arXiv subjects

Simone Zanotto

Publications and source records attributed to Simone Zanotto.

18 recordsLinked to original sources

arXiv2026

Trefftz DG Approximation of the T-Matrix for Scattering by Periodic Layered Structures

We study the scattering of time-harmonic electromagnetic waves by periodic layered gratings, modelled by the 2D Helmholtz equation. The periodic obstacle may include penetrable and impenetrable regions, and consists of a finite number of stacked layers. The boundary value problem is formulated on a single periodic cell using quasi-periodic boundary conditions. The radiation condition in the vertical directions is imposed through Dirichlet-to-Neumann (DtN) operators. To efficiently treat multilayer configurations, we adopt a formulation based on the T-matrix method. The global scattering problem is decomposed into boundary value problems posed on individual layers. On the layer boundaries, the field is expressed in terms of quasi-periodic modal expansions, and the layer T-matrix describes the map between incoming and outgoing wave modes. Each local T-matrix is approximated numerically using a plane-wave based Trefftz Discontinuous Galerkin (TDG) method, which provides an efficient discretization of the layer scattering response. The T-matrix technique leads to linear computational complexity in the number of layers in the grating.

math.NA↗

arXiv2026

Arduino based interferometer stabilizer equipped with a digital lock-in amplifier

Interferometric sensors are ubiquitous in precision metrology, yet their performance is fundamentally limited by environmental noise and thermal drift. To achieve maximum sensitivity, these systems must be actively stabilized at the quadrature point of the interference fringe. Commercial stabilization solutions, typically based on analog lock-in amplifiers or FPGA architectures, are often prohibitively expensive and do not not offer the flexibility needed for custom experimental setups. In this work, we present an open-source, compact and low-cost digital stabilization system built upon the dual-core Arduino Giga R1 microcontroller. The system features a custom analog front-end with programmable gain amplifiers (PGAs) and active signal conditioning, enabling direct integration with standard amplified photodiodes. We implement a firmware-based digital lock-in amplifier running at a 100 kHz sampling rate, which performs real-time demodulation and PID feedback control without the latency bottlenecks of PC-based loops. Experimental characterization demonstrates that the system effectively suppresses long-term thermal drift and actively rejects external perturbations. The resulting device provides a standalone, Arduino-based alternative for laser frequency stabilization and interferometric control in educational and research laboratories.

physics.optics↗

arXiv2025

Coherent absorption reveals colors hidden in a grey Fabry-P\'erot cavity

Thin dielectric films are known to show distinct colors, responsible for the iridescence of various natural and artificial objects such as insect wings and soap bubbles. In the present article we show that a specialized thin film Fabry-P\'erot resonator, that we name conductor-dielectric-conductor (CDC) matched cavity, appears instead completely grey when observed under ordinary conditions (i.e. by analyzing the transmitted or reflected incoherent white light). Nonetheless, the matched CDC cavity still retains spectral information, that clearly appear when the cavity is analyzed by the coherent absorption technique. The CDC system is simply a dielectric thin film sandwiched by two conducting interfaces, whose conductivity shall be appropriately matched depending upon the dielectric refractive index. In practical applications, the ideal conducting interfaces can be safely replaced by thin metal films, making the system easily applicable in particular for cryptographic purposes. We indeed demonstrated experimentally that a visually recognizable thin-film color pattern can be concealed to an ordinary observer, and finally recovered through a dedicated coherent absorption decoding apparatus.

physics.optics↗

arXiv2023

Gigahertz modulation of a fully dielectric nonlocal metasurface

Nonlocal metasurfaces are currently emerging as advanced tools for the manipulation of electromagnetic radiation, going beyond the widely explored Huygens metasurface concept. Nonetheless, the lack of an unified approach for their fast and efficient tunability still represents a serious challenge to overcome. In this article we report on gigahertz modulation of a dielectric slab-based, nonlocal (i.e. angle-dispersive) metasurface, whose operation relies on the optomechanical coupling with a mechanical wave excited piezoelectrically by a transducer integrated on the same chip. Importantly, the metasurface region is free from any conductive material, thus eliminating optical losses, and making our device of potential interest for delicate environments such as high-power apparatuses or quantum optical systems.

