arXiv subjects

Giuseppe D'Aguanno

Publications and source records attributed to Giuseppe D'Aguanno.

14 recordsLinked to original sources

arXiv2026

Fast Synergetic Simulation to Study Slow Evolution of Soliton Patterns in Optical Resonators

Complex patterns in physical and biological systems often emerge through slow collective dynamics governed by a small number of key variables. In nonlinear optical resonators, dissipative Kerr solitons provide an important example, where interactions between well-separated solitons can evolve over timescales far longer than the characteristic loss and gain timescales. Direct numerical simulation of these dynamics is challenging because stiffness forces conventional methods to resolve many rapidly damped degrees-of-freedom with very small time steps. We present a numerical scheme, the synergetic method, that eliminates these rapidly damped degrees-of-freedom and retains the slowly evolving modes, enabling time steps many orders of magnitude larger than those used in conventional approaches. Applied to soliton molecules in driven Kerr cavities, the method achieves speedups of $10^3$ to $10^5$ while capturing dynamics on laboratory timescales. We use it to model the full interaction dynamics of a three-soliton molecule and the evolution of an eight-soliton molecule. The approach provides an efficient framework for studying slow pattern formation in nonlinear systems with widely separated timescales.

nlin.PS↗

arXiv2021

Tree tensor network classifiers for machine learning: from quantum-inspired to quantum-assisted

We describe a quantum-assisted machine learning (QAML) method in which multivariate data is encoded into quantum states in a Hilbert space whose dimension is exponentially large in the length of the data vector. Learning in this space occurs through applying a low-depth quantum circuit with a tree tensor network (TTN) topology, which acts as an unsupervised feature extractor to identify the most relevant quantum states in a data-driven fashion. This unsupervised feature extractor then feeds a supervised linear classifier and encodes the output in a small-dimensional quantum register. In contrast to previous work on \emph{quantum-inspired} TTN classifiers, in which the embedding map and class decision weights did not map the data to well-defined quantum states, we present an approach that can be implemented on gate-based quantum computing devices. In particular, we identify an embedding map with accuracy similar to exponential machines (Novikov \emph{et al.}, arXiv:1605.03795), but which produces valid quantum states from classical data vectors, and utilize manifold-based gradient optimization schemes to produce isometric operations mapping quantum states to a register of qubits defining a class decision. We detail methods for efficiently obtaining one- and two-point correlation functions of the decision boundary vectors of the quantum model, which can be used for model interpretability, as well as methods for obtaining classifications from partial data vectors. Further, we show that the use of isometric tensors can significantly aid in the human interpretability of the correlation functions extracted from the decision weights, and may produce models that are less susceptible to adversarial perturbations. We demonstrate our methodologies in applications utilizing the MNIST handwritten digit dataset and a multivariate timeseries dataset of human activity recognition.

quant-ph↗

arXiv2019

Dissipative cnoidal waves (Turing rolls) and the soliton limit in microring resonators

Single solitons are a special limit of more general waveforms commonly referred to as cnoidal waves or Turing rolls. We theoretically and computationally investigate the stability and accessibility of cnoidal waves in microresonators. We show that they are robust and, in contrast to single solitons, can be easily and deterministically accessed in most cases. Their bandwidth can be comparable to single solitons, in which limit they are effectively a periodic train of solitons and correspond to a frequency comb with increased power. We comprehensively explore the three-dimensional parameter space that consists of detuning, pump amplitude, and mode circumference in order to determine where stable solutions exist. To carry out this task, we use a unique set of computational tools based on dynamical system theory that allow us to rapidly and accurately determine the stable region for each cnoidal wave periodicity and to find the instability mechanisms and their time scales. Finally, we focus on the soliton limit, and we show that the stable region for single solitons almost completely overlaps the stable region for both continuous waves and several higher-periodicity cnoidal waves that are effectively multiple soliton trains. This result explains in part why it is difficult to access single solitons deterministically.

nlin.PS↗

arXiv2017

Coupled Lugiato-Lefever equation for nonlinear frequency comb generation at an avoided crossing of a microresonator

Guided-mode coupling in a microresonator generally manifests itself through avoided crossings of the corresponding resonances. This coupling can strongly modify the resonator local effective dispersion by creating two branches that have dispersions of opposite sign in spectral regions that would otherwise be characterized by either positive (normal) or negative (anomalous) dispersion. In this paper, we study, both analytically and computationally, the general properties of nonlinear frequency comb generation at an avoided crossing using the coupled Lugiato-Lefever equation. In particular, we find that bright solitons and broadband frequency combs can be excited when both branches are pumped for a suitable choice of the pump powers and the detuning parameters. A deterministic path for soliton generation is found.

physics.optics↗

arXiv2016

Nonlinear mode coupling in whispering-gallery-mode resonators

We present a first principle derivation of the coupled nonlinear Schrödinger equations that govern the interaction between two families of modes with different transverse profiles in a generic whispering-gallery-mode resonator. We find regions of modulational instability and the existence of trains of bright solitons both in the normal and in the anomalous dispersion regime.

physics.optics↗

arXiv2012

Broadband Absorbers and Selective Emitters based on Plasmonic Brewster Metasurfaces

We discuss the possibility of realizing utlrabroadband omnidirectional absorbers and angularly selective coherent thermal emitters based on properly patterned plasmonic metastructures. Instead of relying on resonant concentration effects that inherently limit the bandwidth, we base our design on the combination of two inherently nonresonant effects: plasmonic Brewster funneling and adiabatic plasmonic focusing. With this approach, we demonstrate compact, broadband absorption and emission spanning terahertz, infrared and optical frequencies, ideal for various energy and defense applications.

cond-mat.mes-hall↗

arXiv2009

Transmission function properties for multi-layered structures: Application to super-resolution

