications.

Photonic Stochastic Emergent Learning (PSEL) represents an innovative paradigm rooted in mathematical brain modelling and emergent memories. In this study, we explore the intersection of these concepts to address memory storage and classification tasks. Leveraging optical computing principles and random projections, PSEL constructs memory representations from the inherent randomness in nature. Specifically, we select a set of highly similar random states generated by coherent light scattered from a diffusive medium. Classification is performed by organizing the memories spatially into different classes and comparing inputs to those stored memories. The results demonstrate the efficacy of PSEL in memory construction and parallel classification, emphasizing its potential applications in high-performance computing and artificial intelligence systems.

We review recent works in signal shaping and advanced characterization techniques within the framework of nonlinear fiber optics. Here, we focus on characterization methods based on the dispersive Fourier transform to monitor incoherent spectral broadening processes with enhanced resolution and sensitivity. In this framework, we further 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 using suitable machine learning approaches to tailor and optimize incoherent spectral broadening dynamics.

Photonics has proven to be a promising platform for the implementation of neuromorphic architectures. In this context, we implement an optoacoustic recurrent operator (OREO) based on stimulated Brillouin scattering in a highly nonlinear fiber. We demonstrate how OREO can establish a connection between optical pulses through acoustic waves. We show how the depth of our network benefits from cooling the fiber, as this extends the acoustic lifetime. We use OREO under this concept to perform a pattern classification task with 67% accuracy.

High harmonic generation (HHG) stands as one of the most complex processes in strong-field physics, as it enables the conversion of laser light from the infrared to the extreme-ultraviolet or even the soft x-rays, enabling the synthesis and control of pulses lasting as short as tens of attoseconds. Accurately simulating this nonlinear and non-perturbative phenomena requires the coupling the dynamics of laser-driven electronic wavepackets, described by the three-dimensional time-dependent Schrödinger equation (3D-TDSE), with macroscopic Maxwell’s equations. Such calculations are extremely demanding due to the duality of microscopic and macroscopic nature of the process, thereby requiring the use of approximations. We develop a HHG method assisted by artificial intelligence that facilitates the simulation of macroscopic HHG within the framework of 3D-TDSE. This approach is particularly suited to simulate HHG driven by structured laser pulses. In particular, we demonstrate a self-interference effect in HHG driven by Hermite-Gauss beams. The theoretical and experimental agreement allows us to validate the AI-based model, and to identify a unique signature of the quantum nature of the HHG process.

Disordered, self-assembled media, contain a large amount of information, which can be seen as a huge set of random and uncontrolled memory patterns. In the framework of optics, in which an opaque medium may modelled with the transmission matrix approach, each transmitted mode “contains” a memory element which is embodied by the correspondent transmission vector. Even if the stored amount of information in this system is huge, these random memories cannot be tailored easily. Here we present a new approach to write, read, and classify memory patterns: the photonic emergent learning. The writing paradigm is borrowed form a-physical- mathematical model for the biological memory, the emergent archetype, which we translated to photonics. In our approach the random patterns enclosed in the transmitted electromagnetic modes, are used as prototypes which are summed in constructive fashion in order write our target archetype-memory into our disordered optical memory (DOM). The DOM can work as a content addressable memory, retrieving at the lightning speed which memory in the library is the closest to an optically proposed query pattern. Moreover, the optical memories can be organized into super structures containing memories of the same thus efficiently delivering a classification task.

We describe our use of deep learning to optimize the multi-dimensional parameter space of systems-on-chip as an important step towards the scalable production of photonic solutions and their widespread integration into high-volume applications. The challenges of transitioning between prototype and volume production are highlighted, and the suitability of deep neural networks for navigating the multi-dimensional design space of today’s photonic circuits is discussed. We adopt multi-path neural network architectures to reduce the computational requirements of model training and to mitigate the risk of overfitting. We demonstrate the use of a multi-path neural network to optimize the construction parameters of photonic designs in a high-volume production environment. Lastly, we discuss the advantages of using machine learning not only as a highly capable tool for navigating the multi-dimensional design space of complex systems-on-chip but also as an effective strategy for compensating for fabrication process non-uniformities that are undetectable by standard process metrology instruments.