physics.optics↗

arXiv2020

Departure from Babinet principle in metasurfaces supported by subwavelength dielectric slabs

Symmetry principles and theorems are of crucial importance in optics. Indeed, from one side they allow to get direct insights into phenomena by eliminating unphysical interpretations; from the other side, they guide the designer of photonic components by narrowing down the parameter space of design variables. In this Letter we illustrate a significant departure from the Babinet spectral complementarity in a very common and technologically relevant situation: that of a patterned conducting screen placed on a subwavelength dielectric slab. The symmetry property predicted by Babinet theorem is correctly recovered for pairs of geometrically complementary - but less realistic in terms of applications - free-standing patterned screens. Our analysis merges experimental data with fully vectorial electromagnetic modeling, and provides also an alternative form of Babinet theorem that highlights a connection with the concept of electromagnetic duality.

physics.optics↗

arXiv2019

Photonic bands, superchirality, and inverse design of a chiral minimal metasurface

Photonic band structures are a typical fingerprint of periodic optical structures, and are usually observed in spectroscopic quantities such as transmission, reflection and absorption. Here we show that also the chiro-optical response of a metasurface constituted by a lattice of non-centrosymmetric, L-shaped holes in a dielectric slab shows a band structure, where intrinsic and extrinsic chirality effects are clearly recognized and connected to localized and delocalized resonances. Superchiral near-fields can be excited in correspondence to these resonances, and anomalous behaviors as a function of the incidence polarization occur. Moreover, we introduce a singular value decomposition (SVD) approach to show that the above mentioned effects are connected to specific fingerprints of the SVD spectra. Finally, we demonstrate by means of an inverse design technique that the metasurface based on an L-shaped hole array is a minimal one. Indeed, its unit cell geometry depends on the smallest number of parameters needed to implement arbitrary transmission matrices compliant with the general symmetries for 2d-chiral structures. These observations enable more powerful wave operations in a lossless photonic environment.

physics.optics↗

arXiv2019

Multichannel remote polarization control enabled by nanostructured Liquid Crystalline Networks

In this article we demonstrate that a grating fabricated through nanoscale volumetric crosslinking of a liquid crystalline polymer enables remote polarization control over the diffracted channels. This functionality is a consequence of the responsivity of liquid crystal networks upon light stimuli. Tuning the photonic response of the device is obtained thanks to both a refractive index and a shape change of the grating elements induced by a molecular rearrangement under irradiation. In particular, the material anisotropy allows for nontrivial polarization state management over multiple beams. Absence of any liquid component and a time response down to 0.2 milliseconds make our device appealing in the fields of polarimetry and optical communications.

physics.optics↗

arXiv2018

Metasurface reconfiguration through lithium ion intercalation in a transition metal oxide

In the latest years the optical engineer's toolbox has welcomed a new concept, the metasurface. In a metasurface, properly tailored material inclusions are able to reshape the electromagnetic field of an incident beam. Change of amplitude, phase and polarization can be addressed within a thickness of only a fraction of a wavelength. By means of this concept, a radical gain in compactness of optical components is foreseen, even of the most complex ones; other unique features like that of analog computing have also been identified. With this huge potential ready to be disclosed, lack of tunability is still a main barrier to be broken. Metasurfaces must now be made reconfigurable, i.e. able to modify and memorize their state, possibly with a small amount of energy. In this Communication we report low-energy, self-holding metasurface reconfiguration through lithium intercalation in a vanadium pentoxide layer integrated within the photonic device. By a proper meta-atom design, operation on amplitude and phase of linearly polarized light has been demonstrated. In addition, manipulation of circularly polarized light in the form of tunable chirality and tunable handedness-preserving reflection has been implemented. These operations are accomplished using as low as 50 pJ/{\mu}m^{2}, raising lithium intercalation in transition metal oxides as one of the most energy efficient self-holding tuning mechanisms known so far for metasurfaces, with significant perspectives in the whole field of nanophotonics.