We discuss the properties of the transmission function in the k-space for a generic multi-layered structure. In particular we analytically demonstrate that a transmission greater than one in the evanescent spectrum (amplification of the evanescent modes) can be directly linked to the guided modes supported by the structure. Moreover we show that the slope of the phase of the transmission function in the propagating spectrum is inversely proportional to the ability of the structure to compensate the diffraction of the propagating modes. We apply these findings to discuss several examples where super-resolution is achieved thanks to the simultaneous availability of the amplification of the evanescent modes and the diffraction compensation of the propagating modes.

physics.optics↗

arXiv2008

Energy considerations for a superlens based on metal/dielectric multilayers

We investigate the resolution and absorption losses of a Ag/GaP multilayer superlens. For a fixed source to image distance the resolution is independent of the position of the lens but the losses depend strongly on the lens placement. The absorption losses associated with the evanescent waves can be significantly larger than losses associated with the propagating waves especially when the superlens is close to the source. The interpretation of transmittance values greater than unity for evanescent waves is clarified with respect to the associated absorption losses.

physics.optics↗

arXiv2008

Homogenization procedure for a metamaterial and local violation of the second principle of thermodynamics

Classical theory of crystals states that a medium to be considered homogeneous must satisfy the following requirements: a) the dimension of the elementary cell must be much smaller than the incident wavelength; b) the sample must contain a large number of elementary cells, i.e. it must be macroscopic with respect to wavelength. Under these conditions, macroscopic quantities can be introduced in order to describe the optical response of the medium. We analytically demonstrate that for a symmetric elementary cell those requirements can be relaxed, and it is possible to assign a permittivity and a permeability to a composite structure, even if the metamaterial cannot be considered homogeneous under the requirements stated above. However, the effective permittivity and permeability in some cases may give rise to unphysical, effective behaviors inside the medium, notwithstanding the fact that they satisfy requirements like being Kramers-Kronig pairs, for example, and are consistent with all the linear properties outside the structure (i.e. reflection, transmission, and absorption at all frequencies). In some situations the medium is assigned a magnetic response even though the medium is not magnetically active. In particular, we demonstrate that the homogenization procedure can lead to a medium that locally violates the second principle of thermodynamics. We also show that, in the non-homogeneous regime, it is not possible to describe the nonlinear behavior of the structure using an effective parameters approach, despite the possibility to assign an effective linear refractive index.

physics.optics↗

arXiv2008

Influence of the losses on the super-resolution performances of an impedance matched negative index material

We discuss by a Poynting vector analysis how the losses of a negative index material (NIM) affect the resolution performances of a Veselago-Pendry lens and we analyze those performances in the framework of the Abbe criterion. Both the limit of high losses and low losses are explored. We find that the impedance matched NIM is able to resolve 30% better than the limit imposed by the Abbe criterion even when the imaginary part of the refractive index (the material losses) exceeds the absolute value of the real part of the refractive index. The NIM is described by a lossy Drude model with equal permittivity and permeability. By increasing the damping parameter of the Drude model we also explore the regime where both permittivity and permeability are positive and point out the conditions under which the metamaterial is still able to super-resolve.

physics.optics↗

arXiv2008

Ultra-slow light pulses in a nonlinear metamaterial

We find the analytical expression for the threshold intensity necessary to launch ultra-slow light pulses in a metamaterial with simultaneous cubic electric and magnetic nonlinearity. The role played respectively by the permittivity, the permeability, the electric cubic nonlinearity, the magnetic cubic nonlinearity and the pulse duration is clearly identified and discussed.

physics.optics↗

arXiv2006

Broadband superresolving lens with high transparency for propagating and evanescent waves in the visible range

We present a theoretical analysis of a super-resolving lens based on 1-dimensional metallo-dielectric photonic crystals composed of Ag/GaP multilayers. The lens contains a total of 10 optical skin depths of Ag, yet maintains a normal incidence transmittance of ~50% for propagating waves over the super-resolving wavelength range of 500-650 nm. The individual Ag layers are 22 nm thick and can be readily fabricated in conventional deposition systems. The importance of anti-reflection coatings for the transmission of evanescent and propagating waves is illustrated by comparison to periodic and symmetric structures without the coatings. In addition, the reflection for propagating waves is reduced to ~5% across the super-resolving wavelength band diminishing the interference between the object and the lens.

physics.optics↗

arXiv2006

Gap solitons in a nonlinear quadratic negative index cavity

By integrating the full Maxwell's equations we predict the existence of gap solitons in a quadratic, Fabry-Perot negative index cavity. An intense, fundamental pump pulse shifts the band structure that forms when magnetic and electric plasma frequencies are different so that a weak, second harmonic pulse initially tuned inside the gap is almost entirely transmitted. The process is due cascading, which occurs far from phase matching conditions, and causes pulse compression. A nonlinear polarization spawns a dark soliton, while a nonlinear magnetization produces a bright soliton.

physics.optics↗

arXiv2006

Negative refraction and sub-wavelength imaging using transparent metal-dielectric stacks

Negative refraction is known to occur in materials that simultaneously possess a negative electric permittivity and magnetic permeability; hence they are termed negative index materials. However, there are no known natural materials that exhibit a negative index of refraction. In large part, interest in these materials is due to speculation that they could be used as perfect lenses with superresolution. We propose a new way of achieving negative refraction with currently available technology, based on transparent, metallo-dielectric multilayer structures. The advantage of these structures is that both tunability and transmission (well above 50%) can be achieved in the visible wavelength regime. We demonstrate both negative refraction and superresolution in these structures. Our findings point to a simpler way to fabricate a material that exhibits negative refraction. This opens up an entirely new path not only for negative refraction, but also to expand the exploration of wave propagation effects in metals.

physics.optics↗