Light containing twisted phase structures, i.e. light carrying orbital angular momenta (OAM), when propagating inside ring-core fibers leads to a complex interference dynamics resulting in the fundamental self-imaging phenomenon known as the Talbot effect in the angular domain. We study the effect in the classical and quantum optics domain and show that it can be used to implement higher-order beams splitters. Interestingly, such beam splitting operations become more compact the higher the splitting ratio. In addition, we show that a similar self-imaging effect appears for whispering gallery modes carrying OAM in step-index multi-mode fibers, which enables the application of the angular Talbot effect in off-the-shelf components. Finally, we extend the study of the angular Talbot effect through combing it with its Fourier-analog, i.e. the Talbot effect in orbital angular momentum space. Thereby we implement the generalized angle-orbital-angular-momentum Talbot effect, which enables full control over the angular intensity distribution as well as the OAM spectrum of the light field. Moreover, the complex self-imaging dynamics can be used to sort OAM light fields, in principle, without any crosstalk and, thus, can be seen a promising method for OAM multiplexing schemes.

Advancements in structured ultrafast laser sources have significantly contributed to our understanding of the fundamental dynamics of electronic and spin processes in matter. Notably, the development of ultrafast sources structured in their spin and orbital angular momentum has been pivotal in probing chiral systems and magnetic materials at fundamental temporal and spatial scales. Thanks to the highly nonlinear process of high harmonic generation, structured ultrafast laser pulses have been brought into the extreme ultraviolet/attosecond regimes.

This talk will review significant works from the last decade that have advanced the field of attosecond structured pulses. The discussion will focus on how these pulses can be generated—for example, how to create attosecond vortex pulses—, and how they can provide new insights into our understanding of ultrafast electronic dynamics.

We present a theory of the transverse orbital angular momentum (OAM) of spatiotemporal wave packets that explains the different values of the transverse OAM of spatiotemporal optical vortices (STOVs) provided by several authors as belonging to different canonical STOVs. The theory also rules out inaccurate values contributed by other authors, closing the debate on this issue.

A novel class of structured propagating waves with parabolic rotational symmetry is introduced for the first time. These are described by exact solutions of the Helmholtz nonparaxial wave equation. Being the result of the separability of the Helmholtz equation, the intensity of these wavefields remains invariant while propagating along parabolic trajectories exhibiting apparent acceleration. Whe will show that superposition of the different wavefields created can present parabolic, spherical or even rectilinear propagation.

Vector light beams feature a spatially varying optical polarisation and can exhibit localised structures reminiscent of the skyrmions familiar from the study of magnetic media. We present a theory and experimental measurements of such skyrmions in both paraxial and non-paraxial optics. A key feature for our analysis is the skyrmion field which determines the properties of the skyrmions and traces out field lines. In paraxial optics these field lines are lines of constant polarisation, but in non-paraxial optics, the fact the polarisation ellipses are no longer restricted to the transverse plane, makes it necessary to introduce several different skyrmion fields, each representing a different aspect of the three-dimensional optical polarisation.

The fabrication of Diffractive Optical Elements (DOEs) involves the analog patterning of material surfaces on the scale of light wavelength. This typically requires multi-step lithographic processes. Differently from the photoresists of standard lithography, thin films of amorphous azobenzene-containing polymers (azopolymers) can directly produce a structured surface using a single irradiation step with structured light. The resulting surface reliefs can be used directly as planar phase-modulating DOEs without the need for any post-exposure process. Additionally, the surface geometry and its optical functionality can be reconfigured at will. Here, we demonstrate reprogrammable and ready-to-use azopolymer diffractive gratings, lenses, and holographic projectors, produced by grayscale digital holographic patterns. By exploiting the all-optical scheme based of computer-generated holography, the diffraction behavior of the DOEs is optimized during the developing of structured surfaces. Full all-optical reconfigurability of the fabricated devices is also achieved. Our approach provides a versatile, efficient, and all-optical reversible fabrication framework for DOEs, making it a promising option to overcome the demanding, cumbersome, and irreversible fabrication processes typically involved in the realization of planar diffractive optical devices.

Polarization structured heralded single photons have been generated through spontaneous parametric down-conversion in a type-I dual crystal pumped by an inhomogeneously polarized beam in a general Poincaré mode, i.e. an inseparable superposition of two orthogonally polarized states through two orthogonal orbital angular momentum modes. The polarization structure of the signal photons can be controlled by manipulating the polarization state of their idler photon sisters with zero orbital angular. Due to the separate conservations of spin and orbital angular momenta in a type-I dual crystal SPDC process, any projection of the idler polarization state turns into a unitary transformation of the polarization basis of the signal photons, while preserving the orbital angular momentum modes originally included in the pump. We demonstrate, in this way, the ability to toggle between direct and basis-switched pump-single photon transfer by selectively projecting the polarization of the heralding photon before detection.