physics.optics↗

arXiv2018

Structured Optical Materials Controlled by Light

Materials of which the optical response is determined by their structure are of much interest both for their fundamental properties and applications. Examples range from simple gratings to photonic crystals. Obtaining control over the optical properties is of crucial importance in this context, and it is often attempted by electro-optical effect or by using magnetic fields. In this paper, we introduce the use of light to switch and tune the optical response of a structured material, exploiting a physical deformation induced by light itself. In this new strategy, light drives an elastic reshaping, which leads to different spectral properties and hence to a change in the optical response. This is made possible by the use of liquid crystalline networks structured by Direct Laser Writing. As a proof of concept, a grating structure with sub-millisecond time-response is demonstrated for optical beam steering exploiting an optically induced reversible shape-change. Experimental observations are combined with finite-element modeling to understand the actuation process dynamics and to obtain information on how to tune the time and the power response of this technology. This optical beam steerer serves as an example for achieving full optical control of light in broad range of structured optical materials.

physics.optics↗

arXiv2018

Fundamental limits on the losses of phase and amplitude optical actuators

Amplitude and phase are the basic properties of every wave phenomena; as long as optical waves are concerned, the ability to act on these variables is at the root of a wealth of switching devices. To quantify the performance of an optical switching device, an essential aspect is to determine the tradeoff between the insertion loss and the amplitude or phase modulation depth. Here it is shown that every switching optical device is subject to such a tradeoff, intrinsically connected to the dielectric response of the materials employed inside the switching element itself. This limit finds its roots in fundamental physics, as it directly derives from Maxwell's equations for linear dielectrics, and is hence applicable to a wide class of optical components. Furthermore it results that concepts as filtering, resonance and critical coupling could be of advantage in approaching the limit.

physics.optics↗

arXiv2018

Optomechanics of chiral dielectric metasurfaces

Electromagnetic fields coupled with mechanical degrees of freedom have recently shown exceptional and innovative applications, ultimately leading to mesoscopic optomechanical devices operating in the quantum regime of motion. Simultaneously, micromechanical elements have provided new ways to enhance and manipulate the optical properties of passive photonic elements. Following this concept, in this article we show how combining a chiral metasurface with a GaAs suspended micromembrane can offer new scenarios for controlling the polarization state of near-infrared light beams. Starting from the uncommon properties of chiral metasurface to statically realize target polarization states and circular and linear dichroism, we report mechanically induced, ~300 kHz polarization modulation, which favorably compares, in terms of speed, with liquid-crystals commercial devices. Moreover, we demonstrate how the mechanical resonance can be non-trivially affected by the input light polarization (and chiral state) via a thermoelastic effect triggered by intracavity photons. This work inaugurates the field of Polarization Optomechanics, which could pave the way to fast polarimetric devices, polarization modulators and dynamically tunable chiral state generators and detectors, as well as giving access to new form of polarization nonlinearities and control.

physics.optics↗

arXiv2016

Mid-Infrared intersubband polaritons in dispersive metal-insulator-metal resonators

We demonstrate room-temperature strong-coupling between a mid-infrared ($λ$=9.9 $μ$m) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k=0 where - potentially - polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states and - simultaneously - to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the concept of strong critical coupling is highlighted.

cond-mat.mes-hall↗

arXiv2016

Coherent perfect absorption in photonic structures

The ability to drive a system with an external input is a fundamental aspect of light-matter interaction. The coherent perfect absorption (CPA) phenomenon extends to the general multibeam interference phenomenology the well known critical coupling concepts. This interferometric control of absorption can be employed to reach full delivery of optical energy to nanoscale systems such as plasmonic nanoparticles, and multi-port interference can be used to enhance the absorption of a nanoscale device when it is embedded in a strongly scattering system, with potential applications to nanoscale sensing. Here we review the two-port CPA in reference to photonic structures which can resonantly couple to the external fields. A revised two-port theory of CPA is illustrated, which relies on the Scattering Matrix formalism and is valid for all linear two-port systems with reciprocity. Through a semiclassical approach, treating two-port critical coupling conditions in a non-perturbative regime, it is demonstrated that the strong coupling regime and the critical coupling condition can indeed coexist; in this situation, termed strong critical coupling, all the incoming energy is converted into polaritons. Experimental results are presented, which clearly display the elliptical trace of absorption as function of input unbalance in a thin metallo-dielectric metamaterial, and verify polaritonic CPA in an intersubband-polariton photonic-crystal membrane resonator. Concluding remarks discuss the future perspectives of CPA with photonic structures.