A method for the generation of structured laser beams (SLB) and hollow structured laser beams (HSLB) whose transverse profiles are invariant and can propagate to infinity is described. SLBs are formed after passing through an optical system that generates a special waveform as a combination of rotationally symmetric optical aberrations. Transverse profile consists of concentric circles with a very bright central core and a bounding outer-ring. The divergence of the central core 0.01 millirad has been experimentally confirmed. When the system was illuminated with a special vector beam, a hollow SLB (HSLB) beam was generated. Its central part is very narrow and completely dark. Unlike conventional hollow beams, where the electric field strength is zero in the dark areas, an electromagnetic field with the zero Poynting vector is present in this part of the beam. By varying the illumination parameters of the vector beam, it is possible to obtain situations where there is a longitudinal component of the electric field or/and magnetic field in the central core. The simulation results are in good agreement with the SLB profile measurements using a polarization camera.

We analyze polarization diffractive elements with the Fourier transform Jones (FTJ) matrix integrated with the beam coherence-polarization (BCP) matrix. Analytical derivations and experimental results are presented of the intensity, state and degree of polarization and coherence properties of the diffracted field generated by a simple diffractive element consisting in double polarizer rectangular aperture.

We use spatial light modulation to investigate the diffractive effects of gravitational lensing in the laboratory. Using this new platform for laboratory astrophysics, we can overcome the coherence challenges that prevent the observation of diffraction in astronomical imaging. These studies will inform gravitational lensing of gravitational waves when imaging of gravitational waves becomes available. Our previous work involved studying lensing by a single mass, symmetric and elliptical. This work focuses on the patterns produced by a binary-mass system. We observed rich 2-dimensional interference patterns bounded by caustics. Comparison of experimental results with preliminary theoretical calculations is excellent.

The dichroic macular pigment in the Henle fiber layer in the fovea enables humans to perceive entoptic phenomena when viewing polarized blue light. In the standard case of linearly polarized stimuli, a faint bowtie-like pattern known as the Haidinger's brush appears in the central point of fixation. As the shape and clarity of the perceived signal is directly related to the health of the macula, Haidinger's brush has been used as a diagnostic marker in studies of early stage age-related macular degeneration (AMD) and central field visual dysfunction. However, due to the weak nature of the perceived signal the perception of the Haidinger's brush has not been integrated with modern clinical methods. Our group has developed techniques to increase the strength of the perceived signal by employing polarization coupled orbital angular momentum states. We successfully achieved the creation of stimuli with higher numbers of azimuthal fringes, enabling the perception and discrimination of Pancharatnam-Berry phases, measuring the visual angle of entoptic phenomena, retinal imaging using structured light, and the creation of radially varying entoptic stimuli. Our current studies are focusing on applying the structured light toolbox that we developed to subjects that suffer from ocular diseases such as AMD.

Photonic Orbital Angular Momentum (OAM) is becoming a pertinent quantum variable for atom-light interaction, in particular for non-linear interaction which leads to photon entanglement and OAM-entanglement. With two 4-levels atomic schemes, we show that Four Wave Mixing addressed by vortex beams leads to very different OAM-entanglement especially for large OAM values.

We introduce a cutting-edge technique utilizing structured light, specifically linear photonic gears, for ultra-sensitive transverse displacement measurements. Light propagation through periodic liquid-crystal metasurfaces translates displacements into polarization rotations of a laser beam. The system's sensitivity can be enhanced by decreasing the spatial period of these components, achieving resolutions of 400 pm under standard conditions and potentially 50 pm with optimized setups. This compact, cost-effective approach offers high stability and precision, demonstrating significant advancements in applications such as precision component monitoring, material property assessments, and nanofabrication, showcasing the transformative potential of structured light in precision measurement technologies.

We consider a far-red-detuned optical cavity, driven by a pump, which contains an ultracold atomic medium. Using coupled partial differential equations which describe the evolution of the atomic and optical fields, we demonstrate that our model leads to novel self-structuring, led by the optical field through the dipole force, within the ultracold atomic medium. Introducing OAM to the optical pump, we demonstrate that these structures may be made to rotate, forming atomic fields analogous to persistent phase currents.