physics.optics↗

arXiv2016

Photonic bands and defect modes in metallo-dielectric photonic crystal slabs

Photonic components based on structured metallic elements show great potential for device applications where field enhancement and confinement of the radiation on a subwavelength scale is required. In this paper we report a detailed study of a prototypical metallo-dielectric photonic structure, where features well known in the world of dielectric photonic crystals, like band gaps and defect modes, are exported to the metallic counterpart, with interesting applications to infrared science and technology, as for instance in quantum well infrared photodetectors, narrow-band spectral filters, and tailorable thermal emitters.

physics.optics↗

arXiv2016

Perfect energy-feeding into strongly coupled systems and interferometric control of polariton absorption

The ability to feed energy into a system, or - equivalently - to drive that system with an external input is a fundamental aspect of light-matter interaction. The key concept in many photonic applications is the "critical coupling" condition: at criticality, all the energy fed to the system via an input channel is dissipated within the system itself. Although this idea was crucial to enhance the efficiency of many devices, it was never considered in the context of systems operating in a non-perturbative regime. In this so-called strong coupling regime, the matter and light degrees of freedom are in fact mixed into dressed states, leading to new eigenstates called polaritons. Here we demonstrate that the strong coupling regime and the critical coupling condition can indeed coexist; in this situation, which we term strong critical coupling, all the incoming energy is converted into polaritons. A semiclassical theory - equivalently applicable to acoustics or mechanics - reveals that the strong critical coupling corresponds to a special curve in the phase diagram of the coupled light-matter oscillators. In the more general case of a system radiating via two scattering ports, the phenomenology displayed is that of coherent perfect absorption (CPA), which is then naturally understood and described in the framework of critical coupling. Most importantly, we experimentally verify polaritonic CPA in a semiconductor-based intersubband-polariton photonic-crystal membrane resonator. This result opens new avenues in the exploration of polariton physics, making it possible to control the pumping efficiency of a system almost independently of its Rabi energy, i.e., of the energy exchange rate between the electromagnetic field and the material transition.

quant-ph↗

arXiv2016

Saturation and bistability of defect-mode intersubband polaritons

In this article we report about linear and nonlinear optical properties of intersubband cavity polariton samples, where the resonant photonic mode is a defect state in a metallo-dielectric photonic crystal slab. By tuning a single geometric parameter of the resonator, the cavity Q-factor can reach values as large as 85, with a consequent large cooperativity for the light-matter interaction. We show that a device featuring large cooperativity leads to sharp saturation, or even bistability, of the polariton states. This nonlinear dynamics occurs at the crossover between the weak and the strong coupling regimes, where the weak critical coupling concept plays a fundamental role.

cond-mat.mes-hall↗

arXiv2015

Design of a hybrid silicon-plasmonic co-propagant integrated coherent perfect absorber

By a hybrid integration of plasmonic and dielectric waveguide concepts, it is shown that coherent perfect absorption can be achieved in a co-propagant coupler geometry. The device holds promises for classical and quantum signal processing. First, the operating principle of the proposed device is detailed in the context of a more general 2x2 lossy coupler formalism. Then, it is shown how to tune the device in a wide region of possible working points, its broadband operation, and the tolerance to fabrication uncertainties. Finally, a complete picture of the electromagnetic modes inside the hybrid structure is analyzed, shining light onto the potentials which the proposed device holds in view of other applications like nonlinear optics, polarization control, and sensing.

physics.optics↗

arXiv2015

Universal lineshapes at the crossover between weak and strong critical coupling in Fano-resonant coupled oscillators

In this article we discuss a model describing key features concerning the lineshapes and the coherent absorption conditions in Fano-resonant dissipative coupled oscillators. The model treats on the same footing the weak and strong coupling regimes, and includes the critical coupling concept, which is of great relevance in numerous applications; in addition, the role of asymmetry is thoroughly analyzed. Due to the wide generality of the model, which can be adapted to various frameworks like nanophotonics, plasmonics, and optomechanics, we envisage that the analytical formulas presented here will be crucial to effectively design devices and to interpret experimental results.

physics.optics↗